Disscussion on the Tension Capacity with Prying Force of Bolted End-Plate Connections

In the end plate connection with high-strength bolts subjected to bending moment,the end plate occurs bending deformation and produces prying force.In the design of connection joints with weak relative stiffness,the prying force can not be ignored.The end plate connection joints designed according to domestic specifications generally have the problems of large number of bolts and large thickness of end plate.It is necessary to analyze the relationship between prying force Q,joint bearing capacity N_t,bolt tension N_b and bolt tensile bearing capacity N_t^b,and find out the reasons for the conservatism of China's standards through the comparative study of the current specifications formulas and their parameters.The tensile T-stub joint model can be used to simulate the high-strength bolted end-plate connection joint.The tensile T-stub joint test and theoretical analysis at home and abroad show that the first plastic hinge of the tensile T-stub joint with obvious prying force effect first appears near the root of the wing plate of the T-stub.With the gradual increase of the external tension N_t,the wing plate of T-stub gradually enters the elastic-plastic state from the elastic state,and the prying force also gradually increases from nothing until the bolt is broken or the wing plate of T-stub is completely damaged (a second plastic hinge appears near the bolt hole).The external tension N_t is divided into two parts N_t1 and N_t2,where N_t1 corresponds to the external tension when plastic hinge occurs at the wing plate root of T-stub,N_t2 forms a moment balance with the prying force Q near the bolt.The force arm of the external tension N_t is the distance from the root of T-stub to the bolt hole,and the force arm of prying force Q is the distance from the bolt hole to the edge of T-stub.According to the joint failure mode and the bending moment balance condition at the bolt hole in the failure state,the calculation formulas of joint tensile bearing capacity N_t,prying capacity Q,bolt tension N_b and the critical plate thickness of the failure mode are obtained.According to the joint tensile bearing capacity formula,the joint bearing capacity curve can be drawn,and the control conditions of the three failure modes and the relationship between the three failure modes can be obtained.
There are differences in the design methods of high-strength bolted connections considering prying force effect at home and abroad.The comparison results with foreign specifications show that:1) both Chinese and American specifications know the external force N_t and calculate the plate thickness;the European specification is to calculate the tensile bearing capacity N_t of the joint when the plate thickness is known.Although the three have different forms,the calculation formula has the same principle and can be converted to each other.2) The tensile bearing capacity of high-strength bolts in the Code for Design of Steel Structure (GB 50017-2017) has been included in the prying force effect;N_t^b is still used as the upper limit of tensile bearing capacity of high-strength bolts in the calculation formula of relevant joint bearing capacity in other relevant steel structure specifications,which will cause repeated calculation of prying force effect.3) Under the same conditions,the calculation results of European and American specifications are close to the test results,while the calculation results of Chinese specifications are conservative.The failure to correct the position of plastic hinge is an important factor that leads to the conservatism of the current specification in China.4) The latest American specification further limits the calculated width of the flange of tension T-stub.In the European specification,the effective calculated length l_ef of the flange of equivalent T-stub is the minimum yield line length in various possible failure forms as the calculation basis of the joint bearing capacity.The provisions on calculating the wing width of T-stub in Chinese specifications are relatively general,and it is suggested to make them clear.