| The concrete-filled square steel tube structure has the characteristics of strong bearing capacity,high rigidity,good ductility and energy dissipation ability of seismic energy.It is widely used in engineering practice.However,the calculation of bearing capacity of frame joints has been difficult to be solved.The current calculation methods are mainly calculation methods based on the yield line method.And the calculation formula is numerous,the calculation accuracy and the applicable scope are different.There is lack of detailed explanation of mechanical mechanism.Also in the welded frame joints,to prevent the brittle fracture of the scallop part earlier,the form of the scallop was improved from three aspects of shape,height and length.The influence of different scallops for the bearing capacity of frame joints is unknown.The application of the formula based on the yield line method in the case of new scallops needs to be explained.The calculation of local yield flexural capacity of concrete-filled square steel tubular column to steel beam joint with internal diaphragms was discussed.Firstly the characteristics of the calculation method from the ‘Technical Specification for Structures with Concrete-filled Rectangular Steel Tube Members(CECS 159 : 2004)' and two calculation methods based on yield line method proposed by Koji MORITA in Japan were investigated.Then the effect of axial pressure on column was introduced in the three methods to get corresponding improved methods.In order to compare the applicable scope of beam-column flange width ration,parameter analysis for the width ratio was carried out,and the existing data was used for comparison.In order to explain the effect of axial pressure on calculation accuracy and safety,the calculation results before and after the improvement were compared with the existing experimental data.Through comparison and analysis,the improved method based on combined yield mechanism is suitable for all range of beam-column flange width ratio.The yield flexural capacity can be accurately predicted by this method and the calculation is partial to the safety.Also this method is convenient for calculation.So it is suitable for application of design.In order to reveal the mechanism of joint bending,this paper also analyzes the influence of the thickness of column flange,the thickness of inner diaphragm,the pore size of inner diaphragm,the strength of concrete on the local flexural strength of joints.Based on the results of finite element analysis,new calculation formulas are proposed and the rationality of each calculation formula is evaluated.The effects of the interaction of various factors were also investigated.The situations were divided into three cases: the flexural yield strength of local yielding joints is greater than,equal to,and less than the yield strength of yielding flexural strength of beam ends respectively.The influence of the stress distribution of the web on the calculation of local yielding flexural strength of the joints is discussed.The mechanics mechanism of the stress distribution of the webs are described.Formula precision,scope of application and ease of use are discussed using the existing experimental data and finite element analysis data.It is found that the formula of joint yielding mechanism,which does not consider the stress distribution of web,has good properties in terms of accuracy,applicable scope and ease of use,and should be adopted in the project.On the basis of summarizing the new scallops in previous studies,the effects of the new scallops on the local yield strength and the yield strength of the beam end are studied.The results show that scopes has little influence on the local yield strength and have greater influence on the yield strength of the beam end,of which the shape and height of the scallops have less effect on the yield capacity of the beam end than the length of the scallops,while increasing the length of the scallops will significantly reduce the yield capacity of the beam end. |
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