Experimental Study on Overall Buckling Behavior of Q690 High Strength Steel Cold-Formed Square Tube Columns Under Axial Compression

One of the strategies for decarbonizing the construction industry is to enhance the efficiency of engineering design in order to minimize the demand for building materials. Recent advancements in the production of high-strength steel have enabled this possibility. The effective utilization of high strength steel in engineering structures can decrease the dimensions of components and the usage amount of steel, consequently leading to reduced manufacturing, transportation, and construction expenses, which aids in resource conservation and contributes to the reduction of carbon emissions. Compared to the ordinary carbon steel Q355, the Q690 high strength steel exhibits excellent strength to self-weight ratios despite its high yield-to-tensile strength ratio and low elongations at fracture. The properties of high strength steel Q690 can greatly influence structural performance. Therefore, it is crucial to quantify the impact of these properties on structural performance in order to determine their suitability for use in building structures. The calculation method for the overall buckling bearing capacity of axial compression members in the current main structural steel design codes is primarily based on research data for ordinary carbon steels Q235 and Q355, and their applicability to Q690 high strength steel needs to be further verified. So it is very necessary to check the applicability of these design methods for axial compression members made of Q690 high strength steel using various fabrication processes. To investigate the overall buckling of cold-formed square columns made of Q690 high strength steel under axial compression, a total of eight specimens were designed. These specimens included four different cross-sectional sizes and eight slenderness ratios. The plate thicknesses used were 6 mm and 10 mm. The overall buckling of these specimens was examined through axial compression tests. Prior to the tests, measurements were taken to determine the geometrical initial bending, load initial eccentricity, and longitudinal residual stress distribution of the sections. Residual stress measurements revealed large residual tensile strain on both the inner and outer surfaces at the welded seams of the cold-formed square section. Additionally, significant residual tensile and compressive strains were found at the outer and the inner surfaces respectively of the round corners of section. It was found that all specimens exhibited overall buckling as the primary mode of failure under axial compression. The test results were compared with the calculation results of Chinese code GB 50017—2017 and European code Eurocode 3. The results indicate that the calculation results based on the design curves suggested by the Chinese code and Eurocode are conservative, and the Chinese code being more conservative compared to the European code. Based on the comparison of test results and design curves in the design code, it is recommended to use the column curve a in GB 50017—2017 and Eurocode 3 for the design of Q690 high strength steel cold-formed square tube columns.