CSLB General Building (B)Site Work, Foundations and ConcreteHard
A contractor is installing a #4 rebar dowel (1/2-inch diameter) to connect a new concrete slab to an existing foundation wall, using the general rule of thumb development length of 40 times the bar diameter for uncoated bars in normal-weight concrete. What minimum embedment length should the dowel have into the existing concrete?
- A10 inches
- B30 inches
- C20 inches
- D40 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 20 inches
Using the rule-of-thumb development length of 40 times the bar diameter: 40 x 0.5 inch = 20 inches. This is the minimum embedment needed to develop the bar's full tensile capacity through bond with the surrounding concrete.
Why the other options are wrong
- A. 10 inches only represents 20x the bar diameter, which is insufficient.
- B. 30 inches overstates the required embedment for this bar size.
- D. 40 inches would be required only if the bar diameter were 1 inch.
Rebar Development (Embedment) Length
The minimum length a reinforcing bar must be embedded in concrete to develop its full design strength through bond, often estimated using a rule-of-thumb multiplier of bar diameter.
- Common rule of thumb: development length = 40 x bar diameter for uncoated bars
- Actual code-required length depends on concrete strength, bar coating, and spacing per ACI 318
- Insufficient embedment can cause bond failure and dowel pull-out
Memory trick: Forty times the diameter gets the bar fully anchored.