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THESIS Hill DEGREE ”F B. 8.

JAMES OTIS GRANUM
' 1932

 

 

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Time and Construction Study
on the

Dimondale Highway Bridge

A Thesis Submitted to
The Faculty of
MICHIGAN STATE COLLEGE
of
AGRICULTURE AND APPLIED SCIENCE

James Otis Granum

Candidate for the Degree of

Bachelor of Science

June 1932

' THESIS

ACKNOWLEDGEMENT

The author wishes to express his thanks to Professor
L. G. Miller of the Mechanical Engineering department of
this college for his help and suggestions in regard to the
making and uses of a time study, and also for the loan of
a stOp watch and equipment with which to carry on this work.
The author also desires to thank the builders of the
bridge, Hudson, Coons, and Granum, for their interest, co-

Operation, and information.
'Q

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'54»

I
OBJECT

There has been a great deal written on time study,
job analysis, and scientific management as they apply to
industrial operations, but it seems that construction work
has been slighted, particularly in reference to the time
and motion study field. It is true that these principles
are more easily applied to standard Operations in a manu-
facturing plant, and will hold good over a number of years.
However there are many jobs that are practically standard-
ized in the construction field that can be timed and motion
study applied with a view to cutting out waste time and
lost efficiency.

Time study in general makes it possible to secure
information concerning the amount of work which may be
accomplished in a given time. It is often used in the de-
termination of possible improvements in conditions or
methods, but it is essentially a rate-setting device. Rate-
setting, however, also involves motion study and standard-
ized Operation to a great degree. Therefore, due to the
limited time available, it is the object of this thesis,
not primarily to find a standard rate or "should-take" time,
but rather to determine by actual measurement in the field
the average length of time of operations which may be
standardized to some degree. In some cases the “should-
take" time has been estimated by the author and noted, but
due to his limited experience and the comparatively short
periods used, these must be regarded merely as a pure es-
timate based on the knowledge of the work and the statistics

used.

The average length of time for certain work, plus
information as to waste and delayed time, may be used by
estimators or by those who desire to use these figures in
checking their own production when carried out under the
same or similar conditions. They could also be used to
good advantage in a detailed motion study of certain work
with a view to improving conditions or methods, or both.

A secondary object of this thesis is to point out
certain features concerning the actual construction of the
bridge, showing the practical side and the actual carrying
out of the theoretical work of design. The close obser-
vation necessary for good time studies is put to an auxiliary
use therefore, and such methods as are in everyday use and
that are considered good practice are recorded for the
benefit of others who may sometime use them.

It is the hOpe of the writer that this thesis may be
the beginning of a series of time and motion studies with
regard to construction work. There is certainly a wide
field for study here, and such a series would gain in
accuracy and value with each one written. Notes on con?
struction methods in use in conjunction with the above men-
tioned study will prove to be of great value to the man who

intends to go into such work in the future.

II

GENERAL DESCRIPTION OF THE JOB STUDIED

The job studied, as the title indicates, was a high-
way bridge under construction in Dimondale, Michigan, over
the Grand River.v It was built during the summer months of
1952, beginning about April lst, and ending about October
1st - by Hudson, Coons, and Granum. Mr. O. M. Granum, the
writer's father, was superintendent on the job.

The bridge is 180 feet long, with three 60 foot Spans
of the deck girder type of regulation highway bridges, re-
placing an old 180 foot steel truss. As it was necessary
to maintain traffic, the old bridge was moved up river 55
feet and placed on timber cribbing. This was the first job
of its kind ever attempted in Michigan and was very success-
' ful. No time studies were taken on this part of the work,
as it was unusual and the same conditions will probably
never again be duplicated.

The abutments are of the counterfort wall type, approx-
imately 65 feet wide. The building of the east abutment was
the main project studied. This included ripping out the old
abutment, placing and driving the sheet piling of the coffer-
dam, and bracing and pumping out the water from the dam.
Excavation of the earth to the proper level, form and steel
placing, and pouring of concrete were also studied, along
with some of their adherent work.

The labor used was welfare labor - that is, the workers
had to be employed from the list of unemployed in that town-
ship, since this bridge was one of many similar jobs to give

unemployment relief. However five key men, including himself,

 

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were to be hired by the superintendent as he saw fit.

Many Of the laborers hired were inexperienced in such

work, and therefore some of the time calculations may be

tOO great. This can be proven by further study during a
time when these men do not have to be hired. The work done
by these laborers did not require a great deal Of experience
however; in the Opinion Of the superintendent they were
good workers after being weeded out. By this was meant that
the general effort was good and that inexperience did not
detract a great deal, except insofar as a little more skilled
work was required Of them. The ability to direct these men
in order to get the mOst work out Of them is only to be
acquired by practice and experience, combined with complete

knowledge Of the work to be done.

III
ELEMENTS OF TIME STUDY IN CONSTRUCTION WORK

Any portion of construction work, as well as any other
work, entails three fundamental considerations: with what
tools and machines it is to be performed; the method of
doing the job; and the length of time required for doing it.
It is the aim of the construction engineer to coordinate all
work and manage each portion with efficiency so as to cut
down the costs and still maintain quality. Economy is his
watchword, and any methods whereby this can be gained will
be welcomed.

Since the time Of doing work is one Of the three fun-
damentals, it follows that the engineer must always keep it
down to a minimum within the limits set by efficient pro-
duction of all those concerned with the work. This thesis
is based upon the desire of the engineer to know what this
time is, how it compares with other jobs, and how it may be
improved upon. Time study in manufacturing plants is used
to good advantage in rate-setting, but this is ordinarily
done only on a piecework basis. In construction work, the
hourly basis Of payment for work is almost universally used,
and hence we can think of rate-setting here only insofar as
comparison with others is concerned. That is, if a man can-
not keep up to the average time as determined by a series Of
studies Of his job, it would be well to replace him with one
who comes closer to this average. This of course tends to
lower the average time and thus lower costs. It must be
pointed out that there is a physical limit to the speed with

which a man can work, and that it is more economical if he

is not pushed too close to the limit, expecially if the
Job is a long one.

In order to be able to get intelligent studies, it is
necessary to standardize work as far as possible. This is
probably the most difficult thing to do with regard to
building work as far as the time study man is concerned. He
must pick out of the maze Of detailed work to be done only
those things which are more or less standard on every Job, if
his studies are to mean anything to others. It is the job Of
the time-keeper and cost clerk (if there is one) to keep track
Of the total time and costs for general work. It is the job
Of the time study man to separate such items as he can and
determine the constituents of the general notations of the
two former individuals. Therefore, the student must exercise
his judgment as to standard work to be checked and decide
whether or not the methods are standard. Such work has been
studied by the author, and the detailed information is set
down in a later part Of this thesis.

The description Of each Operation must be rather com-
plete in order that full information can be Obtained by the
user Of such studies. If these times are to be Of value,
similar conditions must be had. This point emphasizes the
fact that rate-setting can be but a minor item in the study,
since it is difficult to have similar conditions even from
day to day on the same job. ,What we want, for purposes out-
lined previously, is the average time, coupled with a "fair"
or "should-take" time which will increase with importance
as the experience of the Observor and the number of trials

made grow.

After the standard Operation, or one which can be
standardized by the use Of time and motion studies, is de-
cided upon, it must be separated into its elements. This
predicates the fact that a cycle Of repeated Operations is
found whereby the Observer may make repeated trials. Strict-
ly speaking, for average time alone, separation into elements
would not be necessary, but since the studies are used for
various purposes other than this, it is necessary to have the
elements. Such fine work as the analysis Of the technique Of
shoveling was not attempted, but rather the total time for a
group of laborers to shovel a certain amount was determined,
along with rest periods, delays, and crane Operation. Enough
description of the elements is necessary on the study sheet
itself so that a person looking them over can get a good idea
Of what the operation is and under what conditions the work
was done.

