Study On Residual Stresses In Welded Moderate And Heavy Plate Box Sections Made Of Q460GJ Steel

With the improvement of construction techniques and the transformation of architectural concept,high strength steel has been applied in large span and high-rise structures. Compared with the ordinary low alloy high strength steel, high-rise building structural steel(GJ steel), which has more excellent comprehensive performance, is applied to the key parts of the domestic major construction projects. Though part of the design indicators of Q345 GJ have been included in Code for design of steel structures(GB 50017-201X)[1], the research of mechanical properties, residual stress and overall buckling behavior for high strength GJ steel.Stability bearing capacity of compression members is associated with the overall stability factor ? of component, and the coefficient can be influenced by the mechanical properties, residual stress, geometric defect and the component constrained conditions. Geometric defect and the component constrained conditions barely change with material, however, residual stress distribution shows some difference between high strength GJ steel and high-strength steel, on account of the distinct production and processing technology.Based on the project of National Natural Science Foundation of China(NO. 51578089), a large amount of experimental and theoretical investigations were carried out to study the distribution of residual stress in both medium and heavy welded box sections in this dissertation. The main results are as follows:(1) Material characteristic test of Q460 GJ steel was carried out. Part of mechanical indexes of Q460 GJ steel plates with different thickness were measured, including yield strength, tensile strength, Young's modulus and elongation, which provides a significant prerequisite for the subsequent research on residual stress and overall buckling behavior.(2) Experiment of residual stress in welded box sections made of Q460 GJ steel was carried out. Residual stress distribution was obtained in both medium(12mm) and heavy(25mm) welded box sections by sectioning method; an improvement for traditional sectioning method was adopted and a new correction method was put forward. Then, respective results acquired with different correction methods were compared.(3) Stress distribution models for welded box sections made of Q460 GJ steel were put forward. Two stress distribution models with different thickness were summarized, based on the experimental study and the research results of scholars at home and abroad. At last, detailed calculation formulas for the stress distribution models were put forward, so as to establish the foundation for the research on overall buckling behavior.The main innovative points of this paper are as follows:(1) The residual stress of welded box sections made of Q460 GJ steel were measured for the first time.(2) An improvement for sectioning method was put forward, which can be applied to the residual stress measurement in thick welded box sections with small size.(3) A new correction method named by straightening measurement for sectioning method was proposed.