Rebar Quantity Question

[greenstang232]

There is a question in the 6 Minute Solutions for the Construction Module which asks to calculate the weight of rebar in a 100' long retaining wall.  A cross section sketch shows rebar sizes and shapes as well as the overall dimensions of the wall and footing.  No clear cover is given in the question or shown on the cross section.  

The 'correct' answer in the book does not account for clear cover when coming up with the length of the rebar, it just uses the overall dimensions of the wall to come up with the rebar lengths which would lead to zero clear cover at the bar ends.  Is this the correct way to approach problems on the test?  In real world situations I would account for the clear cover when determining the length of bars, so for this question I came up with nearly 200 lbs less of reinforcement required (which was between two of the multiple choice options). 

 

[Patrick1441 PE]

When in doubt, I'd assume 3" clear cover.  A 100 foot long retaining wall would have longitudinal rebar 99.5 ft in length.  I think I know the problem you're talking about, and when assuming 3" of cover I arrived at an answer of 6,879 pounds and went with answer B) 6,800 pounds as the "most nearly" correct answer.  

One thing to remember on problems like this that might trip you up: With transverse rebar, even with clear cover requirements, a 100 foot long wall with vertical rebar @ 12" O.C. would still have 100 bars because the first and last bars would be 6" away from the ends and wouldn't violate any clear cover requirements.