In building construction, the gradual subsiding of a structure as the soil beneath its foundation consolidates under loading. This may continue for several years after the structure's completion. Primary consolidation occurs as water is squeezed out from the voids within the soil mass. Secondary consolidation results from adjustments in the internal structure of the soil mass under a sustained load. Whenever the possibility of settlement exists, care must be taken to choose a structural system and foundation capable of adapting. Fixed-end beams present a problem as they are incapable of rotating under uneven settlement loads and bend in response to the stress; simply supported beams, the ends of which act as hinges, will rotate slightly and remain straight. Special columns with jacking devices may then be used to level the beams. Floating foundations and piles are often used to overcome the problems of building on yielding soils. See alsosoil mechanics.