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SSSSSS

IdITERIIfiILE

IN BACK OF BOOK

 

   

 

PLACE IN RETURN Box to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

2/05 p:lCIRC/DateDuo.indd-p.1

 

Judd Street Timber Bridge,

East Lansing, Michigan

A Thesis Submitted to
The Faculty of
KICHIGAN STATE COLLEGE
OF

AGEICULTL;T.ATD APPLIED SCIWNCE

by

William L. S emeker

h
‘A
m

Candidate for the Degree of

bachelor of D'cience

June 1943

THESIS

Table of Contents

Page
Introduction 1
‘Appreciation 3
Data 4
Allowable stresses 5
Floor Design 7
Stringer Design 9
Floorbeam Design 15
Truss Design 25
Camber 31
Bracing 51
Deflection 33
Bibliography 35

148235

INTRODUCTION

fhis thesis covers the complete drawings and design for a timber
bridge to connect Judd Street and East halamazoo Street located in East
Lansing, Hichigan.
There is no actual need for a bridge at this place since there is
a bridge across the Red Cedar River two blocks east on Harrison Road,
however for the purpose of this thesis it will be assumed that a bridge
is needed at this point and is to be built in the near fUture.
Because of the war priority on steel a timber bridge was chosen.
A steel bridge would be out of the question, and it would be difficult
to obtain the necessary reinforcing for a concrete structure. The use
of timber to-day is becoming wide spread and is being recognized as one
of the foremost substitutes for steel in roof trusses, bridge trusses
and in many other structures. The use of timber connectors has greatly
increased the strength of timber joints, and the methods of treating
timber have reached the point where if painted and cared for pronerly,
the timber structure will last almost as long as steel.
The advantages of timber for use in bridge construction are many.
Below are listed a few.
1. Low first cost.
2. Naintenance cost is low.
3. Simple erection saves time and costs.
4. Less material and hardware is required.
5. Re-use and salvage value is high.
6. Maximum amount of local labor and material is

used.

The rapid deveIOpment of our highway system, resulting in constant
changes in location and capacity has caused the consideration of 40 to
50 years as a reasonable life for most bridges. Since past history
shows that wood bridges have a life of from 50 to 100 years their
economy is quite apparent over a 40 or 50 year period when the above
mentioned advantages are given full consideration.

Since this bridge is to be built in Michigan the Michigan State
Highway Department Specifications for Highway bridges were followed
unless otherwise noted.

The preliminary survey included in this thesis was carried out

more for the purpose of determining the span necessary and the position

of the bridge relative to the river than for construction purposes.

I would like to express my
appreciation to Fr. Charles A. Miller
of the Michigan State College Civil
Engineering Department, Kr. Gleason of
the Michigan State Highway Department,
Bridge Design Division and to ur. E. S.
Lank, structural engineer for the
Timber Engineering Company for the
advice and cooperation given to me during

the preparation of this thesis.

DATA:

COPPUTATIOKS CR TFE DESIGH

OF THE 72' HOV; TRUSS.

Live load.

 

H-15 (Michigan State Highway Department Specifications)

Impact

Host all of the latest theorys on timber design state
that no account need be taken of impact since the
resilience of the wood is supposed to absorb the shock.
To be on the safe side the Kichigan State Highway
Department's impact formula for steel structures was
used in this design with I== 30% as a maximum.

I == 1 4— 20

61+20

Dead load.

 

Timber is assumed as weighing 60 pounds per cu. ft.

Steel as weighing 490 pounds per cu. ft.

Specifications.

 

Unless otherwise noted the Michigan State highway

specifications for highway bridges were used.

iemperature.

 

No account was taken for temperature differences as

the coefficient of expansion for wood is very small.

Stresses.

The unit stresses used by the hichigan State highway

Department are those recommended by Forest Products

Laboratory, U. 5. Forest Service, for material

complying with structural grades of the American

Society for Testing Materials.

The unit stresses given are for three different

conditions of exposure during use.

