Is it necessary to do strength design for concrete footings assigned t

[Oversee]

Apart from the settlement and overturning requirements (12.13.3 and 12.13.4 of ASCE7-5) for footings as parts of structures assigned to seismic design category B, are their other requirements for concrete isolated or combined footings in terms of strength and detailing?

Thanks

 

[LowLax]

Check uplift, and design per ACI 318 for bending and shear strength.

 

[Oversee]

Thanks!

Uplift - yes, as a part of stability.

ACI 318 for bending and shear strength - do you mean use seismic load combo to size reinforcing bars? But in chapter 21 of ACI 318-08, only foundations of structures to SDC D, E or F are required to resist earthquake induced forces, see 21.12.1.1.

 

[Oversee]

12.1.5 Foundation design section of ASCE7-5 does say that “foundation shall be designed to resist the forces developed and accommodate the movements imparted to structure by the design ground motions”. Does this mean that flexural and shear rebars shall be sized to carry this seismic load apart from the overall stability requirements?

Thanks

 

[strucguy]

ACI-318 chapter 21 contains additional special provisions for design of structural elements when seismic design category is D or higher. You still need to comply with all other reqular provisions for strenth and serviceability no matter what the building's seismic category is. In short yes, you have to design your footing for flexure and shear, and provide rebar to carry the seismic load it is being subjected to using appropriate load combinations(LRFD or ASD). Hope this help.