Other threads on this site have discussed modeling basement walls as pinned-pinned, pinned-fixed, or somewhere in between, as well as transfer of lateral earth pressures into diaphragms and abutting walls. My question is a bit more generic, and I'm interested in hearing how others approach this. Let's say there's a cast-in-place basement wall system with full unbalanced soil on one side. It's a walk-out basement (i.e., concrete walls wrap only part of the building footprint). The geometry of the system in plan has multiple jogs, angles and returns, such that there's obviously some inherent ability for the entire system to self-stabilize, without relying on diaphragms. In fact this would be a relevant condition during construction, if the walls are backfilled prior to the construction of the diaphragm. Designing the wall as a simple 1' long cantilevered retaining wall (not taking into account wall returns) would probably be overly conservative. Designing it as pinned-pinned is not realistic if there's no diaphragm and the contractor doesn't want to temporarily brace the top of the wall, or if the returning walls are minimal or widely spaced. If the wall returns are small or modest in comparison the overall geometry, it seems necessary to model the entire geometry within a generic FEM package, and to approximate the contribution of the returning walls, the partial fixity of the wall to the footing, the two-way spanning of the wall elements, etc. Is it reasonable to go to this level of effort on something like a house, or does it just not get done? One particular question is how people model the fixity of the base of the wall to the footing. Standalone retaining wall packages know how to do this for design of basic wall sections designed in isolation, but within a generic 3d FEM package, it seems like some fake (dummy) buttresses are needed to actually transfer the out-of-plane bending due to lateral earth pressures from the base of the wall to the footing.
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