Research On Static Behavior And Rigid-zone Of Prefabricated K-type Reinforced Joints Of Partially Concrete-filled Square Steel Tube Trusses

With the development of construction economy,the structure has become increasingly long-span,complex,and heavy loaded.There are many intersectant members at the nodes and the stress concentration is obvious,which makes the node area usually become a weak part of structures.This paper aims at K-joints in square steel tube trusses structures and based on various enhancement methods and ideas proposed by industry scholars,mainly to reduce the weight of the structure,optimize the failure mode of the joints and fit the design concept of the prefabricated structure,and solve the problem of stress concentration in the key joints of large-span steel tube structures,excess bearing capacity of members,and lack of bearing capacity of joints,a type of prefabricated K-type reinforced joints of partially concrete-filled square steel tube trusses is proposed.In this paper,finite element method is used to analyze the failure mode,load-carrying performance of the new type joints,and the problem of joints rigidization caused by partially concrete-filled.The main research work and achievements are as follows:(1)Based on the typical K-joints in the trusses structure,optimal design,and 4 kinds of joints detailed form are proposed.(2)On this basis of material constitutive model,contact surface treatment,loading methods,and nonlinear solution settings,a new K-joints refinement finite element model is established,the failure mode and bearing capacity of the new K-joints are analyzed.(3)Parameter analysis.The new K-joints bearing capacity and failure modes are studied,which are related to the gap between two branch tubes,the strength of the inner filling concrete,the main tube diameter thickness ratio,the ratio of main tube to branch tube diameter,and the ratio of main tube to branch tube length.The results show that: The 4 new K-joints can change the traditional failure mode of concrete-filled square steel tubular joints,and effectively realize the design concept of removing the plastic break zone out of the joint core-zone;The ultimate load capacity of the new K-joints is significantly higher than that of the standard hollow steel tube joints,with an increase of approximately 28% to 37%.The partial design of the stiffened plates and casings of it can achieve the desired design results,so that the plastic deformability of the joints can be strengthened and the risk of brittle failure of thejoints can be avoided.(4)The research on the joints rigid-zone model.For the K-type truss joints,firstly,based on the related theoretical methods in structural mechanics,the theoretical relationship of the rigid-zone of the K-joints is deduced.Next,combined with the calculation data of 5 sets of 54 finite element models,the model of the new K-joints rigid-zone was studied and established.(5)The effect of joints rigidization on truss structure.In order to facilitate the application of the new type K-joints design,the rigid-zone coefficient range and corresponding simplified form of the K-joints are given through the simulation analysis of the Warren type Integral trusses: Among them,the new type K-joints in this paper can be designed according to the hinge point in practical project.Meanwhile,it can be used as a reference for actual projects.