Research On The Effects Of Crack Resistance On The Seismic Capacity Of Prestressed Concrete Frame Structures

Prestressed concrete(PC)frame structure is one of the most important structural forms widely used in China.A consensus has been reached on the seismic property of PC flame structures after plenty of work by researchers at home and abroad.The existing specifications are more stringent on the crack control of PC frame structures and more based on the understanding of the ductility of the section of PC structures.A stringent prestressed degree index and mixed reinforcement index are given.What's more,fracture limit and the ductility of the PC frame requirements become a pair of contradictions,which makes the PC structures less economical and less advantageous to the popularization and application of PC structures,A systematic study on PC flame structure at component and structure level is conducted adopting the approaches consisting of theoretical analysis,experimental verification and numerical modeling.The main research contents,together with the conclusions,are as follows.Based on the latest consensus of concrete structure crack control at home and abroad,this paper is focused on improving the seismic capacity of PC frame structures,providing a reference for seismic codes related provisions revised.The main research contents,together with the conclusions,are as follows:(1)Based on a set of prestressed reinforced concrete beams of cyclic loading test,as described in the numerical simulation method of the prestressed concrete components,using OpenSees earthquake engineering simulation platform for the nonlinear finite element simulation of the specimens.Numerical simulation of the hysteresis curve of the specimens and the test results were compared,and the results show that the proposed model has better alignment,which can be used for elastic-plastic analysis of PC beams under cyclic loading.(2)In order to study the influence of the prestressing ratio and crack resistance on the seismic performance of PC beams,ten prestressed concrete beams with different prestressing ratio?crack control level and calculated crack width were established in OpenSees software based on fiber model,then static elasto-plastic analysis were proceeded on each PC beam.Based on the simulation results,damage and mechanical characteristics of the PC beams under low reversed cyclic loading are studied.Hysteretic hoops,skeleton curves,stiffness degradation and energy dissipating capacity are analyzed.Simulation results reveal that,as the prestressing ratio and crack resistance improved,component of the hysteresis curve to knead shrinkage effect is gradually apparent,stiffness shows small variation,displacement ductility ratio and energy dissipation of beams are gradually enhanced.Under the same level of crack control(third level),calculated crack width shows less effects on hysteresis curves,displacement ductility ratio,and energy dissipation,etc.(3)In order to study the influence of the prestressing ratio and crack resistance on the seismic performance of PC frame structure,twenty PC frame structures with different prestressing ratio and crack resistance were established in SAP2000 software.Through Pushover curve,interlayer displacement,plastic hinge distribution of the framework and overall ductility,initially discussed the influence of the prestressing ratio(0.70?0.75?0.80?0.85)and crack resistance(primary?secondary?third level)on the seismic performance of PC frame structures.Simulation results reveal that relaxing the requirements of the degree of prestress and the degree of crack resistance(0.2mm?0.25mm?0.3mm)could improve hinge mechanism,increase the structural ductility and enhance the structural seismic capacity,which is also economical and rational.Therefore,suggestion were given that relaxing the requirements of the degree of prestress and the degree of crack resistance when designing PC frame structures.Through strengthening the side columns and some selected interior columns for PCFS,it could not only achieve a rational mixed energy dissipation mechanism,but also prevent the lateral stiffness from decreasing excessively due to too many plastic hinges in the interior columns.