W

Ml

_.
=
.‘d
—

,_,_
—v_
—
>7 _.
._—————;
_———_
”

WI

‘1

WWW

 

THE ARLINGTON
MEMORIAL BRIDGE. _ .

Thesis for the Degree “of c. 5.

JAMES B. RASBACH
1929

THESIS '

THE ARLINGTON MEMORIAL BRIDG1

EY

4 1'

v

\_ (.1
l
.

V
JAMES B. RASBACH

M

THESIS

 

THE ARLINGTON M MORIAL BRIDGE

CROSSING THE POTCMAC RIVER AT WASHINGTON
IN THE DISTRICT OF COLUMBIA

BY
JAMES B. RASBACH,B8.C.E.
MICHIGAN STATE COLLEGE,CLASS OF 1917

A THESIS PRESENTED
TO THE FACULTY OF MICHIGAN STATE COLLEGE
FOR THE CONFERRING OF THE DEGREE OF CIVIL ENGINEER

WASHINGTON,D.C.
APRIL 1929.

.4.
f“\
is“!
'0‘

u

0 I.

4 ,
k.-
r 1‘

\ss’
r\.~
“a

CONTENTS

CHAPTER ONE
Purpose of the Bridge and Provisions for Its Construction

Conception of Idea; Congressional Action; Early Investigations
and Reports; Act of Authorization and Appropriations....

CHAPTER TWO
Description of Bridge

Organization of Forces; Architectural Type; Engineering Features;
. Draw Span; Aaterials.....

CHAPTER THREE
Methods of Construction

Piers and Abutments; Arches and Superstructure; Draw Span;
Auxiliary Connections. ....

CHAPTER FOUR
Surveying and Inspection Service

Horizontal Control; Vertical Control; Surveying Methods for
Checking; Inspection Service .....

CHAPTER FIVE

Engineering Features of Construction

gggPTER ONE.
Purpose of the Bridge and Provisions for Its Construction.

I. Conception of the Idea and Its Aim.

Bounding the District of Columbia on the West flows
the Potomac River, long noted for its placid beauty and.nav-
igable utility, but more particularly because it formed the
barrier between the "Old Dominion", the Commonwealth of Vir—
ginia, representing the South, and the seatof Government of
the Union during those trying days of the Civil War. Long
prior to that time, however, the desirability for the con-
struction of a memorial bridge spanning the river had been
conceived, the thot in all probability having first origin-
ated in the great mind of one of our most distinguished Pree-
idents, Andrew Jackson. Daniel Webster in an address presented
July 4, 1851 said, as follows:

"Before us is the broad and beautiful river, sep-
arating two of the original thirteen states, which a late
President, a man of determined purpose and inflexible will,
'but patriotic heart, desired to span with arches of ever-
enduring granite, symbolical of the firmly established
union of the North and the South. That President was
Andrew Jackson.“

Ten years after the words of that famous orator were
spoken the Potomac River became the dividing line betweenithe
two warring sections of our country. It becomes entirely fit-
ting then, that those two sections, now again reunited into
a more firmly established Union should construct a span which
shall bind them more closely both literally and symbolically
to the memory of the sons of each who gave their lives in
support of their respective ideals. And.how much more fitting
will it be if such a structure be completed during the life
of the last of the survivors of that great conflict.

II. Preliminary Legislation.

For over eighty years the desirability of such a
structure had not been lost sight of, but it was not until
1901 that the movement received any serious consideration
from Congress, at which time the Senate Park Commission sug~
gested a bridge at the sight of the Lincoln Memorial, a notable
change, since all former proposals had considered a bridge to
be built farther upstream. No action was taken in support of
that suggestion until the passing of the Public Building;

Act of March 4, 1915, providing, as;follows:

Sec.23. That a Commission is hereby created, to
consist of the President of the United States, the
President of the Senate, the Speaker of the House of

 

 

 

Representatives, and the Chairmen of the Committees on
Public Buildings and Grounds of the Senate and House of
Representatives, for the purpose of investigating and
reporting to Congress a suitable design for a Memorial
Bridge across the Potomac River from the city of Rash—
ington to a point at or near the Arlington estate in
the State of Virginia, and the commission is hereby
authorized to expend the sum of $25,000.00 in provid-
ing such designs and for making such surveys and es-
timates of cost as they may deem advisable, and report
as early as may be to Congress.

It was not until nine years later that the funds
were made available thru an appropriation in the executive
and independent offices appropriation act, approved June 12,
1922, as follows:

"To enable the commission created by section 23
of the public buildings act approved March 4, 1913, to
investigate and.report to Congress a suitable design
for a Memorial Bridge across the Potomac River from the
city of Washington to a point at or near the Arlington
estate in the State of Virginia, tOgether with such
surveys and estimates of cost as they may deem advisable,
to be expended under the direction of the commission
and to remain available until expended, $25,000.00"

III. Preliminary Investigation.

The Commission,as constituted by the act of Congress,
comprised of men prominent in the affairs of the Nation; men
having the desire to obtain such a memorial as might surpass
in every way all former attempts at grandeur in such a struct-
ure. It was necessary,however,for the Commission to seek ad-
vice of expert engineers who must be qualified to solve the
multitudinous problems arising,so that the structure might
be sound from an engineering standpoint as well as perfect
from the architectural viewpoint. The Commission,therefore,
appointed the Director of the Office of Public Buildings and
Public Parks of the National Capital to be Executive and Dis-
bursing Officer. That post is filled by appointment by the
President from the commissioned personnel of the Corps of
Engineers of the United States Army. Lieutenant Colonel C. O.
Sherrill,thus,became the Executive and Disbursing Officer.
Colonel Sherrill resigned from the Army in 1926, and his post
was.taken by Lieut. Col. U. S. Grant, 3rd, Corps of Engineers,
and that officer has since rendered invaluable aid to the ’
Commission. The services of an eminent and capable bridge
engineer being required, Mr. John L. Nagle was chosen, and
Mr. Nagle has since remained in the capacity of Designing
Engineer. To himImore than to any other,should go the credit
for the solution of the multifarious problems arising from the
design. The work shall remain a glorious example of his great
skill and accuracy,as an engineer.

 

The Commission decided to employ the services of
famed architects to supply information needed to make the
structure archtecturally perfect, and to collaborate with
and advise the Designing Engineer; The Commission of Fine Arts
was asked to furnish names of suitable artists, and, from the
list suggested the renowned firm of McKim, Mead and White was
chosen, a contract being subsequently entered into for their
services.

Preliminary investigations were then commenced, and,
since various other Federal Committees as well as the Engineer' s
Corps of the U. S. Army had previously recommended the construct-
ion of such a bridge, tOgether with the published plans a/nd
data, the work of the Commission was much simplified. Earlier
plans had contemplated a bridge farther upstream than the
accepted sife, but the proposals for the deveIOpement of the
Mall, following the building of the Lincoln Memorial, con-
vinced the Commission that the most feasible location would
‘be on a line from the Lincoln Memorial to the Lee Mansion in
the Arlington Cemetery. The Mall, which has the form of a
long narrow parkway, has as its principal axis a line thru
the center of the Capitol of the United States and the Wash-
ington Monument, which line is almost due East*and West. In
accordance with the Federal Building Program which is now in
progress, the massive and glorious buildings housing all of
the activities of the Federal Government will be located
along the outside of: the Mall. The stately and massive Lincoln
Memorial is built on the shore of the Potomac River in the
line of the axis of the Mall at a distance of 4249.162 feet
from the washington Monument. and 8748.774 feet from the
center of the Capitol of the United States. The Arlington
Memorial Bridge, as proposed, would diverge to the South from
the axis of the Mall by an angle of about 24 degrees, which
however would be balanced by a roadway entering thru Potomac
Park into Rock Creek and Potomac Parkway.

The project forms the greatest memorial of modern
times, carrying out the treatment of the Nation's Capital in
accordance with the plans of Washington and L' Enfant; and how
much more fitting it becomes when it carries L' Enfant's Mall
to his final resting place at the portico of the Lee Mansion.
The cortege. of the Nation's fallen heroes will pass from the
Capitol, by the Lincoln Memorial, and thence over the glorious
Potomac to their final resting place in the Arlington National
Cemetery.

The bridge will furnish a magnificient entrance into
the city of washington for the Lee Highway, coming across the
entire country from Los Angeles, California And finally, and
perhaps its greatest value lies in the fact that it will com-
plete the binding together of the North and the South into one
great and indivisible Union, knowing no sectional lines.

The accepted bridge would consist of nine spans, four
masonry spans on either side of the river joined by a bascule
draw.span. Its total length would be 2,138 feet, with a total
width of 90 feet, there.being two 15 foot sidewalks flanking
a 60 foot roadway. Theaspans would be of low, graceful curves,
thus avoiding the possibility of dwarffng the dignified and
stately Lincoln Memorial. However, thOcthe arches would.be low,
fully ninety five per cent of the comparatively light river
traffic would easily pass under the masonry arches, thus pre-
venting frequent openings of thevdraw. TheePotomac River is not
navigable past Georgetown whidh is in sight from the bridge.

All of the masonry spans were to be faced with solid
blocks of the finest white granite, and the fébies and pier
heads carved With appropriate figures. Pylons at each end of
the bridge were to be decorated with fine statuary, the gener-
al architecture having been defined as simple and severe.

A plaza in front of the Lincoln Memorial joined to a
monumental flight of steps leading down to the water, where
landings for boats, both large and small, were to be pro-
vided. At the Virginia end of the bridge the plaza opens for
roads passing along Columbia Island, the Lee Highway crossing
to the main land over a separate bridge at the north end of
the island, and the Mount Vernon Boulevard passing in a simi-
lar manner from the south end of the island. WhenltheiArlings’
denjlsmofiaheBridgs_was first designed, the Mount Vernon Boule-
vard had not been authorized, but it has since been joined‘
thereto. The main axis of the bridge was to be carried over a
twin bridge crossing the boundary channel from thesisland to
the Virginia shore and thence to Arlington.

Thru cooperation,between the designing engineer and
theeOffice of Public Buildings and Parks,the needed surveys
were performed. The United States Engineers aided by the tak—-
ing of preliminary soundings and core borings along the pro-
posed center line of the bridge.

The commission reported to congress on April 22,1924,
submitting their complete recommendation together with detail-
ed estimates therefor, and a suggested schedule of appropri+
ations to carry out the project. The text above will convey
the general proposals of the commission and will therefore not
be elaborated upon, the general descriptions of the project
following being in strict accordance with the decision of the
commisetnn. However, there is included below a complete esti-
mate of the cost and the schedule of appropriations as it
appeared in the report, since it is believed that a more com-
prehensive idea of the immensity of the proposal can be obtains
ed thru its consideration.

