Research On The Design Method Of Semi-rigid Steel Frame:Joints And Elements Are Designed Synchronously

Over the past half century,semi-rigid connections have been extensively studied.At present,several major international steel structure design specifications have incorporated this component into their own systems.However,despite the many advantages of semi-rigid connections both in terms of manufacturing cost and ease of on-site installation,which is considered promising,there are few reports on the active use of semi-rigid connections in daily practice due to the lack of design guidance that can be effectively applied to the system level.Before proceeding with the design of semi-rigid steel frames,two key issues need to be addressed: one is how to establish a reliable model for predicting joint properties;the other is how to integrate semi-rigid joint design and element design to achieve synchronous.In view of the above problems,this paper mainly carried out research from the following aspects:(1)Based on the results of existing tests and finite element analysis,the development of internal forces and prying force of the T-stub during the tension process was analyzed to obtain the main factors affecting the distribution of prying force and provide the basis for the subsequent theoretical derivation.The bolt pre-tightening force and different pre-tightening levels,the coordination of bending deformation between bolts and connected plates,the combination of tensile and bending strength of bolts and the distribution of prying force were comprehensively considered.The modified formulas for calculating the properties of T-stub were derived to improve the prediction accuracy and stability of the bending component.Finally,a program for calculating joint characteristics was developed based on this improved model,whose reliability was verified by comparing the test data.(2)The concept of inverse design of joints was proposed,which can be solved by establishing an optimization design framework.The process of reconstruct a joint based on its performance requirements was implemented.Several key issues involved in the optimization were explored,including the establishment of a cost model based on the production process,a unified coding system suitable for the complex construction of bolted connections,and the synchronous automatic design of multiple types of connections.Then the program for designing joints in an inverse way was developed.By comparing with the existing experimental data,it is confirmed that this method can ensure the performance of the joint while reducing its cost.(3)This study analyzed the essence of structural calculation and put forward a general methodology suitable for simultaneous design of complex parts(such as connections,braces or shear walls)and elements.On the basis of the traditional design method of steel frames,the simple assumption of pinned or rigid joints was generalized to abstract joints with certain performance.Then combined with the joint inverse solution technology,a design method for semi-rigid steel frames based on synchronously reconstruct joint was proposed.Its core is to skip the previous design route from apparent geometry to internal performance,but directly seek the appropriate matching of performance requirements between joints and elements,and reconstruct joints synchronously,to ensure the refined design of the structure and meet the needs of daily practice.Through the analysis of the specific joint data,this study discussed how to choose a proper joint fixity factor in the preliminary design,which can reduce the invalid calculation and improve the efficiency.(4)In this study,the objective existence and invariance of the mechanical properties of the joints formed by the predetermined set of element section were expounded,and an alternative design method of semi-rigid steel frames through the performance-based connection database was developed.The key technical indicators needed to establish the performance-based connection database were studied,especially the influence of the rotational stiffness of semirigid joints on the response of the moment resistance frame,including displacement and bearing capacity.A quantitative criterion for refined classification of joints according to the initial rotational stiffness,flexural capacity and ductility was proposed,which further broadens the scope of joint classification in EN1993-1-8:2005.