167 CE Midterm #2
Fall 2000
Prof. C.W. Ibbs
Solution Manual
Question #1 [5 points apiece--10 points total]
The following questions pertain to the book From the Ground Up. Keep answers
concise and to the point.
(a) The book goes into great detail about problems with the building excavation.
Describe (briefly but in detail) the causes and ramifications of the problem.
The contractor was excavating the pit for the foundation too much too fast (in
other words, they were removing soil in windows that were too large,
causing the sides of the excavation to be unstable). The result of this was
that sidewalks and underground pipelines adjacent to the site began to
crack, and the lagging system used to stabilize the pit began to fail.
Additionally, the resulting rework and schedule delays meant that the
excavation costs would end up being more than $6 million (the bulk of the $6
million is due blowing the schedule, and thus missing out on potential rents).
(b) What kinds of insurance and/or bonding could an owner insist that a general
contractor have to ensure a problem similar to the one described above will
not threaten completion of a project?
The owner could require Performance Bonds and you could make an
argument for Builders Risk Insurance. (I gave Brian a lot of discretion for
the grading of this question.)
Question #2 [10 points]
How are responsibilities apportioned with a bill of quantities contract? Who is
affected if the quantities are overestimated? How and why?
In a Bill of Quantities (BOQ) contract, the owner is responsible for the quantities
and the contractor is responsible for unit prices. If the owner overestimated the
quantities, the contractor can be negatively affected because the contractor
calculates the unit price based on expected fixed costs plus direct (variable)
costs and profit. Therefore, the fixed costs are apportioned out over the
expected quantity. If this quantity is reduced, then more money per unit is taken
up with fixed costs, and there is less money left for direct costs and profit.
The only advantage for the contractor in having the quantities overestimated is
that there will probably be less time pressure to complete the project (there are
fewer units to install). The owner is affected by the overestimation in the sense
that he/she will not have to pay as much as originally anticipated. If the quantity
estimation is grossly wrong (15%) then the contract usually allows room for
renegotiating a new, fairer unit price.
Question #3 [10 points]
On the first day of a project, a crew can drive 100 piles with 40 person hours.
How long will it take that same crew to drive piles on the 5th day, assuming a
learning rate of 0.93?
n = 0.93
K = 40 hours/100 piles (first unit)
x = 5th unit
s = (log n)/(log 2) = (log 0.93)/(log 2) = -0.1047
yx = K(x)s y5 = 40(5)-0.1047
y5 = 33.8 hours (or 33:48) to drive 100 piles on the 5th day.
Question #4 [15 points]
A 500,000 square-foot building was built in Phoenix, Arizona in 1993 with a total
cost of construction of $12.5 million. A similar building is proposed for Las
Vegas, Nevada in 2000, though it will be 600,000 square-feet. Prepare a
preliminary cost estimate considering the following factors:
The cost capacity factor for this type of building is 0.75
Inflation has averaged 5% per year
The location indexes for AZ and NV are 0.91 and 0.85, respectively
FVArizona Plant 2000 = PVArizona Plant 1993(1 +i)n = $12.5 million(1.05)7 = $17.59 million
The Arizona plant built in 1993 is worth $17.59 million in year 2000 dollars (you
have to compare apples to apples).
Cnew = [Creference x Inew]/Ireference = [$17.59M x 0.85]/0.91 = $16.43M
Cost of a new (NV) facility of comparable is size $16.43 million. (Note: this
becomes your reference facility)
Cc = Creference x [Qnew/Qreference]x = $16.43M x [600,000/500,000]0.75 = $18.84M
The total preliminary cost of the Las Vegas, NV facility is $18.84 million
Question #5 [12 points]
You have the You have following data:
Cubic yards of
concrete
150
250
325
450
Time to pour (hours)
7
13
25
30
Using linear regression, determine approximately how long it will take to pour 400
and 500 cubic yards of concrete.