The exposure in

this case being occasionally wet.

Where

4" and thinner S" and thicker

1,370 #/sq. in. 1,515 #/sq. in.
265 #/sq. in. 265 §/sq. in.‘
105 fi/sq. in. 105 #/sq. in.

Allowable stress in extreme fiber due
to bending and axial tension.
Compression perpendicular to grain.

Iorizontal shear.

For compression parallel to grain see table below.

 

RATIO OF LENGTH To LEAST DINEN~510N

 

 

 

 

 

 

 

 

 

 

 

 

\-\o )2 I4 06 18 20 25’ 30
mes use me [.083 apes 97/ 702 487
Fig. 1

Fodulus of elasticity== 1,600,000

These values are for Douglas Fir-dense select
structural grade. All lumber shall be of a
structural grade (848). All lumber shall be
fabricated before treatment and then pressure
treated with creosote by the empty cell process

with a retention of not less than 8 5 per cu. ft.

Truss.

Type - Howe

Span - 72' (Four panels)

tidth - 23 ' Center to center of trusses.

Height - 15'.

DESIGY OF FLOORITG:

15 Ton truck of H-15 loading has rear wheel as shown.

 

 

 

 

u. V Fig. 2
l5"

 

 

 

Say use 2"x6”
Live moment - (occuring at center of outer two stringers)

M= 7/40 x Pl= 7/40 x 12,000 x 3: 6,300'#

 

Impact.

Eleigl :: 60.5w so use 30%

181—20

.30 x 6,300 = 1,5190%;
Dead load -

15 I 6 q 1.;

( 144~v—) x 00— “7.517

2 17?

M = 1/14 wl = 1/14 x 37.5 x 9 = 24.0

Total -

6,300 + 24 + 1,890 = 8,214'53'

0"

EC

5:: __.
I

1"“ M= 8.214 x 12: 98,500";}

0 == 3”

‘.

I =bh3= 1524215 = 270

12 12
3 == 1,515g/sq. in.

S::98,5OO x 3 =2 1,100m/sq. in.
270

Since the allowable is 1,515 #/sq. in. and the negative moment

will be less, the 2"x6" flooring will be safe.

q§fRINGER DESIGN:

 

In accordance with the Michigan State Highway Department
Specification, timber stringers shall be of sufficient length to
take bearing over the full width of caps or floorbeams, except
outside stringers which may have butt joings. Preferably they
shall be of two panel lengths placed with staggered Joints. The
lapped ends of untreated stringers shall be separated at least
in for air circulation. stringers shall be adequately secured to
caps or floorbeams. stringers shall be adequately braced by cross
bridging in each panel. The bridging shall not be less in size

than 2” x 4”. The stringers will be arrainged as shown below.

FLOORBEAM

 

IO ‘78

 

 

I

Ins-2f

 

 

 

 

-!-

I

 

/Z ”a atnhyer

 

 

 

 

 

I

~02? *2

 

 

 

 

F

l

 

 

 

 

 

 

 

 

 

 

I

pus 4— ——¢?C,+ -4z?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 3

Each stringer is nailed to the floorbeam and cap with 4-300 nails.
2"x6” bridging at panel points and mid panel points is nailed to
stringers with 4-l6d nails.

The maximum moment for this 18' stringer will occur when the
rear truck wheels are at the center of the panel and the front
wheels in the adjacent panel. The rear wheel load for H-15 loading
is .4 of the total weight of the truck or 12,000é. The moment due
to this load is pl/4 where Pis the load and 1, the length of the
stringer. This moment is increased for impact and the dead moment

of 1/8 w12 is added.

