huangyhg

too much reinforcing in concrete wall?
i am working on a wwtp where the precaster would like to keep a wall thickness to 14". i can make this thickness work for the loads, however, the reinforcing is becoming quite heavy on the inside face mat. i would need to use #9 bar @ 4" o.c. although this still falls below the maximum steel ratio and the spcaing of the bars is wide enough to allow the largest aggregate to easily pass through i am having concerns about this configuration. what are your thoughts? is there a good reason that i should insist on going with a thicker wall?
thanks
as long as you meet the reinforcing requirements per aci 318, what's wrong? can you use a larger bar size?
before attending an aci seminar not too long ago i would not have thought much of it. during the seminar the speaker worked through a sample problem and the reinforcing came out to #8 bars @ 5" o.c. which he dismissed as unrealistic and went to a thicker wall. this stuck in my head because i could re
in my mind #9 @ 4 inches are too close. even if you meet the maximum reinforcing ratio in the old code of .75*rho balanced, you're probably not going to meet the strain restricted requirements of the aci 318-02. not to mention, there's not going to be very much clearance between wall bars, especially when you put in the steel in the other direction. we had a engineer in our office attend an aci seminar and they said that you should try not to exceed 1.75 percent.
how tall is your wall? what are the load conditions that require a 14" thick wall? are you resisting both gravity and wind/seismic loads? if you think about the wall being a simply supported beam 12" wide and 14" deep, would 3 #9 bottom bars be too close together? if you think of the wall as a 12" wide x 14" long column, would 3 #9 bars on one face be too much? perhaps that's oversimplified, but as long as you satisfy all of the reinforcing criteria of aci 318 for the design, which includes the strain criteria, the #9 at 4" o.c. should be ok.
the wall is 18' tall. the loading condition that is being designed for is soil pressure plus a large surcharge.
i might not be as concerned about the #9 @ 4" in the wall as i would be in making sure the connection from the wall to the foundation is healthy enough to take what sounds like a very large moment. i mean, the #9 @ 4" sounds excessive, but if it works, it works. can you increase concrete strength to get a little larger spacing?
although aci 350 does not appear to have a wall deflection criteria, i would suggest that you calculate and be comfortable with your wall deflections. pca publication "rectangular concrete tanks" has wall deflection coefficients.
they will have a lot of difficulty not getting voids - especially if the wall is tall.
#11@6" may be better for setting concrete - if it works numberwise.
just re

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