The sheets made up for the study were designed by the
author to fit a small space. They do not carry a great num-
ber Of elements, but if more elements are found than there
is space for, the study is carried over to the next sheet
which is then to be used simultaneously with the first. All
the information required should be placed on the sheet in the
spaces provided. The elements are placed along the tOp line,
so that a complete trial reads from left tO right. The last
vertical column should be left for a "totals" column, but if
six or more elements are required, it would be permissable
to place the totals on a summary sheet, which has been done
in several cases. The total at the bottom of each column is

the sum total of the number of trials of each element indi-

cated. A "delays" column on the right denotes each delay by
letter, and leaves a space for description of the delay and
for the time consumed.

A stop watch is needed - preferably one reading to
decimals of an hour, although this was not obtainable by the
author and so the next best (reading to hundredths of a min-
ute) was used. It is best Operated by procuring a regular
time study board Which has a watch holder and a clip for
holding the sheet. This is convenient, easy to carry around,
and allows good Operation of the watch.

There are several methods of taking time studies, two Of
which are most common. In one method, the watch is re-set to
zero after each reading. This makes calculations simpler,
but is far less accurate. The best method and the one used
here is that Of allowing the watch to run all the time, only
resetting occasionally. Each successive reading at the end
of an element is marked down in the column marked "R". Then
by later subtracting the previous reading at the end of the
last element from the reading at the end of the next element,
the total time for that element to be completed is found.

In case Of delays or waste time, the procedure is as follows:
at the point where the delay starts, the time is noted and

placed both in the column marked "R" under the element which
is interrupted, and in the space provided in "delay" column.

The chief difficulty in making good time studies in
construction work is the varied character of the work which
the common labor does. They are seldom called upon to work
long enough at some assignment to become very skilled in the
procedure. Of course there are exceptions such as brick-

layers, steel men tying steel mats, and others who hardly

come under the class Of common labor. In carrying out the
day's work, many different things have to be done by common
labor which are seldom, if ever, done again in the same
manner and under similar conditions. Nevertheless, men who
can be worked up to, or do better than the average in such
work as we have time studies Of, can be expected to put the
same amount Of effort and brains into other work Which can-
not be timed. Therefore in using these comparative values
on other jobs, a basis can be formed upon which to judge an
Opinion of a man's effort_and skill to show whether or not

he is doing a "fair" day's work.

A. Clam-shell Operation.

In order to place the sheet-piling it was necessary to
take out the Old abutment of the previous bridge. The Old
abutment was composed Of large boulders cemented together
with some sort of cement grout. Its condition was poor, and
it was not difficult to demolish. The clam picked Off much
of the abutment above the surface, but that portion below
the surface had to be blasted out, and the rabble therefore
had to be picked off the bottom. This was the portion of
clam-shell Operation studied. The fact that the clam was
grabbing blindly in the water, sometimes digging in for a
good load and sometimes slipping over the surface Of the
rocks without picking them up, made large variations in
the second item of this study - "grab load". This is espec-
ially true because more than one grab was Often made since
the first one might not have picked up a load. The swings
of the crane can be easily checked, as they vary but little
in comparison. However, this part of the placing of a coffer-
dam is no doubt encountered on other work, and since the
same difficulties will probably airse, the average time for
each swing and grab should prove to be a fairly representative
cross-section Of such work.

It is necessary to show that, although the bucket is
marked as % yard, % of a yard was seldom taken out, and that
the average excavation was probably something less than-%
yard. Boulders encountered Often kept the jaws from closing
fully, thereby preventing a full load, and some timbers as

well as rocks were removed by the teeth on the clam without

removing any dirt at all.

The "swing up" and "swing back" items include only the
turning Of the crane from grab position to dump position,
and the "grab load" item includes the dropping and raising
Of the bucket about 20 tO 25 feet.

Statistical study on the clam-shell Operation

1. Study of the elements

 

 

 

Trial #1 Total time Trials Av. time Best time
1. Swing up 900 2.65 13 .20 .14
2. Grab load 4.64 13 .44 .17
3. Swing back 90° 2.45 15 .19 .15
Trial #2
1. As above 2.75 13 .21 .15
2. 6.31 13 .49 .11
3. 2.29 13 .18 .15
Trial #3
1. As above 2.52 13 .19 .16
2. 5.21 13 .40, .12
3. 2.56 13 .20 .14
Element 1.
A. Average of average times for each trial : .20 min.
B. Average Of best times for each trial - .15 min.
C. Fair time (average Of average and best) : .175 min.
Element 2.
A. As above .443 min.
B. .133 min.
C. .288 min.
Element 3.
A. .19 min.
B. .14 min.
CO .165 min.

If all abnormal times, which are those times which

more or less than 50% Of the average above or below the

are

ave 1"

age, are discarded, and new averages drawn, it is interesting

to note how much these changes affect the average times

fair times Of the first study. All abnormal values are

and

shown

in red on the study sheet. Abnormal values for this study:

Element . 1 " o 50 , o 10
2 - .66, .22
5 - .28, .09

Total time Trials Av. time Best time

Trial 1
Element 1 2.32 12 .19 .14
2 2.97 7 .42 .22
3 2.17 12 .18 .13
Trial #2
Element 1 2.44 12 .20 .15
2 2.74 6 .46 .35
3 2.29 13 .18 .15
Trial 3
Element 1 2.52 13 .19 .16
2 2.49 6 .42 .26
3 2.23 12 .19 .14
Element 1 Element 2 Element 3
A .193 .433 .183
B .15 .276 .14
C .171 .355 .16

This changes the average time for the first element by
only .007 min.: for the second, .01 min.; for the third,
.007 min. This shows that a few large abnormal times are
balanced by several small ones, and so the average time given
is accurate, even though the spread between greatest and least
values is large. But since we have more smaller values, throw-
ing out abnormal times tends to raise the best time, as is
shown in the second element, the one with the largest variation
Of time due tO character Of work performed. Therefore this
will raise the fair time for the second element to .355 min.,
a difference Of .07 min., which may possibly be considered
fair to do under the circumstances. At any rate, the difference
is sO little as to be hardly noticeable.

It has Often been said that, while methods of time study
are or can be scientific, the rate or fair time is largely a

matter of experience and judgment on the part of the Observer.

Since we are not using this study for wage payment, but for

an actual determination of prevailing amounts Of time necessary
to do the work, the average time should be sufficient. The
fair time is based on a mathematical average and discards all
judgment Of the Observer, although this method Of Obtaining

the fair time is personal judgment. But this judgment is
agreed to by several authors, and is given here as being
something to work toward and to maintain if possible.

The latter part Of the previous statistical study Of the
elements is given in order to prove that the average time Of
all elements combined should give a fair average Of time in
which to do this work. This, Of course, includes all the ex-
cessively great and small times; but these can be expected
on the job and should be included. Discarding abnormal values
is largely a matter Of judgment of the Observer and the use to
which the studies are to be put. Therefore, in the further
development Of these time studies, the first method will be

followed throughout.

2. Study Of the total times for each trial:

Trials
Trial 1 a 9.74 13
3 = 11.59 E
Totals 32.48 39

Average time for 1 Operation is .833
(This of course can be found also by the average of all the

elements added together)

Average time - .833

Best time .47

II
0
0'8
0"

Fair time

3. Study of the total delayed time:

Total amount of delayed time = .45 & 1.45 : 1.90 min.
Total time consumed a 34.38 min.
% of delayed time : 5.5%

This delay proved to be necessary delay, and therefore

should be allowed in the total time.

