When there is tension reinforcement(steel) embedded in concrete, does it not also undergo bearing stresses on account of the weight of the concrete and other forces which are acting above the steel? Does bearing stress have no impact on the yielding of the said reinforcement. Why is it that we only discuss bending stresses as a the only cause of yielding in steel and ignore the effects of bearing stresses?
By definition, bearing stress is the resulting stress between two rigid bodies in contact. It is relevant to concrete only because of its brittle nature, and prone to crack (weak in shear). On the other hand, reinforcing steel does not have such weakness, while it shares/feels the stress, the result rarely be meaningful and detrimental. So for all practical purpose, the bearing stress on reinforcing steel is simply ignored.
Not only there may be wight of the concrete above the bar, but there may also be other loads as well like floor machinery. (we always mind the punching shear though).
but all those loads will translate into tension by the bending of the beam under the moment. Except at supports where the beam can not bend, hence the sheer tie bars.
In columns on the other hand the column load works against the tension needed to counter the moment. that why the column design charts have additional moment capacity when the normal force increases, up to a certain point.