Research On The Influence Of The Degree Of Prestress To Re-centering Behavior Of Unbonded Partially Prestressed Concrete Columns

The maintainability of structure becomes the topic which urgently awaits to study immediately, because the earthquake which is one of the largest natural disasters on the Earth, brings to people of terrible loss and severe affliction. Residual deformation is a key indicator to assess whether a structure can be reused or restored after an earthquake. Studies are needed to effectively control the residual deformation of Reinforced Concrete (RC) structures after an earthquake and to buildup a self-centering RC structure. From existing earthquake experience, the residual deformation of RC structures mainly comes from their vertical load-carrying structural elements, which mean the RC columns. Hence, the study on the quantity and the control method of the residual deformation of RC columns is the foundation and the key to achieve a self-centering RC structure.During an earthquake, the RC columns are under complicated load conditions including axial force, bending moment and shear force. Current design codes and methods only specify the load and deformation capacity of RC columns, without the consideration of the residual deformation. Focused on this problem, with the general analysis of existing research results, The paper researches on the on the influence of the degree of prestress to re-centering behavior of unbonded partially prestressed concrete columns. The main works are as follows:(1) The low-cyclic reversed loading test was conduct on three unbonded partially prestressed concrete columns for researches on residual deformation, re-centering capacity, carrying capacity, ductility and seismic behavior so on.(2) Based on the way of fitting, the influence of the degree of prestress to re-centering behavior of unbonded partially prestressed concrete columns is analyzed under different limit displacement. The relationship of function between the coefficient of re-centering capacity and limit displacement and the degree of prestress is proposed, and good agreements of these equations are achieved. The evolution of model for the ability of replacement to be opposite in the displacement and the degree of prestress is obtained.(3) Based on the software of ANSYS, a 3-Dfiber model program is developed on the unbonded partially prestressed concrete columns. The numerical results by ANSYS are compared with the experimental results and a good agreement is achieved for precise hysteresis constitutive laws of concrete and steel reinforcement.(4) The basic conception of re-centering capacity of structure and component was presented , and the assessment index of ability to resumption corresponded to different force-deformation is expounded. The numerical relationship between various co- efficients of re-centering capacity is established. The foundation of the different coefficient of re-centering capacity is displacement coefficient of re-centering capacity, and the key for conversion is submitting curvature and the length of equivalent plastic hinge.