Civil Engineering PE Structural Analysis of Trusses Questions and Answers

Question 1

Which of the following is NOT a standard assumption made in the analysis of an ideal truss?

Accepted Answer

Members are connected by rigid, moment-resisting joints.

Answer

The fundamental assumption for an ideal truss is that members are connected by frictionless pins, which cannot resist moments. This simplifies the analysis by ensuring that members are only subjected to axial forces (tension or compression). Rigid, moment-resisting joints are characteristic of frame structures, not ideal trusses.

Question 2

For the truss shown, which member is a zero-force member? (Note: A is a pin support, E is a roller support). [Image of a standard Fink roof truss with a vertical load at joint B. Joints are labeled A-G from left to right, bottom to top. Bottom chord: A, F, G, E. Top Chord: A, B, C, D, E. Webbing: BF, BG, CG, CD, DG, DH. Load is at B. A is pin, E is roller.]

Accepted Answer

Member DH

Answer

A zero-force member can be identified by inspection using two primary rules. Rule 2 applies at joint H: If three members form a joint at which no external load is applied, and two of the members are collinear, then the third member (the non-collinear one) is a zero-force member. At joint H, members GH and HE are collinear, and no external load is applied. Therefore, member DH is a zero-force member.

Question 3

An engineer needs to determine the force in member CD of the Pratt truss shown below. The truss is subjected to several vertical loads on its top chord. Which analysis method is generally the most direct and efficient for finding the force in only member CD? [Image of a multi-panel Pratt truss with vertical loads on the top chord.]

Accepted Answer

Method of Sections

Answer

The Method of Sections is the most efficient technique when the forces in only a few specific members, particularly those near the center of a large truss, are required. By making a vertical cut through members CD, CJ, and IJ, the engineer can treat the left or right portion as a rigid body and use the equations of equilibrium (specifically, summing moments about joint J) to solve directly for the force in member CD without analyzing every joint.

Question 4

A planar truss is composed of 13 members (m) and is supported by a pin at one end and a roller at the other. The truss has 8 joints (j). Based on the relationship m + r = 2j, how would this truss be classified?

Accepted Answer

Statically determinate and stable

Answer

The formula for the static determinacy of a planar truss is m + r = 2j, where m is the number of members, r is the number of reaction forces, and j is the number of joints. In this case, m = 13. A pin support provides 2 reactions, and a roller provides 1 reaction, so r = 3. The number of joints is j = 8. Plugging these values into the formula: 13 + 3 = 16. For the other side of the equation: 2 * 8 = 16. Since 16 = 16 (or m + r = 2j), the truss is statically determinate and stable, assuming it is properly arranged.

Question 5

In the Warren truss shown, a single vertical downward load is applied at joint G. Which of the following statements is most likely true regarding the forces in the top and bottom chord members?

Accepted Answer

Top chord members (BC, CD) are in compression; bottom chord members (FG, GH) are in tension.

Answer

For a simply supported truss subjected to downward vertical loads, the overall behavior mimics that of a simple beam. The top of the 'beam' (the top chord) experiences compression, while the bottom of the 'beam' (the bottom chord) experiences tension. Therefore, the top chord members will be in compression, and the bottom chord members will be in tension to resist the bending effect of the load.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Structural Analysis of Trusses Questions and Answers