y = bx + a equation for a line
xi-xavg
yi-yavg
(xi-xavg)
2
(xi-xavg)(yi-yavg)
x
y
x
y
x
150
250
325
450
7
13
25
30
-143.75
-43.75
31.25
156.75
-11.75
-5.75
6.25
11.25
20664.1
1,914.1
976.6
24570.6
1689.1
251.6
195.3
1763.4
sum: 48125.4
3899.4
xavg = 293.75 yavg = 18.75
x y
2
(xi-xavg)(yi-yavg)
a = yavg-bxavg
b=
(xi-xavg)
3899.4
a = 18.75 - (0.081)(293.75)
b=
48125.4
a = -5.044
b = 0.081
y = 0.081x 5.044
For 400 cubic yards: t = [(0.081)(400)] 5.044 = 27.35 hours to pour
For 500 cubic yards: t = [(0.081)(500)] 5.044 = 35.46 hours to pour
(Note: this process produces approximate results)
Question #6 [25 points]
Compute the ES, EF, LS, LF, FF, and TF for the schedule below. Record your
answers in tabular format in your bluebook. Durations are listed after the activity
name (e.g. Activity A has a duration of 3, Activity B has a duration of 2, etc.).
B2
E 14
FF8
SS3
A3
F6
D 10
FS4
J6
SS4
G5
FF9
C8
I4
H4
Starting on Day 0:
Activity
A
B
C
D
E
F
G
H
I
J
ES
0
3
3
3
5
13
11
11
21
25
EF
3
5
11
13
19
19
16
15
25
31
LS
0
7
3
5
9
15
11
17
21
25
LF
3
9
11
15
23
21
16
21
25
31
TF
0
4
0
2
4
2
0
6
0
0
FF
0
0
0
0
4
2
0
6
0
0
Starting on Day 1:
Activity
A
B
C
D
E
F
G
H
I
J
ES
1
4
4
4
6
14
12
12
22
26
EF
4
6
12
14
20
20
17
16
26
32
LS
1
8
4
6
10
16
12
18
22
26
LF
4
10
12
16
24
22
17
22
26
32
TF
0
4
0
2
4
2
0
6
0
0
FF
0
0
0
0
4
2
0
6
0
0
Question #7 [18 points]
An activity on the critical path of a project was scheduled to be completed in 15
weeks with a budget of $50,000. During a performance review that took place 5
weeks after the activity was initiated, it was found that 40% of the work had
already been completed and the actual cost was $22,000. A second review was
performed 10 weeks after the project was initiated, and it was found that 60% of
the work had been completed and the actual cost was $45,000.
Total time = 15 weeks @ $50,000 = $3333.33/week
a) Calculate the earned value of the activity after 5 and 10 weeks.
Week 5:
Earned Value = BCWP
BCWP5 = ($50,000)(40%) = $20,000
BCWP10 = ($50,000)(60%) = $30,000
b) Calculate the cost and schedule indices after 5 and 10 weeks.
CI = BCWP/ACWP
SI = BCWP/BCWS
CI5 = $20,000/$22,000 = 0.91
SI5 = $20,000/[($3333.33)(5 weeks)] = 1.20
CI10 = $30,000/$45,000 = 0.66
SI10 = $30,000/[($3333.33)(10 weeks)] = 0.90
c) Calculate the cost and schedule variances after 5 and 10 weeks.
CV = BCWP ACWP
SV = BCWPBCWS
CV5 = $20,000 - $22,000 = -$2000
SV5 = $20,000 [($3333.33)(5 weeks)] = $3333.33
CV10 = $30,000 - $45,000 = -$15,000
SV10 = $30,000 [($3333.33)(10)] = -$3333.33
d) Discuss the progression of the project between weeks 5 and 10. Is the
progress getting better or worse? Why? Supplement your answer with
graphical representation.
SI
At week 5, the project is ahead
of schedule, but has overspent
the budget estimated for that
point in time.
2
Week 5
1
0
Week 10
0
Equations
y = a + bx
a = y bx
b=
( x i x )( y i y)
( x i x ) 2
yx = k(x)s
s=
log n
log 2
2
CI
At week 10, the project is behind
schedule and has overspent the
budget estimated for that point
in time.
So, the project went from bad to
worse, and is now in the worst
possible position: Over budget
and over schedule.