Improved Effective Width Method Considering Distortional Buckling for Cold-Formed Thin-Walled Steel Members with Lipped Channel Section

The local buckling, distortional buckling, and overall buckling would occur for cold-formed thin-walled steel members with lipped channel section. The effective width method is used to considering the effect of local and distortional buckling on load-carrying capacity of member in Chinese code. Especially, a very conservative stability coefficient of partially stiffened elements used to considering the local buckling and distortional buckling of flange of lipped channel sections. In this paper, the half-wave length, the elastic buckling stress of distortional-buckling of cold-formed thin-walled steel members with lipped channel section and the corresponding stability coefficient of partially stiffened elements were developed based on the energy method. With comparison among the calculated results of elastic buckling stress and half-wave length using the improved method and the Finite Strip Method, suitability and precision of the improved method were illuminated. Then, a uniform formula for the stability coefficient of partially stiffened elements considering both local and distortional buckling effect was established based on the proposed method. Finally, with comparison on lipped channel sections in the appendix of Chinese code and existing test results conducted by many researchers and the proposed method, it is shown that the proposed uniform formula had higher precision to calculate the stability coefficient of partially stiffened elements and the ultimate load-carrying capacity of cold-formed thin-walled steel members with lipped channel section

Shear Behavior of Screw Connections for Cold-formed Thin-walled Steel Structures

Self-drilling screws are the primary mean s to fasten cold-formed thin-walled steel members in construction. There are several failure modes for shear connections with self-drilling screws, including screw tilting, hole bearing, edge tearing, tensile fracture in net s ection of connected elements and shear fracture of screws. Meanwhile, the “g roup effect” will exist when a large number of screws are used in a shear connection. A series of tests (75 specimens) on single lap shear connections with self-drilling screws has been carried out and the results report ed in this paper. The end distance, screw spacing, pattern of screws arra ngement and number of screws was varied to determine their influence on shear connection strength. The study focused on the analysis of factors af fecting the shear connection strength, the shear strength estimation of self-drilling screw connections based on different failure modes and the influence of group effect. Finally, a proposed design method and recommendations for Chinese specification GB50018 are presented

Test and Finite Element Analysis on Distortional Buckling of Cold-formed Thin-walled Steel Lipped Channel Columns

High-strength cold-formed thin-walled steel sections have been widely used in the recent several years. However, distortional buckli ng or interaction between it and local buckling can occur for high strength cold-formed thin- walled steel members. This paper desc ribes a series of compression tests performed on lipped channel section columns with V-shape intermediate stiffener in the web and flanges fabricated from cold-formed high strength steel of thickness 0.48 and 0.6mm with nominal yield stress 550MPa. The lipped channel sections were tested to failure with both ends of the columns fixed. The test results of 16 specimens show that the local buckling usually appears before distortional buckling of the specimens and it makes the distortional buckling occur in advance. This interaction of local and distortional buckling may have the effect of reducing the stiffness and bearing capacity of the columns. The comparison on ultimate strength and buckling mode between test results and results of finite element analysis considering geometric and material nonlinear show that finite element method (FEM) can simulate the distortional buckling of cold-formed steel channel columns effectively. The calculative results using Direct Strength Method (DSM) of the North American Specification show that this design method couldn’t consider the reverse effect of interaction between local and distortional buckling on ultimate strength. Direct Strength Method (DSM) considering interaction between local and distortional buckling should be developed

Distortional Buckling Experiment on Cold-Formed Steel Lipped Channel Columns with Circle Holes under Axial Compression