Extract of Pagest44-51 Report of Arlington Memorial
Bridge Commission dated April 22, 1924 i.e. estimate of
cost; summary for entire period:

Estimates of Cost- Summaries for entire period

 

 

 

 

Substituting concrete
All granite for granite where
construction feasible
as proposed
by the arch- Omitting for- As proposed
itects. mal treatment by the Execu-
of Columbia tive Officer.
Island,and
Memorial Ent-
rance
ProposaliI Proposal II Proposal III
Memorial Bridge proper $9,250,000 $7,250,000 $7,250,000
Bridge plaza and;
waten*gate 2,300,000 1,000,000 1,000,000
Columbia Island .6,480,000 1,200,000 2,880,000
Parkway and Memorial En»
trance to Cemetery 2,390,000 480,000 1,590,000
Extension of B Street ,
Eastward to Capitol
and widening to 120' 2,070,000 2,070,000 2,070,000
Widening Twenty-third
Street from washingb
ton Circle to B St. 160,000 160,000 160,000
Grand total for project 22,650,000 12,160,000 14,750,000

 

 

 

 

 

Proposal 1: Constitutes the ideal solution; it contemplates
the completion of the entire project ascindicated on the draw-
ings, using*white granite for all steps, walls, walks, soffits
of arches, and all other visible faces excepting the pavement

of the roadways.
Proposal II:

Represents the most economical solution con-

sistent with reasonable demands of appropriateness; it contem-
plates the completion of the project as indicated on the draw-

ings, omitting the formal treatment of Columbia Island,
Lee Highway Bridge across the boundary channel, and the
Entrance to the Cemetery (but retaing the avenue across
Island as indicated), substituting concrete for granite

the
Memorial
Columbia
in all

sidewalks, steps, and soffits of all arches excepting a return
of suitable width in granite along the faces of the arches,
using granite elsewhere as in Proposal I.

Proposal III:

Is a mean between the two foregoing proposals

and is a satisfactory solution having due regard to economy; it
contemplates the completion of the entire project as indicated,
substituting concrete for granite as in Proposal II.

(Note by author: the report of the Commission recommended the
acceptance by Congress of Proposal III.)

Ten-year prOgram of expenditures and construction

End of-—

First year

Second year
Third year

Fourth year

Fifth year

Sixth year
Seventh year
Eighth year
Ninth year
Tenth year

Expanded
during year

$500,000

3,500,000
2,500,000

2,500,000

8,000,000

1,000,000
1,000,000
1,000,000
1,000,000
1,000,000

be,
Work tobcompleted during year

Engineering forces organized;equip-
ment,plant,instruments,and furnit-
ure purchased;working drawings pre-
pared,grading and dredging finished,
consultants retained,and contracts
let for actual construction work
on bridge.

Work on river piers half completed.

Work on piers completed and con-
struction of arches and superstruct-
ure begun.

Arches and superstructure finished;
draw span installed;plaza and water
gate at Lincoln Memorial,avenue
across Columbia Island,twin bridge
over boundary channel,parkway to
Cemetery half finished.

Ornamentation of main bridge and
twin bridge over boundary channel
and all work started in fourth year
finished,thus providing access
across bridge into Cemetery over
completed avenue.

In the last five years the formal
treatment on Columbia Island will go
forward with the filling of the 13-
land by the dredging in Virginia
Channel and by dumping from trucks.
The memorial entrance to the Cem-
etery and all landscape work will be
finished at the end of this period,
including the improvement of B Street
and Twenty-third Street.

The above program is based on Proposal III, involving a
total expenditure of $14,750,000.

If Proposal I is adopted, the yearly expenditure after the
second year as indicated above will be increased about 67 per
cent, the expenditures for the first two years remaining un-

changed.

f Proposal II is adopted, the expenditures for the first
five years will remain as above, those for the last five years
will be reduced to about 50 per cent, making $500,000 per

year for the period.

Detailed Estimates.
Memorial Bridge.

 

Engineering ,
iers, 100, 000 cubic yards concrete, at I28 $2,800,000
Arches and deck, 24,000 cubic yards rein-
forced concrete, at I30 720,000
Structural steel, 1,800 tone, at I150 270,000
Draw span, complete with lifting mechanism
but not ornamented 450,000
Protection for draw span 50,000
Grading for approaches, 100,000 cubic yards
earth, at IO. 75 . 75,000
Dredging, 800,000 cubic yards, at I:HO 12 96,000
Engineering and contingencies $52,909
Total ------ $4,900,000
Ornamentation and embellis ment:
Ornamentation of draw span 250,000
Granite facing for piers, spandrel walls,
and balustrades, 120,000 cubic feet,at I10 1,200,000
Statues along balustrades, 40, at I9, 800 392,000
Entrance pylons--
Groups, 4, at I28, 000 112,000
Baa—reliefs, 16, at I9, 000 144,000
Eagles, 4, at I3, 000 12,000
Ornamental lamp Poets, 40, at I460 18,400
Models 4,150
Architecture and contingencies 217,450
Total------I§,§§0,00Q
Total for Memorial bridge as
recommended herein --------------------------- I7,250,000
Bridge Plaza and Water Gate.
Engineering.
Dredging, 150, 000 cubic yards, at IO, 12 $18,000
Sea wall, 2,000 linear feet, at I75 150,000
Piling, 32, 000 linear feet, at I1 32,000
Asphalt paving, 30, 000 cubic yards, at I4. 50 135,000
Curbing, 8,000 linear feet, at I2. 25 18,000
’Sidewalks, concrete, 10,000 square ' ,'5‘
yards, at I2,4O 24,000
Concrete for steps, back walls, etc., ',‘,,
g5,000 cubic yards at I30 150,000
Engineering and contingencies 43,000

Total-----;$570,000

Ornamentation and embellishment:
Granite facing, copings, walls, etc.,

30,000 cubic feet, at I10 $300,000
Sculpture-

Groups, 2, at $28,000 56,000

Lions, 8, at $3,000 24,000

Eagles, 2, at $3,000 6,000
Ornamental iron lamp standard8,20, at I460 9,200
Models 1,800
Architecture and contingencies 3;,000

Tota l—-—------—Ig§Q,OQQ
Total for Bridge Plaza and Water Gate as
recommended herein-------------------------—--I ,000,000
Formal Treatment of Columbia Island.
Engineering:
Sea wall, 2,000 linear feet, at $75 $150,000
Piling, 30,000 linear feet, at I1 30,000
Asphalt paving, 75,000 square yards,at I4.50 337,500
Curbing, 12,000 linear feet, at $2.25 27,000
Sidewalks-

Concrete, 20,000 square yards, at I2.40 48,000

Gravel, 10,000 square yards, at I1.25 12,500
Twin bridge over boundary channel, 10,000

cubic yards reinforced concrete, at I30, 300,000

without ornamentation
Lee Highway Bridge, 6,500 cubic yards,at I30 195,000
Steps, boat landings, etc., concrete,

8,000 cubic yards, at I30 240,000
Sodding, trees, shrubbery, etc 100,000
Engineering and contingencies 140,000

Totalsa -------- $1,580,000
Ornamentation and.embenishment:
Granite facing for twin bridge, 30,000 300.000
cubic feet, at I10
Granite facing for Lee Highway Bridge,

15,000 cubic feet, at I10 150,000
Granite facing, copings, walls pavilions,

etc., 37,000 cubic feet, at I10 370,000
Sculpture-

Seated figures 6, at $10,000 60,000

Groups, 2, at I28,000 56,000

Figures at top of c01umns,2,at I20,000 40,000

Statues, 8, at $9,800 78,400
Ornamental iron lamp standards,40,at I460 18,400

Baa-relief at base of column (14 feet
by 48 feet 6 inches)

100,000

10.

Ornamentation and embeniehment continued

Models $6,000
Architecture and contingencies 121.200
Total ---------- $1,300,000

Total for treatment of Columbia Island
as recommended herein— — ———==----$2,880,000

 

Parkway and Memorial Entrance to Cemetery.

Engineering: _
Asphalt paving, 32, 000 square yards at $4. 50 $144,000
Sidewalks, 8, 000 square yards, a t {12,40 19,200
Curbing, 10, 000 linear feet, at 42 25 22,500

Crossing Pennsylvania Railway-—
Reinforced concrete, 3,000 cubic yards, at $30 90,000

 

Back filling,% ,000 cubic yards, at $0. 50 12,500
Concrete back walls, steps, etc. ,

5,000 cubic yards, at s30 150,000
Sodding, trees, shrubbery, etc., 10,000
Driveways through Cemeter ,

three-fourths mile, at 160,000 45,000
Engineering and contingencies 46,800

Total -------- $540,000)
Ornamentation and embellishment:
Granite facing, copings, walls
etc., 60,000 cubic feet, at $10 $600,000
Sculpture
Statues in niches,8, at 38,000 64,000
Busts 0n colums, 34, at @500 17,000
Equestrian in court 30,000
Ornamental iron lamp-posts, 40, at$460 18,400
Ornamental iron fence, 400 linear feet, at $115 46,000
Models 2,600
Architecture and contingencies 72,000
Tota1-------$aso 000
Total for parkway and memorial entrance
to Cemetery as recommended herein 1,390,000
Straightening and Widening B Street
Property and improvements to be acquired $1,300,000
Asphalt paving, 96, 000 square yards, at $4. 50 432,000
Curbing,28, 220 linear feet, at$2. 25 63,495

Sidewalks, 50,000 square yards, at $2. 40 120,000

11.

Straightening and Widening B Street-Continued

Engineering and Contingencies $154,000
Total --------------- $3,070,000

Widening of Twenty-third Street

Asphalt paving, 23,000 square yards,at $4.50 $103,500
Resetting curbs, 8,000 linear feet, at 1.50 12,000
Sidewalks, 13,500 square yards, at $3.40 32,400

Engineering and Contingencies

 

Total-—-‘ -——— —$160,000

The extract from the report as shown above includes only
those items contained in Proposal III, Whereas the report
submitted to Congress contained, in addition, the extra costs
applicable to Proposal I as well as the possible reductions
obtainable from the adoption of Proposal II.

IV. Authorization for Construction.

The findings of the Commission and its report were app-
roved by the 68th Congress in Public Act 463, which was signed
by the President February 24, 1925. The Act accepted the rec-
ommendation of the Commission authorizing the construction of
the project in accordance with the suggestion contained in
Pro osal III and.pr0vided for the appropriation of the sum
Of 14,750,000 over the period of ten years-

Thus became possible the greatest memorial project ever
attempted.by any nation, the cost of which was to exceed by far
that of any similar structure in the world, involving the ex-
penditure of nearly $15,000,000, and providing as it does a
magnificent correlary for the massive $50,000,000 Federal
Building program adjacent to the bridge appraaches.

