Integrated Buildings & Structures

Hi!
 I am working on this project in a seismic zone and was wondering if it is required by the code to check crack widths in concrete under the seismic load combinations following LRFD. I am following ACI 224 code for crack check.

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Rocio Rodriguez P.E., M.ASCE
Structural Engineer
Orlando FL
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I would say for extreme event limit state such as seismic events, the structure as a whole and its components need to be checked to resist collapse due to extreme events.  Crack widths need to be investigated at  service limit states.


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Gergis William Ph.D., P.E., F.ASCE
AECOM
Morgantown WV
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Dear Mr. Rodriguez,
I believe checking crack width would be part of Serviceability Limit State (stress limitation, aesthetics, drainage, deflection, creep, vibrations, reinforcement corrosion, watertightness) using load factors of 1.0 unless you are conducting a special limit state analsyis. The reinforcement tensile stress limitation rules at SLS in ACI 318 (e.g limiting f_s to 2/3 of f_y) along with minimum reinforcement ratio and maximum reinforcement spacing rules are intended to limit crack widths without having to calculate them directly. 

See ASCE 7-10 Commentary Appendix C - Serviceability Considerations for load combinations (mostly for static loads) used to check SLS. Load combinations may include wind to check drift but I can't think of a situation where they would include seismic loads (maybe for critical tank structures??).

Hope this is helpful :)

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Robert Yates P.E., M.ASCE
Senior Civil Engineer
ROY Structural and Materials Engineering
Roseville, CA
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