Civil Engineering PE Structural Analysis of Trusses 4

Question 1

In the analysis of a space (3D) truss, the determinacy condition is m + r = 3j. A space truss has 30 members, 6 reactions, and 12 joints. The truss is:

Accepted Answer

Statically determinate

Answer

For a 3D truss: m + r = 30 + 6 = 36 = 3j = 3(12) = 36, confirming the truss is statically determinate.

Question 2

The influence line for the force in a diagonal tension member of a Pratt truss shows that the member carries tension when the live load is placed:

Accepted Answer

In the panel where the member is located and extending to one support

Answer

For a diagonal tension member in a Pratt truss, the critical live load position occupies the panel containing the member and extends to the nearest support.

Question 3

A composite truss has steel top and bottom chords with timber web members. Under gravity loading, which chord is in compression?

Accepted Answer

Top chord

Answer

Under gravity (downward) loading, the top chord of a simply supported truss acts as a compression element, analogous to the top fiber of a beam.

Question 4

For the Cremona (graphical) method of truss analysis, forces are found by:

Accepted Answer

Drawing a force polygon (Maxwell diagram) where member forces close the polygon at each joint

Answer

The Cremona/Maxwell diagram is a graphical force polygon technique where equilibrium at each joint is satisfied when the force polygon closes.

Question 5

A truss bridge deck girder delivers concentrated loads only at panel points. This is a critical requirement because:

Accepted Answer

Loads applied between joints would cause bending in chord members, violating the two-force member assumption

Answer

Classical truss analysis assumes members are two-force members (axial only); loading between joints introduces bending moments that the analysis ignores.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Structural Analysis of Trusses 4