CEE 379 Problem Set 7 Autumn 2007
(Due Nov. 2nd, in class or 4:30 PM in 233 More)
Problem 1. Consider the same truss (shown in the figures below) that you considered in
Problem Set 4. For each member, the elastic modulus, E = 29,000 ksi. the cross-sectional
area, A = 8 in.2 and the yield stress is 50 ksi.
USING EXCEL, develop a spreadsheet to automatically complete this problem and the
next one. The equations should be dynamic, such that updating the member properties,
jont locations and applied forces should automatically lead to the updating of the end
displacements and member forces.
For each problem, submit the printout of a neat spreadsheet output, in which major results
are clearly identified.
a) Compute the element stiffness matrix, k, for each of the six truss members.
b) Express the equations of equilibrium at the free kinematic DOF in terms of the
applied external loads, the member properties and the displacements at the free kinematic
DOF. (i.e., Qk = K11Du)
c) For θ = 135 degrees, compute the unknown joint displacements, and sketch the
deflected structure.
d) For θ = 135 degrees, compute the element forces at the end of each truss member.
Then, show the member axial forces on a neat drawing of the structure.
e) Compute the axial stress in each member. (σ = P/A). Compare this value with
the yield stress? Which members have yielded, if any?
12 ft
15
ft
15
ft
15
ft
θ
P2=5
0k
1
4
2
3
5
6
2
1
4
3
6
5
8
7
DOF
θ
P1=20k
