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Footing reinforcing requirements Question - ACI 318-77

Footing reinforcing requirements Question - ACI 318-77

Footing reinforcing requirements Question - ACI 318-77


I am looking at an existing building wanting to add a floor.  But it appears to me that there is not enough steel in the footings.  Basically, the building was designed to accomodate an additional floor.  I am even under the stated allowable additional column load.  But I decided to check things out anyway.  When I check the footings using ACI 318-99 and FBC2001 requirements, I find that I don't ahve enough flexural reinforcing in the footings for the DL + LL load case.  It looks like the original designer did not factor the loads when he checked the reinforcing.

The design was done to ACI 318-77 and and SBC 1982 ed.

Does anyone know if the loads needed to be factored back then for footing design?  I don't have these codes and have not been in this business for that long too remember myself.
If so, what were teh live/dead factors?

Also, was live load reduction allowed for footings back then?

Thanks much in advance.

RE: Footing reinforcing requirements Question - ACI 318-77

Live load reductions were certainly allowable for all structural elements. However,they would have been specified in the local Building Code, not in ACI-318. I believe the factored loads for ultimate strength were usually combined into a combined factor of 1.65 for footings, assuming they were not designed by the old elastic method.

RE: Footing reinforcing requirements Question - ACI 318-77

Section 9.2 of ACI 318-77 does have load factors of 1.4DL and 1.7LL. Earthquake and Wind Loads are also shown there.
It may be the original design was done using the Working Sress Method, in which case a completely different set of design values must of been used. Also live load reduction formulas may of been used per the local Building Codes not per ACI. Make sure you have the CORRECT Soil Bearing Pressure/Capacity. Good Luck.

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