The objective of this paper is to research the distortional buckling mode and load-carrying capacity of cold-formed thin-walled steel columns with circle holes in web. Compression tests were conducted on 26 intermediate length columns with and without holes. The test members included four different kinds of circle holes. Test results show that the distortional buckling occurred for intermediate columns with holes and the strength of columns with holes was less than that of columns without circle hole. The ultimate strength of columns decreased with the increase of the total transverse width of hole in cross-section of members. For each specimen, a shell finite element Eigen-buckling analysis and nonlinear analysis was also conducted. Analysis results show that the holes can affect on the elastic buckling stress of columns. The shell finite element can be used to model the buckling modes of columns with holes and analyze the load-carrying capacities of members with holes. The comparison on ultimate strength between test results and calculated results using Chinese code GB50018-2002, North American specification AISI S100-2016 and nonlinear Finite Element method was made. The calculated ultimate strength show that results predicted with AISI S100-2016 and analyzed using finite element method are close to test results. The calculated results using Chinese code is higher than test results because Chinese code has no provision to calculate the ultimate strength of members with holes. So the calculated method for cold-formed steel columns with circle holes was proposed. The calculated results using this proposed method show good agreement with test results and can be used in engineering design of cold-formed steel columns with circle hole

Design Method of Bending Load-Carrying Capacity for Sandwich Panels with Different Metal Panel on Both Sides

The sandwich panels, with plain and shallow grain pressed metal plate as the face sheets, and glass wools, rigid polyurethane foam, and rock wools as core materials, have excellent heat insulation and mechanical behavior, and been used as curtain walls for tall buildings in recent years in China. Since wind load and temperature action are the main actions for curtain walls, the sandwich panels are flexural members. In this paper, the design method and design formula of flexural load-carrying capacity and flexural deflection of a kind of sandwich plates with different metal panel on both sides are discussed and proposed. This proposed method considers the different load types, like uniform load, concentrated load, and temperature action, and different core materials. The FE Method can be verified by comparing on shear force distribution coefficients for different sandwich panels with same metal panels on both sides between FE results and calculated results. Then the FE Method can be used to verify the proposed method for shear force distribution coefficients of sandwich plates with different metal panel on both sides. Finally, the proposed method for bending load-carrying capacities for sandwich plates with different metal panel on both sides is verified using FE Method. These verifies show that the proposed method for shear force distribution coefficients and bending load-carrying capacities for sandwich plates with different metal panel on both sides is safe and suitable

Load-carrying Capacity Estimation on Cold-formed Thin-walled Steel Columns with Built-up Box Section

The use of cold-formed thin-walled steel structural members has increased in recent years, and most of their sections are open section with only one symmetrical axis, which would likely fail by twisting and interaction with the others buckling mode, such as local buckling and distortional buckling. To improve the ultimate strength of columns, built-up box section can be used. In this paper, a series of loading capacity tests on high-strength cold- formed steel columns with built-up bo x section are presented, including 21 axially-compressed columns and 19 eccentrically-compressed columns sub- jected to bending moments about weak axis as well as strong axis. The test specimens are built up by two channel sections with two intermediate stiffeners in the web, and they connect at their flanges using self-drilling screws. It was shown that distortional buckling and twisting do not occur and the ultimate load-carrying capacity is 10 to 20 percent higher than the sum of the ultimate load-carrying capacity of each lipped channel section columns. According to the test results and theoretical analysis, an improved method based on the suggestion of current China code ‘Technical code of cold-formed thin-walled steel struct ures’ (GB50018-2002) considering the plate-coupling effect was proposed to estimate the ultimate load-carrying capacity of built-up box section column. With the proposed method, the calculated results are close and conservative to the test results

Recent Progress on Catalysts towards Electrocatalytic Nitrogen Reduction Reaction

The energy-intensive Haber-Bosch process currently dominants the production of ammonia (NH3), an indispensable chemical for humans. For the sustainable development of society, highly efficient and green strategies to convert nitrogen (N2) to NH3 are urgently required. Electrocatalytic N2 reduction reaction (eNRR) is universally regarded as a promising strategy owing to the mild operating conditions and renewable energy supply. The key for eNRR is the high-performance catalysts, which activate the inert N-N triple bond and thus decrease the energy barrier. Herein, the recent theoretical and experimental progress on eNRR catalysts at room temperature and ambient pressure is summarized, aiming to provide a reference for future design of high-performance eNRR catalysts

Distortion Buckling Test and Design Method of Cold-Formed Thin-Wall Steel Built-Up Members Under Axial Compression

