General Contractor Practice Exam

In a concrete wall, if you were to move the bottom bar up 2 inches, by what percentage would the strength of the wall be changed?

1. 10%

2. 15%

3. 20%

4. 25%

The correct answer is: 20%

Moving the bottom bar of a concrete wall up by 2 inches affects the wall's structural integrity and strength due to the critical role that rebar (reinforcing bar) plays in providing tensile strength to concrete. Concrete is strong in compression but weak in tension, which is why reinforcing bars are used. When the bottom bar is raised, it shifts the position of reinforcement, reducing the effective leverage of the rebar to resist tensile forces at critical stress points, especially near the base of the wall where bending moments typically concentrate. This alteration in the position of the rebar can lead to a significant decrease in the wall's overall strength because it may not be as effective in handling loads that typically produce tension. A 20% reduction in strength is a reasonable assessment based on structural engineering principles; this reflects the impact of rebar repositioning on the wall's performance under load. The strength reduction is influenced by how critical the positioning of reinforcement is for maintaining structural capacity, particularly in elements subject to bending. The calculated percentage reflects a general understanding of structural design in concrete applications.