| RC frame structures are widely used in our country.Because the strengthening effect of floor slabs on beams were not considered in the early specifications and the quality problems during construction,quite a few old frame structure systems are unreasonable,and plastic hinges are easily formed at the column ends,which cannot meet the seismic design ideas of "strong columns and weak beams".Therefore,more and more scholars are devoted to the strengthening of column in old frame structures,and the excellent mechanical properties of the new cementitious composite material(ECC,UHP-SHCC)provide new ideas for the strengthening of frame columns.Therefore,based on the finite element numerical simulation,this subject studies the seismic performance of the frame columns strengthened by new cementitious composite material,and the following work is carried out:(1)Conduct an in-depth discussion on the concrete damage plasticity model(CDP model)of concrete studied in ABAQUS,and select the ECC and UHP-SHCC constitutive models suitable for this study and the hysteretic constitutive model of steel bars to simulate the bond-slip effect between steel bars and concrete.The two groups of column strengthening experiments of Hu Hongbo and Li Xu were selected to verify the reliability of numerical simulation of enclosure strengthening and replacement strengthening respectively,and compare the hysteresis curves of the test and simulation.The analysis results show that the shapes of the hysteresis curves of the simulation and the test are in good agreement,and the average relative deviation of the yield displacement,peak load and displacement ductility coefficient is less than 10%.The tension damage cloud can better reflect the crack development and failure of the member.(2)Design the full-scale model of the column according to the corresponding specifications,formulate four strengthening measures for the two strengthening materials of ECC and UHP-SHCC under the two strengthening methods of enclosure strengthening and replacement strengthening,with the help of ABAQUS,pseudo static analysis of 20 frame column members are carried out to study various performance indicators of concrete frame columns before and after strengthening under different axial compression ratios(0.2,0.4,0.6,0.8),including hysteretic curves,skeleton curves,crack distribution,stiffness degradation,mechanical performance,ductility and energy dissipation capacity,compare the advantages and disadvantages and applicable scope of various strengthening measures.The analysis results show that the four kinds of strengthening measures can improve the seismic performance of column members,but the improvement of various mechanical performance indicators is different,and should be selected according to the actual situation.On the whole,the UHP-SHCC enclosure strengthening has the strongest seismic performance.(3)Select UHP-SHCC enclosure strengthening to strengthen the frame column section of the "strong beam and weak column" type frame structure,and formulate two strengthening measures for the bottom of each layer column and the bottom and top of each layer column.The time-history analysis of frame structure under EL-Centro seismic wave is carried out by ABAQUS,study various performance indicators before and after strengthening,including crack distribution,maximum floor displacement,the interlayer displacement angle and maximum base shear,to study the strengthening effect of different positions.The analysis results show that the two methods can reduce the floor displacement and the interlayer displacement angle,and the seismic effect of the two-way strengthening is higher than that of the lower strengthening. |
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