 

 

 

 

 

 

 

 

57* , . _ ’i
LOAD AT CENTER
OF‘ FLOOR
g_ ste'
1
.EL
4.
f

 

 

. MOMENT D‘AGRAM
Fig. 4

Dead load

Assume the stringer as being 18" x 10".

foot per stringer will be ~-

(19.75 x 21?. x 60) x .1.
12 6

 

 

 

 

 

Then the dead load per

90.5fi/ft. (flooring)

 

 

10 x 18 3
——-——-—~ == .' ft. 1 r
( 144 ) x 60 vsr/ (str near)
Total = 165.5 ff/ft.
n =1/a w12= 1/8 x 165.5 x (1a)2=—_ 6,700'#
Live load
The live load is equal to --
To which impact is added.
= 184-20 _
1084-20'_' 30”
.30 x 54,000'#= 16,200'#
Total moment== 54,000-r 6,700 +-16,200 == 77,900'#
3 = 1.9.
I
\ I= 3’3 486w
12
3::
/ .8"
' 8:901!
,_ 486w
11g. 5
\ or
)~— W" —>1 1 :2?”
486.5

80

1
H
‘0
,N

qu
)”

x 12;: 11.4"

,p.
(T)
C}

11

use a 12” x 18" stringer.

Check the above designed stringer for vertical shear.

F’

A

e 9 # e

Fig. 6

 

 

 

 

 

Place the rear wheel just on the stringer as in fig. 7' .

ufibo

 

mssfika

 

 

 

Fig, 7

 

 

R1: 165.5 x 9: 14905‘
41
R2: 1490 + 12,000 + .3 x 12,000 = 17,090"r
Shearing stress = 124929_.= 795/sq. in.
18 x 12
O.K. Since less than allowable.

Check for horizontal shear.

 

 

 

 

Fig. 8

The maximum horizontal shearing stress in a wood beam is found by

the fermula --

Q==-¥% Where q== faximum horizontal shear stress.
V= External shear.
I== Moment of inertia of section about
neutral axis.
t== hidth of beam at neutral axis.
Q:= Statical Moment of section about
neutral axis.
Q: 17,090 x 440 = 107.0,7/8q. in.
5840 x 12
This is satisfactory even though 2 pounds above allowable, since
the stringer is actually continuous for two spans of 18'.
Hence it is satisfactory to use a 12" x 18" stringer. The
end stringers, that is the ones placed beneath the curbs,
normally receive less load than the center stringers and could be

Lade proportionally smaller. This is seldom done though because

of the high impact stress they would receive if a trUCk were to

strike the curb.

FLOORBEAH DESIGN:

 

In accordance with the Michigan State Highway Department
Specifications, timber floorbeams shall be sized at bearing points.
In floorbeams composed of two or more members, the timbers shall be
separated by at least 2' for air circulation.

Because of the rather long panel lengths,the floorbeams in
this bridge take a larger load than usual. In view of this fact I
believe that a built up or trussed floorbeam will be lighter and
more satisfactory in this case than a single wood beam. The floor-
‘beam.truss was designed so as to give adequate support to the
stringers resting upon it. Impact was computed using the formula
given under Data, using for 1 the length of the floorbeam with a
maximum of 30%.

Dead load. Consists of flooring, stringers, guards, bridging,

 

railing, railing posts, hardware, bracing and weight

of floorbeam itself.

45 RAILING * POST

-$TR|NGER

cos a '
S no FLOORING '1;
t . l‘ . » 1
\\¥
' .,3Rmmmm
‘

 

 

 

 

 

 

x XXV/x :

é

 

 

 

 

 

 

 

1 noonssm/
TRUSB

 

Fig. 9

The load is transmitted to the floorbeam by the stringers at

points 1, 2, 3 and 4.

 

 

 

Flooring " (1E' I gig. x 19.75!) 60 =9,770#
(2x6)
Stringer - (18' x l§_£-19 ) 6O ==lq620§
(12x18) 144
* G ards - (18' x 10 x 10 ) 60 z: 7503
YlelO) 144
Bridcing - (3.3 x 2 x 6 I x 2 x 6 I 2 x 60 :2 400%
(2x3) 144
‘* 3 x 8 __ ,g
Railing - (18 x _ ) x 2 x 60 __ 360”
(3x8) 144
* Railing Posts - (5 x 5 X E ) x 2 x 60 == 200.#
(6 x 8) 144

Hardware - Taken into account in rounding out loads.

