Residual Capacity of HSC Thermally Damaged Deep Beams

Abstract

High-strength concretes containing siliceous aggregates are very sensitive to high temperatures, as shown by the marked decrease of their mechanical properties both at high temperatures and after cooling down to room temperature (residual properties). However, because of the greater nonlinearity of concrete due to thermal damage, the structural behavior is generally less affected by high temperatures than the constitutive behavior, as is shown in this study on the residual behavior of three lightly reinforced and three unreinforced deep beams (f_c = 72 MPa). Four specimens were tested after a single thermal cycle (T = 250 or 400°C) and two specimens were tested in the virgin state (T = 20°C), in order (1) to measure the complete load-displacement response in three-point bending; (2) to study crack formation; and (3) to assess the roles of the various “complementary” shear resistant mechanisms. The results show that the ultimate capacity decreases markedly in the unreinforced specimens, but not as much as the tensile strength, and that the role of the complementary shear-resistant mechanisms increases in both reinforced and unreinforced beams, in spite of the worsening mechanical properties of concrete.