Experimental And Theoretical Study On Bending Bearing Behavior Of 550MPa High Strength Cold-Formed Steel Purlins

The bearing capacity behavior of 550MPa high strength cold-formed steel hat section 27 simply supported purlins and 27 lapped continuous purlins under bending has been studied in this paper. All the specimens are classified into TOPSPAN 40 and TOPSPAN 61. According to section thickness t=0.48mm or 0.6mm, specimens TOPSPAN 40 are divided into two groups, whose spans are Z,=1200mm 1800mm 2400mm separately, while according to section thickness t=0.75mm or 1.00mm, specimens TOPSPAN 61 are divided into two groups, whose spans are L=1800mm 2400mm 3000mm separately. The test results show that it is unsafe to calculate the ultimate bending bearing capacity of 550MPa high strength cold-formed steel purlins according to the current Chinese specification GB50018-2002.Based on the test results, the finite element program ANSYS 9.0 is applied to carry out the nonlinear finite element analysis of 550MPa high strength cold-formed steel purlins under bending. The results of the finite element method are much close to the test results. This paper also includes some parameter analysis by using ANSYS, such as the effect of section thickness to the ultimate bearing capacity of simply supported purlins, the effect of overlapping length and constructional detail to lapped continuous purlins. Meanwhile, the method of coupling linear displacement is proposed to substitute for touching effect in the self-drilling screws in the overlapping part of lapped continuous purlins. The results of analysis show that it is ideal to use this method.Considering the material characteristics of high strength steel, the method of reducing yield strength is applied to calculate the ultimate bearing capacity of purlins under bending. Comparing the calculated results of simply supported purlins by effective width method and direct strength method with the test results, this paper suggests that the strength reduction coefficient γ of specimens with section thickness t=0.48mm 0.6mm and 0.75mm be 0.80, while coefficient γ of specimens with section thickness t=1.00mm be 0.90. According to the determined strength reduction coefficient γ and test results, the stiffness coefficient β of overlapping part of lapped continuous specimens TS40-0.48 and TS40-0.60 is proposed to be 1.2, while the stiffness coefficient β of specimens TS61-0.75 and TS61-1.00 be 1.5. Then the calculated results by using effective width method specified by GB50018-2002 are close to the test results.