Study On The Mechanical Performance Of An Innovative Modular Steel Building Connection With Installed Bolts In The Columns

Modular buildings have the highest levels of precasting in the current building system,the key link of which is to install the prefabricated modules as a whole in the construction site,that is,to connect the modules with each other by modular connection.The research shows that the modular structure is often broken from the modular connection,which will determine the bearing capacity of the whole building.Besides,the greatest advantage and significance of modular architecture are rapid construction,and the structure of modular connection is the decisive factor of construction speed.Therefore,modular connection is the focus and difficulty of modular building.However,there are some defects in present modular connections,such as the difficulties of construction,the weakening of the bearing capacity of beams or columns,and damage to decorations.This paper presents an innovative modular connection with installed bolts in the columns(IBC connection),which can meet the requirements of modular architecture.Two symmetrical monotonous static loading tests were conducted to explore the flexural behavior of the innovative connection.Meanwhile,the moment–rotation relations,destruction process,ultimate bearing capacity,stiffness classification and internal stress distribution were analyzed.The results show that there are two failure modes: weld crack and inward deformation of beam.The weld quality between beams and columns is the key to guarantee the bearing capacity.The diagonal stiffeners play a key role in the force transfer.Increasing the size of the diagonal stiffeners can improve the stiffness and bearing capacity of the connection.Under the condition of good weld quality and reasonable diagonal stiffeners size,the failure of the joint is caused by the buckling of the beam at the connection between the diagonal stiffeners and the upper beam.The connection failures occurred on the beam or beam–column joints,while the connection between modules remained undamaged,which showed that the new connection has a good bearing capacity under the action of bending moment and pressure.Through a full-size column-column bending experiment to explore the new connection tensile and compressive properties,the results show that the new connection has good performance under pressure and have a certain performance under tensile performance.The mechanical properties under tension are closely related to weld strength and weld quality,therefore,construction with high tension at joints should improve weld quality and use high strength weld as much aspossible,and in necessity,the tensile strength of connection can be improved by increasing the number of end plates thus increasing the number of weld bars.Three kinds of test specimens were simulated by ABAQUS finite element software.The finite element results were compared with the test results,and the stress characteristics of the specimens were further analyzed.Then through the ABAQUS software,the mechanical properties of IBC connection under transverse force,tension and shear were investigated.The results show that the bolts are the component with the largest stress when the joint is under tension and shear,so the high-strength bolt should be selected for the tall building with the larger wind load when the joint is under tension and shear.Besides,the upper end plate should also be of sufficient thickness to bear the tensile force or shear force.The parameters were analyzed by finite element software,and the effects of the stiffness ratio of upper and lower beams,the size of the diagonal stiffeners,the thickness of the base plate,the axial force of the column,the preload force of the bolt,the length of the base plate and the steel material on the performance of the connection were investigated.The results show that the stiffness ratio of upper and lower beams has an obvious influence on the diagonal stiffeners and flexural capacity of connection.Increasing the stiffeners ratio of floor beam to ceiling beam will increase the stiffness and flexural capacity of connection,but increasing the beam size will increase the column load.The increase of the diagonal stiffeners' length can slightly increase the stiffness and flexural capacity of the joints,and cause the plastic hinge to move out.The changes of base plate thickness,column axial force and bolt preload have little influence on the overall stiffness and bending resistance of the connection,but the decrease of plate thickness,the increase of column axial force and the increase of bolt preload will lead to the increase of stress of base plate,column and bolt.The increase of the plate length has little effect on the joints,but when the length reaches the plastic hinge region,the plastic rotational stiffness can be increased.The increase of steel yield strength can significantly increase the flexural capacity of joints without changing the stiffness of connection.Based on the finite element and experimental analysis results,this paper gives some suggestions on the construction measures of IBC connection under static load.According to the European specification 3,the stiffness of the joints is classified.A simplified finite element model of IBC connection is presented,which can be used in structural system analysis.And the formula solution of the moment-rotation curve ofthe IBC connection is obtained,which provides reference for the practical engineering design.There are 133 figures,11 tables and 87 references in the thesis.