| A lot of framed buildings in our country are facing the problem of loading deterioration and durability.Now that the existing framework structure has produced different degrees of corrosion,it is difficult to assess its durability,and the damage caused by the declining loading capacity of existing frame joints is likely to cause life-threatening and property losses.However,the analysis of the loading capacity and seismic performance of the joints in the existing frame is complex,so it is necessary to study the servicing time and seismic resistance of the concrete frame buildings.This paper mainly studies the shear capacity of joints in the existing frame,and provides analysis contents and research theories for the bearing capacity and durability of the existing frame building.The following work in this paper:1.In the case of corrosion,the degradation formula for concrete properties,the formula for declining mechanical properties of stressed tendons,the calculation model for the degradation of bond strength,and the calculation of relevant parameters are summarized.The bonding area is mainly divided into two parts:the bond slip area and the bond degeneration area,and it is simplified as a reasonable calculation formula for the bond strength considering the slip.2.Make two assumptions for the joints in the frame to make it an ideal model,and calculate the loading capacity according to the truss model and the tension and compression rod model.Finally,it compares with the existing experimental data loading capacity and selects the more compatible theoretical model and calculation theory.The trmss theory model can be used to calculate the bearing capacity of corroded joints.3.Use the finite element software to establish a digital experiment of 15 groups of monotonic loading with different axial compression ratios and corrosion rates.Under the different parameters of 5 kinds of corrosion degree and 3 kinds of axial pressure ratio,the stress and strain cloud diagram obtained by the finite element software was analyzed,and the law was studied and the law was found.In the case of non-corrosion or low corrosion rate,the bearing capacity of the joints is indistinguishable from that of the general joints.When the corrosion rate increases to about 6%,the bond strength at the tensile longitudinal rebar deteriorates remarkably,and the degradation degree is very fast.When the corrosion rate is not changed,the axial pressure ratio has little effect on the corrosion rate of 0 and 3%,but the joints with 6%corrosion rate has a great change in the axial compression ratio of 0.3 and 0.5,0.7.4.Select an engineering instance and take out an existing interior joint in the framework for performance analysis.Under the influence of corrosion and service time,five time spans are set:0,25,50,75,and 100 years.The ABAQUS simulation was performed on the joints in the existing frame in five cases,and the load displacement curves were plotted and analyzed by combining theoretical research and finite element analysis.Finally,it is concluded that the service time of the existing frame building is 50 years.Too long time is not good for the loading capacity and earthquake resistance of the building,and the service time should not exceed 75 years. |
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