Study On Shear Resistance Properties Of Multi-leg Joints Of CFST Columnr-RC Beam In Reverse Excavation Subway Station

In the development process in recent years,with the acceleration of the urbanization process,the development of urban rail transit has been greatly promoted.Against this background,the Hohhot region also carried out corresponding work in the construction of urban rail transit,and began the construction of rail transit lines 1 and 2.In these two lines,the three stations of Xinhua Square,West Street and Zhongshan Road are constructed by the method of cover and excavation.When using the reverse construction method,the concrete-filled steel tube column and post-cast beam node cannot be completed synchronously.The shear resistance of the node at the connection is very important.When designing,the design of the beam and column node as a major difficulty requires specific research.In order to meet the requirements of nodes to withstand large shear forces,a new type of double-dark corbel and multi-corbel joints are designed.However,at present,the shear resistance,force transmission mechanism,failure mode and Problems such as seismic performance are unclear and need further study.To this end,this paper adopts the numerical simulation of indoor 1: 4 scale model test and other methods,and gives corresponding analysis on the shear resistance and seismic performance of this kind of node.In the course of research,the conclusions obtained are:(1)According to the experimental results,the shear force shared by the lower corbel in the double dark corbel is about 2.4 times that of the upper corbel,which is consistent with the numerical simulation results and verifies the reliability of the simulation.(2)The ultimate bearing capacity of the three-legged joint is 2300 KN,which is slightly larger than that of the double-dark corbel.It can be seen that the double-dark corbel plays a major role in the sharing of shear force,and the bright corbel plays a safety reserve role.(3)It can be seen from the analysis of the failure process of the nodes that they are concentrated at the lower edge of the beam,and the cracks at this position will gradually expand along the corbel,and then turn into through cracks.When this crack penetrates the main diagonal crack,shear failure will occur.(4)Increasing the reinforcement ratio,beam width,and concrete strength of the beam has little effect on the improvement of the shear bearing capacity of the joint,but it is not obvious.Increasing the height of the beam,increasing the thickness of the steel pipe,the number of rib plates,and the number of annular corbels The number can effectively improve the shear capacity of the node.(5)Under the repeated load,the failure characteristics of the two types of nodes are similar to the stress changes.The cracks first appeared at the junction of the ring beam and the reinforced ring,which can also show the characteristics of "strong columns,weak beams,and strong nodes".(6)Under load,the bearing capacity of node 5 and node 1 have a high similarity.At the same time,the fullness corresponding to the hysteresis loop is also relatively high,and the node stiffness and strength stability are improved.(7)The node ductility coefficient is above 2 and the damping coefficient is around 0.3,indicating that the node ductility and plastic deformation ability are good,and the energy dissipation ability is strong.