| With the acceleration of urbanization process,the conflict between urban construction and land resources has become increasingly prominent.The method of adding light steel to the upper part of RC frame structure can effectively increase the use area of houses and alleviate a series of resource and environmental problems such as the loss of cultivated land.However,due to the sudden change of mass and stiffness between the upper and lower structures of the RC frame-mixed structure with adding light steels,it is easy to form the weak layer of the structure,and the joint nodes plays an important role in ensuring the overall cooperative work and seismic performance of the structure.In this paper,pseudo-static test and ABAQUS finite element analysis were used to study the transmission path,internal force distribution characteristics,energy dissipation capacity,failure mechanism and other seismic performance of exposed rigid joints which were widely used in RC frame light steel storey adding hybrid structure,and the corresponding design suggestions were put forward to provide certain theoretical basis and reference for the research of light steel storey adding joint.(1)Two 1:2 scale models of exposed rigid nodes with I-shaped and box-shaped upper steel columns were designed and tested under low cycle load reversals.The failure modes,hysteresis curves,skeleton curves,rotation of plastic hinge zone at beam end,stiffness,strength degradation and energy dissipation capacity of joints were compared and analyzed.The results showed that both specimens have shear failure at the root of concrete beams.For the node with box-shaped column,its hysteresis loop is more full and pinch phenomenon of hysteresis curve is less,its ability of delayed degradation of bearing capacity,strength and stiffness degradation,equivalent viscous damping coefficient and energy dissipation capacity are better than the node with I-shaped column.Keeping the lower structure unchanged,box shaped column for upper steel column is beneficial to improve the seismic performance of the node.(2)The nonlinear finite element simulation of the exposed rigid joints was carried out by ABAQUS.The internal force distribution characteristics,failure modes and force transmission mechanism of the joints were studied in depth,and compared with the experimental results.The correctness of the finite element model was verified by comparing with the test results.The results show that the failure characteristics of the joint simulated by finite element method were similar to those of the test.The steel column can effectively transfer the internal force to the lower concrete through the anchor bolt.The steel column was always in the elastic stage,and the stress of the anchor bolt reaches yield.The concrete beam mainly bears the joint action of bending moment and shear force.The longitudinal reinforcement of the beam at the intersection of the beam and the column first yields,and the concrete at the root of the beam produces shear cracks and continues to extend the plastic hinge was formed by the normal section failure,and the ultimate bearing capacity of the specimen was lost due to the plastic hinge failure of the beam.The error between the load value of the characteristic point of the bearing capacity and the degradation rate of the stiffness obtained by the finite element simulation was within a reasonable range,which was in good agreement with the test results,indicating the correctness of the model.(3)Studying on the influence of relevant parameters on the seismic performance of exposed rigid joints by changing the section shape of the upper steel column,the axial compression ratio,the diameter of the anchor bolt and the depth of the planting bar.The results show that:①Changing the section form of the upper steel column has a great influence on the stress of the upper steel column,and the hysteretic curve and the final degradation degree of the rigidity have not changed significantly.The double webs of box column and cross column selected for the upper steel column have good flexural and torsional rigidity and good out of plane stability,which can improve the bearing capacity and energy consumption capacity of the joint to a certain extent,and ensure the safety and stability of the structure.②With the increasing of axial compression ratio,the stress of steel column increases obviously,and the hysteretic curve does not change obviously.The proper increasing of axial compression ratio is conducive to increase the bearing capacity of the joint and slow down the rate of stiffness degradation.③The anchor bolts play the role of ensuring the connection of the upper and lower structures and transmitting the internal force.Changing the diameter of the anchor bolts and the depth of the planting bar have no obvious influence on the hysteresis curve,the bearing capacity and the stiffness degradation curve. |
