Study On Mechanical Properties Of Stud Connectors Under Complex Loading Modes

Stud connector is widely used in bridge engineering for its convenient construction and reasonable stress.Most of the related researches focus on the mechanical properties of bolted joints under single load mode through model test or finite element analysis,while few researches focus on the mechanical properties of bolted joints under complex load mode.By combining model test,finite element analysis and theoretical analysis,in this thesis,the mechanical behavior of stud under the combined load of tension-shear composite and compression-shear is studied.The main research work is as follows:(1)Push-out test research on stud connector mechanical properties under complex loadThe mechanical properties of six groups of stud connectors under shear,pull-out,tensionshear composite and compression-shear composite loads were tested.Under the action of the structure and load parameters studied in this paperthe,it was found that failure mode of the specimens behaved as fractures at the root of the stud,and the axial tension of the stud reduced its shear bearing capacity and shear stiffness.The greater the tension,the more obvious the shear bearing capacity and shear stiffness decreased.The shear bearing capacity and shear stiffness of the stud increase under the pressure.Under the action of the same axial pressure,the greater the contact interface friction,the greater the shear bearing capacity and shear stiffness.The formulas for calculating shear stiffness under the combined action of tensionshear and compression-shear are put forward.(2)Mechanical behavor of stud connector under complex load modeThe nonlinear numerical simulation analyses of the mechanical behavior of bolted connections under shear,tension-shear composite and compression-shear composite loads were carried out.The results show that the main bearing section of the stud is near its root,and the stress of the concrete around the stud is mainly divided into three areas: the concrete under the stud root is compressed,the concrete above the stud root is tensioned and the concrete near the stud cap is pulled out under different load modes,and the stress ranges will be different.The established nonlinear finite element model can accurately simulate the mechanical behavior of bolted connectors under complex load modes.Through parameter analyses,the influence of different concrete strengths and axial load levels on the mechanical properties of studs was studied.It was found that the strength of concrete has little influence on the bearing capacity of studs under the combined action of tension-shear and compression-shear.The shear bearing capacity and shear stiffness of bolted connections decrease with the increase of axial tension and increase with the increase of axial pressure.(3)Mechanical model of stud connector under complex load modeBased on the theory of elastic foundation beam,the mechanical model of bolted connection under complex load mode was deduced,and a calculation method of shear capacity based on the length of plastic extrusion section was proposed.The model can be used to predict the development law of the load-slip curve of bolted joints under complex stress modes,which provides a theoretical reference for exploring the influence of complex stress modes on the mechanical properties of bolted joints.