CHAPTER TWO.

Description of the Bridge.
I. Organization of Forces.

The actual work of completing the final desi of the
bridge devolved upon the Designing Engineer, Mr. ohn L. Nagle,
with the invaluable aid of the Executive and Disbursing Officer,
Lieut. 001. U. S. Grant, 3rd, Director of the Office of Public
Building and Public Parks of the National Capitol. The Assist-
ant Director of that office, Major J. C. Mehaffey, Corps of
Engineers, U. S. A., and the Chief of the Engineering Division,
was given immediate charge of the design.

A complete staff of Engineers, Draftsmen and Computors
was immediately employed, great care being exercised to obtain
a high class of personnel, which was made possible by allowing
the Commission to engage experts from civil life without being
governed by the Civil Service Regulations. Thus no salary
limits became necessary, and it was not required of an appli-
cant to have been enrolled on the Civil Service Register.

The staff was immediately engaged in performing the vast
amount of detail work which was necessary before any contracts
might be let. Presumably there was never before such a bridge
designed, nor one for which the minutest details were so care-
fully worked out, involving such complete investigations and
exhausting calculations.

The Commission was most fortunate in having available the
services and advice of many experts in the various departments
of the Government , many of whena were equipped to.render in-
valuable assistance. The Federal Fine Arts Commission, whose
approval of design was necessary, contributed much advice, and
the United States Engineers Office cooperated to the fullest
extent. In addition various groups of citizens as well as in-
dividuals aided to the best of their ability, and so, when the
project in its entirety is completed, the whole community,
peculiarly symbolical of the Nation as it is, may look upon
the structure with just pride in its achievement.

The Commission contracted with Mr, W. J. Douglas of New
York City, one of the world's foremost bridge engineers, to
act as consultant, and his services have since been available
when required. It was the original intention of Congress that
the consulting architects and engineers be obtained by com-
petative bids for their services, but permission was granted
to secure them by choice and that policy was carried out.

14.

II. Final Design of the Bridge

1. Architectural Type.

The axis of the bridge will pass thru the center of mass
of the Lincoln Memorial and the Lee Mansion in the Arlington
National Cemetery. It will be composed of nine spans, the one
in the center being a bascule draw. The face of the shore abut-
ment on the District of Columbia side is located at a distance
of 760 feet from the center of the Lincoln Memorial, from which
point all stationings are referred, while the corresponding
face of the abutment on Columbia Island has a stationing of
2,618 feet. Between these points are the spans of varying_
lengths,afimmetrical about the center of the draw span, numbers
one and nine measuring 182 feet from the face of the abutment
to the center line of the piers; numbers two a/nd eight being
205.17 feet between the centers of the piers; numbers three
and seven being 211.33 feet between the centers of the piers;
spans four and six being 228 feet from the centers of the piers
to the centers of the draw span abutments. The draw span will
have a length of 225 feet between the centers of the abutments.

The roadway at the center of the draw span will be at an
elevation of 43 feet above mean low water. From that point it
-will slope downward in each direction along the line of an
inverted parabolic curve, its elevation becom.ing 31 feet at
the pylons forming the entrances to the bridge. The curve of
the arches is in the form of a segment of a circle, which
shape was considered to be the most graceful and to allow the
most pleasing proportions. The arches,having a large span in
comparison to their center height,are low and flat, thereby
increasing the beauty of their lines, and at the same time
furnishing an attractive structure which will in no way dwarf.
the stately Lincoln Memorial to which it leads.

The eight spans flanking the bascule draw will be con-
'structed of reinforced concrete faced with white granite. The
draw span, which will be of the bascule leaf type, will be
constructed of metal so treated that it exactly correspondeto
the adjacent masonry spans. All operating machinery, lookout
stations, tenders, etc., will be contained within the abutments,
so that there may be no jarring note to the beauty of the bridge.

The bridge will have a width of 60 feet between curbs,
providing for six lanes of moving traffic. There will be no
street car tracks. On either side of the roadway there will be
15 foot sidewalk flanked by a carved stone balustrsde, bringing
the total width of the bridge to 94 feet from face to face of
the granite spandrel walls.

The pier fépies will each have carved figures of the
American Eagle, and other such decorations, and there will be
carved figures above each pier. Two pylons mark the entrance

15.

to the bridge at each end, and these will have a height of
40.feet. They will be adorned in different ways by sculptural
groups, representing the indivisibility of the Nation, and
the joining together again of the North and the South. The
bridge will be 2,138 feet long between these pylons.

An underpass will be built thru each shore abutment,
thereby providing for traffic to pass at right angles to the
structure without interfering with the main bridge traffic.
The distance between the faces of these underpass abutments
to 2,056.66 feet.

Columbia Island, which forms the terminus at the Vir-
ginia end, is taken into the main project since it is desired
to formally develop that area so that it may increase the
grandeur of the project. The Island was originally a marshy
place in the Potomac River which was covered by the high tide.
The United States Engineers Office constructed the Island
from material dredged out of the channel of the river, such
that its present area is approximately 130 acres. The shore
lines have been changed so that they lie at right angles to
the axis of the brid e. The Island being long and naerw with
its major axis paral e1 to the Virginia shore, from which it
is separated by a narrow channel known as the Boundary Channel,
provides an ideal site for a formal park developement. A
plaza will be constructed here upon which will be placed two
stately columns, each having a height of 166 feet, one being
symbolical of the North and the other of the South, each sur-
mounted by statues of Victory. These shafts will form a magb
nificent frame for the Lincoln Memorial as it is viewed from
the Virginia shore.

The plaza will also furnish a terminus for roads coming
from the North and the South, these being respectively the
Lee Highway and the recently authorized Mount Vernon Boulevard,
while the main axis of the bridge will be produced thru the
plaza by two roads having a 'tapis vert“ between. This latter,
bounded by hedges and rows of elms, rises by a gentle s10pe
to the foot of the steep hill in front of the Lee Mansion,
which point forms the ideal spot for the chief memorial ent-
rance to the Arlington Naational Cemetery.

At the washington end of the bridge a corresponding
plaza will be constructed. The axis of the bridge bears south
about 24 degrees from the axis of the Mall; therefore for
symmetry a similar roadway will be constructed at a corres-
ponding angle to the north. The latter will lead into the
Rock Creek and Potomac Parkway, which when it is completed,
will provide an unbroken park drive extending from the tip of
Hain's Point in East Potomac Park, thendQKWest Potomac Park,
over the bridge plaza, and continuing thru the Rock Creek and
Potomac Parkway, National ZOOIOgical Park and Rock Creek Park
to the Maryland boundary. Thus a motorist can, by either
using the bridge plaza or the underpass thru the shore abut-
ment, enjoy a park drive of approximately ten miles in length
without any interference from the main city traffic. The

18.

underpass was provided to prevent any congestion between the
bridge traffic and that on the park drives.

At the entrance to the Cemetery will be constructed an
additional plaza, the rear of which will be in the form of a
semi-circular retaining wall 30 feet high, which will be dec-
orated with niches, pilasters, and tablets emblematic of the
Sacred Shrine to which the traveler approaches. From the terrace
surmounting this retaining wall there will be fra med, thru
the lofty columns on Columbia Island, the Memorial Bridge over
the placid Potomac, the Lincoln Memorial 5,808 feet distant,
that lofty spire which is the Washington Monument, and in the
far distance, 14,556 feet away, the glistening white dome of
the Nation's Capitol.

The roadways leading from the Cemetery plaza will connect
with the existing roads, there being contemplated few changes
in the Cemetery proper, except the construction of a roadway
leading more directly to the Amphitheatre and the Tomb of the
Unknown Soldier.

An important part of the bridge project is in the widen-
ing of North B Street from the Capitol Grounds to the river, .
thus providing a direct and adequate approach to the bridge, —»»
bordered as it will eventually be by the massive and handsome
government buildings, and the world famed parks. This grand
boulevard will also greatly relieve the present congested
traffic on Pennsylvania Avenue, which it nearly parallels.

 

The final project to be consummated by the Commission
will be the widening and developement of 23rd Street from
Washington Circle southward to B Street, at a point directly
north of the Lincoln Memorial. Thus will be provided an out-
let for all bridge traffic directly in the northwest section
of the city, as well as an increased outlet during times of
increased traffic in West Potomac Park

2. Engineering Features.

All foundations for the bridge and its subsidiary struct-
ures are carried down to hard bedprock, the piers and abut-
ments of the bridge proper being constructed of solid masses
of concrete faced with granite from a point 3 feet below mean
low water. taken as the datum plane, to the springing line at
a height of 10 feet above the same datum. The six piers are
of three different sizes, in groups of two to each size, in
accordance with their positions about the draw span, tho apll
of them have parallel faces for a distance of 48 feet on each
side of the bridge axis, the differences in length being in
the cut-waters. The upstream cut-waters are constructed of
circular segments swung from off-center rabdii, such that the
intersections of their arcs present a dull point to the current,

17.

a tangent to these segments splaying out to the full width

of the pier. The downstream cut-waters are in the form of cir—
cular segments having similar tangents splaying to the full
width of thi pier. Piers l and 6 have overall lengths of

128 feet 1 n inches, and widths of 38 feet; Piers 2 and 5 are
129 feet 1% inches long and 39 feet in width;.and Piers 3 and
4 are 131 feet 1% inches in length and 41 feet in width. The
widths given are at the rock beds, and continue upwards to

the granite line at which point there is a setéback, and above
which there is one other,suoh that the pier widths above the
water line are in each case 6 feet less than the values given.

The draw span abutments have a length of 136 feet 3% inches
thru the cut-waters, with a width of 60 feet at the rock bed
13 feet of which is in the form of a footing to balance the
thrust of the fixed arches, which footings, having a vertical “
height of 7 feet, then gradually taper back, so that the abut- *
ments have a width of 47 feet at a point 15 feet below mean
low water, from which they continue with that width to the
granite line. The main width of the draw span abutments above
the water line is 41 feet.

The shore abutments are of rectangular shape having no
cut-waters. They,are 96 feet in length and have a width and
similar cross section, less the cut-water ends, as the draw
span abutments at the bed rockpsurface, their footings being
on the shore side to balance the thrust of the end arches.

{AM-‘4 --.L_~.-flf-.a on L, fi--u o". .. .‘J‘ _.

