THE THEORY OF ESTIMATING

:

Thesis for Degree of C. E.

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FENT EDWIN N. THATCHER

 

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THESIS
YH THeORY OF iSTIMATING.
Its relations to thse shops, cost of pro-
duction :nd the conditions of supply and demund.
Thesis by
Fent iadwin N. Thatchor.
For the degres of Civil Engineosr.

1913.
<HES!3

_— ee eee eee
Prefacs.

oan ~at eu

Tne author of this thesis is indebted to
the following people for the privilege of being able
to write for ths Civil Engineer's degree. To Philip
P. Schnorbach of Mus'*tegon, Mich., for his interest
taken in me aftsr leaving high school by giving me
a job as timekseper on government pier construction
at Ludington. To Tom F. Rogers of Ravenna, Mich.
( M.A.C. 1874) for advising me to take the Enginesring
course at the tiichigan Agricultural College. To ny
parents for maxing it possible for me to attend collesrs.
To the Enginesring departmant of the M.A.C. for the
theoretical knowledge I received and for advico I
have received which I hope has been apvlied success=
fully. To C, Ulrich “alin of the Shaw Elsctric Crane
Company of Muskegon, isich., for my training in
practical estimating. To H. J. Cox of the ifississipnvi
Central R. R., and Chas T. Bird of tne Amsrican Steel
Foundries. Alliance, Ohio, ror my training in practical
construction. To Fred W. Brown, Supt., Beach fg. Co.,
Charlotte, “ich., for making many of my designs
practical as regards shop worx and erection. To Chester
A. Brewor for my training in bassball, many points
of which have served me allesorically since leaving
school. I have this to say of mysolf- that it is
"up to me" to make good in order to show my.
appreciation,

Fent Edwin N. Thatchor.

LOG9S
\ Kistimating is that process which

teaches us to arrive at a reasonable figure on any
proposed object, by basing that figure upon known
figures for objects of a like nature.

By reasonable figure, I mean a figure
such that its nearness to the final figure will be
within certain limits which are determined bv the
other factors in the problem. This limit is fixed
to a certain degree by the amount of data one has of
similar problems which have previously been completed.

To begin with, nothing in practice can
be measured exactly, but it can be made closs enough
for the purpose at hand. We moasure structural steel
to a 32nd of an inch, we shear it to within a quarter
of an inch, we saw to a closer limit, we grind it to
a fifth of a thousandth of an inch; but the smaller
the limit the higher the cost. When we buy stesl we
work to a specification which makes an allowance in
weight for the inaccuracy of the mill.

And it is this vart of estimating (which
comes under tha head of structural steel) that this

thesis will tend to show. The fundamental thot in
estimating comes from the fact that man must sat in
order to live and that in order to live each man is
depsndent upon every other man. From this fact,

every estimate must be figured finally in financial
terms. The two main parties interested in the estimate
are the people who have to eat and the peonle they arse
dependent upon. Suppose a bridge is destroyed between
a town and a farming district. This raisss prices in
the town and the difference in price creates a desire
for a new bridge. The consumers estimate the value

of the bridge.

The peonvle upon whom they depend estimate
what such a bridge will cost and then fix the price
which is between the actual value of the bridge and the
cost of same and is as near the actual value as is
possible while sstimating thse price to be lower than
that fixed by their competitors for they in turn must
eat. This is the theoretical condition affecting the
sale. Hence the greater the competition the lower
the price, on the bid. This is the SALESMAN'S estimate.
He knows the cost and he ostimates ths rest.

The salesman however gets his cost from
te

the Sales Departmant. They get the cost from the
following data»

(A) Weight of steel bought at mill prices
multiplied by cost per pound.

(B) Weight of steel bought at warehouse
price multiplied by cost per pound.

(C) Cost of production as estimated from
previous work.

(D) Cost of loadings

(E) Overhead percantage, to take care
of selling, engineering, office and factory
superintendencs, cost of upkeep of shops, interest
on investment.

(F) Freight and hauling.

(G) Erection.

an estimate sheet should show these various
parts of the problem.

Every company keeps a record of steel
on hand, steel requisitioned for various jobs and steel

on order. From this record and the rolling schedules
af the mills they are able to figure what they must
buy short from the warehouses.

From this they estimate the proportion
of steel at mill prices f.0.b. cars at shops and that
from the warehouses which will go into the job. They
get the estimated weights from the Engineering
Departirent, together with the amount of work to be
Gone on each piece. Their costs for the work are
figured from the reeords of the cost department, which
also furnishes them basis for adding an overhead
expense percentage. To this is added the freight and
hauling and cost of erection , wnich is determined
by the engineering and cost departments.

