Study And Numerical Analysis On The Tri-axial Behavior Of Cracked Reinforced Concrete Elements

In the past few decades,the mechanical properties of two-dimensional reinforced concrete elements and the design of two-dimensional structures have been extensively studied.However,in many complex engineering structures,such as nuclear power plant shielded buildings,concrete offshore structures,high-rise structures,etc.,many are subject to triaxial loads.The design of these structures and components requires a theory of the three-dimensional element’s mechanical properties and the three-dimensional constitutive relationship of the reinforced concrete elements.In this dissertation,two common reinforced concrete composite structures,reinforced concrete and steel-plate-steel concrete are taken as examples.Based on the existing two-dimensional reinforced concrete element disturbed stress field theory(DSFM),the theoretical model of two-dimensional steel-plate-steel concrete element is obtained by analogy.The element crack force transmission mechanism extends the twodimensional element theory to the three-dimensional reinforced concrete element and the three-dimensional steel-plate-steel concrete element.This dissertation deduces the material constitutive relationship.Based on the classical elastoplastic theory,the nonlinear uniform strength criterion of concrete materials in the literature is used as the yield function,and the plastic shear strain is used as the hardening parameter in the loading process.The three-dimensional incremental constitutive relationship of concrete materials is derived in tensor form.Based on the Prandtl-Reuss model,the perrfect elastoplastic incremental constitutive relation of steel plate after yielding is derived,and the explicit solution under plane stress state is given.The reinforced steel adopts a uniaxial perrfect elastoplastic constitutive relation.Based on the existing DSFM theory of reinforced concrete two-dimensional element,the DSFM theoretical model for the two-dimensional element of steel plate concrete is established from two aspects of balance relationship and deformation coordination.An appropriate iterative solution full-scale algorithm for reinforced concrete two-dimensional elements and an appropriate iterative solution incremental algorithm for two-dimensional elements of steel reinforced concrete are given.Based on the equilibrium relationship between the two-dimensional element and the mechanism of crack propagation,the mechanism of the transfer of triaxial stress at the crack of the steel-mixed element is studied.The equilibrium relationship of threedimensional reinforced concrete elements is analyzed from the two aspects of element average stress and local stress of crack,and the relationship between the main tensile stress of concrete,the shear stress of concrete crack surface and the stress increment of crack at the crack is established.Based on 2D DSFM theory model,the deformation coordination relationship of the element is analyzed from the two dimensions of discrete strain caused by continuous strain of concrete and slip of concrete.An iterative solution incremental algorithm for reinforced concrete 3D element model is given by using the elastoplastic incremental constitutive model of the material.Since the elastoplastic incremental stiffness matrix of concrete is irreversible,this paper directly uses the flow rule to solve the plastic strain increment of concrete,and avoids the inverse of the elastoplastic incremental stiffness matrix of concrete in the calculation process.The theoretical model and solution algorithm for the three-dimensional element of the steel plate concrete are given in the same way.Using the given calculation model,the reinforced concrete two-dimensional force element and some three-dimensional force elements,as well as some steel plate concrete two-dimensional force elements are numerically simulated.The calculated results are in good agreement,which verifies the applicability of the theoretical model and the accuracy of the algorithm.