Research On The Shear Force Transfer Performance Of Cold-formed Thin-walled Section Steel With High Strength Bolted Connections

The addition of sections to the existing cold-formed thin-walled steel structure is a strengthening method based on the theory of increasing the cross-sectional area.The old and new cold-formed thin-walled sections can work together depends on whether they are tightly connected,i.e.,whether the load on the existing cold-formed thin-walled sections can be effectively transferred to the new cold-formed thin-walled sections.For the actual member to be strengthed,this dissertation proposes the use of high-strength bolt connection to achieve the transfer of shear force.However,in the calculation of the strengthening design,there are no relevant studies and specifications given for the thickness of the plates used for strengthening,the diameter of the bolts used for strengthening,and the size of the shear force value that can be transferred by a single bolt.In this dissertation,28 samples are tested in tension test using cold-formed thin-walled section steel high-strength bolted connections as the research object.By observing the damage mode of the connectors under different parameter and analyzing the load-strain curve of each connector,the magnitude of the shear force transfer value on the strengthed steel plate and its influencing factors are investigated.The test results show that the bolt arrangement of the connection and the thickness of the strengthed steel plate are not important influencing factors for improving the shear transfer value on the strengthed steel plate;the bolt preload has a greater influence on it,and the shear transfer behavior increases less when the bolt preload is less than 0.8 P_c,and more when the bolt preload is greater than 0.8 P_c and less than P_c,and the shear transfer behavior increases more when the bolt preload is greater than P_c,the shear transfer behavior starts to decrease gradually;and the shear transfer value increases non-linearly with the increase of the number of bolts and bolt diameter,and also has the"group discount effect".Based on the tensile test,the numerical simulations are carried out with the finite element analysis software ABAQUS,and results of the numerical analysis are verified by comparing with the test results;meanwhile,adding two parameters of bolt spacing and thickness of the steel plate to be strengthed to further investigate the relationship between them and the shear force transfer value.The analysis results show that when 3D≤S≤4D(S is the connection bolt spacing;D is the connection bolt diameter),the shear transfer value of the strengthed steel plate increases with the increase of bolt spacing;the thickness of the steel plate to be strengthed has a great influence on the shear transfer value on the strengthed steel plate,and the shear transfer value increases linearly with the increase of thickness.Finally,combining the test and finite element variable parameter analysis results,the recommended design formula for the shear transfer value on the strengthed steel plate of the connection is proposed and some suggestions for the construction of the actual strengthening project.