The cost department keeps a record of
each job as it goes through the shops in such a manner
that the engineering department is able to make designs
of saving value which at the same time do not impair
the strength of tho member. The cost department also
keeps a record of all expenses termed overhead which is

spread upon the jobs according to their proportion of
Phe total jobs. This overhead of course is an estimated
quantity for future work and in order to make a higher
profit a company tries "to cut down the overhead".
Upon the Engineering department falls
the greatest proportion of the efficiency work in a
structural shops. The Engineering departnont furnishes
the "show" drawings, which gives the size of the members,
the stresses in each piece, the specification worked
to, and with the drawing, it also furnishes the estimated
weights of the steel. The salesman's job then reduces
itself, as far as costs are concerned, to a case of
simple multiplication. In other words tho salesman
multiplies the weight by the cost psr pound and adds
some percentage furnished him by the selling department.
These show drawings are always based on
the most economical use of the steel as regards cost.
For instance, take a 10"~40# beam for a span of 12
feetwhich carries a safe load of 28210# and, without
doing any harm to the structure, it would be advisable

to change to a 12"-31 1/2# beam, which is good for
é
31,970#. The 10-407 cannot be gotton from the mills

in less time than 2 months, while the 12"- 31 1/2 { is
in stock. This would be a saving of 8 1/2# or possibly
£0 cents ner ft., while the time is worth much more
than this. Or take a 41/2 X 3 X 3/8, weight 9.14
which bought at warehouse price might equal 9.1 X 2.1¢ =
19.117 per ft., while a 5 X 3 X3/8 angle, weight 9.3#,
would be in stock and is worth 9.8# X 1.2¢ = 11.75¢

per ft. It would pay to use the heavier angle, which
at the same tims could be sold for more money: taking
the two cases in the same problem and we would have a
balanced job, but would be able to deliver the same in
less time. As delivery is an imvortant factor in

any case, it is up to the Enginsoering departnant to
watch this phase of the work in the design.

Another thing affecting the design of the
job is the facilities a shop has for doing a certain
class of work. The umnginesrs must Know the shop
equipment and be able to determine from the records

gnd by judgment the best possible way to do work,
, The whole essence of in estimate mav be
summed up in the following words,

To get a design that will sell.

To get a design that is not costly.

To get a design that can be made in the
shops efficiently.

To get a design that can bs shipped.

©

To get design that can be oereactod at

a low cost.

To get a design of sufficient strength
and beauty to sell another job in the same locality.

To do these things makes a business
profitable, and this roflects upon the Engineer, who,
in turn, is able to command mors money for his work.

Again to have the interest of all
parties in mind, and to vork honestly along these
lines, makes the estimator successful.

No concern can be profitable unless the
shops work to an advantage . An Engineer plans his

work for the benefit of the shops and the shops must
try to do their part. If the Enginser has
judgment the shop foreman should make this

ingineer. In so doing, he lowers the cost

erred in
plain to the

of the next

design and keeps the shops busy on a class of work

which is profitable. This fixes the pay of the mon

in the shops.

One purpose of this thesis is
that an estimator in order to do good work
all the actions and reactions which may be
the problem he has in hand. Knowing these
relations, he is able to go ahead with any

estimate and do justice to it.

to show
must value
caused by
general

specific
PRACTICAL ESTIMATING.

Below is shown the cost of steel and the
cost of fabricating the same. The cost of steel is
always given at some price which is known as the
base. Each company has its costs for doing work which
are fixed for an indefinite period and is the constanb.
The base is the variable so that the net selling price
is the base plus fabrication multiplied by the number
of pounds,

The way of figuring costs is as near as
we can get to the actual cost under the present system.
As long as all shops use the same formula each will
have the same chance in competition. The error in
figuring this way is the shops can punch one one=
sized hole in a 100# of steel at less than thsy can

punch ten one sized holes, but these things average up.
' STEEL = COST AND FABRICATING.
FOR APRIL 1912.