The objective of this paper is to research the distortion buckling performance and capacity of cold-formed thin-walled steel built-up I-shaped section column. 12 built-up columns connected by self-drilling screws were conducted under the axial compression. The test members includes four different sections and the specimen length is 1000mm. Test results show that the local buckling and distortion buckling occur for all built-up sections. The finite element software ABAQUS was used to analysis the test specimens. The finite element results were in good agreement with the experimental results about the buckling mode and load-carrying capacities. The direct strength method is used to calculate the load-carrying capacities of the specimens. The calculation results show that the direct strength method is unsafe, so the direct strength method to calculate distortional buckling strength is modified on the basis of the test results. 1The author gratefully acknowledgements the financial support provided by National Natural Science Foundation Projects of China(No:51868049), Department of Education Science and Technology Projects of Jiangxi Province in China (No:GJJ180932, GJJ170983),Natural Science Foundation Projects of Jiangxi Province in China (No:20181BAB206040),Nanchang Institute of Technology 2019 Postgraduate Innovation Program (No:YJSCX20190012) and Academic and Technical Leaders in Major Subject Areas projects of Jiangxi Province in China(No: 0172BCB22022)

Experimental Study and Proposal to Improve the EWM Design of Cold-Formed Steel Lipped Channel Columns with Circular Holes under Axial Compression

The cold-formed steel (CFS) lipped channel section with circular holes has been widely used in low-rise and multistory building structures as the column. However, the circular hole in the web makes the lipped channel column become susceptible to buckle. A total of 54 CFS lipped channel axial compression columns with and without circular holes were used to study the buckling behavior and the effective width design method. The interaction of the local buckling and the distortional buckling were observed for the short and intermediate columns, while the slender columns were controlled by the interaction of the local buckling, distortional buckling, and flexural buckling or flexural-torsional buckling. The experimental failure loads were gradually decreased with the increase in the diameter of the circular hole for the specimens with the same section. The failure loads of the specimens with two holes were lower than those of the specimens with one hole with same section and same diameter of holes. Then, the experimental results were used to validate a nonlinear finite element model (FEM) previously developed by the authors. The validated FEM was subsequently used to obtain additional 36 numerical failure results concerning the effects of the length, the section, and the diameter and the number of the circular holes. Furthermore, the proposal to calculate the distortional buckling coefficient of the CFS lipped channel section with circular holes were put forward based on numerical analysis considering the reduction of effect of holes. Finally, a proposal to improve the effective width method (EWM) design approach for CFS lipped channel sections with circular holes under axial compression was presented. The comparisons between experimental and numerical capacities and their calculations provided by the proposed EWM design method illustrate a great application of the proposed approach

Shear Behaviors of Light-gauge Composite Walls under Monotonic and Cyclic Loading

Shear properties of cold-formed thin-walled steel composite walls are af- fected by many factors, including the section of light-gauge studs, the space of self-drilling screws, the panel on both sides of wall, the distribution of hold down device, etc, which makes it is difficult to estimate the shear strength. In this paper, twelve Q345 light-gauge composite wall specimens with a dimension of 2400mm wide and 3000mm high were designed for shear capacity test. Two kinds of panel combination in the specimens were considered, one is gypsum board on one side and OSB board on another side, the other is gypsum board on one side and corrugated steel sheet on another side. In order to understand the effect of opening holes in the wall on the shear behavior, three kinds of opening patterns, i.e., window open- ings of 600X1200 mm and 1200X1200 mm, and door openings of 1200 X2100 mm were simulated in the tests. It was shown that, the main failure modes of the test specimens were local fragmentation of gypsum boards, shear buckling of corrugated steel sheets, and yielding of end stud near the bottom. Based on the test data, lateral stiffness, shear strength, displacement ductility and energy dissipation coefficient of the composite walls under dif- ferent loading conditions were studied. Finally, based on domestic and for- eign research achievements, analysis method of shear strength of the light- gauge composite walls considering opening under monotonic and cyclic loading was investigated, and design methods for horizontal shear resistance and aseismic design were proposed