| Steel structure has been widely used in architectural design due to its light weight,high strength and good ductility.The Northridge earthquake in the United States in 1994 and the Kobe earthquake in Japan in 1995 fully showed that the steel structure connections designed by the traditional theory had serious brittle fracture and the mechanical behavior of connections in steel structure were sufficient to affect the seismic performance of the overall structure.Therefore,the concept of steel structure design extends from single bearing capacity to ductility consideration.Under the seismic design principle of ensuring "strong column and weak beam,strong connection and weak member ",the new ductile beam-column connections of steel structure can not only move the plastic hinge away from beam end under earthquake action,but also enhance the plasticity of beam-column connections,thus greatly reducing the possibility of brittle fracture of the weld.The double-ribbed reinforced beam-column connection in steel frames is one of the new ductile connections.In this paper,the hysteretic behavior and fracture performance of the double-ribbed reinforced connections made of Q345B steel are studied.The specific research contents and results are as follows:(1)Material performance test and weld parameter test:Through the monotonic tensile test of the Q345B plate used in the main connection and the joint plate welded by E5015 electrode,the main material performance parameters of the two materials were obtained.The tension-compression cycle test was carried out on the welded joint plate,the damage model curve were calculated according to the hysteresis curve and compared with the test value.It is finally concluded that the energy damage model can better simulate the damage degradation process of this weld.(2)Quasi-static test and finite element analysis of traditional beam-column connection(NBN)and double-ribbed reinforced beam-column connection(RRN):two types of connections were loaded by low-cycle reciprocating load,and the failure mode,hysteresis curve.skeleton curve,bearing capacity,energy consumption and damage degradation were analysed.The results show that the plastic hinge of RRN is farther away from it in NBN by about 120mm,the ultimate bearing capacity is increased by 20.56%,the ductility is increased by 36.70%,the maximum plastic rotation angle is more than 0.03rad and the maximum total rotation angle is more than 0.05rad,the equivalent viscous damping coefficient is higher than 18.97%,which shows better hysteretic capacity.The damage degradation process of the connections can be simulated better by using energy damage model combine with power function,and the damage degradation of the RRN is slower.Considering material nonlinearity,geometric nonlinearity and boundry nonlinearity,three-dimensional finite element analysis models with the same conditions as test were established by ABAQUS,the material parameters obtained by the material test are substituted for calculation.The analysis results are consistent with the experimental conclusions and the model is effective(4)Optimization of rib parameters based on fracture performance:15 finite element analysis models with different geometric parameters of ribs were established.The length a,width b and thickness ts of the ribbed plates were optimized from the stress triaxiality,equivalent plastic strain index,cracking index and crack development law.The results show that the length and thicknes of rib plate have great influence on the fracture and crack development,the width of rib plate has substantially no effect.Through comparative analysis,the optimal value of geometric parameters of rib plate is obtained:a=0.7hb,b=0.5a,ts=1.5tf(where hb is the height of beam and ts is the thickness of beam flange). |
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