 

Per 100#

Mills Warehouse
Bars and bands Base Charlotts----% 1.10 ---% 1.59
Angles, channels, tees
under 3" Base fob Charlotte--- 1,.10-=--- 1,50
Plates and structurals
Base fob Charlotte--- 1.20 --—- 1.60

SHOPWORK

Punched channels and beams---=
One sized hole in either flange---------------- 015
One sized hole web and flange or both---=------- 025
Hach additional sized hole ----<<------~- <--=-— 015
for buildinys only.
Punched angles----=<= “===
Not less than 1 ft. 0.¢.----- / 035
3X3. 4X4. 5X3 1/2-----

Riveted back to back----------------- re 61.90
 

 

 

 

 

 

 

 

 

 

Add for putting beams together

with separators, ----~-----<

Punching 6 X 6. 6 X 4. 5 XK 5.--- 020
Riveted back to bacK--<<<-<--<- 60
BEAMS AND CHANNELS-~

12 & 15".--------~------- ~ f 1 Ld .50
18, 20 & 24-------4.---- ; ; 40
7, 8, 9 & 10-----------= 075
3, 4, 5 & 6e----=-- Ma ee _  $ 1,00
Countersinking add----- a ~10
Coping beams and channels with

conn. angles------------ ow OD
7s 3, 9, over §!'------- _ 50
3, 4, 5, 6 over 5'----- _ 1,00
above includes punching.

Add for C I separators and connection angles __-—-s-_—-«i1.55

~10

 

over

12!
MSTIMATCING THI: WiulGHT.

Plain beams, angles, etc. are gotten by
multiplying the total numbor of lineal feet bv the
weight per foot and adding a small percent, say %%,
to take care of the scrap. This percentage is
forgotten by some estimators, but it should be added
in for the reason that the shops have to buy more than
they sell and the difference is the scrap percentage.

SCRAP PERCENTAGE.

 

tons
Steel on hand Jan.1,1912 500
Ant, of steel recd.-6 mon. 200
Amt. steel used= shipping wt. 496
Amt. steel on hand July 1,1912 183
Amt. scrap 21
700 700

Scrap divided by number tons actually
sold equals % or 21 = 496 = 4.24% Hence in checking
up for 6 months of estimating we would be short 1.24%
For the next period we would add 5% and
at the end of that time would check against the records

and correct again.
To figure beams punched and riveted together
or connected by means of separators, and beams with
connection angles on. Figure plain beams, then connsction
angles, separators, etc. As the beams in a building
are nearly always around a certain length for a certain
heigth of beam wa can from a number of cases figure
a percentage which will practically take care of the
connections, etc. This however would be used only
in case of a rush job.

For Trusso9s.

We are always able to get the length of the
members, but cannot take time to calculate rivet
heads and size of gussets. From actual designs, it is
found that in trusses of any certain type the weight
of rivets and gussets bear a ratio to the main members.
In Fan or Fink types trusses of ordinary span the
ratio is 5% for rivets, 16% for gussots, and say 3%
for scrap or in other words 24% is added to the main

members,

Anothsr way is to plot curves of trusses
of any type and use this :curve for estimating purposoas.
Columns in buildings mav be worked out
in the same way although a short column is heavier

in proportion at the ends than a long column.

Problem--
A 85' span, 16' roadway, concrete floor,
5 panel low, rivetod Warren truss. Live load; uniform
100# per sq. ft. of roading, concentrated, 15 tons
roller, 10 tons on rear axle and 5 tons on front
axle. Wisconsin State Highway Bridge Specification.
From the problem we get the following

stress diagram and the resulting members are shown.

 

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In order to work out the weights we

find that the 70' X 16' bridge will apply. Using

this bridge we take the end posts first. Their weight
is 2134#. Section is made up of 2 = 8" = 11 1/4#
channels with a top plate of 14 X 1/4. The weight
per foot runs 34.4#. Length of each post is 9.90.

The section of the 65' bridge is made of 12 X 5/16

top plate, and two 7" = 12 1/4# channels, total

weight per foot is 37.25. Length of post 9.2'. From

proportion we have 2134 X 37.25 X 9.2 = 2144# which
— 34.4 X 9.9

 

is the weight of the end posts.

The top chord has ths same sections as
the snd posts respectively. Weight of 70' bridge
chords is 5220. Length of 70' snan is 58'. Length

of 65' is 52'. Hence 5220 X 37.25 X 52= 5250# weight
34.4 KX 96 _

of top chords.
The verticals weigh 479% in the 70°
bridge, length 7'= 0. In 85", sune section, S'= &.

Hence 479 X 1 X &.5 = 445# for verticals.
1 X 70

 
ae)

4 angles

CO

4 angles

<2 angles 3

2 angles 9
2 angle: 4

2 angles 3

vary as 70

diagonal.

