工程科学与技术 (Jan 2024)
Experimental Study on Axial Compression Performance of Corroded Cold-formed Thin-walled Steel I-shaped Column
Abstract
ObjectiveIn order to obtain the working mechanism and mechanical property degradation law of corrosion cold-formed thin-walled I-shaped built-up columns connected by self-tapping screws-pulling rivets under axial compression load, 24 I-shaped built-up columns were designed and fabricated for axial compression testing. And a modified formula for calculating the ultimate bearing capacity was proposed. This revised method serves as a reference for the safety evaluation of the bearing capacity of these composite columns in corrosive environments.Methods24 I-shaped built-up columns with different lengths (450mm,1500mm), connector spacing (150mm, 300mm, 450mm) and connection arrangement (pulling rivets and self-tapping screws are distributed in a row, while self-tapping screws and pulling rivets in a staggered arrangement) were designed and manufactured. The specimens were subjected to axial compression test after neutral salt spray, The test load-axial displacement curve, the ultimate bearing capacity, deformation characteristics and failure mode were measured, and compared with the test results of uncorroded built-up columns. Finally, following the reduction in specimen thickness based on the weight loss rate, the stress values associated with local buckling, distortion buckling, and overall buckling are computed using the CUFSM. Based on the test results and the theory of North American direct strength method, the calculation formula of ultimate bearing capacity suitable for corroded built-up columns was deduced and modified to verify its accuracy and applicability.Results and Discussions Compared to non-corroded specimens, the failure location of the 450mm and 1500mm series composite columns shifted from the mid-span to the column base. This shift was primarily due to the accumulation of salt spray at the column base, leading to severe localized corrosion and exposing the column base as a critical weak point. The flanges of the 450 mm series specimens exhibited pronounced opening deformation both before and after corrosion. However, the deformation amplitude of specimens with a staggered arrangement of pulling rivets and self-tapping screws after corrosion was markedly reduced compared to that observed before corrosion. The flanges of the specimens with 1500 mm series of pulling rivets and self-tapping screws distributed in a row changed from concave to slightly convex. The flange convex amplitude of the specimens with staggered arrangement of pulling rivets and self-tapping screws was more obvious after corrosion, and the separation trend between the two limbs became more obvious with the increase of the spacing of the connectors. The failure modes of the specimen series remain unchanged. The 450mm series exhibited local-distortion-related buckling, while the 1500mm series displayed local-distortion-overall bending related buckling. An analysis of the test load-axial displacement curve of revealed that the 1500mm series underwent a precipitous decline upon attaining its bearing capacity, signifying abrupt failure and incapacity to endure additional loads. In contrast, the 450mm series did not exhibit such behavior. Moreover, the initial stiffness of certain 450 mm series and 1500 mm series specimens after corrosion exceeded that of non-corroded specimens. The rationale is that at the initial stage of loading, the augmentation effect of the bonding due to corrosion on the initial stiffness surpasses the weakening effect of the corrosion on the connector. As connector spacing increased, the average ultimate bearing capacity for the 450mm series decreased by 7.05% and 5.58%, while the 1500mm series decreased by 4.13% and 5.47%, respectively. This indicates that connector spacing had a more pronounced impact on the ultimate bearing capacity of the 450mm series. However, the rate of load reduction diminished as the spacing increased further. Compared to non-corroded specimens, corrosion caused maximum ultimate bearing capacity reductions of 10.7% and 23.94% for the 450mm and 1500mm series, respectively. The largest reductions occurred in specimens with pulling rivets and self-tapping screws distributed in separate rows. Conversely, specimens with a staggered arrangement of pulling rivets and self-tapping demonstrated significantly higher ultimate bearing capacity, underscoring the effectiveness of this arrangement in mitigating buckling deformation, enhancing load-bearing capacity, and improving ductility. After corrosion, the ultimate bearing capacity determined via the North American Direct Strength Method (DSM) surpassed the experimental values for both specimen series, yielding a maximum test-to-calculated ratio of 1.54. After modifications to the DSM formula informed by experimental outcomes for corroded built-up columns, the ratio of calculated to experimental values averaged 1.04, validating the reliability and accuracy of the modified formula.ConclusionCorrosion significantly impacted the axial compression performance of cold-formed thin-walled steel I-shaped built-up columns, specifically manifesting as reductions in the bearing capacity, increased deformation, and shifts in failure location. Meanwhile, optimizing the connection method-- using an alternating arrangement of self-tapping screws and pulling rivets effectively enhanced the load-bearing capacity and ductility of corroded built-up columns. The modified bearing capacity calculation formula, based on experimental results, provides a reliable theoretical basis for evaluating the load-bearing performance of corroded built-up columns.