Bracing — (25.4 x 3 x 8 ) 60 :2 254i
(3X8) 144

 

Weight of floorbeam itself -

Say E—ZLEQ. x 3 x 60 :: isoi/rt.
144

Distribution of Dead Load.
At (1.) l/6 x 9,770 == 1,630#Flooring.
- 1,620#Stringer.
- 750$ Guard.
1/6 x 400 2: 675Bridging.
- 350% Railing.

- 2003 Railing posts.

* Only apply to end points. - (l)

l/7 x 254

3 x 160
Total

At (2). (5) 8c (4)

Total

2: 480f

Cross Bracing.

floorbeam.

 

5,144;

1,630#
1,620§
6'7}?
37;;

480;

Say 5 , 200)];

flooring.
Stringer.
Bridging.
Bracing.

Floorbeam.

 

3,854fi

 

Say 3 , 9007f

Distribution of Dead Load Stresses.

 

 

 

 

 

3,200 a, see 2, 900 a; 900
c~
a m b (Hi (3) d (
,U- l 7w: ) 7 Un< / a iv: 3 .3) U4;
\ I ’ ‘
A / A /
J 3
/ I ( ’1 “m
i \r ) K V i
L 1 a 1 i J
o ' L. r \ >
#— gi-a) :J': ? 6' R ____" L‘ .\
\b c d
mesa ‘
Fig. 10
Section a-a
14,950

 

 

Vert. comp. of U0L1=

25.92 =

stress‘UuLl== 14,950 x ____.
3

Joint U1

Stress U.Ll==

Section b-b

Sect

Vert. comp. of L1U2= 14,950-5,200=

fig—z

Stress L1U2== 9,750 x

ion c-c

Vert. compo Of U2L2 = 14,950-5’200-3’900=

f2—=

Stress Ung

Section d—d

5,850 x

 

19,5005 ten.

5,200# comp.

9,750

13,800# Comp.

5,850

e,500§ Ten.

wert. comp. of LZU4===14,950-5,200-2x5,900 == 1,950

Stress L2U4= 1,950 x J??— = 2,760}; comp.
Joint U3

Stress [131,2 = ’ 5,900,? Comp.
Joint U1

Stress UOU1= 0102: 19,500 x 325% = 12.42057" Comp.
Joint U2

Stress 0203': 0304: 12,420+9,750+s,500 = 50,470,}? Comp.
Joint L1 '

Stress 1.11.2: 12,420+9,750 = 22,170,? Ten.
Joint L2

Stress L2L3:= 22,170+—5,a50+—1,950== 29,970§ Ten.

 

 

Live Load

 

 

V

 

 

~——-—— Ie'—————~w

iF cg———-I4'-—-----
“(1 NH |
4.

F {

 

 

 

 

 

 

 

 

 

fig. 11

with the truck as in Fig. 11 the distribution of the live load will be
as follows. The entire rear wheel loads will be transmitted to the
floorbeam and 4/18 of the front wheel load. These loads will be
transmitted to the floorbeam by the stringers at points 1, 2, 3 and 4 as
shown below.

(1) --- 6,334fi say 6,4005

(2) --- 5,554# say 6,400?

(3) --- 6,334” say 6,4005

(4) ---12,5e7r say 12,700#

Impact §§é§§§6.== 55.6 use 505.
(1) --- 6,400 x 1.5 == 8,320#
(2) --- 6,400 x 1.5 == 8,520#
(5) --- 6,400 x 1.5 == 8,520f

(4) --- 12,667 x 1.5 =216,5102

20

Distribution of Live Load Stresses.

