KennyG
Super Member
Tensile strength is the correct term, but for foundations, bending forces are the cause of the tensile loading. If you can imagine a beam that is being bent by a load, the top part of the beam is in compression because it has to shorten and the bottom part is in tension because it is lengthened.
The two general approaches we use for concrete is to reinforce it so the steel will take the tension (which works as long as the steel is oriented along the direction that is in tension) or making the concrete section so massive that the compressive strength will prevent it from deflecting (bending) enough to cause significant tension loads.
More sophisticated designs load the concrete in compression after it sets up so that during the initial deformation, it stays in compression and doesn't experience tension until it is past it's design load.
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