COMMENTS

It must be realized that this is only the study Of the
time consumed in actual Operation. Preparation, such as
loosening the Old abutment, building trestle to allow the
crane to Operate, etc., can never be accounted for except in
a general cost and time analysis of the whole bridge when com-
pleted. These things must be pro-rated according to their
value on different parts of the job. If it were possible to
have an observer on the job at all times, he could make such
a study and find all the data on the prerequisites necessary
for Operations such as are considered in this thesis.

An improvement could easily be made in this and all other
portions Of the work requiring excavation, by the use Of an
orange-peel bucket which would do the job much more satisfac-
torily than the clam shell. The contractor recognized this,
but as is Often the case, a clam shell was available While an
orange-peel was not; and so the equipment available is Often
the controlling factor rather than that which should be used.
The state required most of the excavation to be done by hand
instead of machinery; otherwise it might have been cheaper
in the long run to buy an orange-peel bucket particularly for

the occasion.

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B. Placing steel sheet piling.

 

After the bottom was freed from boulders as much as
possible as determined by sounding along the proposed line Of
the cofferdam, the steel sheeting was placed. The cofferdam
walls consisted Of Lackawanna steel sheet piling 20 feet long
and 14 inches wide. This type Of sheeting is the double claw
type Of interlock rather than the claw and ball Of the U. 8.
Steel Company. The sheeting had been used several times and
was again to be pulled after the abutment was in, hence it
was in a rather battered condition requiring the use Of a
torch to cut some of the ends or claws and otherwise make it
suitable for driving. The sheeting was all piled up in the
Old roadway leading to the bridge, and the crane was between
them and the river, as the diagram of the layout shows. This
necessitated a 180 degree swing which might have been improved
upon had there another place been available for the piling.
Only 8 or 10 piles were placed at one time, as more would
cause too much bending out Of line. After placing this number,
the hammer was hooked on and that sheeting driven down a few
feet to hold the next group Of sheeting to be placed.

The first element - hook on - is the time necessary to
run the cable through the hole in the end Of the piling and
hook it on, attach the tag line (rOpe held by a workman in
order to guide and keep the pile from swinging), and hoist the
pile clear Of the ground ready to swing the crane carrying the
pile through 180 degrees (on the average) to approximately.
near its position. There was a workman sitting on top Of the
piles already placed, ready to guide the end Of the swinging
pile held by the cable into mesh with the interlock of the

last sheet placed. This constitutes the third element. The
fourth, called "set in", is the time necessary to drOp and
pick up the pile into and up from the bottom several successive
times, the pile merely sliding up and down in the interlock
of the one already placed. This is done in order to set the
pile into the bottom so that it will stand there and form a
guide for the next pile until it is driven. The time is quite
variable in this element, since a comparatively soft spot in
the bottom might be hit, in which case the weight Of the
sheeting will carry itself down each time it is picked up and
drOpped. Therefore it is good practice to allow the crane
Operator to do this until penetration is small - probably an
inch or less. This may be done several times, or in case of
hard ground, only once or twice, leaving the rest for the
hammer. In the last element, the workman unfastens the hook,
and the crance swings back to pick up another pile, during
which time the workman should hitch his saddle forward to the
pile just put in and be ready to guide the next one into place.
In the two following sheets of study, it will be Observed
that the elements are slightly changed in order. The above
explanation applies to the second study sheet as being the
better Of the two. The first (taken at 2:00 PM ) differs from
the second in the following manner: the study starts with the
swing rather than the hook-on, no time is given for lining up,
and the item Of unhooking is placed there. The second sheet
starts the sequence more logically than does the first; since
lining up is an important item, it should be included; and
the item of unhooking is relatively small and unimportant as

can be seen by the time for it on the first sheet. The total

time of course can be compared, as can the individual elements
alike on both sheets, but the other elements have been com-

bined or broken apart into their components as the following

study indicates.

 

 

\

 

 

 

 

 

 

H

t J.

:3
C3

Statistical study ongplacing sheet piling

1. Study Of the elements

 

Trial #1 Total time Trials Av. time Best time
1. Swing up 1350

(with pile) 4.34 10 .43 .18
2. Set in piling

(including lining up) 8.47 8 1.06 .60
3. Unhook , .96 8 .12 .07
40 Swing baCk 2000 9 e22 e15
5. Hook on ' 7.30 10 .73 .30
Trial #2
1. Hook on (#5 in #1) 9.52 7 1.36 .77
2. Swing 180 degrees 2.98 7 .43 .35
3. Line up 7.21 7 1.03 .30
4. Set in 6.95 7 .99 .62
5. Unhook & swing back 4.46 7 .64 .53

Average Of like elements in these two studies:

#1 in trial #2, #5 in trial #1
A. Average Of average times for each trial a 1.05 min.
B. Average of best times for each trial a 0.54 min.

C. Fair time 0.79 min.

#2 in trial #2, #1 in trial #1

A. As above .43 min.
B. .27 min.
C. .35 min.

By combining or separating, as the case may be, averages,
based on trial #2 elements, may be arrived at. Element 2 in
trial #1 is composed Of 3 & 4 in trial #2; while 5 in trial
#2 is composed of 3 & 4 in trial #1. It seems reasonable to
divide the element 2 into its prOportional parts and to place
it in elements 3 & 4 in trial #2, and to combine 3 & 4 in
trial #1 into element 5 in trial #2. The proportional parts

are to be arranged according to their % value.

In trial #2, element 3 a 51%, and element 4 : 49% Of the
two taken together. Therefore element 2 in trial #1 can be
divided in elements 3 and 4 in trial #2 as follows respectively:
51% x 1.06 = .54; 49% x 1.06 : .52. Elements 3 and 4 in
trial #1 may be combined to equal .34 for element 5 in trial

#2.

#3 in trial #2:

A. Average of average times for each trial a .79
B. Average Of best times for each trial a .30
C. Fair time u .55

#4 in trial #2:

A. As above I .76
B. -..46
Ce . 061

#5 in trial #2:

A. As above : .49
Be 3 .38
Co = 044

2. Study of the total times for each trial.

Trials Average

Trial #1 : 19.97 8 2.49

2 = 31.12 7 4.45
Average of both trials : 3.47 min.
Average Of best times = 2.27 min.
Fair time a 2.87 min.

As can be noted, the average time for each trial is
quite different in the two trials. These statistics were
taken on different days, but under similar conditions. It
would seem that these averages should be closer together, but
there is an explanation or the difference between the two days,
and that is that on the second sheet beginning at 3:33 the
piling that was being placed was further away from the center.
This necessitated a flat boom which made the lining up and
setting in more difficult. When the piling is being placed
at the limit of the boom it is necessary for the man guiding
the pile into place to take more time to swing it into posi-
tion. These studies show this difference very well. It will
be further noted that the average Of the "hook-on" times is
larger in the later study. This is due to the fact that the
sheeting on tOp of the pile was easier to hook on, and as the
pile went down, some were under others or placed cross-ways,
and in general were more difficult to snake out and hook on.

While there is this difference between the two, never-
theless this should provide a good average Of time according

to reasons outlined under the previous Operation.

3. Study of the delayed time.

Trial #1:
Necessary delay a 2.64 min., or 11% of the total time

Unnecessary " 1.70 min., or 7% of the total time

Trial #2:
Necessary delay : 2.30 min., or 6% Of the total time

Unnecessary " a 3.40 min., or 9% of the total time

Average percentage of necessary delay = 8%%

8%

Average percentage of unnecessary delay

The percentage Of unnecessary delay is the part that
needs attention Of the Observer. In trial #1, delay B was
unnecessary as it was the job Of the helper at the pile Of
sheeting to see that the piling was ready for placing, and to
choose the next pile so that there would be no delay as in
A, B, and D in trial #2. Delay E in trial #2 was the fault
Of the man on the sheeting already in place, as he should not
have left his position. Since only 8 or 10 piles are placed
at one time before driving, there was no need for him to
leave until the set was completed. Here then is one place to
speed up the Operation - by requiring that man to be a little
more alert in supplying this sheeting to the crane.