 

A
V
I
i
I

 

 

 

 

 

 

 

292 re 6‘ L s— ’
332L5- a (b [Q A

Fig. 12

Section a-a

Vert. Comp. 75L; ==- 53,215#

Stress V5L1== 33,215 x.§é2§ ~==45,400# Ten.
Joint U1

Stress UlLl 2: 8,320# Comp.

Section b-b

Vert. Comp. L1U1= 55,215-8,520 = 24,895“?

Stress LlUl==24'895 x / 2 ===55,200# Comp.
Section c-c

Vert. Comp. Usz= 55,215-2 x 8,320-16,575fi

Stress U2L2= 16,575 x / 2 = 23,400,? Ten.
Joint U3
Stress U3L2 :2; 8,320# Comp.

Section d-d .
J1
Vert. Comp. L2U4=53,215 - 5x8520==8,255”

Stress L204=8,255 x( 2 :2: ll,680# Comp.

21

Joint U6

 

Stress Uouizruiué :: 42,200 x 2:22
Joint U2

Stress UEU3==0304 == 26,900+—24,895-Fl6,575
Joint Ll

Stress L1L22235,215-+-24,895
Joint L2

Stress L2L3=58,1104-16,575-8,255

22

:226,900# Comp.

:2 68,370? Comp.

==82,940# Ten.

 

Floorbeam Data

 

 

 

 

 

U° 0: {/2 Us
1., 1., 4 2
Fig. 13
Member Total D"tress Length c-c Area
V511 62,900f Ten 2.921 42 sq. in.
V111 15,5204 Comp 5.001 12 sq, in,
L102 49,0005 Comp. 4.241 44 sq. in.
U2L2 51,700; Ten. 4.241 21 sq. in.
0312 12,2205 Comp. 5.001 11 sq. in.
L2U4 14,4405 Comp. 4.241 13 sq. in.
U001 59,5204 Comp. 2.50l ' 35 Sq' in'
U102 59,520r Comp. 5.001 55 sq. in.
UZUS 98,840# Comp. 5.001 87 sq. in.
U3U4 98,840# Comp. 3.001 87 sq. in.
LoLl 0 2.501 o
L1L2 80,2805 Ten. 6.001 55 sq. in.
1 1 112,910# Ten. 6.001 74.7 sq. in.

 

' 430¢IBMEKS

 

 

 

V4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 14

The floorbeam is to be constructed as shown in Fig. 14. Split
ring connectors are to be used in all stressed joints. The table below
gives the no. and size of connectors to be used. For details of the

Joints see the drawings accompanying this thesis.

Hember K0. Rings Ring Size Bolt Size
Vol.1 5 4' 5/4"
Lle 10 4" 5/4"

’ 0sz 5 4" 5/4"
L2U4 4 4" 5/4"
Truss 8 4' 5/4"

The floorbeam is checked for shear.

50 000
W = 250 lbs. per sq. in.

The bolt holes for the 3/4" bolts shall be 11/16".

DESIGN OF 72' HOWE -USS:
In the truss design the loading shown in Fig. 15 was used.

CONCENTRATED LOAD
v: (9500"
M =13,500‘

L 4807”". op LANE j

 

Fig. 15
The dead load transmitted at the panel points will be the dead load
figured in the floorbeam design plus the true weight of the floorbeam.
The dead load stresses are figured directly and the live load stresses
are figured by means of influence lines.

Dead Load Stresses.

 

 

 

 

 

 

| U!-
I. l o l. ‘ L 3 l- b,
T (aéooo 5,000 (g 0..
H" 22,300 4
Fig. 16

Stress L Us=22,500 x 25.42 ==55,300# Comp.

0 o -jfi;—-
Stress L U ==7,5OO x 25.42 ==ll,7lOfi Comp.

1 1 “15*

Stress UOL1=15,OOO +-7,500 ==22,500f Ten.

Stress L011f55,300 x 18 ==27,200# Ten.
25.42
Stress 1112' 27,200 +1l,710 X2332 -36,2OO,{3 ‘Een.
Stress U L =15.000f.-" Ten-
1 2
Stress U U =- 35,300 x 18 =27,200;,*' Comp.
0 l --:-——
20.42

Live Load Stresses.

