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Re: [Fwd: eccentric footings][Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: [Fwd: eccentric footings]
- From: Anand Nene <AnandNene(--nospam--at)aol.com>
- Date: Wed, 18 Mar 1998 11:49:45 EST
Yes, "calculated" bearing pressures on typical single story residential footings can be pretty high. The problem is more significant in older residential buildings where typical exterior footing is trapezoidal with 8" stem at the top 12" wide at base, 12" ~ 14" thick with top of footing at grade or marginally above grade. Exterior face is typically flush with outside face of stud wall. I have reviewed many older residential structures in the East Bay area. Many show signs of settlement and tilt causing cracks in the footing, exterior stucco but reaching a stable state. In most cases, you will find that the eccentricity is beyond the middle third and the pressures on exterior corner quite high. As Bruno Cote mentioned, the resultant does not necessarily have to be in middle third. However, in soft soils, you will experience settlement, tilt and resulting distress to the structure. The problem is less significant in conventional T footings. Note that the "calculated" pressures are very sensitive in small footings. A lot would depend on the assumptions, loads, soil conditions, slight differential in interior and exterior grade, etc. You could get radically different answers by small changes in your assumptions. I have repaired many old trapezoidal footings by reinforcing from outside or by adding small footings at about 4' to 6' o.c. below existing footing. If you have a footing on property line, be sure to tie the floor slab (if on non expansive soil) or provide grade beams at regular interval and designed to take the eccentricity. Anand Nene, S. E.
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