 

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Time started ——Z—~—-0—-Q £474 Sheet 110. --_. of
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Name of Operation

 

 

 

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C. Driving steel sheet piling,

The next operation after placing the sheet piling is to
drive it down into the bottom approximately 5 or 6 feet. This
is done by a 5000# steam hammer carried by the crane. The
work is done in series with the placing - that is, after 8 or
10 piles have been placed, the hammer is hooked on and the
piles driven in order to provide a guide for the rest of the
piling. The sheeting is driven two at a time, as the hammer
is large enough to do this.

The bottom was hard blue clay, and the driving therefore
rather difficult as the piles went into hard ground which
later develOped into a shale formation mixed in with and
underlying the clay. However these studies treat only of the
first part - that is, through the clay only, not into the
shaly mixture. Occasionally a boulder was hit which necessi-
tated leaving the piling sticking up until some on the other
side were driven, and then the piling on top of the boulder
was driven if possible. Very often this expedient was
sufficient to force the stone to one side, or perhaps the
pile was bent a little out of line, but not harmfully so.
Again it was necessary to pull the piling and attempt to get
the rock out and then replace the piling.

Of course it was necessary to keep the line of sheeting
as straight as possible. To do this, it was sometimes neces-
sary to put a set of rOpe falls on the piling to pull it into
the prOper position while hammering was going on. The piling
was set against a floating frame which formed the general

line of the cofferdam and later became the first set of walers.

In the study sheet, the first element consists of lift-
ing the hammer off one group of piling and resetting on the
next two. Occasionally this took a little more than a min-
ute due to difficulty in getting the hammer set on just right
to accomplish the most work. The next element shows the time
taken for the actual driving of the sheeting to the depth
shown. This did not remain the depth as they were driven
down deeper later on to take care of a bad sand-boil which
occurred, and also because the design of the abutment was
changed, after the bottom was disclosed, requiring the founda-
tion to be two feet lower than originally planned. The ori-
ginal plans called for caissons under the footing, but the
bottom was discovered to be so hard that these were not neces-
sary. The reason for lowering the foundation was to be sure
that no scour would occur around or under it in case a dam

about 400 yards downstream should ever go out.

Statistical study of pile driving.

1. Study of the elements:

Total time Trials Av. time Best time

1. Lift off and set on 9.76 13 .75 .25
2. Drive 5 to 6 feet 38.29 11 3.48 2.00

Element #1 - Fair time = av. of average & best times a .50 min.
2 - Fair time ditto , 2.74 min.

In these figures, the two groups of piles left standing
high were eliminated, as they were not yet completed and could

not be compared to the rest.

2. Study of the total times:

The total time less the two not completed was 46.48 min.,
with 11 trials. The average time was 4.22 min., and the best
time being 2.70, and therefore a fair time is set at the av-

erage of the two, and is 3.46 minutes.

5. Study of the delayed times:

The delays as noted were all necessary ones, since they
had to do with lining up the piling, and one in which the
crane had to lower the boom in order to reach the piling.
Hence these delays should all be expected in the course of
driving a cofferdam and should be added in. The amount of
time consumed was 15.62 min., or a total time of 55.39 plus

15.62 or 67.01 minutes, of which the delayed time is 20%.

It would be advisable to cut down this delayed time, of
course, but the result of the delays was to get a very straight
wall and one which lined up very well. Therefore these delays
no doubt made up for themselves in saving trouble later on in
the closure. There should be no delays for fatigue, etc., be-
cause the two men who are charged against this Operation have
nothing to do as long as everything goes smoothly, other than
to signal the crane operator as to the position of the hammer.
They are there to place the falls and hold the lines if needed.

It may seem like a waste of time to set in only 8 or 10
piles, attach-the hammer, drive then, take hammer off, and re-
peat the process - since it usually takes about 15 minutes to
put on and take off the hammer. The writer noticed this de-
lay, and thought that it would be more economical if several
guide piles were placed along the framework, with the walers
and another set of parallel timbers hooked on to these piles
to act as guides for the sheeting. In this way, all of the
sheeting along one side could be placed at once and then
driven without the necessity of spending so much time taking
the hammer off and on. However the author was assured by the
contractor that it would take much more time to place the
guide timbers and piles than would be saved in doing away with
the necessity of changing the hammer. This is purely a ques-
tion of time which might be settled at some future time by
some sort of time studies intended to show the difference be-
tween the two. It may be that the method is impractical and
that no one uses it, but if it is in use a comparison could
be made between the time necessary for placing by this method,
which would be the average time of the set in sheet, plus

about 15 minutes for every 8 or 10 piles, plus the average

time of the driving sheet (divided by 2 for l piling), plus
the delays shown, as compared to the time per pile for the

other method.

L -... ..V.. “_._ . .--- -.—.-..—_.._..~‘ . -... -_.._.,-_._--._.—..‘-._ —. -”—-.- “-.-

 

Time started -—--—-——- ~-—--—- Sheet No. ___- of
Time finished

 

—._— _.— -——--. ..-.--

Name of Operation

No. of men T‘J” 2 jZ‘JI/E 5' 74331....”2éé2t-
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D. Study of wet excavation.

The wet excavation is started after the cofferdam is
completed and braced sufficiently to allow the water to be
pumped out. After leveling off, the second set of walers and
struts was placed about six feet below the first set, and after
further excavation, the third set was placed about five feet
under the second and the excavation carried down about three
feet below this level. The bottom of the footing is about
14% feet below water level and the toe hold of the 20 foot
piling is about 3 feet.

Perhaps the term "wet excavation" should be explained.
This does not mean that the excavation is done under water by
clam-shell, but rather means all excavation within the walls
of the cofferdam. Ordinarily this, too, is done by clam-
shell, but due to the unemployment situation, the contract
called for hand excavation of the material. This could be
done either by shoveling out in stages, or by filling the
clamshell by hand and hoisting out and dumping. The latter
was done as it was by far the easiest and cheapest method.
Great care was necessary to see that the bucket in going up
and down between the struts did not touch or Jam any of them,
as it could have easily knocked out one of the struts which
might have caused a cave-in of the cofferdam.

In the study of any excavation, the character of the
ground is of course the most important consideration. After
going through the first few inches of tOp soil over which the
river had been flowing, the ground encountered was a hard

blue clay which kept getting harder as it went down, finally

developing into an underlying bed of shaly clay and actual
blue shale which required quite a little picking to get loose.
The hole was a remarkably dry one however, and it was kept
that way by digging a trench clear around the outside edge of
the cofferdam to lead off the water seeping through the walls
and to collect the water from two or three small sandboils
whose flow was led into the side ditches which led to a sum?
where the water was pumped out. »The pumps used for emptying
the cofferdam were two 5 inch centrifugal pumps powered by
gas engines. After emptying, the hole was kept dry by a 1
cylinder, 2 inch force pump. This pump was bought for the
purpose of filling the tank on the concrete mixer, and thus
did double duty and reduced Operating expense of the large
pumps to quite an extent. A dry hole is much better to work
in, and it should be kept as dry as possible to provide a
good bottom.

The next important consideration in a study of excava-
tion is the method of doing it, which has already been out-
lined, and the effort and experience of the men doing the ex-
cavation. This welfare labor, while willing, nevertheless
varied quite a little in their ability to shovel this dirt.
The difference between a man who takes large shovelsfull and
keeps it up steadily all day long, and the one who is erratic
in his effort and in the amount carried in by his shovel, is
easily discernable. Here the contractor was forced to take
good and bad, and although the worst ones were discharged,
there were still some who could have been improved upon but

who had to be kept on to get the work done. Hence the average

time per man is probably somewhat lower than the average

during normal times when the best men available can be hired.

