load combination and allowable stress increase for masonry wall

[tcaoz]

I am doing a masonry retaining wall design. cbc 2007 section 2107 says for allowable stress design shall use chapter 2 of aci-530 but delete section 2.1.2.1 (load combination) in ACI-530. I am wondering can I still increase allowable stress by one third per aci-530 section 2.1.2.3 for seismic load?

 

[bnickeson]

I don't have the CBC, but if it is anything like the IBC, it will not permit the 1/3 stress increase. Section 1605.3.1.1 in the IBC states that no increase in allowable stress is permitted except for the duration of load factor for wood design. I would assume the CBC is similar. Check the corresponding section in the CBC to be sure.

 

[StructuralEngGuy]

I also ran into this same issue recently while using the CBC. It has you delete the portion of the ACI code with load combinations in it, but does not tell you to delete the paragraph about stress increases for load combinations using wind or seismic. But in the end I decided to play it safe and not to use the increase since it's been removed from everything else.

 

[kslee1000]

When in doubt, apply the overstress allowrance only if the design is done by ASD (allowable stress design method), and its associate strength reduction factors.

 

[tcaoz]

bnickeson, ibc cbc probably the same thing. For that allowable stress increase, I think if you choose to use the alternative basic load combinations in 1605.3.2, you are permitted to do that.

 

[tcaoz]

StructuralEngGuy, this thing really makes me confuse. If I don't do the 1/3 increase, I ended up to use twice as much rebar as what needed by doing a strength design.

 

[tcaoz]

Thank you, kslee1000

 

[kslee1000]

"Thank you" note well accepted, but for what???
Wish you have found correct way out, good luck.