Experimental And Theoretical Study On Local Stability And Section Bearing Capacity Of Concrete-Filled High-Strength L-Shaped Steel Tubular Columns

With the development of modern pumpcrete pouring technique,concrete-filled steel tubular structures(CFSTs)have become one of the solutions to green building and building industrialization.The structural bearing performance can be further optimized with highstrength steel tubes.However,the higher strength member leads to a smaller sectional dimension of column under the same bearing capacity,finally resulting in the local instability of high-strength steel column.The local instability problem is more prominent in comparison with ordinary steel member.To solve the problem above,the width-thickness ratio of plate is explicitly specified in the domestic and foreign design codes.The smaller ratio above along with the increase of strength definitely sets restrictions on the use of highstrength steel in the columns with large width-thickness ratio.The theoretical research shows that the global compression buckling performance of plates with less corrugation repeating number is superior to that of plates with more number under certain conditions.As for the local instability of high-strength steel tubular columns under a large width-thickness ratio,the single-corrugated plates are proposed and applied to Q690 high-strength steel tubular columns in this paper.A set of 10 tests were conducted on both hollow steel and steel-concrete composited sections to investigate the axial load behavior of L-shaped single-corrugated tubes,and the parameters of concrete-filled highstrength L-shaped steel tubular stub columns were analyzed based on the calibrated FE model.The main research work is as follows:1)By studying the corrugation repeating number effect of corrugated sheet steel and analyzing the parameters of the global buckling performance of single-corrugated plate,the optimal corrugation was obtained.The global compression buckling of simply supported corrugated steel plates was studied using the equivalent orthotropic plate model and the buckling critical stress formulas applicable to multi-corrugated steel plates were deduced.The theoretical model of corrugated sheet steel deformation was established,the analytical formulas of global buckling critical stress of simply supported single-corrugated plates were deduced based on the basic assumptions and the energy conservation principle.Compared with flat steel plates,the economy of single-corrugated steel plates was discussed.2)The axial compression tests of the concrete-filled high-strength L-shaped steel tubular stub columns and hollow steel tubular columns were conducted,and the influence of different width-thickness ratios and corrugation settings on the local stability and axial compression ultimate bearing capacity was investigated.With the tests,the failure pattern of specimens was described in detail,and the load-displacement,load-strain curve relation curve was measured.The test results were compared with the existing codes formulas,and the applicability of the existing codes was discussed3)ABAQUS FE model was established and calibrated with the test results;the axial compression working mechanism of high-strength concrete-filled steel tubular L-shaped columns was studied.The influence of different corrugation and width-thickness ratios on local buckling of L-shaped hollow steel tubular stub columns was studied by orthogonal design method and the corrugation structure was optimized;the influence of steel yield strength,concrete strength,width-thickness ratios and different corrugations on the mechanical property of L-shaped concrete-filled steel tubular stub columns were studied via parameter analysis.Moreover,the simplified calculation formulas of axial compression bearing were proposed respectively for the common section and single-corrugated section based on the tests and parameter analysis.