A certain degree of intelligence is also required in that the
hole must be kept higher in the center in order to allow good
drainage of any water towards the edges. Men tend to work in
the center of the hole, and the foreman must keep them on the
edges if they do not do it themselves. As the excavation nears
the grade care must be taken to see that no one digs below

this level, as it must be filled with concrete, and not back-
filled with clay to the proper level.

There was not a constant number of men engaged in filling
the bucket at all times, as study of the observation sheet
shows. Some men were instructed to cut out the ditch at the
side, and if the bucket came down near them they would throw
their dirt into it; otherwise it would be piled up on the
bottom of the hole. Occasionally one would pick instead of
shovel during the time the clam was lowered. When a man
worked half the time without throwing any clay into the bucket,
but during the other half did his share of filling, this fact
is accounted for by noting a "%" man at the side showing the
number of men actually engaged in filling.

The character of the ground was sometimes variable also,
as the softer clay tOp might be peeled off and shaly clay
struck underneath. These variables make it difficult to de-
termine exactly the time needed to fill the clamshell, but
the average of all the times should be a good indication of J
the time nexessary for filling and depositing, according to
the principle illustrated under "Clamshell operation."

The first element "Load bucket" is merely the time

necessary for the indicated number of men to fill the clam-
shell with about % yard of excavation. Although the clam-
shell was of f yard capacity, the voids Of the shoveled ma-
terial brought it down. In order to bring the time for each
trial to a common average it was necessary to find the num-
ber Of "man-minutes" (number Of men multiplied by number of
minutes) required to load the clamshell. Therefore in the
analysis to follow, the first element has been divided in
this way. The total number of man-minutes is summarized at
the end of the observation sheets on this Operation. This
shows only the actual time necessary for loading as shown in
the summary of statistical data under element 1. The total
time for each yard given in the total number of man-minutes
including the time for the bucket to be dumped is found at
the end of the statistical data under "study or total time“.

The distinction between these two is that the first
shows the time it would take one man to shovel a yard of this
sort of excavation, averaging soft and hard, with no rest
periods in between, while the second shows the actual number
Of man-minutes consumed on this job per yard, including all
time except the noted delayed times. This data should apply
as a general rule since the study was conducted throughout
one whole day, thus averaging the results of early morning»
and late afternoon work.

The next group of elements comprise the mechanical por-
tion of the Operation. The second element - raise 25' - is
the time necessary to raise the full bucket from the bottom
up to a height sufficient to be dumped on the pile. This

time included a stop or two necessary to stop the swinging

Of the bucket so that it could be hoisted without danger of
hitting a strut. The next two elements are self-explanatory:
swing back 90°, and dump and swing back. The last (lower) is
similar to the second, the bucket being guided by someone
standing on the top strut. The men all have a chance to rest
a short ime while the bucket is being dumped, as shown in the
statistical study. This is no doubt a saving factor in the

results of fatigue as is also shown in the study.

Statistical study of wet excavation.

1. Study of the elements:

 

Element 1
Trial #1 (started at 2:30) :

A. Total number of man-minutes s 453.85
B. Total amount of excavation : 6% cu. yds.
C. Average man-minutes/yard = 69.75 min.
D. Best time/yard

(sum Of 2 best trials) - 58.45 min.

E. Fair time

( av. of best & av. times) 64.10 man-min.

Trial #2 (started at 7:16):

A. As above 427.20
B. 6.5 '
C. 65.60
D. 53.30
E. 59.50

Trial # 3 (started at 11:05):

A. As above 234.90
B. 3.0
C. 78.30
D. 68.10
E. 73.20

- Other elements -

Trial #1 Total time Trials Av. time Best time
Element 2
(Raise 25 feet) 5.70 13 .44 .25
Element 3
(Swing 45° 8. empty) 2.07 13 .16 .08
Element 4
(Swing back) 2.38 13 .18 .10
Element 5 '
(Lower) 5.49 13 .42 .25
Trial #2
Element 2 6.25 13 .48 .30
3 2.22 13 .17 .13
4 2.56 12 .21 .16
5 8.13 12 .68 .47

Trial #3 Total time Trials Av. time Best time

Element 2 2.00 5 .40 .25
3 1.15 5 .23 .13
4 1.16 5 .23 .17
5 2.65 5 .53 .33

Summary Of elements:
Element 1 - throughout a day

A. Average man-minutes per yard : 71.25

B. Average of best times - 59.95
0. Fair time I 65.60
Element 2
A. Average of av. times for each trial = .44 min.
B. Average of best times = .26 min.
0. Fair time (av. Of A & B) a .35 min.
Element 3
A. As above .19
B. .11
C. .15
Element 4
A. As above .21
BO .14
C. .18
Element 5
A. As above .54
B. .35
C. .45

The action of workmen as the day progresses is strikingly
illustrated in this study. If the element Of manual labor,
#1, is studied according to hour Of the day the studies were
made, it will be noticed that the fastest progress was made
during the early morning from about 7-9 AM, both in average
time and in the best time. The second best occured in the
afternoon between 2:30 and 4:23. The least productive time
in this study was between 11 and 12. Unfortunately there was

no Opportunity to get data between 5 and 6 which might have
proved that this was the slowest time. With more data it

would be interesting to show how the production varied with
time due tO fatigue of the laborers, but that is beyond the

scope of this thesis.

2. Study of the total times.

 

This study must be conducted in a little different man-
ner than in the former cases. To get an equitable average,
the average time multiplied by the average number of men is
determined in order to get an average number Of maneminutes for
each 4 yard. To get a fair "best time", the best times of
each number of men are averaged together according to the above
method. Study Of the average and best times according to the
time of day is made in a summary of the results for each trial
immediately before the day's average is made up. 'The totals
for each trial are then made into a grand average covering a
whole day's work, and shows what may be expected on a job Of

this kind.

Trial £1 (2:30 - 4:23)

Total time 86.29 min.

NO. of trials 13

Average time 6.64 min.
Total number of men 85
Average " " 6.54

Average number of man-minutes n6.54 x 6.64

 

.43040
Best times:
NO. of men Least time Trials Weighted times

7 5.45 8 43.60
6 5.56 4 22.20
5 10.97 1 10.97

13 76.77
Average best time = 76°77 = 5.90 min.

13

Best time = 5.90 x 6.54 a 38.60 man-min.

Fair time (average Of best and average times):

Fair time = 41.00 man-min./%yd. (1 clamshell)

Trial £2 (7:16 - 9:05) (Excluding trial #9)

Total time 94.51 min.
No. of trials 12
Average time 7.88 min.

Total no. of men 64
Average " " " 5.33

Average no. of man-minutes : 5.33 x 7.88 = 42.00

Best times:

 

NO. of men Least time Trials Weighted times
7 4.98 2 9.96
6 6.47 l 6.47
5 7.13 7 49.91
4% 8.86 _2__ 17.72
12 ' 84.06

Average best time : 84.06/l2 : 7.00 min.

7.00 x 5.33 a 37.33 man-min.
39.86 man-min.

Best time
Fair time

Trial £3

Best

Trial £4

Best

(11:05 - 12:02) (Excluding trial #6)

Total time 45.66 min.
NO. of trials 5
Average time 9.13 min.
Total no. of men 25.5
Average " " " 5.10

Average no. of man-minutes - 5.10 x 9.13 a 46.60

times:
NO. of men Least time Trials Weighted times
6 8.69 l 8.69
5 8.08 3 24.24
4% 9.22 l 9.22
5 42.15

Average best time s 42.15/5 8.43 min.
Best time = 8.43 x 5.10 : 43 man-min.