2 angles 3

2 angles 6

leangle 6

For the diagonals w2 have in the 70's

1/2 X 2 1/2 X 5/16, first set,woight per foot 20.0

1/2 X 21/2 X 1/4, second set,weight ner foot 16.4

XK

x

A

x

21/2 X 5/16, third set,weight ner foot 11.2

 

For the 65' span, wa get--

3 1/2 X 5/16. first sot, 17.4

3 X 5/18, second set, 14.4

21/2 X 5/16, third set, 11.2
Adding - ~ 43,0 —

The length of the diagonals in the bridges

is to 65. Weight of diagonals in 70' is 2439#,

Hence 2439 X 65 X 43 = 2050#, weight of
70 X 47.6

 

For lower chords, we get the 70' span,

1/2 X21/2 X 5/16 9 ----- - 12.2
X 3 1/2 x 1/2 eee =e 30.6
X4X 1/2 9 ma---- 16.2

 
‘ Note that for the center panel we use

only half of the angle in ordor to keep the proportion.

For the 65' bridge,

2 angles 3 X 21/2 X 5/16 --- 11.2
2 angles 5X 31/2 X 1/2 --—= 27,2
l angle 6 X 4 X 1/2 --- 16.2

| 54.6

Now the lower chords vary in length as
the span and the weight per linsal foot. Taking
weight of 70' as 4638#.

4638 X 65 X 54.6 = 3980#,
: 70 X 59.0

Extrag ( bolts, etc.) 361 plus 57= 4284

428 X_70 = 396
65
396 X_70 = 368
eee erneen
754

e —

764 — 2 = 53°24 or this i3 the mean
. ®

between ths spans and the square of tho spans.
8 Floor beams ara 18" = S5# I 8s in both
cases, and ars of the same length. There are four in
gach bridge. Hence we take the weight of the 70'
span as givon, which is 4312#. Same with tho wall
plates - S04.

Railings 1494# X 65 = 15354.
70

The stringsras in the 70' weigh 1113°#,
and are 6 = 9" = 214 13 and ©£ - 9" - 13 1/4#
channels with two 2 X 2 X 1/4 angles on top. Hencs for

each foot of the span w2 would get :

6 X¥ 21 = L26

2X 13,25 = 25.50

2 x 342 = 6.4
158.9 |

In the 65! bridge we get

3 KX 21 = 126
2X 15 = 30
1567 ner foot.

X 156 = 101704 for stringers.

 

69 X 196
70 X 152.9
Lateral rods in the 70' weigh 314# and
are 3/4" rounds and weigh 1 1/2#, in the 65' are

21/2 x2 x 5/18

21 is to 20.

314 X 20 X 4.5
21 X 1.5

Tie rods weigh the same, 357).

Summing up, “s get

angles which woigh 4.5#,

= 395#

 

mond Posts a Leb
Top Chord 5250
Verticals 445
Diagonals 2050
Lower Chord 3980
Extras 332
Floorbeams 4312
Wall Plates 204
Railings 1385
Lateral Rods 895
Tis Rods 85
stringers | 10180

41312

istimated weight of structurs3

Varv a3
4% for scraps etc. 1252
Total weight 32564 —
Estimated weight of the steol used in the structure 32600.
The above problem shows that in order
to get the weights we use the ratiosof the length
of the known néembers to the estimated members and the
ratio of the weight per foot of tne main parts of the
known members to the similar parts in the estimated
member. The error that enters is offset by adding the
porcentagzs for scraps, etc. Some shows record ths
estimated weights for say six months and the actural
weights and get a relation to be used for ths next
six months. This percentages would vary with different
kinds of work, for instance in bins the nercentaze
of scrap would be very Jarzg?. However, this must
be figured in relation to the shops where ons is
working.
The use of graphs is very useful to an
estimator. For instance, one can plot the weights

sor a like nature and from the curves got any intermediate
weight near enough for making the stress calculations.
Again, from graphs it is readily soen that

in cutting down, say from a 70' to a 65' we get a

higher weight than in raising from a 60' to a 65',

The reason is that the details will run heavier in

proportion to the main parts of a momber ina longer

bridge.

Conc lusion--

No matter what the tyne of the structural
job is, the same general method of estim.ting is used.
The estimator has always to bear in mind the relation
betwsen ths shops and the drafting department, tne
cost of the materials used, the amount of time for
deliveries from the mill and then the figuring of the

weight is a case of proportion.
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