The influence lines used in finding the live load stresses are

shown below.

 

 

 

 

 

L L L 1:13 -72' ————.——,-l

STRESS 1.0. = 232-12, IN COMP. (SHEARaa)

 

 

 

STRESS L,UI 'VALUE SHOWN - 1.55 (SHEAR 61.)

 

, 74xtss
///T:\ 1,
\ C
' sztss
24' = 1 48' *1

 

 

 

26

STRESS U.L.,'R. (SHEAR cc)

9/4

 

VERT. u,Lz
. 1
STRESS 0.0, - Rnr ‘6- conp, (Ma/1,1,.)

STRESS L L2 = 2M

/

STRESS L,L, % R. a ‘Is'

 

9/10

/\

2'7.

dy means of the

below were found,

Stress LOUO= 72

8 z:
tress LlUl 48

==24

Stress U0L1= 72
S ==
tress LoLl 72
Stress L1L2== 72
Stress Ung' 36

Stress U U '72
o l

influence lines the live

x .78 x 1/2
x .39 x 1/2
x .75 x 1/2
x .90 x 1/2
x 1.2 x 1/2
x

X

I

I

I

480+ 1.17

480 + .78
480 +‘.39

480 -‘\- .75

480 4-.90

480-+1.2

1/2 x 480 +-19,500

x 1/2 x .90 x 4eo-+.90 x

load stresses listed

x 19,500

x 19,500
x 19,500

x 19,500

x 19,500

x 13,500

15,500

==43,100§ Comp.
no reversal

==.24,250# comp.
: 9 ,870;§a Ten 0

no reversal

== 33,200? Ten.
no reversal

4. 57,000; Ten.
no reversal

==2s,150# Ten.
no reversal.

==27,800# Comp.
no reversal

Using the impact formula and adding dead and live load stresses the

table shown in Fig. 17 was computed.

Since the dead load compressive

stress in member LlUl is greater than the live load tension obtained by

the stress reversal no counters are needed.

ihe compressive members must

be designed as columns keeping in mind the ratio of (l/d).

28

Member Total Stress Length c—c Area

LoUo 89,300# Comp. 23.42' 114 sq. in.
LlUl 43,3105 Comp. 23.42‘ 63 sq. in.
UOLl 56,000# Ten. 15.00' 38 sq. in.
LoLl 69,000# Ten. 18.00' 46 sq. in.
1112 a5,000§ Ten. 12.00' 56 sq. in.
Ule 51,200fi Ten. 15.00" 55 sq. in.
UoUl 57,2005 Comp. 18.00' 122 sq.in.
fig. 17

The date shown in Fig. 19 is determined from the above stresses, taking
into account the angle of the load to the grain. The number of rings

shown is the minimum and in most cases has had to be increased in order to
balance the load. ihe cross sectional area of the members given in Fig. 17
has also been increased to allow for net section, placing of connectors

and in compression members to obtain a l/d ratio of less than 30.

 

 

 

 

 

u. ~52: u. u,
’5

Q? s “‘5' Q

’9 t, / g

t \

‘O. *"o° *- .1 0
1'0 LI L t L) L4

Fig. 18

in figuring the connectors for LOUO the vertical component of the stress
was assumed as passing directly to the reaction. The horizontal component
is equal and opposite to the stress in LOL1,. Using 4" Connectors the

Strength per connector in timber 3" and thicker is as follows.

Angle to grain strength
0° 6,400r

40° 5,600:
500 5.4002
90O 4,600s

29

Yember No. Rings Angle to grain Bolt size

0

LOUo 15 40 5 /4"
1.101 a 40° 5/4"
001.1 12 90° 5 /4"
LOLl 11 0° 5/4"
1le 15 0° 5 /4"
U112 12 90° 5/4"
UoUl 9 0° 5/4"

Fig. 19

Details of all joints and splices are shown on the drawings accompanying
this thesis. The number of connectors in the vertical at joint Ll may be
greatly reduced, since the floor beam load is applied above this joint

and the member is in tension.