Fair time

44.80 man-min.

(2:00 - 3:27) (This trial shows total times only as
the author was busy taking notes, and could only de-
termine the time by recurrence Of an element.)

Total time 94.30 min.
NO. of trials 13
Average time 7.25 min.
Total no. of men 87.5
Average ” " ' 6.74

Average no. of man-minutes : 6.74 x 7.25 = 49.00

 

times:

NO. of men Least time Trials Weighted times
9 6.35 2 12.70
8 6.40 3 19.20
7 7.70 l 7.70
16% 7.15 1 7.15
6 6.95 3 20.85
5 6.85 2 13.70
4 8.75 _1_ 8.75

13 90.05
Average best time = 90.05/15 = 6.92 min.

Best time = 6.92 x 6.74 46.60 man-min.

Fair time a 47.80 man-min.

Summary of trials by time of day:

Time of day Average time in Best time in Fair time in
man-minutes man-minutes man-minutes
7:16 - 9:05 (#2) 42.00 37.33 39.86
11:05 - 12:02 (#3) 46.60 43.00 44.80
2:00 - 3:27 (#4) 49.00 46.60 47.80
2:30 - 4:23 (#1) 43.40 38.60 41.00

This summary shows how fatigue of the worker tends to
increase from morning to noon through the early part of the

afternoon, and evidently decreases again in the latter part

 

Of the afternoon. These last two studies overlap a bit, but
the last one extends over an hour beyond number 4. However
this is not entirely a good case to base such a statement
on, as shown in "Study of delayed time".

An average for the day can now be found by averaging all
of the above times. A criticism may be found in doing this in
that not all trials were the same length of time, and that
they should be weighted to find a true average. However, the
author does not believe that this is necessary here because
each trial is a representative one. Therefore we have total
times, given in man-minutes, to excavate % yard of the prev-
iously described soil. TO this must be added the time Of 2
men in digging ditches, or picking, l crane Operator, and l

superintendent.

Average 45.25 man-minutes
Best 41.38 man-minutes

Fair 43.31 man-minutes

3. Study of the delayed time. (All necessary)

 

Trials Total delayed time % of total time
#1 23.15 min. 21%

2 1.10 1%

5 1.81 4%

In order to get a good idea of the amount of rest the
shovellers had, the difference between the total amounts of
element 1 and the total amount of "total" times for each trial
is shown here. To this time must be added the time for delays.
The men then got a chance to rest a little between each load-
ing when the bucket was being dumped. It has been mentioned
that the fatigue seemed to lessen the latter part of the aft-
ernoon, as the average time was smaller. However it can be
Observed now that during this time there was a large amount
of delay (21%) during which the men had a chance to rest and
freshen up for the next loading.

Amount of rest allowed:

Trial ,1

86.29 - 70.66 - 15.63 min. plus 23.15 = 38.78 min.

Average of 58.78/15 ; 2.98 min. per load of 4 yd.
(It must be kept in mind that this is excessive due to the
large amount of delayed time. The extra rest shows up plainly
in the increased speed of the men during loading in this
period, but should not be regarded as a general rule.
Trial 2

94.51 - 84.98 : 9.53 plus 1.10 : 10.63 min.

Average of 10.63/13 3 0.82 min. per load of % yd.
(In spite of this handicap of a smaller amount of rest,

this period shows the best time for loading as it is early

in the morning.)

Trial #3 (Except #6)

45.66 - 38.70 = 6.96 plus 1.81 - 8.77
Average of 8.77/5 : 1.75 min. per load of % yd.

(This increased rest period does not overcome the fact that
this is later in the day and therefore the production becomes

slower.)
COMMENTS

While primarily this study was undertaken to show the
actual time and labor consumed, yet we have here a problem
Iwhich could, with sufficient data carried out in the same
manner, be continued in the building field for all forms of
labor.

A study Of fatigue of the laboring man in heavy, out-
door work might prove Of value in scientific management of
such labor. This is never done in the field - experience
being the best guide. ‘But it has worked out in industrial
lplants, and the author is of the Opinion that this study
might someday be removed from the field of the theoretical,

and be given practical consideration.

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E. Study of Concrete Pouring.

 

All preliminary work necessary has been done. The
cofferdam has been made, the prOper level of excavation has
been reached, and forms and steel have been placed in readi-
ness. The concrete gang is ready and the observer is ready
to start observation. This portion of the work was the
footing which is 2 feet thick, about 65 feet long and about
12 feet wide.

The layout is shown in a diagram in this thesis and was
considered as an ideal layout by the contractor. It was so
designed as to permit a steady flow of materials through the
mixer without any delay or without particularly long hauls.
The mixer used was a 21 S paver which was too large for this
type of job, but as it was lying idle at the time, it was
used in place of buying a 10 S mixer which was the proper
size to use here._ In order to get a good, even, and constant
mix, it is necessary to run a concrete mixer to somewhere
near its full capacity. It was impossible to do this, as the
space available for placing was limited, necessarily limiting
the number of men who could place and distribute the concrete.
Only 9 men were used here - 3 to handle the concrete in the
chutes, 2 to strike off to the proper level, and 4 to handle,
distribute, and spade. Therefore the batch was limited to a
4 sack batch instead of 6 sacks, the regular capacity of the
mixer. It should have been less than 4 but this was the least
the mixer could handle efficiently.

The batch as designed by the engineer was: 4 bags of

cement, 158# (16.6 gallons) of water, 4 wheelbarrows of stone

(each to weigh 297#), and 3 wheelbarrows of sand (each to

weigh 266#). This produced about 16 cubic feet of concrete
with a 3 inch slump, instead of the 21 cubic feet regular
capacity. The concrete was very uniform, but rather stiff

to place around all the reinforcing steel. It would have

been permissable to allow a little more water, making the
placing easier, as subsequent tests on sample beams showed

a breaking point of 750 pounds per square inch at 7 days,
which was better than required at 28 days. This prOportion
of sand to gravel presented a problem. Gravel is harder to.
shovel than sand, and one more barrow was required. So 5

men were placed on the gravel and 2 on the sand. Later on,

as it became apparent that the gravel was slow in getting to
the mixer, another man was added. The balance of time must

be maintained between the two so that the men work continu-
ously and yet have time enough between batches to load the
skip. It will be seen that most of the delay due to the skip
not being loaded was due to the gravel being a little late.
This delay was eliminated when the 4th man was put to work on
the gravel pile. The time of mix was set at 1% minutes. This
presumably meant that the first part of the batch was not to
be discharged for 1% minutes. However, even though an auto-
matic timing device was on the mixer, this time was often short,
although the average of the first and last parts of the batch
out was usually over 1% minutes. It is to the advantage of the
contractor if he can cut the mixing time short a little, and
as the inspector was present and did not object, and further
since the test beams showed high strength, it seems that this

was permissable.

It was necessary to weigh each wheelbarrow full of agg-
regate, so a man was added soon after the start whose sole job
was to check the weight and adjust. It may seem that each man
wheeling a barrow could do this for himself, but as the obser-
ver noted some delay and confusion in doing this, the extra
man was put on, which decreased the delay very considerably.
This fact is especially noticeable on the first and second
sheets of observations. Immediately after the weight adjuster
was added, the delayed time due to the skip not being loaded
was nearly eliminated, but near the bottom of the first sheet,
this man was sent on another errand, and immediately delay due
tO‘this cause was noticeable and continued until the man came
back (on the second sheet). There is one criticism which may
be made of this analysis, and that is the fact that the time
between the raising of the skip and the batch emptied seemed
to be shorter than usual during the time the weight adjuster
was gone. This did not allow the average time for loading
the skip and naturally would cause some delay in itself.
However it is the Opinion of the writer, formed on the few
cases where this man was not present and on personal observa-.
tion, that the weight adjuster was necessary and added to the
Speed of the work. ~

In the concrete gang were also included one mixer Opera-
tor, two men to wheel the buggies about 75 feet and back, and
one man to put in the cement. He was later augmented by another
man to bring the cement nearer the mixer as the pile grew
smaller. The men wheeling the aggregate only had to go an
average distance of about 10 feet to the scales, and another 6
feet into the skip. There was one superintendent and one fore-

man whose job was the placing of the concrete. Thus there was

a total Of 10 men making and wheeling the concrete and 9
handling and placing it, not including the foreman‘and the
superintendent.

