Abstract:In order to study the mechanical properties under concrete biaxial force, the true triaxial machine was used to study the biaxial compression and biaxial tension and compressive test of ordinary concrete(OPC) and lightweight aggregate concrete(LWAC). The damage form and stress strain curve of concrete under different lateral stresses were obtained. The experimental results of LWAC were compared, and the influence of the main stress and the main tensile stress on the concrete under different lateral pressures and its failure mechanism was analyzed. The results show that the damage of OPC biaxial stress is mainly the damage of cement cementations layer, which is different from the damage of the shale ceramist aggregate of LWAC. Under the biaxial compressive condition, the main compressive stress of LWAC is affected by the lateral stress and the degree is lower than that of OPC. The degree of lateral stress reduction is slightly higher than that of LWAC. Finally, based on the Kupfers failure criterion, the biaxial compression pressure and biaxial tension and compressive failure criterion equation for OPC and LWAC under the fixed side loading is proposed.