It has been previously stated that the bridge is being
constructed of long flat arches having in general a circular
shape. The dimensions of these arches was the subject of much
discussion and involved computations, since there were many
unusual problems met with in the course of their design.
Elaborate formulae were derived to fit both the intrados and
the extrados, so that accurate coordinates could be computed
for any point about a vertical plane thru the crown of the
arch, which was taken as the origin of coordinates. The clear-
ance at the crown, measured from the springing line, is 22.725
feet for arches l and 9; 24.725 feet for arches 2 and 8;
26.356 feet for arches 3 and 7; and 27.378 feet for arches
4 and 6. Since the springing line is at an elevation of 10
feet above mean low water, and since the maximum tide is
only about 3 feet , it is readily seen that'fisr arches 4 and
6, those being nearest the draw span, there will be about 34
feet clearance to the water at high tide. Furthermore the
clear elevation of those arches at a point 27 feet from the
crown is over 32 feet above high tide, and at 45 feet from
the crown there is an elevation of the soffit sufficient to
give a clearance of 28 feet to the highest normal water. It
is thus seen that there is ample clearance for much of the
normal traffic on the river without the necessity of opening
the draw. Georgetown, forming the western part of the city
of Washington, is the head of the navigable portion of the
river, and since the channel has not a great depth few large
boats pass the site of the bridge. Perhaps 2% of the compar-
itively light traffic may require the Opening of the draw.

18.

The firures above, which incidentally, give an excel-
lent criterion of the flatness of the arches, are not ar-
pliable to the river at flood stage, which has shown as high
as 13% feet above mean low water, altho the normal floods do
not usually exceed 5 feet.

The main part of the arch barrel is constructed of rein-
forced concrete, the sides being faced with huge blocks of
granite, in the form of voussoir stones. In general the arch
barrels have a thickness of 6 feet at the skewback, at which
point they join to the piers or abutments, gradually tapering
to a uniform thickness of 2.25 feet at the crown point. Their
thickness at a point 5 feet in from the skewback varies from
4.57 to 4.59 feet, from which point the extrados splays to
the greater thickness at the skewback. Each arch barrel is
provided with five key blocks, one at each skewback, one at
veach quarter point, (half way up the arch), and one at the .
crown.

Cross walls are spaced 8 feet in the clear and have a
thickness of 2 feet, their reinforcing bars running down into
the main arch barrel. Passages are provided thru the cross walls
so that it will be possible to walk under the deck from the
shore abutments to the draw span abutments. Conduits, pipe
passages drainage etc., are provided thru openings let into the
cross walls.

The deck, consisting of the roadway and sidewalk slabs
of reinforced concrete, is supported by the cross walls. Over
the piers and abutments the deck is supported by heavy end
beams of concrete resting on longitudinal beams which are in
turn supported by columns and diagonals, all being of the
same material, and being very heavily reinforced.

The roa way has a general thichness of 11 inches with
a crown of 7' inches, while the sidewalk has a thickness of
6 inches and slopes ;% inch per foot toward the curb.

The granite voussoir stones form the soffit of the arches
at their bottoms, which are cut to the true intrados curves.
Their top surfaces form steps, there being eight such steps
for the shortest arch and eleven for the long arch next to the
draw span, the intermediate arches having a proportional number.
The voussoir stones are keyed and anchored to the cross walls
and arch ring. The spaces formed between the steps in the tops
of the voussoir stones and the pier stones will be filled by
courses of granite ashlar stones, there being seven and ten
courses, respectively, for the shortest and longest arches as
named above. This granite ashlar masonry thus forms the facing
of the spandrel walls, to which they are securely anchored.

The courses of stones run in straight lines from the steps in

the voussoirs, thru the ashlar masonry, and match the courses

in the Pier stones. Tho these courses are on straight grades

they are not exactly horizontal, from a consideration of which
some idea of the vast amount of labor involved in the computation
of the dimensions of the stones may be obtained. Furthermore,

’k.‘_- r-....___‘_._._. -5 -Lf—_7,_-r._..g€- .‘Ju

19.

the top course of stones, over the voussoirs, ashlars, and pier
stones, have their tOp surfaces cut to the true parabolic curve
of the bridge, thus greatly complicating the work of computing
their dimensions and preparing them in the quarry. Above the
top ashlar course comes the coping course, which will be sur-
mounted by the balustrade course also of carved masonry. The
voussoir stones are cut to have a thickness of 2 feet and 2 in-
ches on their top surfaces. The ashlar stones which rest upon
them vary in thickness from ten inches to one foot, the concrete
coming in the rear of the ashlar stones bringing the total
thickness of the spandrel walls to the dimension of the tops

of the voussoir stones.

The bascule draw span was not designed in the office of
the Commission, which submitted bids to firms specializing in
such designs. These bids were returned by several companies
who entered into the contest, and who subsequently offered
their designs, Many excellent plans were submitted but the
Strauss Engineering Corporation won the award, and a contract ;
was made with them for the amount of $31,000.00. This sum was t
in payment for the complete design and for inspection service i
during the erection. The span will be in the form of two jack— 3
knives which will swing on trunnions from each of the draw
span abutments. The spans will be counterbalanced, and will be
actuated by electric motors housed over the abutments and under
the decks in such a manner that no machinery will be visible.
The spans will be of steel construction faced with rustproof pl-
ates and surmounted by aluminum balustrades, all of the exterior
surfaces being so treated as to exactly resemble the adjacent
masonry spans.

3. iaterials of Construction.

One purpose of the bridge being to present an attractively
decorated structure from an architectural standpoint, it was
decided that in order to obtain the best possible appearance,
and the quality of white granite desired, the Government would
select and purchase all stone, and that the construction con-
tractors would only be required to properly place the stones on
the structure. The Commission,therefore,advertized for bids,
and,after carefully testing and studying the various samples
submitted, let contracts for the granite as follows:

A. Granite for piers and abutments in the amount
of $303,140.84 to the Stone Mountain Granite Corpor-
ation of Georgia.

B. Granite for the superstructure in the amount
of $1,350,000.00 to the North Carolina Granite Cor-
poration, with quarries at Mt. Airy.

C. Granite for the boundary channel bridge in the
total amount of $282,900.00 was let to three separate
companies, since the contracting companies had been
asked to bid on three separate classes, and it became
necessary to accept the lowest bid for satisfactory
stone.

 

20.

The quality and type of the cement and steel used in
the structure will not be discussed at this time except to
say that the specifications very completely covered the
subject, and were in agreement with the most rigid practices.

Storage facilities in ample quantity were available for
the various contracting companies, who were allotted all nec-
essary space on the Washington end of the bridge. The major-
ity of the materials have been brot to the site in barges,
and since gravel and sand formed by far the greatest amount
of material needed, those substances being dredged from the
bed of the river in the near vicinity, it was not necessary
to store them upon the shore, the material being taken direct-
ly from the barges as required. The Government constructed
an elaborate granite storage yard upon the Virginia shore
with adequate trackage facilities connected to the P. B. &

W. R. R., over which all of the stones have been freighted.
From the storage yard the stones are loaded upon barges and
taken to the bridge as needed. All stones being cut to exact
dimensions, and not being interchangeable, it became necessary
that they be plainly and accurately marked and numbered, and
that the storage system be so designed and managed as to
avoid costly mistakes and confusion.

21.
CHAPTERfiTHREE.

 

I. Piers and Abutments.

It was decided to let contracts for the construction of
the bridge in three separate contracts rather than to give
the enire work out in one contract. There was to be a contract
for the piers and abutments, one for the superstructure, and
one for the bascule draw span. ‘

Accordingly, in November of 1925 bids were advertised for
the construction of the piers and abutments to be built in
accordance with very rigid specifications. Eleven companies
submitted bids, the figures running from $1,299,000 to $3,022,
000$ a very wide range, with the average amount in the vicinity
of e2,000,000. It is interesting to note that the Designing
Engineer had estimated that the bids should run only a little
less than the average of the bids actually received. However,
the H. P. Converse Company of Boston, by far the lowest bidder,
was given the contract. The specified time of completion of
the work was to be from 550 to 730 days, weight having been
given the various bidders in accordance with the dates of com-
pletion which they had offered in their bids, $400.00 being
allowed for each day. Thus that amount per day was used in
canvassing of the various bids, and that sum was to be allowed
the contractor for every day less than his specified time
limit which he required to complete the work, limited only to
the minimum of 550 days. An equal amount per day, however, was
to be forfited by the contractor for every day over his spec-
ified time limit which he required.

As a matter of fact the Converse Company did not complete
their work before the date specified in their contract, but
time extensions were allowed because of additional work later
contracted for, and because of delays which were beyond his
power to prevent, and so he was not held to lose by his fail-
ure to complete the work on time. The company received, for
the original contract and the extra work, the total sum of
$1,396,875.43.

The work covered by this, the first contract, called for
the construction of six piers and four abutments as described
above, extending from bed-rock, at an average elevation of a
little over 40 feet below mean low water, to the elevation of
the springing line at 10 feet above the same datum. The contract
also called for the setting of granite facing from an elevation
of -3 feet to the top, together with the setting of the skew-
back stones. All stones were to be completely anchored to the
concrete backing them up, and were to be set to extremely ac—
curate limits.

The estimated quantitiee furnished in the adverti ements
had called for 31,867 cubic yards of Class B concrete 132:4
mixture); 54,822 cubic yards of Class 0 concrete (1:3:5 mix);

,..——7- - _ ..-...__. .-_._,..____,,._.-.¢——sv—_ “mu-Ail)?

460,224 pounds of reinforcing steel; and the setting of

58,457 cubic feet of granite. These estimates were essentually
accurate, except that in all probability more of the Class C
concrete was required because of the unevenees of the rock
surface, but the added quantity was negligible. Payment sched-
ules were allowed in accordance with the degree of completion
of the work, certain sums being allowed when a specified amount
of work had been completed.

The method of exposing the surface of the bed-rock was
optional with the contractor, but the entire surface had to
be exposed over the whole area of the pier and in the dry.
Furthermore,all loose material and rock of less than % cubic
yard in size were to be removed. It was specified that, should
the rock surface be smooth, holes be bored and dowels be in-
serted for the purpose of holding the mass of the piers in
true position.

Obviously, the open caisson method formed the simplest
means of accomplishing the desired results, and the contractor
used that method, driving 5/8 th inch sheet steel piling to
the rock surface, the piling being held in place and complete-
ly braced by 12 by 12 inch timbers on the inside. The water
and mud were then excavated and spilled into the river, except
at the shore abutments, where it was deposited on the shore.

II. Superstructure

The contract for the arches of the brid: e, ccxhp 056:).
of the erection of the entire superstructure .ithin the limits
of the entrance pylons, less the bascule draw s an, was adver-
tised for bids on October 10, 1727. The advertisement was in
the form of a pamphlet which contained 31 pages of general and
detailed specifications, and was accompanied by a set of con-
tract drawings containing 35 sheets of very detailed plans,
all prepaired in the office of the Commission. The time for
the completion of the contract was limited to 730 days, and the
work contemplated was the “construction of the arch barrels
and superstructures of the eight masonry spans, the super-
structures of the six intermediate piers and the two shore
abutments, and the foundations, superstructures, and under-
pass arches of the approaches to the shore abutments." It is
thus seen that this contract provided for the completion of
the bridge proper, less the draw span, except for the erection
and carving of certain of the ornamental features at the
‘bridge entrances, and for the special carving on the féhies
of the piers. It should be noted that this contract called for
the construction of the underpass abutments, which had not
been included in the previous contract, since it had been
decided to construct an underpass on each shore providing
for traffic following the river, subsequent to the awarding
of the first contract.

The contract for the construction of the superstructure,
which, tho it had the designation of Contract 15 was the

33.

second construction contract , was awarded to the Hunkin-
Conkey Company of Cleveland, Ohio, the low bidder, the sum
named being $1 576,000.00.Extras have since been allowed to
the amount of $75,376.00, and it is believed that before the
work is completed an additional $10,000.00 will be allowed,
bringing the total to $1,561,000.00.

Carefully prepared estimates of quantities showed that
41,690 cubic yards of concrete and 5,919,900 pounds of rein—
forcing steel would be required, and that 224,300 cubic feet
of granite, furnished without cost to the contractor, must
be set. It is obviously impossible in a work of this length
to completely describe all of the details, either of the pro-
posed work or the manner of its accomplishment, so that it be—
comes necessary to merely outline herein the more important
considerations of this contract.

The specifications stated that the 'arch barrels shall
be constructed in four longitudinal sections, each approximat-
ely one-fourth the width of the barrel, face to face of gran-
ite with a longitudinal key-block between adjacent sections;
the precise width of each longitudinal section being such that
the total weight of each, having regard to the weight of the
granite voussoirs of the two outside sections, shall be the
same". Because of the four various span lengths, the contractor
was required to furnish four steel arch centers, each proper- tr'
1y designed to carry the full load, and to be so adjustable
that when loaded the centers would be deflected to the true
position of the soffits. Provision had been previously pro-
vided for their support and anchorage on a shelf below the
water line on each pier and abutment. The program of pouring
each longitudinal section was provided in the specifications,
each section being divided into four blocks, the two adjacent
to the piers to be poured first and simultaniously, followed
by the two central blocks, similarly poured, all being sep-
arated by tranverse key-blocks, at the crown, each skewback,
and at the quarter points. The order of pouring of the var-
ious longitudinal sections was also specified. In the actual
construction, the steel arch centers , composed of braced
Parallel steel ribs, hinged at the crown, were floated into
position in half sections, fastened at the crown, and jacked
into place after which they were fastened and tied.

_ __ .44; __.—.- a."
x LI. ’ - ~

The lagging was to be blocked from the steel centers, and
was to be smooth finished and entirely free from any knots or
other markings, and to be formed to the true intradosal curves
of the arches. Three-ply laminated sheets of a size approx-
imately 4 feet by 8 feet were used, the quality of such a
grade that it resembled that used in the manufacture of the
best furniture.

In the outside sections the granite voussoirs were to be
set first, and in accordance with rigid specifications, the
blocks to be moved as often as necessary to place them in their
true positions. Great care was taken in the placing of the

24.

concrete on the soffits, no gravel being used in the 3% inches
nearest thereto, granite chips in rich cement being required.
The soffits were required to be rusticated and tooled to sim-
ulate the six-cut brush-hammering of the soffit of the gran-
ite voussoirs for a distance of ten feet measured from the
face of the bridge.

The method of construction of the spandrel walls, cross
walls, sidewalk and roadway slabs, t0gether with the expansion
joints and such required features as the drainage system, etc.,
were fully covered by rigid specifications in accordance with
the accepted close standards, and while necessarily most im-
portant in the actual bridge are not of sufficient importance
to be accorded further space in this work.

The superstructure contractor was required to move all ,
granite from the granite storage yard upon the Virginia shore, t
all Lewis and dag holes necessary for lifting and handling

the stones, as well as all holes for clamps, anchors, bolts,
etc., having been previously cut at the quarries. All of the E
stones were in reach of a 45 ton crane travelling on a stand- T
ard gauge sidetrack, and the maximum weight of a single stone 1
was specified not to exceed 15 tons. The contractor was re-
quired to do no ornamental carving, that service either have-
ing been previously done or to become the subject of subse-
quent contracts.

The stones were required to be set to line, level, and
position, having joints of uniform thickness, all stones to
be thorroughly washed and cleaned and wet before setting, and
each to lay in a full flush bed of rich,fresh mortar, to be
composed of non-staining waterproof Portland cement, and sand,
all to be of an approved color. The proportions specified were
to be one part cement and two parts and, and all face joints
were to be raked out to a depth of 1 inches and pointed with
a mortar of equal proportions of cement and sand. Vertical
joints were to be rammed full with thin flat blades.

All stones were required to be firmly anchored to all back-
up concrete eenerete, which was to be poured after the setting
of each two courses of stone. (This was later amended to require
the backing-up after each course of stone was in position, and
the leaving of one full day between each Operation.)

The joints of the coping and balustrade courses, and or-
namental courses above the sidewalk line were to be raked out
and filled with a plastic material, composed of Whiting mixed
‘with drying and non-drying oils having the property of oxidiz-
ing and hardening at the exposed surface, but of remaining-
plastic beneath the surface.

The stones had been previously cut to very accurate limits,
and the contractor was therefore required to set the stone to a
tolerance of 3 thousandths of a foot. After the setting of the

VOHSBOir stoneg the courses of the pier stones were set so as to

agree with any slight discrepancies in the former. After both
the voussoir stones and the pier stones had been set,very ac-
curate levels were run to determine the differences from the
contract elevations. Great care had been previously taken to
prevent any of the stones falling below their true elevations,
since it was obviously impossible to enlarge a stone tho it
could be trimmed down so that its tOp came at the true level.
The results of the levelling over the stones determined the
amount to be trimmed,if any, before the setting of the ashlar
stones. However, the work had been so carefully done, and the
stones had been reset if found incorrect in their original pos-
itions, that the amount of trimming was surprisingly small.

III. Draw Span.

As previously stated, the Strauss Engineering Corporation v
won the award of the design of the draw span. They prepared t
elaborate plane and specifications, which may be more fully
appreciated when it is said that in the advertisement for bids,
which was dated June 15, 1928, there were 46 pages of general
and detailed specifications, and in addition, a bound set of
55 pages of contract drawings. The contract, which was given
the number 83, called for completion of the work before the
expiration of 560 days after the awarding of the contract. The ~
Phoenix Bridge Company of Chicago was the low bidder, and re- an-
ceived the award for the sum of $913,611.00. At the time that
this is written the company named has not begun the work of
erection, tho they have much of the needed material at the
site, and will shortly begin to set it in place.

There can be contained herein only a breif summary of the
contemplated work, since of itself, the draw span if fully des-
cribed, and.analyzed, would require a thesis of as great a“
length as perhaps all of the rest of the main bridge.

The span will consist of two bascule leaves, operated
about trunnions, and balanced by counterweights. The trunnions
will be 216 feet center to center, and the leaves when opened
will allow 140 feet in the clear. Each leaf comprises two main
bascule trusses, which will be 66 feet, center to center, con-
nected by floor beam trusses carrying the floor s ringers.
There will also be fascia trusses, each 11 feet 9 inches
outside of the bascule trusses, the measurement given being
center to center.

The fascia will be composed of formed sheets of 3/16 inch
rustproof plates fastened to structural steel girts by spot
welding, there being on each side of each leaf, 34 panels
equally spaced, and in the form of the voussoir stones of the
masonry arches. Surmounting these will be formed plates of thesame
material, above which will be placed Torus moulding and the
balustrade with caps, both of the latter being of aluminum,
each balustrade being cast in one piece. All discs, buttons,
key-blocks, base moulding, cap and hand rail will also made of
cast aluminum, all of which will have a thickness of 3/8 inch.

26.

There will be two navigation lamps both on the upstream
and downstream sides, one being on each side of the ornamental
casting forming the centerline of the span.

The contract calls for the construction of a reinforced
concrete road slab, flanked on either side by a reinforced
sidewalk slab, which shall match those features on the adjacent
masonry spans. The roadway will later receive an asphalt sur-
facing. Granite curbs are to be set, as is also all granite
work,on the fascae of the abutments, the abutment cut-water
caps, and the abutment tOps including the granite deck seats
and the operator's and guard's cabins. As has been elsewhere
stated, these cabins are housed in the abutments, and actual-
ly form a part of the ornamentation of the bridge, the occu-
pants thus having their quarters housed in such a manner
that there will be no detraction from the beauty of the bridge.

In part the specifications say: “that the bascule leaves
.shall be erected in closed positions, and it is intended that
the east half shall be completely erected and opened before
erection of the forward arm of the west half extends beyond
the panel point No. 9." The panel point named is comparitively
near the abutment,.and so it is seen that provisions have been
made for keeping the channel open for navigation while erection

is going on, the actual opening being,however, only about 80 feet.

A partial extract of the estimated quantities entering
into the construction of the bascule draw span show:

Structural steel

 

 

 

 

 

 

 

 

 

Carbon steel ----------------------- 2,560,000 lbs.
Silicon " ------ 1,256,000 “
Rust-resistant steel Fascia plates ---- 59,000 "
Cast aluminum balustrades, mould-
ings, key-blocks, etc. - --- 39,200 “
Roadway deck
Concrete --------------------------- 360 cu. yds.
Reinforcing steel — ————-—--—- 104,300 lbs.
Sidewalk deck
Concrete —— — — ~ — w 92 cu. yds.
Reinforcing steel - ——— — — 3,900 lbs.
Counterweights
Concrete at 271 lbs per cu. ft.
East leaf — _ —— ————— —- 638 cu. yds.
Adjustment blocks — — — ——_— 102 "
Concrete at 262 lbs per cu. ft.
west leaf ——— —- ——— ‘638 ” "
Reinforcing steel — - — 87,300 lbs.

The rust-proof ornamental steel fascia plates are to
receive one shop coat of red lead paint, as is also all
structural steel, while the cast aluminum ornamental work
is to be given one shop coat of aluminum primer, both on
the inside and outside surfaces.

After erection all of the ornamental work shall re-
ceive one coat of Detroit Graphite Company's, No. 426 gray,
or equal, followed by a second coat of Detroit Graphite

an»- A ..«. n— -.-._§-.-~‘ Jul-.L.JA£E
. - .

27.