In sheet 1 of the observations the first element is
called "Load - skip up and down". After further study, it
was decided that the difference between this time and the
time the first batch was discharged would not give the true
mixing time. This is because the load leaves the skip, and
the Operator holds it up for some little time waiting for all
of the material to slide in, and perhaps he jerks it two or
three times, and it is then dropped for a new load. Of course
the concrete is being mixed before the skip comes down, so in
the statistical study the element 1 on the first observation
sheet (beginning at 8:00) has been divided into two parts
according to data procured on the second and following sheets.
That is, in this study, trials on sheets 2, 5, 4, and 5 are
analyzed first, and the data procured on element 1 and 2 is
used to divide element 1 on sheet 1 into two parts.

The third element (on all except first sheet) shows the
difference in time between the time that the skip was down
ready to be re-filled and the time of the first part Of the
batch out of the mixer into the concrete buggies. The times
of element 2 and element 3 added together give the true mixing
time of the least mixed concrete, while element 4 shows the
length of time between the first and last batch out. This is
quite large due to the fact that only 2 buggy men were used
and they required some time to travel that 75 feet to the
chutes. More could have been used for faster Operation, but

this was asfast as the handlers could place it.

For efficient mixer operation, there should be no delay
between the emptying of the last batch and the raising of the
skip with the new one. Observation showed that there was very
often a delay which could be put down to one of two causes;
the most important being that the skip was not yet loaded,
and the second being due to the Operator not quickly enough
raising the skip. Because one of these things usually occurred,
this time was inserted as an extra element, with a letter desig-
nating the reason and a subscript classifying the delay due to

sand or gravel not being ready.

 

 

 

Detail of pouring
layout. Note ex-

tra mixer for

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Statistical study of concreting Operations.

 

1. Study Of the elements:

 

Trial £2 (Sheet 2 of trial beginning at 8:00)
Total Trials Aver. Best Fair

time time time time
Element 1
(First load in) 2.35 12 .20 .15 .18
Element 2
(Skip down) 2.64 12 .22 .12 .17
Element 3
(First batch out) 15.00 13 1.15 1.00% 1.08
Element 4
(Last batch out) 17.05 13 1.31 1.10 1.20'
Element 5
(Delay) 2.70 13 .21 .00 .10

Trial #3 (Sheet 1 & 2 of trial beginning at 10:45 added together)

Element 1 3.35 17 .20 .17 .18
2 2.82 17 .17 .12 .14
5 10.82 15 .72 .54* .65
4 20.84 16 1.31 1.10 1.20
5 12.53** 16 .78** .OO .39

Trial #4 (Sheet beginning at 1:00)

Element 1 1.05 6 .18 .10 .14
2 1.08 6 .18 .15 .16
3 6.87 6 1.15 1.00% 1.08
4 5.72 5 1.14 1.02 1.08
5 5.85** 5 1.17** .00 .58

* -The best time of this element should not be considered as
the least time. This is the main part of the mixing time and
should be at least a minute. Nothing can be done in the way
of improving methods or getting better workers to shorten this
period. Therefore this time has been left out of calculations
for fair time. The fair time has been calculated by sub-
tracting from 1% minutes (supposedly the least mixing time)
the fair time of element 2 which is the other part of the

true mixing time.

*‘ -These totals show excessive delays due to the time needed

for changing direction of the concreting chutes. They do not
show the average of delays for each trial, although computed

as though they did. Rather these times show an average dis-

tribution of delay over the whole period. More will be said

on this subject under "Study of the delayed time".

A summary of elements 1 & 2 of the preceding trials will
now be’made to determine a suitable percentage of division
these two combined in trial #1. It will be noted that trials
#2 & #3 are given a weight of 2 to 1 since they are about

twice as long as the other one.

 

 

Element 1 Aver. time Fair time Weight
Trial #2 .40 .36 2
3 .40 .36 2
4 .18 .14 1
.98 .86 5
Aver. time in min. .20 .17
Element 2
Trial #2 .44 .34 2
3 .34 .28 2
4 .18 .16 1
.96 .78 5
Aver. time in min. .19 .16
Percent of total of E1 51% 51%
E2 49% 49%

For purposes of division of elements 1 & 2 in trial #1,

50% for each will be taken.

Trial #1 (Sheet 1 of trial beginning at 8:00)

Total Trials Aver. Best Fair

time time time time

Element 1 2.79 13 .21 .15 .18
2 2.79 13 .21 .15 .18

3 12.66 13 .97 ---* ---

4 16.26 13 1.25 1.06 1.16

5 6.90 13 .53 .00 .26

Summary of elements

 

 

 

 

Element 1 Average time Best time Fair time
Trial #1 .21 .15 .18
2 .20 .15 .18
3 .20 .17 .18
4 .18 .10 .14
.79 .57 .68
Average for run .20 .14 .17
Element 2
Trial #1 .21 .15 .18
2 .22 .12 .17
3 .17 .12 .14
4 .18 .15 .16
.78 .54 .65
Average for run .195 .135 .16
Element 3 Average time only
Trial #1 .97
2 1.15
3 .72
4 1.14
3.98
Average for run 1.00

(This element shows a great variation which should not be
present under the circumstances as explained. The average of
this time, added to that of element 2 is 1.20 minutes, and is
the average time of mix for the first part of the batch.)

 

Element 4 Average time Best time Fair time
Trial #1 1.25 1.06 1.16
2 1.31 1.10 1.20
3 1.31 1.10 1.20
4 1.14 1.02 1.08
5.01 4.28 4.64
Average for run 1.25 1.07 1.16

2. Study of the total times.

 

Total Trials Aver. Best Fair

time time time time

Trial #1 42.50_ 13 3.27 2.75 3.01
2 40.18 13 3.09 2.70 2.90

3* 44.08 15 2.94 2.25 2.60

4** 10.80 4 2.70 2.48 2.59

12.00 10.18 11.10

* Including sheet 2, omitting #3 on sheet 1
** Omitting #2

Average time for 1 batch . 12.00/4 . 3.00 min.
Average of best times " " : 10.18/4 : 2.55 min.
Fair time for 1 batch = z 2.78 min.

These times are exclusive of large delays such as occured in
those trials omitted above. These were usually due to chang-
ing the chutes and, while necessary, should not be included
in the batch time. The above averages do include the delays
of Operation and of loading which are not necessary.

3. Study of the delayed time. (Element 5)

Total time Trials Aver. time/batch
Trial #1 6.90 13 .53
2 2.70 13 .21
3 14.53 16 .91
4 5.85 5 1.17
2.82

Average time/batch for all runs - 2.82/4 2 .705 min.

This is high, including as it does all delays, necessary and

unnecessary. If the delays due to change of chutes are elim-
inated, the following is shown:
Trial #1 6.90 13 .53
2 2.70 13 .21
3&4 5.88 19 .31
1.05

Average time of actual unnecessary delay per batch
equals 1.05/3 = .35 min.

