huangyhg

shear wall maximum rebar
the design example and commentary i am using to design a concrete masonry shear wall/pier states, "tension steel, "as", shall be placed at the ends of the wall such that "as" does not exceed 6% of the area of the masonry cell into which it is placed."
though this seems reasonable, i cannot find support of this in aci 530-99. what is the maximum allowable rebar in a cell for shear walls?
any comments?

maybe the example is referencing a different standard such as ubc 2107.2.2.1, "maximum reinforcement area in cells shall be 6 percent of the cell area..."
if 6% is the maximum reinforcement area in cells, does this apply also where splices occur, or are splices exempt from this limitation? why or why not?
thank you!
12 percent at splices
ibc 2000, section 2107.2.4 modifies aci 530 to say "the bar diameter shall not exceed one-eighth of the nominal wall thickness". this means a #9 bar for 8" cmu and #10 for 12" cmu. section 2107.2.5 states that "reinforcing bars larger than #9 in size shall be spliced using mechanical connectors". my experience has shown the actual construction of reinforced masonry walls is difficult and is not precise. keeping the cells clean enough to grout properly and ensuring proper clearances around even small bars is not easy, especially at splices. therefore we try to use maximum bar sizes of #7.
an excellent point by rrmiv, and i would take it even a step further and try not to do anything more than a 20m (#6) bar, and reinforce more cells if possible. our experience is identical to rrmiv, in practice the mason's often don't prescribe exactly to the standards of construction, and getting a fully grouted core can be a challange. another problem we occasionally come across is keeping the reinforcment continuous through floor levels. seems the mason's don't like having the bars protruding from the top of the walls or something...anyway, keep an eye out if this is something you will have to deal with.
dutchie

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