Question of tension softening versus tension stiffening in plain and reinforced concrete

Stress transfer from concrete into steel is one of the fundamental mechanisms behind the significant ductility of reinforced concrete. Considering the low value of cracking strain of plain concrete, it is the stress transfer that takes place during debonding when the steel strain approaches the yield limit at a level which is an order of magnitude larger than the cracking limit of concrete. This technical note examines the difference of "tension softening" of plain concrete versus "tension stiffening" of reinforced concrete which describes the stress transfer mechanism from concrete into the embedded reinforcing bars. Using three-dimensional finite-element simulations the fracture energy arguments of Mode I versus Mode II are reexamined when the axial response behavior of plain concrete in tension softening is compared with that of reinforced concrete exhibiting tension stiffening in long and short tension members.