Studies On Axial Compressive Loading Capacity Of CHS T/Y-Joints Strengthening With External Stiffeners Welded Under Load

The circular hollow section(CHS)joints are common in steel structures.Compared to general joints,they are highly favored for their simple and beautiful appearance,high torsional stiffness,and superior fluid dynamic characteristics.Typically,the joints of a structure are prone to damage,and the reinforcement of the joints can effectively improve the overall performance of the structure.In engineering practice,reinforcement often needs to be applied under normal service conditions not to affect production and life.However,at present,research on welding reinforcement under load is mostly focused on H-shaped steel beams and columns.Therefore,research on the reinforcement of CHS joints under load is helpful in reducing construction difficulty and promoting welded reinforcement under load.This paper aims to investigate the axial compression capacity of CHS T/Y-joints strengthening with stiffeners under load.Firstly,finite element simulations using ABAQUS were verified by the experimental results of joints strengthening with stiffeners welded under load and T-joint welding tests.The effects of welding under load on residual stress,residual deformation,and bearing capacity of the joints were analyzed.To address the issue of welding deformation leading to the out-of-plane inclination of the brace,a welding sequence optimization was proposed to adjust the welding residual deformation.Subsequently,a simplified modeling method was used to establish a total of 760 T/Y-shaped joint models,including reinforced and unreinforced joints.The sets were used to train a Bayesian regularized BP neural network.By analyzing the Pearson correlation and the significance of the data,the effects of various parameters on the ultimate bearing capacity of the joints were determined.A formula was derived to calculate the improvement rate of the ultimate bearing capacity of the CHS T/Y-joints strengthening with stiffeners welded under load.The main conclusions obtained in this paper are as follows:The finite element model using the thermo-mechanical coupling and the birth-and-death element method can simulate the experimental phenomena,residual stress,and residual deformation distribution of the joints welded under load.The simulation shows that the welding reinforcement under load has little effect on the ultimate bearing capacity of the joints and the residual stress in the welds.The residual stress around the weld after the welding reinforcement under load is higher than that after the unloading welding.And welding under load results in larger residual deformation compared to unloading welding.Moreover,with the increase of the load factor,the degree of out-of-plane inclination after welding increases.Six different welding sequences were designed and simulated,and the residual stress distribution,vertical deformation,and out-of-plane inclination deformation were compared.Based on the residual deformation after welding,it was found that rotating welding around the center axis of the brace can effectively reduce the residual deformation of welding.In addition,the difference in residual deformation between segmented backhand welding and segmented sequential welding is small,and vertical upward welding should be prioritized to ensure welding quality during construction.Latin hypercube sampling was used to obtain the target parameters,and a Python script for modeling was constructed based on the parameters.Three data sets with sizes of 60,120,and 180 and a validation set with a size of 20 were obtained.A BP neural network model with Bayesian regularization was established and trained to predict the ultimate bearing capacity of CHS joints strengthening with stiffeners.The results show that when the number of data sets exceeds 100,the bearing capacity can be predicted with an average error of less than 0.5%.The neural network model can be used for parametric analysis.The trained neural network model was used for parametric analysis,and a formula for calculating the improvement rate of the ultimate compressive bearing capacity of CHS T/Y-joints strengthening with stiffeners was obtained based on regression theory.The formula was tested through simulation results in the validation set,and the fitting effect was good with an R~2 of 0.941.It can be used as a design reference in engineering practice.