Companies Degraco, or equivalent, having a color which, in
the opinion of the contracting officer, satisfactorily
matches the color of the granite work. Since the underside
of the leaves will not receive any ornamental covering, not
being readily seen except when passing under the draw, or
when the latter is in the raised position, the structural
steel contained in each leaf will receive a first coat
similar to that described above, followed by a second field
coat of Detroit Graphite Companies' No. 38, light, or equal.

However, there seems to be a pOpular beleif that the
undersides of the leaves will eventually be covered by alum-
inum plates, to prevent the possibility of any unsightly
feature of the bridge being visible from any viewpoint.

There will be alternating electric current, 60-cycle,
3-phase, 4,000 volts, delivered to the draw span for the
operation of a motor-generator set used in providing oper— _
ating current for all draw span motors. All operating 5
machinery will be furnished, and erected by the contractor. ;
The motor-generator will transform the alternating to direct ,
current for the use of all operating motors, and will be in g
the form of a 4dunit set, consisting of one 300 horsepower g
induction motor, two loo-kilowatt SOC-volt direct current i
generators, and one 25-kilowatt exciter.

Provision is made for a possible failure of the electric
current, the contract calling for the furnishing and erecting
of a gasoline engine generator set, capable of operating all
machinery in an emergency. The engine must develop 240-brake
horsepower, and will be a 3-unit set, consisting of the engine,
one loo-kilowatt direct current generator, and one 25-kilowatt
exciter.

IV. Auxiliary Connections.

Whereas the auxiliary connections of the bridge are of
extreme importance, in the completion of the project from a
memorial as well as an utility standpoint, it remains that
those connections come as a subsequent developement, second—
ary to the main bridge structure. Naturally they are of suf-
ficient importance to receive complete descriptions in a
treatise purporting to fully cover the entire project. How-
ever, it is believed that the general description already
furnished should suffice in such a work as this, being, as
it is, a thesis dealing principally with the main structure.
Furthermore, the actual work of construction has not yet
been begun on any of the auxiliary connections, with the
single exception of the boundary channel bridge, tho the
dredging incidental to the construction of the water gate
at the Washington entrance to the bridge will, in all prob—
ability, be started during the coming summer.

The boundary channel bridge,having a span of 100 feet,
crossing from Columbia Island to the Virginia shore on a

28.

prolongation of the main bridge axis, is now in a preliminary
stage of construction. In general, it will be exactly sim-
ilar in appearance to the main bridge, from which it is sep-
arated by 852.67 feet, the distance from the westernmost
underpass abutment of the longer bridge, to the centerline of
the shorter structure, which centerline is at a distance of
3570 feet from the center of the Lincoln Memorial. A 50 foot
underpass is provided thru each aoutment. The granite for the
boundary channel bridjge was purchased at a cost of $282,900. 00.
The contract for the construction of the foundations and super-
structure, inoluding the placing of the granite, was awarded
to the N. P. Severn Company, of Chicago, for the sum of $338,
000.00. The specifications contained in the advertisement for
bids were very similar to those for the larger bridge, there
being 36 pages of printed general and detailed specifications.

It is interesting to,note that the rock bed is nearer
the surface at the site of the boundary channel bridge, and
the contractor has successfully used built-up wood piling,
consisting of 3 pieces of 3 by 12 inch timbers, 20 feet long,
so formed tOgether that the center piece mal es a tongue and
groove, allowing for a tight joint in the seams. At the
present writing the contractor has not yet reached bed-rcclc,
tho he is in a strata of rotten-rock immediately surmounting
the hard bed.

’..q._-_v..._..—._—.‘. ”wan—9A....“ an n J

HAPTER FOUR.

 

Surveying and Inspection Service.

I. Horizontal Control.

After the ccmaissicn was first appointed, preliminary
surveys were prepared, these being later revised and enlarged
so that a comparatively accurate tOpOgraphic map was com-
pleted. For the preliminary study that map was sufficient,
but the extreme limits of accuracy decided upon made an elab-
orate system of precise stations necessary, whose distances
and directions from the origvn of stationings, the center of
mass of the Lincoln Memorial, must be known to the smallest
possible limits. All of the survey work has been ably done
under the direction of Mr. George E. Clark, Chief of the
Survey and Drafting Section of the Office of Public Build-
ings and Public Parks, to whom the author has acted-as—ae-be‘d"
as First Assistant Chief for the last three years.

The problem was further complicated by the fact that
the saw-tooth glass roof construction of the Lincoln Memorial
prevented the exact center of the building being occupied as a I
an instrument station, altho a signal was erected so as to an”'
rest directly over the true center, and an instrument station
was established on the upper parapet of the structure, which
station was on the exact line thru the center of the Lincoln
Memorial, and the center of the Lee Mansion, the accepted
axis of the bridge. It was possible to accurately measure the
distance to the parapet station, and all subsequent stationings
were referred to it.

'4' " .- “‘""T‘ —'v‘TT' 37‘7’77"'

There were available a rather large number of triangulation
stations, which had been established by the United States
Coast and Geodetic Survey, but unfortunately these stations
had been established at different times, and for varying pur-
poses, and had never been adjusted into a common net. Some
few of them had been closely connected to the prime stations
of the Survey, but the majority were of third order triang-
ulation.

It was decided to utilize certain of the more precise
stations for the establishment of geographic positions, and
geodetic azimuths, and to connect these to a separate system
of triangulation for the bridge, which system should consist
of a large quadrilateral of approxitately rectangular shape,
having a measured base on either side of the river. Consequent-
ly, two stations were chosen on each shore, all four of which
were visible, each from the other. One of those on the Washing-
ton shore was placed in the granite sub-base of the Ericsson
Memorial, about 875 feet south of the bridge axis. The other
stations were marked by U. S. P. B. & P. P. standard brass
triangulation markers. Sub-surface markers were set at these
points, at a depth of about five feet, and directly above
them, in solid concrete structures, not connected directly
to the sub-surface markers, were placed similar surface markers.

30.

The two bases were then measured by the most precise
chaining methods, thru the use of invar tapes, the tapes
being supported upon chaining stakes placed in accordance
with the method used in the standardization of the tapes,
which service had been sup1.lied by the United States Bure.; 'tu
of Standards. Accurate levels were obtained over the ch lining
stakes, and the Ineasured results were reduced to the horizon-
tal. Temperatures were obtained from cente3rade thermozneters
attached to each end of the ts . The measures v.ere repeated
several times, the results obtained after computing showing
the East Base, on the Washington side, to have a length of
2579.273? feet, and a probable error of l in 1,101,000,
while the West base was found to have a length of 2405.6064
feet, and a probable error of l in 2,327,715. The results
of the measurements were most satisfactory, particularly
those of the base on the Virginia shore, while the East base
showed a precission far above the accepted standards. t'

The turning of the horizontal angrles was next accom— g
plished, and it became necessary to take many sets from each '
station, in order to have the angles of a sufficiently pre-
cise nature to be comparable to the precision of the distance
measurements. Several sets of direction angles were turned 5
from the quadrilateral corners, but a number of sets of rep- 1,
etition angles were found to give more satisfactory results. 1
For this purpose an excellent transit, having verniers read- “*3
ing to 10 seconds of arc, was found to give remarkable results.
All angles were turned from each station, and in addition,
all of the accepted trian~u1ation stations previously mentioned
were cut in. The horizontal angles were turned in the follow-
ing manner:

1. With the telesc0pe direct, and the plates set at
zero, both vernier readings being recorded, the angle
from the left to the right station was read, and both
verniers again recorded.

2. With the plates clamped at the first reading the
left station was again sighted by using the lower motion,
and the angle to the right station again turned as above.
This was continued until the angle had been turned six
times, the results being accumulated in the plates, which
were then read and recorded. Naturally l/Sth of the pls te
reading was the mean of the 6 turnings.

3. The telescope was then reversed, and without dis-
turbing the plate setting, the exterior, or horizon angle
from the right to the left station was turned six times
as described above. This comprised one-half of a set. The
method, which is somewhat enmilar to the method usually
employed for repetion angles, except for the order of
ppintings, and the manner of computation of the results,
tended to remove instrument errors as well as furnishing
six turnings of each angle.

If the plates had returned to zero after the turn—
ing of the exterior angle six times, as they should, the
the original value was checked. If however there was a
remainder left in the plates, of say, 30", the reading

being, 359-59‘—30", one-sixth of the difference was

31.

added to the mean of the first six turnings, and a mean
of the two results taken.

If however, the plates had gone past zero, and had
a reading of say, OO°-OO'-30", one-sixth of the dif-
ference was subtracted from the mean of the first six
turnings, and the mean taken as above.

4. The plates were then again set to zero, and the
process was repeated, turning this time,however, the
exterior angle first.

When the work had been finished there had been
taken 12 turnings of each angle. The summation of
the final results should add to 360'-OO'-OO", but
should they not, a preporticnate horizon correction
was applied to each. The 24 turnings comprised one set,
and to be accepted, the horizon closure must have
been less than 03", and in addition, not more than
05“ was allowed between the direct and reverse turn—
ings of any angle.

Several sets of all of the angles from each station
were observed, and the means taken. The results were re-
markably close, entirely within the desired precision.

After all required field data had been obtained a
"Least Square Adjustment” of the quadrilateral was com-
puted by the Doolittle method. The small residuals obtain-
ed were an added criterion, tending to prove the accuracy
of the field work.

Stations exterior to the main quadrilateral were placed
upon the bridge axis on the washingtcn shore, and these were
accurately connected to the quadrilateral. Thru them excellent
means of determining stations were available, since they were
closely connected to the origin of stationing. However the
bridge axis cutting, as it did, thru the quadrilateral near
its middle, and at right angles, approximately, to the bass
lines, the stations on the-on—the Virginia shore were useless
as measuring stations. It therefore seemed advisable to ex-
pand the main figure, thru the inclusion of two more stations
at the intersection of the bridge axis with the bass lines.
These were then established, and while the final results were
satisfactory, from the standpoint of line,since they were ‘
proven to be directly on the bridge axis, they were found to
be slightly off from the original bass lines, the the dis-
crepancy was but a fraction of an inch in each case. All nec-
essary data for these additional stations was then determined,
the turning of angles to them from all of the original stations
being required, as well as all angles from the new stations
to all others in the system. The results of the original
quadrilateral were not disturbed however, the figure presenting
a double quadrilateral contained within the original figure,
thereby greatly complicating the computing of the adjustment,
which however, the author hereof accomplished in such a man-
ner as to allow of all necessary control of a rather high order
of precision. The least square adjustment, which was made by

32.

the Direction Liethod, required ll condition equations in order
not to disturb the ori:;: inal fi3ure. These condition equations
comprised 6 an 3le equations, 3 length equations, and 2 side
equations. The results showed a probable error of an observed
direction to be plus or minus 4.90", which, altho it may appear
high upon first inspection, was however rather satisfactory,
since no local corrections nor weight adjustments had been
previously applied to the observed angles. In the description
of the method of turnin: the an gles as described above, the
angles were computed for horizon closure, and so corrected
merely as a criterion of their worth, the actual read values
being used for the adjustment, causing the apparant probable
error to be larger than tho the local adjustments had been
previously applied. All of those corrections therefore appear-
ed in the conditional equations, and furthermore, the fact
that the angles required to meet the conditions of the double
quadrilateral, were required conditionally to agree with the
angles which had been previously adjusted in the original fig—
ure. Those circumstances therefore made the V's appear to be
relatively higher than they would otherwise have been, and
consequently the Probable Error appears relatively high. It is
the belief of some eminent authorities, with which the author
concurs, that the general practise of applying the so called
"Least Square" adjustments to the individual angles, while it
‘undoubtedly offers-lower apparent probable errors, actually
does not reduce the true probable error, and is actually more
apt to increase the error of any observed direction. That, of
course, does not ap; ly to we ight adjustments, which however,
were not ap;;lied in this case, since th e an3les were all turn-
ed under similar conditions, and were furthermore, because of
position, of equal worth.

