Civil Engineering PE Reinforced Concrete Design Questions and Answers

Question 1

According to ACI 318, what is the primary purpose of providing minimum flexural reinforcement (As,min) in a reinforced concrete beam?

Accepted Answer

To prevent a sudden, brittle failure immediately after the concrete cracks.

Answer

To increase the ultimate shear strength of the beam.

Answer

To provide support for the shear stirrups during concrete placement.

Answer

To control long-term deflections caused by concrete creep and shrinkage.

Question 2

A rectangular concrete beam has a width (bw) of 12 inches, an effective depth (d) of 20 inches, and is made with 4,000 psi concrete and Grade 60 reinforcement. At a critical section, the factored shear force (Vu) is 52 kips. The design shear strength provided by the concrete (φVc) is 30 kips. Using No. 3 vertical U-stirrups, what is the required spacing (s) to resist the factored shear?

Accepted Answer

9 in

Answer

12 in

Answer

6 in

Answer

15 in

Question 3

Which of the following modifications would result in the SHORTEST required development length for a No. 8 reinforcing bar in tension, assuming all other factors are held constant?

Accepted Answer

Using uncoated (black) steel instead of epoxy-coated steel.

Answer

Placing the bar as a 'top bar' with more than 12 inches of fresh concrete cast below it.

Answer

Using lightweight aggregate concrete instead of normal-weight concrete.

Answer

Decreasing the concrete compressive strength (f'c) from 5,000 psi to 3,000 psi.

Question 4

An engineer is checking the adequacy of a tied reinforced concrete column using its design interaction diagram. The column is subjected to a factored axial load (Pu) of 400 kips and a factored moment (Mu) of 200 kip-ft. The point representing (Mu, Pu) on the diagram plots inside the design strength curve (φMn, φPn). What does this indicate?

Accepted Answer

The column design is adequate to resist the applied loads.

Answer

The column design is inadequate and must be revised.

Answer

The column is over-reinforced and will fail in a brittle manner.

Answer

The column is controlled by tension, and the strength reduction factor (φ) must be 0.90.

Question 5

According to ACI 318, for a solid, non-prestressed one-way slab not supporting or attached to partitions liable to be damaged by large deflections, what is the minimum required thickness (h) for a simply supported span of length L, assuming normal weight concrete and Grade 60 reinforcement?

Accepted Answer

L/20

Answer

L/24

Answer

L/28

Answer

L/16

Question 6

Which of the following BEST describes the primary purpose of the strength reduction factor (φ) in the LRFD design of reinforced concrete members?

Accepted Answer

To account for potential under-strength members due to variations in material strengths, dimensions, and inaccuracies in design equations.

Answer

To account for uncertainties in the magnitude and distribution of applied loads.

Answer

To provide a factor of safety against brittle concrete crushing failure before ductile steel yielding.

Answer

To increase the design strength to match the expected actual strength of the member.