huangyhg

minimum strip foundation sizes!!
hi guys,
i know this is pretty basic stuff but i wanted to confirm i was right! so here it is:
q1) what is the minimum width and depth as stated in bs 8004 required for a traditional strip foundation supporting a cavity wall of 300mm nominal width and a load per metre run of 55kn/m. the soil consists of made ground up to 1.4m with a dense gravel with some brown sand there after.
q2)what factors affect the depth of the formation level?

1. depends on the allowable soil bearing pressure, either by code or soils report. depends on whether one or two storu structure if residential. normally i use the widch of the block plus four inches to either side as a minimum width for construction.
2. as for the depth of burial, it depends on the frost depth, the presence or not of a basement, the required depth to design or needed bearing.
mike mccann
mmc engineering
the m inimum width is thickness of wall + 150 and minimum depth 150mm but these days strip ffoundation is not accepted and the minimum width is 450mm and 1m deep trenchfill.
the minimum depth below ground should be 400mm.
2' or 600mm wide (or 1'6" (450mm wide))
1' or 300mm deep (d of 8" or 200mm)
what part of the world and what conditions?
normally, the width of a strip footing is determined by the wall width and the footing thickness to avoid any real need for transverse reinforcement. obviously greater width may be required by code or the width necessary determined by the soil bearing conditions.
dick
i agree with mike and also would say that it depends on the general geometry of the wall that lead to considerable wind loads and seismic loads which in turn will have some effect on the embeddment of the wall to the ground.
tony
i think that the earlier post might be from the uk where, so they don't have to use formwork for the footings, and so, they make narrow strip foundations (see tomlinson's foundation design and construction, 6th edition, section 4.2. he does mention bs8103 (?) and use of 1 m deep in clays and 450mm elsewhere with some caveats. has more to do with speed and time than design.
kal:
your question leads me to believe you are practicing at an location ouside of the region that is under the cover of bs code. if this is the case, suggest to look for local practices rather than blindly assume bs code provisions are common everywhere around.
there is an allowable tolerance of 75mm each way for foundations, so the width has to allow for this. our standard practice for a cavity wall is usually 600mm.
making it as narrow as possible is false economy.
minimum depths are specified in the code, but it is dictated by:
required bearing strata
frost depth
shrink/swell of clays
nearby trees.

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