Study On Defect Simulation And Analysis Methods For Bearing Capacity Of Existing Grid Structures

Spatial grid structure is widely used in public buildings and industrial buildings due to its rich modeling,convenient fabrication and installation.However,defects and damage caused by construction errors or untimely maintenance will reduce the bearing capacity of the structure,and even cause engineering safety accidents,resulting in casualties and economic losses.Therefore,regular testing and load-bearing performance evaluation of existing grid structures are very important to ensure the safety of structures,and relevant theoretical issues have important research significance.Based on a large number of existing research results,this paper firstly systematically summarized the types,detection and identification theories,characterization methods and simulation analysis methods of common defects and damages in grid structures.Then,the initial geometric imperfection simulation of single-layer reticulated shell structure,the bearing performance analysis of members with large initial curvature,and the sampling detection methods and global stability analysis methods of existing grid structure were studied.Finally,a static loading failure test of a single-layer reticulated shell was carried out,and some of the methods proposed in this paper were verified based on the test data.Single-layer reticulated shell structure is the most common type of grid structure,which is sensitive to geometric defects.A reasonable numerical model is an important prerequisite for accurate analysis of its load-bearing performance.The existing simulation methods of node coordinate deviation defects ignore the constraint of component length on node position coordinates,which leads to the inconsistency between the component length in numerical model and the actual structure,and the existing methods cannot consider the influence of construction sequence on node coordinate deviation defects.To solve these problems,an improved random imperfection mode method was proposed.The method can consider not only the randomness of node coordinate deviation defects but also the influence of component length and construction sequence,which makes the imperfection mode more reasonable.The numerical simulation results showed that compared with the traditional random imperfection mode method,the calculation results of ultimate bearing capacity constructed by the method in this paper are more concentrated and more referential.The axial compression member is the most basic member in the existing grid structure.It has been shown that the initial bending defect has a significant influence on the stable bearing capacity of the axial compression member.Therefore,various countries have put forward a definite limit of the bending defect of the axial bearing member in the design specifications.In this paper,the load-bearing capacity analysis method of axial compression members with large initial bending defect was studied.Firstly,an iterative calculation method was proposed to calculate initial bending defectΔ₀ based on measured bending defectΔ_m.Secondly,on the basis of the commonly used formula for calculating the stability coefficient of axial compression members,the bending defect factorΔ₀/l was proposed as a characterization parameter,and the formula for calculating the stability coefficient of axial compression members which can quantify the initial bending defect was derived.Based on a large number of finite element simulation results,the above formula was modified to consider the influence of residual stress and material plastic development.Finally,a practical formula for calculating the stability coefficient of axial compression circular steel tube members considering any initial bending defects was obtained.The effectiveness of the proposed method was verified by applying it to the identification analysis of a two-layer spatial grid structure.Sampling inspection is one of the most commonly used methods in the inspection of existing structures.The inspection and appraisal standards suggest that the calculation model used in the analysis of existing structures should conform to the actual working state of structures.For the detection of coordinate deviation of existing grid structure nodes and global stability analysis,this paper proposed a set of procedures for sampling inspection and stable bearing performance analysis of existing grid structure based on partial measured data,including methods of the node coordinates deviation detection spatial system sampling,correlation analysis of node coordinate deviation and the method of building grid structure model and the overall stability analysis method.Taking an existing single-layer K6 steel reticulated shell structure as an example,numerical models of the structure were constructed by using the proposed method and other methods,and the ultimate bearing capacity were calculated.The comparison of the calculation results showed that the ultimate bearing capacity of the structure is closer to the actual bearing capacity.A single layer reticulated shell structure containing damaged members was constructed.Before loading,the node coordinate deviation,initial curvature and initial eccentricity of members were measured.During the loading process,the strain of members and displacement of nodes were recorded until the whole structure collapsed.Based on the measured data,the deformation and stress characteristics of reticulated shell structure were analyzed,and the whole loading process of the structure was divided into four stages.Based on the measured information,a finite element numerical model with high precision was established.The whole loading process was simulated,and the average error of simulation calculation of key load steps in each stage is 7.14%,and the simulation error of the ultimate bearing capacity is about 5%.It shows the validity and accuracy of the load-bearing performance analysis method of the existing grid structure based on the measured information.In addition,based on the measured defect data,the influence of different defects on structural stability bearing capacity was analyzed,and the method proposed above were verified and further analyzed.