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

In the virtual work method for trusses, 'n' is the axial force in each member caused by a unit (virtual) load applied at the point and in the direction of the desired deflection.

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

δ = PL/AE = (80)(10×12)/[(4)(29,000)] = 9,600/116,000 = 0.00828 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

The direct stiffness method transforms each member's local stiffness matrix to global coordinates and adds contributions to the shared degrees of freedom in the global stiffness matrix.

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

Slender compression members in a truss buckle elastically per Euler's formula, where KL is the effective length and I is the moment of inertia about the weak axis.

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

In a statically determinate structure, thermal deformations can occur freely without inducing additional member forces.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Structural Analysis of Trusses 5