Civil Engineering PE Structural Analysis of Trusses 5

Question 1

When using virtual work to find the deflection of a truss joint, the virtual work equation is δ = Σ(nNL/AE). In this equation, 'n' represents:

Accepted Answer

Member forces due to a unit virtual load applied at the joint of interest

Answer

Member forces due to the actual applied loads

Answer

Cross-sectional area of each member

Answer

Member length divided by elastic modulus

Question 2

A truss member with cross-sectional area A = 4 in², length L = 10 ft, E = 29,000 ksi, and axial force P = 80 kips has an axial deformation of:

Accepted Answer

0.00828 in

Answer

0.0828 in

Answer

0.828 in

Answer

8.28 in

Question 3

In the stiffness (direct stiffness) method for truss analysis, the global stiffness matrix is assembled by:

Accepted Answer

Superimposing member stiffness matrices transformed to global coordinates at shared DOFs

Answer

Inverting the flexibility matrix directly

Answer

Applying moment distribution to each panel

Answer

Solving the force polygon at every joint iteratively

Question 4

A pin-jointed truss member is slender and subjected to axial compression. The critical buckling load is governed by:

Accepted Answer

Euler's formula: Pcr = π²EI/(KL)²

Answer

The plastic moment capacity: Mp = FyZ

Answer

Shear flow: q = VQ/I

Answer

Torsional warping constant: Cw

Question 5

A truss experiences differential thermal expansion where the top chord heats up more than the bottom chord. In a statically determinate truss, the effect on member forces is:

Accepted Answer

No change in member forces; the truss deforms freely without inducing forces

Answer

Compression in all members due to thermal expansion

Answer

Tension in the top chord and compression in the bottom chord

Answer

Indeterminate without knowing the temperature gradient

Question 6

An influence line for the reaction at the left support of a simply supported truss spans 60 ft with panels at 10 ft each. The influence line ordinate at a point 20 ft from the left support is:

Accepted Answer

0.667

Answer

0.333

Answer

1.000

Answer

0.500

Question 7

A truss is analyzed using the flexibility method. The compatibility equation used for a single degree of indeterminacy is:

Accepted Answer

δ₁₀ + δ₁₁·X₁ = 0

Answer

K·u = F

Answer

ΣFy = 0 with unknown redundant

Answer

δ = PL/AE for each member