Since the average time per batch is 3.00 minutes, the un-
necessary delay proves to be .35/3.35 x 100 - 10.5%

This percentage should be as small as possible as it is waste
time. This cannot be out out entirely, but a comparison of
this percentage with some other study, making due allowances
for difference in conditions, will indicate the relative
efficienty of the organization. This organization on this
job can be considered good, as a good effort was put forth,
the layout was good, and other conditions as noted before.

Other items of interest to the contractor and time study
man can be found from these figures. The contractor will no
doubt be more interested in the number of batches which he has
put out in a certain elapsed time, regardless of divisions for
study purposes. This information is given here. The sum of
all the total times a 42.50 plus 40.18 plus 45.22 plus 8.31
plus 19.50 a 155.70 minutes, elapsed time during the studies.
The number of batches was 47. Therefore the average time per
batch was 3.32 minutes, and each batch constituted approximately
16 cubic feet of dry mix.

Another thing interesting to the contractor in the inter-
ests of better prOportioning of men is the percent of delay
due to the lateness of sand or of gravel. Therefore the delays
due to these causes can be separated. The sum of the delays
due to lateness of gravel in all the trials is 8.45 minutes.)
The delay due to lateness of the sand is 3.09 minutes. In
percent of the total due to these causes, the gravel was 73%
of the time behind. Whether another man should be put on to
out down this time is problematical. A little harder work
on the part of the gravel workers would often have cut this
delay down, and another man would probably have added dis-
preportionately to the cost, since the concrete was coming

then about as fast as those placing it could handle it.

.... —. ..-- ...—.

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IV

SOME DETAILS OF CONSTRUCTION

The cofferdam construction was of the usual type of
bracing (walers and struts) for the pouring of the footing.
The counterforted wall extended higher than the piling, and
since the state would not allow the struts to be boxed
through the wall while it was being poured, another method
had to be chosen to reinforce the cofferdam walls. Therefore'
the method to be described was used. (See drawing A)

After the footing was poured, the change of bracing was
begun. The scheme was to carry the pressure of the coffer-
dam by upright posts amounting to vertical beams supported
laterally by short braces on either side of the poured foun-
dation and at the upper end a timber between the two Opposite
posts high enough to clear the height of wall to be poured.
These vertical posts then carry the pressure through the
walers which give the posts two comparatively concentrated
loads. Since the greatest pressure comes on the lower set of
walers, extreme care must be taken to see that a good full
bearing is had by the walers on the post. To obtain this,
the vertical posts are set in at a small angle leaning in from
the tOp, and held in place by a piece of 2 x 4 between oppo-
site posts. The piece of 12 x 12 timber was then cut to the
proper length to be placed between the footing and the lower
end of the post. Then the heavy cross timber between Opposite
posts was forced into place with blows of a sledge hammer.
This timber forced the vertical posts against the walers and

assured a good bearing on the lower set.

Thaw/y}: 170k: /'/7 J‘fieeffq

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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The corners and ends of the cofferdam were secured by

"a" (in drawing B), and separated by a

two vertical posts
short block B about 2 feet long in order to leave the original
strut (shown in dotted lines) in until the new bracing was
erected. These were braced at their lower end in a manner
similar to the other vertical posts, but differently at the
upper ends. One strut was left in near the end of the coffer-
dam, as it was not interfering with the wall construction.
The two verticals were braced by short timbers to this strut,
and the strut held in turn by a %" steel cable pulled tight
by a turn-buckle. The manner of placing the cable is shown
in the drawing. In addition, these center timbers were
braced for any possible sidewise motion by means of two lat-
eral timbers placed at an angle and set against the sheet
piling as shown.

Another detail of interest is in the anchoring of the
vertical posts on one side of the cofferdam. On this side
due to a change in design, there was no room to place the
posts down between the walls of the cofferdam and the footing,
and someother system of supporting the lower end had to be
devised. It was done by the use of angles and bolts as
shown in drawing C. The vertical posts were set down on top
of the footing as shown. Then two angles about two feet long
were attached to the back side of the timber by 2 bolts which
carried through to a face plate on the front side of the timber.
The angles extended beyond the timber about a foot and had their
hearing on the footing. All dimensions for the angles and
bolts are shown on the drawing.

The_working trestle for carrying the 32 ton crane and its

loads is also of interest. It consisted of a series of 4

pile bents spaced 15 feet apart with sway bracing and a 12 x
12 cap. The stringers were 12 x 12 and 10 x 12 timbers with

a 12" I-beam under each tread. It requires only two sets of
these heavy stringers, as they can be moved ahead as necessary.
Of course lighter stringers and floor boards are used to

form a runway for concrete and other materials. Longitudinal
sway bracing was used on every fourth bay only, the trestle
being held together by this bracing and two of the 12 x 12
stringers bolted to the cap for every bay. This is an item of
importance as trestles are often built with lengthwise bracing
in every bay, which is costly and unnecessary.

All forms used for concrete were built in sections so as
to be re-used later on in other parts of the work. Universal
form clamps with %" bars were used to tie the forms together.
The wall was 18" thick, and the number of clamps necessary
was figured on a pouring rate of about 4 feet per hour. While
the pressure is greatest at the bottom of the wall and is in-
creased by the impact of the concrete falling 15 feet, the
number of clamps to be used per square foot can be less than
the number called for by considering the full height of the
wall because the concrete acquires an initial set long before

the whole height is poured, thereby taking the strain off of
the forms.

In tying reinforcing steel, it is necessary to hold it in
place while doing so. An experienced hand can easily hold it
in place and tie it at the same time, but on this job this was

not the case, as only one man had ever done this work before.

Verf/ca/ - P047
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So a simple method was used for holding the horizontal steel
in its proper position against the vertical steel while being
tied. Pieces of 2 x 4 were marked off with the proper spacing
of the steel, and spikes driven at these markings. The 2 x 4'3
were then placed vertically at intervals along the line of
steel, and each bar laid across the respective spikes which
held it accurately until tied.

On this job, during the excavation a large sandboil started
in the middle of the night. This boil was a stream of water
evidently coming through a gravel seam just under the lower
edge of the sheeting, while the top of the sheeting was still
six or seven feet above the water level. The pumps couldn't
keep up with the stream of water, and the sides of the dam
were apt to give way due to the loss of bearing around this
seam, so the cofferdam was allowed to fill up, the piling was
driven several more feet along that side, and the hole plugged
with sandbags. This adequately cared for the emergency, and
no further trouble was encountered.

The last iém of general interest to be inserted is that
a gas operated crane should never by used for this type Of
work, or any other industrial work. It lacks the smoothness
of Operation of steam, depending as it does upon the brake
for control of the load, while steam would give power control
of the load. Smoothness and ease and accuracy of control are
essential, since it would be highly dangerous to knock any
strut out of a cofferdam, or to lose control of any heavy

Object with men below.

 

 

 

 

<§r04§n02

 

 

 

d

01
‘4

I.

V

CONCLUSION

The author has attempted to branch into a new field for
the time study man. This thesis makes no attempt to inquire
into rate-setting which is the chief value of industrial
time studies. Rather it shows the actual time values of as
many construction operations as time permitted, and only of
those which were apt to be repeated again in approximately
the same manner. The detailed setting forth of each operation
has been given partly for use in the time study and partly
as a construction methods study. Every effort has been made
to give the best averages - those which come closest to the
actual facts, and to give explanations and suggestions con-
cerning the use of the studies.

The close observation necessary to take these times
force upon the observer an excellent opportunity to see details
and to study methods which otherwise might be missed. The
greatest value therefore lies in the experience gained by the
observer, concerning how much work men can do and the methods
of doing it.

It is sincerely hoped that someone will take Up this
idea and carry it on by further investigation in the construc-
tion field, or comparison of these results to results on a
similar job. It is felt that a series of theses such as

this one will prove of real value both in time comparisons

and job methods.

Git-'51 .Y.,

 

31293 01.748 4688