Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
where j = 7, m = 11, and 2j – m – 3 = 0
15 members:
19 members:
8-9. Download the West Point Bridge Designer software from http://bridgecontest.usma.edu
and use it to design a truss.
No solution offered here. Please go to the web site for extensive documentation on how
to run this software.
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
Problems for Geotechnical Engineering
Refer to this table for Exercises 8.10 and 8.11.
Dry Weight Densities of Different Soils
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
)385(.4.62 VVF skeletonwB
24.0 V lbf
where V is the volume of the soil sample.
12. In arriving at Equation (8.12), we assumed that the water table was even with ground
level. Now assume the water table is located a distance, d, below ground level and
develop a new expression for effective stress valid for z ≥ d. (Hint: Follow a procedure
similar to the one used in Example 8.2b; that is, (1) draw the free-body diagram of the
soil section, this time including the weights of both the dry and saturated layers of soil,
(2) find Fn from summation of forces in the vertical direction, (3) substitute Fn into the
definition of pressure to get total stress, (4) redefine pore pressure to be pn = γw(z – d), (5)
subtract pore pressure from total stress to obtain effective stress in terms of γsat, γdry, γw, z
and d.
Need: An expression for effective stress
Know: The water table is located a distance d below ground level
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
)( dzd
LT
F
satdry
n
Define pore pressure to be:
pp = γw(z – d)
since the column of water is of height z-d. Finally, subtract pore pressure from
stress to define effective stress for this special case:
))((‘ dzd wsatdry
13. Referring to Example 8.2 in the section on geotechnical engineering, use Excel to plot
the depth, z, versus the effective stress for values of z ranging from 0.00 to 4.50 ft. Feel
free to use any results obtained in Example 8.2 to assist you with creating the graph.
Need: A plot of
‘
versus z for 0 < z < 4.50
Know: The results of Example 8.2
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
Divide the normal force by the area of the bottom face to calculate
Finally, subtract pore pressure from stress to determine effective stress:
2
Problems for Water Resources Engineering
15. A proposed reservoir has the geometry described by Figure 7.15 and Equation (7.13).
The local topography constrains the dimensions H, W, and L of this geometry to have the
relative proportions 1 to 5 to 20, respectively. Assuming the required capacity has been
estimated at 5.00 × 108 ft3, use Excel to plot the water level height versus the stored
volume for water level heights ranging from 0 to H.
Need: A plot of water level height, h, versus stored volume, V.
Know: Required capacity is 5.00 × 108 ft3; local topography has the
shape illustrated in Figure 7.15.
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
tffSV
i
i
out
i
instored
5
1
0)(
in which
i
out
i
in ff
is the net flow rate in during the ith hour; and
t
= 1.00
hr = 3600 s. Substituting known values now yields:
)3600)(583.832(.)3600)(541.810(.)3600)(553.734(.
)3600)(598.567(.)3600)(645.436(..90000
stored
V
or
.1652.90000
stored
V
91652 = 9170 ft3
17. Use sequent-peak analysis, with the cumulative storage versus the time graph
provided to estimate reservoir capacity.
Need: An estimate of reservoir capacity.
Know: Cumulative storage versus time
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
From which we can estimate required capacity as follows:
No
Peak
(×108 ft3)
Min
(×108 ft3)
P-M
(×108 ft3)
1
2.0
-3.6
5.6
2
5.0
-4.5
9.5
3
5.6
-2.2
7.8
)(max
1
3
ii
iMPC
= 9.5×108 ft3
18. The monthly inflow of water to a proposed reservoir site is listed in the following
table for a critical 3–year period associated with low rainfall. Average consumer demand
for water over the same 3–year period was estimated to be 2.86 × 107 ft3/month1. Based
on these data, determine
a, An estimate of yield in ft3/month.
b. An estimate for reservoir capacity in ft3.
c. The required dimensions of the reservoir if it has the geometry described by
Figure 8.15 and Equation (8.13), and H, W, and L have the relative proportions 1 to 4
to 40, respectively.
Yr 1
Inflow
(×107 ft3)
Yr 2
Inflow
(×107 ft3)
Yr 3
Inflow
(×107 ft3)
1.26
1.42
1.72
0.985
1.27
1.68
1.01
3.06
2.01
1.78
6.85
4.87
4.86
4.71
7.93
3.50
4.98
3.97
5.91
6.21
4.97
4.33
4.79
3.38
3.01
4.03
8.34
2.37
4.21
3.76
1.89
2.23
2.89
1.35
1.90
2.26
(a) Need: An estimate of yield
1 Note to Instructor: The average consumer demand for water should be 2.86×107 ft3/month, not 2.86x108
ft3/month as in the textbook.
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
Know: Monthly inflow data for a 3-yr period
month
month1
t
(b) Need: An estimate for reservoir capacity
Know: Monthly inflow data for a 3-yr period; average monthly consumer
demand is 2.86 × 107 ft3/month
Also shown in the graph are the sequent peaks and minima, from which
we can estimate capacity as follows:
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
No
Peak
(×108 ft3)
Min
(×108 ft3)
P-M
(×108 ft3)
1
0.00
-0.641
0.641
2
.0755
-0.510
0.586
3
1.09
0.611
0.479
4
2.33
2.27
0.06
)(max
1
4
ii
iMPC
= 0.641×108 ft3
(c) Need: Required dimensions of the reservoir
Know: Reservoir capacity is 0.641×108 ft3 (from part (b) above); H, W,
and L have the relative proportions 1 to 4.00 to 40.0, respectively.
Engineering Ethics Problems
8.19 In 1985 a judge found the structural engineers for the Hyatt Regency Hotel guilty
of gross negligence in the July 17, 1981 collapse of two suspended walkways in the hotel
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
lobby that killed 114 and injured 200 people. Many of those killed were dancing on the
32-ton walkways when an arrangement of rods and box beams suspending them from the
ceiling failed.
The judge found the project manager guilty of “a conscious indifference to his
professional duties as the Hyatt project engineer who was primarily responsible for the
preparation of design drawings and review of shop drawings for that project.” He also
concluded that the chief engineer’s failure to closely monitor the project manager’s work
betrayed “a conscious indifference to his professional duties as an engineer of record.”
Responsibility for the collapse, it was decided, lay in the engineering design for the
suspended walkways. Expert testimony claimed that even the original beam design fell
short of minimum safety standards. Substantially less safe, however, was the design that
actually was used.
Use the Engineering Ethics Matrix to analyze the ethical issues that occurred in this case.
In this case, the engineers involved had two options:
a) Approve the design
b) Reject the design
Options
Canons
a. Approve
b. Reject
Hold
paramount
the safety,
health and
welfare of
the public.
No
Yes
Perform
services
only in the
area of your
competence
Yes
Yes
Issue public
statements
only in an
objective
and truthful
manner
Maybe- not
clear if
public
statements
were made
Maybe not
clear if
public
statements
were made
Act for each
employer or
client as
No– as an
agent, you
are expected
No– as an
agent, you
are expected
Kosky, Balmer, Keat and Wise: Exploring Engineering, Fourth Edition
faithful
agents or
trustees
to alert
management
to potential
problems
to alert
management
to potential
problems
Avoid
deceptive
acts
Maybe-not
clear if
deception
was
involved
Maybe-not
clear if
deception
was involved
Conduct
themselves
honorably
…
No-showed
“conscious
indifference”
No-showed
“conscious
indifference”
Hold paramount the safety, health and welfare of the public. This is the controlling
phrase. So b) reject the design is the only ethical conclusion.