30

Camber:
The bridge is to be cambered as follows:
Increase the lengths of top chord members UOUl each by 1/4".
fiaise floor beam at LgUl by 1/4".
Lower end caps by 1/4".
Bracing:
There is no need for knee bracing since the floor beam acts as a
knee brace itself. Since the truss is shallow and of a fairly short
span the wind load will be small. 3"x8" bracing as shown is used as

wind braces.

Truss lembers:

 

[embers LOUD, UoUl and L101 carry compressive loads and will be
designed as columns.

Take member LoUo first. Since this nember carries quite a large
stress it will be built up of three timbers and designed as a solid
column. Kember Loco will be considered as an intermediate column where
the l/d ratio is between 11 and K. K is a constant depending on E and

0 of the timber.

K‘ ‘64 #5- Where E=lfodulus of elasticity 1.6 x 10‘5
C=eAllowable unit stress parallel to grain
= 1,1005'7/5‘10 in.

For intermediate columns
P . “1.3.1
/” €11 3(Kd)

According to the data in Fig. 17, computed from unit stresses, LoUo
should have a cross sectional area of 114 sq. in. Two 3" x 14” and
one 6" x 8' would give on area of 119 sq. in. and a d of 14".

Rearranging the above formula we get.

 

f7 :

1

41- 4(a)“)
Solving for A we get

‘==ll6 sq. in. which is satisfactory.

16 connectors will be needed between the center member and the
outside members to develop the full strength of the member.

Member LlUl has a K of 24.4 and trying two 3" x 12" and one
6.1 Suwe have a d of 12". Substituting in the above formula for
A we get.

A==50 sq. in. which is satisfactory.

:ember UOUl will be designed as a spaced column as it would other-

wise collect water.

For intermediate spaced columns

 

1.
F7 s p. i
.11- 6(5)?

32

fry two 6" x 16" timbers separated by a 8" block. d'-6" Then for

A we get A.=:60 sq. in. “all within limits.

ihe remaining members carry teisial stresses and the areas of Fig. 17
must be adhered to. These timber members as well as the compressive
timber members may have to be increased in size to allow fer connector
spacing at the joints and also for net section reduction due to bolt
holes.

Deflection:

 

'U
H
N

For deflection of the compressive members: 8 =~

“I

(0
ts:
H

for LOUo

5 a 89,300}: (23.42)2x144

==.345”.
2 x (1.6 x106ix3,200

 

for LlUl

 

5 __ 43,3102: (23.42)2 x 144
_. 6 2.404”
2x(1.6xlO )x2,640

for UoUl

6“ 57,200 x (18)2 x 144
2x(l.6 x 1015):; 2,050 = .406"

 

1he floorbeams are to be connected to the verticals by split rings.
The maximum floorbeam reaction is 50,000? requiring 8 rings.

All bolts will have washers under the head and nut in accordance with
Michigan State Highway Department Dpecifications. ‘

her general notes see specifications for the Design of Highway
firidges adopted by the hichigan State Highway Department, January, 1936

numbers 129 through 149.

34

BIBLIOGRAPHY

Michigan State Lighway Uepartrent Specifications for the Design of

highway bridges.

A Course in hodern Timber Lngineering - howard J. Hansen

Wood Structural Design Data - Vol. 1 - lV‘ational Lumber henufacturers
Association.

Elements of dtrength of Katerials - Timoshenko and fee Cullough.

Wood Columns — safe Loads - Supplement 1-o. 4 - hational Lumber Lanufacturers
Association.

Hood Trusses - Supplement No. 5 - Hational Lumber n‘anufacturers Associ-

ation.

C)?
()1

111111 11111“ 1111111111 1,1 11

 

31293 50026

 

 

   

11
9'!