From the known triangulation stations, whose geOgraphic
positions were known, the data for computing the geodetic
positions of the stations of the bridge system was obtained,
the resulting positions furnishing geodetic cccordinates used
in locating the stations on the maps. Accurate geodetic az-
imuths were computed between all stations. The azimuth of the
bridge axis, from Station East, on the axis of the bridge at
the Washington shore, was found to be 65 °-05'-55. 34", the
azimuth being measured from the south.

The most valuable result of the system of triangulation
was the establishment of the exact position and stationing,
referred to the origin, of that station on the bridge axis
on the Virginia shore, which was called West, since it there-
by furnished a means of locating work from from that end of
the bridge, and within exacting limits, a feat otherwise im—
possible since there was no way of making a direct measure-
ment across the river.

The corners were also used for the purpose of locating
range points, and for the centering of the cofferdams, as well
as for the checking of the forms after the cofferdams were un-
watered. These stations proved to be of great value until the
piers had been built up to such a point that the bridge center—
line could be accurately and permantly located upon them.

33.
II. Vertical Control.

The District of Columbia is included in the general ad-
justment of the precise level net of the United States, as
established by the United States Coast and Geodetic Survey,
there being several bench marks of that net in the District.
The key bench, however, is the so called "Capitol Bench Mark“,
located on the Capitol building, and it was from this that
the levels establishing the elevations of the bench marks used
in the construction of the bridge were run. The Office of
Public Building and Public Parks ran a closed loop from the
Capitol bench, thru a series of benches which they located
in the vicinity of the Lincoln Memorial. The levels were run
with a standard U. S. C. & G. S. Precise Level, and the 100p
was subjected to a rigid least square adjustment, the result—
ing elevations of the bench marks being referred to the datum
of the United States Engineers Office, being mean low water
in the Potomac River. The elevations obtained were specified
for use in all work in connectionovflfithe bridge.

All of the preliminary work was referred directly to
those bench marks, but as the work pr0gressed, and as the
bridge began to take shape, secondary benches were established
at the site, thereby avoiding the necessity of running level
lines of any great length. After the piers and abutments had
been constructed up to an elevation of plus 10 feet, being
the limit of Contract No. l, plugs were set into the cement
on the bridge axis, and at the ends of each pier and abut-
ment. These plugs were very carefully located for line, the
axis being repeatedly thrown down from the parapet station
before the centerline was established, and the off-set plugs
were set at equal and exact distances from those in the center,
and at right angles to the axis of the bridge. Careful measure-
ments were made, and accurate stationings determined, such
that all subsequent work could be located from these plugs.
Precise level lines were then run over all plugs, and,after
many check runs,the elevations determined. Thus were provided
stations which served both as accurate line and position
stations, and as precise bench marks as well. Subsequently,
as the work progressed the plugs were used to carry elevations
and lines to points higher up, and after the decks had been
poured over the various arches, and piers and abutments, ad-
ditional plugs were placed in a manner similar to that already
described. Obviously, because of the temperature deflection of
the arches, which, measured from the reference temperature of
55 degrees, Fahrenheit, has a variance, plus or minus, of
about three-eighths of an inch, the upper bench mark plugs
could not be located on the arches. They were,therefore, set
into the deck, over the piers and abutments, and tho the
granite and concrete forming the latter naturally expands and
contracts with the varyong temperatures, the divergences are
negligible.

Precise level lines of the same accuracy, and connected
into the same 100ps, were run over the Virginia shore, fur-
nishing bench marks for the work located there.

34.
III. Surveying Hethods.

flush of the surveying work has been covered in the
description of the control surveys, but there is a vast
amount of routine work connected with the construction
of such a bridge, and there will,therefore, be included
herein a brief outline of the methods employed.

The various contractors have been required to lay out
all work, and to be entirely responsible in having each part
come at its true pos-tion and 3rade, er id they have been re—
quired to move any part or piece as often as necessary in
order to place it in its proper relation to the rest of the
structure.

The government has , however, maintained a survey party
at the site, whose purpose it ha been to check all work
layed out by th e contractors, as s.vell as to do any survey-
ing work incidental to any part of the project not yet fully
determined. This party, .hich is furnislied by the Office of
Public Euildin3s and Public Parks, has seen composed of from
four to eight men, or more, varying with the se ason, and with.
the amount of work bein3 carried on. The chiefs of party have
been graduate Civil Engineers, and have been picked for their
ability, those chosen usually having had the rank of Assist-
ant Engineer in the Civil Service, or its equivalent, if em-
ployed on the Arlington memorial Bridge roll, which is not
subject to the Civil Service Regulations. The personnel have,
for the most part, been student engineers of George Washing-
ton University, pursuing their studies during the evening
hours, or those who liave had some technical education else-
where, or its equivalent in experience. Thus a rat her hi: h type
of survey party has been assi 3ned to1he checkinv work, all
members of which have been carefully selected for ability, and
thoroughly trained and coached in the requirements of their
work.

The instruments and equipment furnished have been of an
excellent grade. While it is not intended to advertise ncr
to condemn, the product of any company, it is only just to
say that Berger transits and levels have given excellent re-
sults, and a DGurley level has proven most sa.tisfactory. For
almost all of the work short sights have been obtainable, and
New York level rods, without tar3ets, have given good results,
but for the most accurate work of an ordinary nature, tarjets
have been used. Of course, when precise levels have been run,
precise rods of the yard type have been used. All level rods
have been sent to the Bureau of Standards for comparison with
the standards of the United States, before bein3 us ed in the
field, and the necessary corrections applied to th -e results
obtained from their use. All tapes and chains used at the
bridge have been of th is finest quality procurable, and they
have also been previously sent to the Bureau 0 Standards for
calibration, the values being supplied for each ten foot mark,
and when used the corrections made prOportionate between the
two nearest calibrated marks. Furthermore , after they have been
in use for some time, and it becomes possible that their lengths
have changed, th ey are a3ain sent to the Bureau. Invar chains

35.

of 50 meters and of 100 feet in length have been used for the
most accurate work, while steel chains of 300 feet, 800 feet,
and 100 feet have been used for all ordinary work. A good
quality of box tape, in lengths of 50 feet and 100 feet have been
commonly used by the surveyors, these also having been pre-
viously calibrated at the Bureau of Standards. The tests at
the Bureau have always been for the tape when supported thru-
out its entire len3th, and also when swung as a catenary, the
corrections then being given from the zero end to each of the
10 foot marks, when swung as a catenary. This greatly facil—
itated the computing of the results. Temperatures have been
recorded on accurate thermometeres, but great difficulty has
been had in insuring that the thermometer recorded the actual
temperature of the tape. On certain occasions, when measuring
from pier to pier, the 100p of the tape would hang near the
water, while the ends would rest upon the concrete well above
the water line, and in consequence, great difficulty was had
in getting the true temperature of the tape. Standard tension
apparatus has been used for all accurate measures, and chain-
ing levels have been run so as to be comparable to the accuracy
of the distance measurements.

As has been previously stated all work is held to very
close limits. It might be generally said that all important
features, such as the granite and its joints, are so accurate-
ly set that no discrepancies are discernible to the naked eye.
As an illustration of this , it is only necessary to say that
the top of the cOpin3 course, which,at the time of this writing,
is being set on the Washington end of the bridge, will at one
point be 3/8 th of an inch above its true elevation on the
parabolic curve of the bridge axis, but that this point of ex-
treme divergence is prOportionately compensated to the true
grade at points nearly 200 feet distant each way. The average
discrepancy in the elevation.of the balustrade will, in all
probability, be less than 1/16 th inch. It must be understood
that these are accumulated errors, being only a few thousandths
of a foot in perhaps each of the courses beneath the cOping
course. The stone lines, and the mortar joints are so nearly
perfect that it requires very careful study to find the few
points where the stones vary evenlslightly from their true
positions. All mortar joints are a inch in size, and so care-
fully are the stones cut and set, that the eye can hardly
find.a.variance from course to course, and.then only by care-
fully following the stone lines, while suspended upon scaffolds
over the side of the bridge, in such a position as will not
be provided an observer after the completion of the bridge.

The chief of the survey party keeps in very close contact
with the work in pragress, and the contemplations of the
various contractors. Obviously, when any work is laid out the
contractor is desirous of completing that particular unit, and
it consequently becomes necessary for the government surveyors
to promptly complete their work of checking. Adequate bench
marks and line points are provided, and these are utilized by
the checkers, who go about their work in a very systematic
and orderly manner.

A rather large amount of computation work has been re-
quired of the survey party assigned to the bridge, by far
the greatest part being the computations of the elevations
of the joints of the ashlar masonry, and of the coping course
above it; On each arch, after the voussoir stones and pier
stones were in place, accurate levels were run over their
tops, and the discrepancies from the true elevations deter-
mined The cuts were then specified, and it became necess try
to compute the elevation of each joint, to the nearest thousand-
ths of a foot, involving a great deal of work because of the
inequalities of the stone dimensions, and the sIOped grades
of their tops. All vertical joints are staggered, the joints
of every other course being vertically above the joints of
the alternate courses below them. The tOp ashlar course, and
the coping course above it, are on the parabolic curve, and
the computation of the corrected elevations of the joints of
these courses required a vast amount of work.

