Civil Engineering PE Structural Analysis of Trusses 2

Question 1

A Pratt truss has vertical members under compression and diagonal members under tension when subjected to gravity loads. Which statement correctly describes the force distribution in a Pratt truss?

Accepted Answer

Diagonals are in tension and verticals are in compression

Answer

In a Pratt truss under gravity loading, diagonal members carry tension forces while vertical members carry compression forces.

Question 2

Using the method of sections, a cut through a truss exposes three unknown member forces. To solve for all three unknowns, you need to apply which set of equilibrium equations?

Accepted Answer

ΣFx = 0, ΣFy = 0, and ΣM = 0 about a strategic point

Answer

Three equilibrium equations (ΣFx=0, ΣFy=0, ΣM=0) are needed to solve for three unknowns when using the method of sections.

Question 3

A truss panel point has two members meeting at 45° and 90° to the horizontal, with no external load applied. The member at 90° (vertical) carries zero force. What is the force in the 45° member?

Accepted Answer

Zero

Answer

By the zero-force member rule, if two members meet at an unloaded joint and one is collinear with no load, the other carries zero force as well.

Question 4

For a simply supported Pratt truss with span L and panel width d, how many panels does the truss have if the top chord members are all horizontal and there are 8 vertical members?

Accepted Answer

8

Answer

A Pratt truss with 8 vertical interior members has 8 panels, since each panel contains one vertical member.

Question 5

A K-truss has members arranged in a K-pattern. Compared to a Pratt truss of the same span and load, the K-truss is typically used to:

Accepted Answer

Reduce the unsupported length of compression chord members

Answer

The K-truss subdivides the panels so that vertical members have intermediate bracing points, reducing the effective buckling length of compression chords.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Structural Analysis of Trusses 2