Research On Dynamic Collapse Resistance Of Bolt-welded Beam-column Substructure In Steel Frame

Steel frame structure has been widely used in practical engineering by virtue of its superior mechanical properties and rapid on-site assembly.Due to impacts,explosions and other disasters,steel frame structures are seriously damaged and collapse progressively.The impact resistance evaluation and design of frame structures have attracted much attention from scholars and designers.When rea ching collapse limit state,the structural performance of steel frame is mainly determined by the material performance of steel components,and the local structural features of steel joints.Therefore,this paper takes the bolt-welded beam-column substructure in steel frame as the research object,and the dynamic impact mechanical behaviour of the factors affecting the performance of the joint,such as steel material types and high-strength bolts,shear connectors in composite beams,details of weld access hole,retrofitted methods and with or without concrete slab in the joints are studied,so as to analyze and evaluate the dynamic collapse resistance mechanism of such typed joints.The research work is summarized as follows:（1）Under different impact height and impact velocity(strain rate range is10¹s^-1～10²s^-1),the dynamic material properties of Q345 steel commonly used in engineering were tested considering the influence of thickness by using the drop hammer impact device.The failure mode,stress and strain time history curve and the law of stress-strain relationship curve of Q345 steel were studied and analyzed.Afterwards,the relationship between dynamic increase factor（DIF）and strain rate of Q345 steel was summarized.Furthermore,the fitted yield strength prediction formula was proposed,and the applicability of ultimate strength prediction formula was finally verified.（2）Dynamic tensile tests of high strength steel Q690 under different strain rates were carried out by a servo hydraulic high sp eed testing machine.The stress-strain curves with strain rates ranging from 0.00025 to 760s^-1 were obtained.The strain rate effect of Q690 and S690 steels was compared.Then,a constitutive model for predicting the relationship between the DIF and strain rate for the yield strength and ultimate tensile strength of Q690 steel was established.（3）Dynamic tensile and shear mechanical properties of high strength bolts commonly used in engineering were studied by the drop hammer impact device.Dynamic mechanical properties of high-strength bolts with strain rates ranging from10¹s^-1 to 10³s^-1 were investigated under different impact heights,i.e.,varying impact energy to obtain different impact velocities.The failure mode,dynamic time history curve,dynamic force-displacement relationship curve,and the law of the dynamic energy dissipation for high strength bolts are studied and analyzed,compared with the tensile and shear mechanics performance of high strength bolt under static loadings.Finally,the relationship between the DIF of bolt strength and strain rate is evaluated and inductively analyzed.The formulas for predicting the tensile and shear strength of bolts based on static formulas are proposed,which can be used to predict and check the final failure modes of bolted connections under dynamic loadings.（4）Based on the results of dynamic tests on shear connectors in composite beams,a prediction method for the bearing capacity of shear connectors under dynamic loadings considering the strain rate effect of stud and concrete is proposed.（5）Based on the theoretical and experimental research basis of the catenary effect of steel joints,the analysis method of steel joints under catenary action is presented.Through finite element analysis,the energy dissipation performance of the beam-column substructures with different weld access holes under static and impact loadings is evaluated.Based on the above research results,considering the influence of dynamic loadings,retrofitted methods and the composite effect of concrete slabs on the collapse resistance of the beam-column substructure,the parameter analysis is carried out,and the development of the catenary action of steel joints under impact loadings and the internal force mechanism of the composite joints are given in detail.