Considerable work was done for the purpose of determin-
ing the effect of temperature upon the deflection of the arches.
Naturally, some accurate data had to be procured before 'the
setting of the voussoir stones of any arch could be preperly
accomplished, and in order to insure that the various arches,
set at different temperatures, would be relatively the same.
After the first arch had been set, using the theoretical
amounts of deflection, and allowing consequently for the ex-
pansbn or contraction due to the temperature, accurate levels
were run at frequent intervals, the temperatures being record-
ed at the time of each run. Curves were then plotted, and com-
putations performed, from which was found that the previously
computed theoretical values very closely checked the amounts
actually observed, both for the arch ring, and after the deck
had been poured, and that no appreciable errors would arise
from the use of the theoretical equations. An excellent Oppor-
tunity for very exhaustive tests on the subject of the temper-
ature deflection of arches was presented, that subject never
previously having been fully or completely determined, and
there being no accurate or reliable data available, based on
actual observations in the field. The United States Bureau of
Standards was therefore engaged in the making of those tests,
and to that end there was installed much equipment, and many
valuable and extremely accurate instruments and recording de-
vices. The work is not yet completed, and no data has been pub-
lished, but will be made the subject of a complete report and
discussion at some subsequent date. The author hereof had
hoped to include in this work a complete discussion of the
method employed, tOgether with a discussion of the results
obtained, but because of the above circumstances is forced to
omit that work

IV. Inspection Service.

In addition to the survey party assigned to the bridge,
the government has a corps of inspectors on the site, whose
purpose it is to carefully observe all work. These are headed
by a Resident Engineer, Mr. H. N. Crichton, who has as his

37.

assistants, competent engineers, and in addition, experienced
granite, concrete, and steel inspectors, each of whom is
charged with observing all construction in his respective
line, which goes into the make—up of the structure. The
quality of the various component parts of all concrete, and
of the varying types of all mortars used, is very closely
watched. Slump tests are made from samples of each pour, and
cylinders are made from each batch of strength concrete, which
are subjected to compressive tests, the forms for all impor-
tant-work remaining in place until the tests show the desired

strength. The compression tests are made at the Bureau of
Standards.

The government secured the services of a granite expert,
before the awarding of any contracts for the purchase of stone,
and his advice was utilized in the making of selections from
the various samples submitted. In addition, there has been
maintained a complete staff of granite inspectors and checkers,
at the quarries, whose duty it has been to carefully watch all
stones, for both quality, and the cutting to exact dimensions.

CHAPTER FIVE.

 

Engineering Features of Construction.

There have been included in the text above, a great many
of the multifarious problems of interest from an en ineerin:
standpoint, which have been observed during the course of
construction. They were included with those portions of the
description to which they applied, since it was thot that
they would thus more nearly clarify, in the mind of the read-
er, a conception of the immensity of the work. Mention should
be made, however, of some of the more unusual features ob-
served during the course of construction, up to the present
time.

As this is written, the Washington end of the bridge is
rapidly nearing completion, from the standpoint of the super-
structure contract, there remaining but a single course of
ashlar stones to be laid at the ends of the majority of the
arches. The coping course, part of which is in place, will

follow, after which will come the balustrade and rail courses.

The cut-water cap stones will not be placed until all danger
of damage to them, from falling objects, is removed, thru the
completion of the work above. The Virginia end of the bridge
will require the rest of this year for completion. The arch
rings and all voussoir stones are in place, while the cross
walls on one arch have been poured, the deck on that arch
now in the process of being poured. The contractor has, nat-
urally, benefited from his experience in constructing the
Washington end, and the work will go forward more smoothly
on the other half.

The contractor for the draw span construction, who will
shortly begin his work, will require from 8 to 10 months to

complete the erection. The work on the boundary channel bridge

will, in all probability, be completed during this year. When
the word completion is used, it should be understood to refer
to the finishing of the present contracts, and the making of

a structurally complete bridge. There will remain, however,

the special ornamentation, carving, and completion of the ent-

rance pylons before the main structure is complete. The work,
closely connected to the bridge, which is not yet begun, in-
cludes the construction of the water gate, plazas, entrance
pylons, etc., not to mention the construction of the roadways.
Within a year the bridge would be usable, if the roadways
across Columbia Island, and on the Virginia shore were com-
pleted, but those features will retard the actual utilization
of the structure, until, perhaps, the autumn of 1930.

There will be required five more years for the completion

of the entire project, during which time the formal treatment

38.

of Columbia Island, memorial entrance to the Cemetery, improve—

ment of B Street, and Twenty-third Street, and all landscape
work will be finished.

39.

It may be seen, however, that the main part of the pro-
gram, the bridge proper, will be practically completed during
this year, or early in the following year, at which time there
will have passed, four years, since the first work of con-
struction began.

The excavation for Abutment l, which was the first work
attempted, gave more trouble than all of the rest of work in
the first contract. The shore, at its rear, was "made ground“,
being composed of a fill of earth, brick, Cinders, broken con-
crete, etc. When the caisson was excavated, the spilled earth
was piled on the shore side, and because of its great weight,
on the filled ground, the bank pushed out carrying the caisson
with it. Whereas, there had been an 18 inch clearance allowed,
from the neat cement line to the sheet steel piling, the latter,
after bein' moved out, was found to be nearly 8 feet inside the
concrete line at one point. The contractor was not forced to
construct a new caisson, but was required to place an equal
amount of concrete to that lost at the moved point, at some
other section of the abutment, so as to maintain the same
net volume. The concrete was poured against the piling on the
shore side, no forms being laid, and the steel was not removed.
The rock surface at the southeast end of this abutment wa
found to be nearly 60 feet below the water line, and the Iziling
beinf too short, required splicing, which g:ave some difficulty
in keep ing the water out. Floods overtopped the pilin three
times, causing some delay and expense. Grains of wheat were
forced into the joints in the sheet steel pilingz, which, when
they expanded, rendered the caisson nearly water ti: ght. Some
difficulty was had with Pier 5, the piling not havin.g been
driven to rock, resulting in mud washing in. This was stopped
by placing weak concrete, which was later cut out, and replaced
with the proper mixture, to the correct form lines.

The rock surface was found to slope gradually from the
Virginia end, downward toward the Washington end, which was
as had been indicated by the core borings. The surface of the
rock was everywhere most satisfactory, being sufficiently
rough to insuse the proper holding of the piers and abutments,
without the use of dowels.

The first contractor had acne difficulty in the placing
of back-up concrete, behind the face stones of one of the piers,
near its top. He had attempted to make one fill behind two
courses of stone, which was equal to about 10 feet in height,
the concrete, when placed,moving the stones out. It was then
necessary to cut out a large amount of concrete, remove the
stones, and.reset them.

The remarkable accuracy of the computat one of the de-
flections of the steel arch centers, afteflf59 the full load
‘upon them, has been discussed. They'were so constructed, how-
ever, that little was left to chance, and provisions had been
made on the sides of the piers for their support. Not so,
however, with the centers 1hr the underpass abutments. These

40.

centers were constructed of timber bents, with the lagging
wedged into place. The bents rested upon the ground, and it
was difficult to determine the pr0per position of the bed,
such that, when loaded, it would be deflected to the true
position. When the centers were removed, it was found that
both the upstream and downstream voussoirs were nearly % inch
too high at the Washington end, while the Virginia underpass
was more nearly to true grade. The high stones were then trim—
med, so that their tOps came at the true elevation.

Weather conditions have been generally favorable for all
contractors. Floods in the river have caused some delay, tho
there have been no unusually high waters. Ice has formed no
serious drawback, the river not having frozen over to such an
extent that the tug boats could not readily break the thin
ice crust which had formed. High winds have caused more
damage, particularly to the superstructure contractor, Who
has lost forms on several occasions, and whose concrete plant
was once blown over, and destroyed, during a wind storm.

The setting of granite has not been allowed during the
winter months, between the dates of November 15 th, and
March 15 th, because of the inability of preventing the
freezing of the mortar. The pouring of concrete has been
allowed thruout the winter, however, tho the contractor
was required to thoroughly heat all materials, and protect
all concrete, when in place, from the possibility of freezing.

The quality of the work having been of a high degree,
the contractors have, of necessity, been forced to employ
many skilled artisans, to whom they have paid a relatively
high wage. There have been no labor troubles, and at no time
have the contractors had any difficulty in procuring help,
either skilled or unskilled.

There have been a surprisingly low number of serious
accidents, and these have been, for the most part, due to the
carelessness of the workmen. One death was caused, by the
failure of the steel boom of a large derrick, engaged in
the pulling of sheet steel piling, the boom bending under
the strain and, swinging around, striking three men, two of
whom were not so seriously injured.

41.

W

There remains little to be said. It is believed that
the thesis as presented above, very fully and accurately
covers the subject, as titled, both as to description of
the project in its entirety, and of the manner of its ac-
complishment, to date. It is believed, that its perusal
should give the reader a comprehensive idea of the immensity
of the work, and the glory, and grandeur, which will be,
once it is completed, that greatest memorial structure ever
gonceived and accomplished by man, The Arlington Memorial

ridge.

BIBLIOGRAPHY.

Acknowledgement is made, and thanks given, by the author
for information gained from:

1. The Report of the Arlington Memorial Bridge
Commission, which it presented to the 68th Congress
of the United States;

8. The sets of complete drawings and specifications
for the various contracts, which have been issued to
date;

3. The conversations which the author has had with
the various officials interested in the structure, all
of whom have been named herein;

4. And, finally, to the position of Associate
Engineer, and Assistant Chief of the Surveying Section
of the Office of Public Buildings and Public arks,
which the author has held, giving him an unusual op-
portunity to observe the work during its progress.

 

l ’0' I. .0 v V CON ..u . l r990, . I . e3 ..
e I- C II I a, I ..v o 0 u . . o. r, .
x07“. .. ems.-. s.......x- . 1......L» . - i--- . 3.... ..

. .. . . _u...c..§_u.r..u&.wn-_M. : t.. , .‘

v|l.'v.e Joel!- I‘tk-fr (V W... ... D"¢~JIL . s.- 31 _. |ultlns slide 4
a.“ .. a. «mafifiunswkfim carts. 1.. .

V ' 0C .
A a. .vJ-ro I’m. (or... own. :1"

 

 

 

 

a. Iv.X I.

1.1...

   

 

    

aimless... ..
The. .... litres.

 

 

 

 

 

.44; in! . "Isl .I It PIN:FII-n.. ‘4 . 4
bier; .v- .p, .. \, wt. t v....:‘§.fl... 4 :J. . v .1 wt. «‘1. ~££2fv1§r\.~\\$al.3hve «I! I, f, .:, .i. i . i...,.r II» P? .. . 352...»? ,n v .1. .{h}. .I, hid. rifle}.

 

IIIllhlilllfljlfllfllmuIllifltljlflllsllllwlwmHIIH