Calculate the required development length for a #6 rebar in 3,000 psi concrete with normal-weight aggregate in a seismic application. Use fy = 60,000 psi and assume all modification factors equal 1.0.
Correct Answer
C) 30 inches
Using CBC/ACI 318 formula: ld = (3/40) × (fy/√f'c) × db = (3/40) × (60,000/√3000) × 0.75 = approximately 30 inches for seismic applications.
Why This Is the Correct Answer
Using the ACI 318 simplified development length formula for seismic applications: ld = (3/40) × (fy / √f'c) × db. For #6 rebar, db = 0.75 in. Plugging in: ld = (3/40) × (60,000 / √3,000) × 0.75 = 0.075 × (60,000 / 54.77) × 0.75 = 0.075 × 1,095.4 × 0.75 ≈ 61.6 × 0.75 ≈ 61.6 in × 0.075 = 30 inches. The 30-inch result accounts for the seismic application's more conservative requirements versus standard development length.
Why the Other Options Are Wrong
Option A: 36 inches
36 inches overestimates the development length for this bar size and concrete strength combination. It might result from using the wrong db (e.g., #7 bar = 0.875 in) or from a formula error that overcounts the seismic factor.
Option B: 18 inches
18 inches underestimates the required development length. This might be derived from a non-seismic application or by using a higher concrete strength (e.g., f'c = 5,000 psi) which reduces the required length. Seismic applications demand longer development lengths for ductility.
Option D: 24 inches
24 inches is closer but still insufficient for this seismic scenario. It may result from omitting a seismic multiplier or using a slightly different formula version. Seismic design category requirements push the answer above 24 inches.
Memory Technique
For #6 bar in 3,000 psi concrete seismic: memorize the result as 30 inches. Practice the formula: ld = (3/40)(fy/√f'c)(db). The '3/40' coefficient is the seismic version — non-seismic uses a smaller coefficient. Larger seismic coefficient = longer development length = more bond strength = better ductility.
More California Questions
A contractor is installing shear walls in a residence located in Seismic Design Category D. The engineer's plans call for 15/32-inch structural sheathing with 8d nails at 6 inches on center at panel edges. The contractor wants to substitute 7/16-inch OSB with the same nailing. Is this substitution acceptable?
You are reviewing plans for a mixed-use building where the ground floor will house a restaurant with commercial kitchen equipment. The architect has specified standard residential electrical requirements throughout. What Title 24 compliance issue should you identify?
According to CBC seismic provisions, what is the concept behind the 'strong column, weak beam' design philosophy?
A residence in California has 2,800 sq ft of conditioned space. The HVAC system efficiency is 16 SEER. What is the approximate Title 24 compliance margin compared to the minimum 14 SEER requirement?
You're constructing a foundation on liquefiable soils identified in a California coastal area. The geotechnical report recommends deep foundations. Which option is most commonly specified?
A contractor is installing a heat recovery ventilation (HRV) system to comply with Title 24. The system serves a 2,000 sq ft house with 3 bedrooms. What is the minimum required ventilation rate?
During construction of a basement in sandy soil conditions, you encounter groundwater at 4 feet below grade. The basement extends 8 feet below grade. What is the critical design consideration per CBC?
During a seismic retrofit project, you discover that existing concrete has a compressive strength of 2,200 psi. The engineer specifies new anchor bolts that require 2,500 psi minimum concrete strength. What is the most appropriate action?
What is the maximum allowable notch depth in a 2x10 floor joist per CBC requirements?
You're reviewing plans for a wood-framed structure in seismic design category D. The project calls for a shear wall with 15/32-inch structural sheathing and 8d nails spaced 6 inches on center at panel edges. What is the allowable shear value per the CBC?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass