Monotonic shear tests of cold-formed steel wall frames with sheathing

This research is focused on the experimental study of the structural strength of cold-formed steel wall frames with sheathing under monotonic shear loading. Two aspect ratios, 1.0 and 2.0 were utilized in the design of wall specimens. Three different kinds of sheathing material, gypsum board, calcium silicate board, and oriented-strand board, with two different thicknesses (9 and 12 mm) were adopted in the test specimens. The ultimate strength, stiffness, energy absorption, and ductility ratio were studied for each test specimen. In final, the ductility ratios of the cold-formed steel wall frames similar to the wall configuration conducted in this study are proposed.     

Design of steel sheathed cold-formed steel framed shear walls

A method for the design of steel sheathed cold-formed steel framed shear walls has been developed for inclusion in the American Iron and Steel Institute's North American standards for lateral design using a comprehensive database of single-storey shear wall tests carried out in Canada and in the United States. The wall configurations differed in terms of wall aspect ratio, framing and sheathing thickness, screw fastener schedule and framing reinforcement. The Equivalent Energy Elastic–Plastic (EEEP) analysis approach was used to derive key design information from the test data, including: nominal shear resistance, a resistance factor, an over-strength factor for capacity based seismic design and ‘test-based’ seismic force modification factors for ductility and over-strength.     

A statistical and experimental investigation into the accuracy of capacity reduction factor for cold-formed steel shear walls with steel sheathing

Buildings constructed of cold-formed steel members are increasingly used in many countries. In recent years, cold-formed steel shear walls with steel sheathing were introduced as lateral force resisting systems. Design provisions of these structures require that the shear strength of shear walls with a height to width aspect ratio (h/w) greater than 2:1 be reduced by the factor 2w/h for satisfying allowable story drift limit. In this research, the accuracy of the factor is investigated using the results of previous tests and the tests performed by the researcher. Results show that the reduction factor (2w/h) is conservative. Thus, a relation is proposed for the reduction factor.     

Steel sheathed cold-formed steel framed shear walls subjected to lateral and gravity loading

The design of steel sheathed cold-formed steel (CFS) framed shear walls is not addressed in Canadian design standards. A program of displacement based loading tests was carried out on single-storey shear walls of various configurations to investigate their performance and to establish a comprehensive database of information. The walls, which were subjected to lateral loading and combined lateral plus gravity loading, differed in sheathing thickness, screw fastener detailing, framing thickness, aspect ratio and framing reinforcement. The performance under loading was directly related to the sheathing connection pattern; however, when the framing elements were not blocked tension field forces resulted in significant damage to the chord studs. Details of the test program and general results are presented in this paper.     

Strength and stiffness determination of shear wall panels in cold-formed steel framing

Shear wall panels, as the one of the primary lateral load resisting elements, have been extensively used in lightweight framing of low- and mid-rise residential construction, particularly in seismic applications. In current practice, lateral strengths of shear wall panels with cold-formed steel framing are primarily determined by tests, owing to the lack of applicable analytical methods. Meanwhile, the use of numerical methods such as the finite element method has rarely been employed in the design practice to determine the lateral strength of shear wall panels due to the extensive amount of computational effort associated with the modelling. Presented in this paper is an analytical method to determine the ultimate lateral strength of the shear wall panel and its associated displacement. The method takes into account the factors that primarily affect the behaviour and the strength of the shear wall panel, such as material properties, geometrical dimensions and construction details. Lateral strengths obtained from the proposed method for shear wall panels with different sheathing materials and steel stud thicknesses, sizes and spacing of sheathing-to-stud fasteners were compared with those of recent experimental investigations. The comparison demonstrates that the predicted results are in good agreement with those of the tests. Therefore, it is recommended that the proposed method be used in engineering practice.     

Monotonic and cyclic loading tests for cold-formed steel wall frames sheathed with calcium silicate board

This research is concentrated on the structural strength and behavior of cold-formed steel wall frame sheathed with calcium silicate board under shear load. Test specimens with two different thicknesses of sheathing were assembled, 9 mm and 12 mm, with one-side or two-side of attachment. Monotonic shear and cyclic loading tests are conducted on wall specimens utilizing two C sections connected back-to-back to be as chord studs and calcium silicate board sheathing on the exterior. Based on the test results, detailed discussions on the strength, stiffness, energy absorption, ductility ratio, and failure mode of cold-formed steel wall specimens are given. It is noted that the failure mostly occurred at the bottom track of wall specimens due to the large deformation or tearing failure of track. The wall strength is not affected by the change of sheathing's thickness significantly, but wall frames attached with two-side calcium silicate board sheathing provide higher resisting strength and stiffness than those attached with one-side sheathing. In this study, test results are also used to compare with the previous study that single chord stud was used in the assembly of wall frame. In addition, the suggested response modification factor of the wall sheathed with calcium silicate board is proposed for design purpose.     

Efficiency reduction due to shear lag on bolted cold-formed steel angles

This work presents 66 new experimental tests carried out on cold-formed steel angles fastened with bolts and under tension. In order to calculate tension-members’ ultimate capacity, net-section failure is considered. The shear-lag phenomenon reduces net-section capacity. This reduction is computed through the reduction coefficient which is a function of two parameters: length of the connection and distance of the shear plane to the centroid of the cross-section. This article examines the reduction coefficient performance based upon the new tests and data available in the literature, comprising a total of 108 lab tests. A new expression for the net-section reduction coefficient is suggested.     

冷弯薄壁型钢混凝土剪力墙受剪性能试验研究

通过7个冷弯薄壁型钢混凝土(CTSRC)剪力墙的拟静力水平往复试验,研究了其破坏过程和破坏模式,分析了混凝土强度、剪跨比、轴压比、水平分布筋和竖向型钢量等参数对其受剪性能的影响。试验结果表明：随着水平配筋率、轴压比和混凝土强度的增加受剪承载力提高;随着剪跨比提高,墙体受剪承载力降低;轴压比增加可提高墙体刚度,推迟墙体裂缝的出现,但不利于墙体延性;增加水平配筋可使墙体峰值后的承载力保持稳定。研究表明：CTSRC剪力墙与传统钢筋混凝土剪力墙的破坏特征和受力性能不同,在水平力作用下将出现沿冷弯薄壁型钢的竖向裂缝,经历整体墙到分缝墙的演变,避免了脆性剪切破坏。通过合理设计,CTSRC剪力墙可实现正常使用阶段有较高的刚度、峰值后有较好的延性、破坏时仍具有较高的竖向承载能力的目标。     

Test of shear transfer enhancement in symmetric cold-formed steel-concrete composite beams

An experimental programme was conducted to study the strength and behaviour of a bent-up tab shear transfer enhancement. Sixty eight push-out test specimens of cold-formed steel lipped channel sections (CFS) embedded in concrete planks which make use of the new proposed shear transfer enhancement called bent-up triangular tab shear transfer (BTTST) were tested in this programme. This paper summarises the results of the experimental study and develops an expression in order to predict the innovative shear transfer enhancement mechanism, BTTST in a new type of precast composite beam comprising CFS embedded in a precast concrete plank. The results show that specimens employed with shear transfer enhancements increase the shear capacities of the specimens as compared to those relying only on a natural bond between cold-formed steel and concrete. In this investigation, BTTST provided better performance in terms of strength. Furthermore the effects of different angles and sizes for BTTST, different thickness for CFS and different strengths for concrete are also discussed. It is concluded that the proposed shear transfer enhancement has sufficient strength and is also feasible.     

冷弯型钢骨架墙体受剪承载力计算方法研究

为了获得冷弯型钢骨架墙体最大受剪承载力实用计算公式,提出了墙体在水平力作用下的两种可能破坏模式,即边立柱在抗拔连接件处的净截面破坏和墙体周边或墙板拼缝处大多数自攻螺钉连接破坏。根据墙体破坏模式提出了相应的最大受剪承载力计算模型,并结合试验数据和有限元结果,得到了单面覆石膏板墙体、单面覆OSB板墙体和单面覆带肋钢板墙体最大受剪承载力实用计算公式,公式计算结果同试验、有限元分析结果吻合较好。最后,给出了冷弯型钢骨架墙体受剪承载力实用计算公式应用算例,以供设计参考。     

Axial load capacity of cold-formed steel wall stud with sheathing

A cold-formed steel wall panel consists of a cold-formed steel frame and sheathing on one or two sides, the latter attached to the frame by self-driving screws. It is observed during tests that the axial behaviour of a wall stud in the panel is significantly different from that of an individual stud. This paper presents an analytical model for predicting the axial failure load of the wall stud with sheathing. The sheathing is simplified as continuous elastic support to the stud. The spring stiffness of the elastic support is calculated by analytical and finite element methods. The predicted results are compared with measurements from full-scale tests. For the range of parameters considered, it is found that: (a) the Poisson ratio of the sheathing material as well as screw spacing have negligibly small influence on panel failure load; (b) the elastic modulus of the sheathing material has a significant influence on the failure load, only if it is smaller than 1000 N/mm²; (c) although in general the thickness of sheathing affects the stud failure load, thinner sheathing may be used without changing the stud load capacity considerably; (d) stud spacing has moderate influence on stud failure load. The results presented in this paper can be used to guide practical wall panel designs.     

LQ550高强冷弯薄壁型钢组合墙体受剪性能试验研究

为研究OSB板和水泥纤维板作为LQ550高强冷弯薄壁型钢组合墙体结构面板时的受力性能,进行7个不同结构面板的LQ550高强冷弯薄壁型钢组合墙体试件的水平单调加载和低周反复加载试验研究,分析了组合墙体的受剪承载力、延性系数、耗能系数等。结果表明：面板拼缝是组合墙体的薄弱部位;在水平接缝处设置宽而完整钢衬板的墙体试件具有较高的受剪承载力和抗侧刚度;单面水泥纤维板单调加载时比低周反复加载时承载力提高约8.79%~12.27%,其受剪承载力较低,但屈服前试件基本完好;对于双面板墙体试件,无论在单调加载还是反复加载时,其承载力、抗侧刚度约为各单面板试件相应指标之和。低周反复加载试件的耗能系数基本接近。     

Inelastic performance of cold-formed steel strap braced walls

The inelastic performance of sixteen 2.44 m×2.44 m cold-formed steel strap braced walls was evaluated experimentally. The performance was affected by the holddown detail, which in many cases did not allow the test specimens to reach or maintain a yield capacity and severely diminished the overall system ductility. “Test-based” R_d×R_o values of 3.65, 2.11 and 1.72 indicate the low ductility levels, which were not adequate to warrant the use of a seismic response modification coefficient of R=4.0 in design. Capacity design of the SFRS elements must account for the overstrength of the strap material.     

冷弯薄壁型钢混凝土剪力墙受剪承载力计算模型

冷弯薄壁型钢混凝土剪力墙（CTSRC剪力墙）在水平地震作用下经历整截面墙体受力和分缝墙体受力两个阶段,破坏模式和受力机理与传统剪力墙不同。剪跨比小于2.0 的CTSRC剪力墙在峰值荷载前表现为整截面墙体的受力性能,峰值荷载时宏观竖向裂缝两侧混凝土发生滑移,墙体逐渐演变为分缝剪力墙,有较好的耗能能力。针对CTSRC剪力墙的受力特征,将钢筋混凝土剪力墙的软化拉压杆模型与混凝土界面直剪受力的软化拉压杆模型相结合,考虑竖向裂缝处短细斜裂缝间混凝土破坏引起的竖向裂缝两侧混凝土的滑移,建立了CTSRC剪力墙受剪承载力的拉压杆－滑移分析模型和计算方法,计算结果和试验结果吻合良好,表明拉压杆 滑移模型可以较好地反映剪跨比小于2的CTSRC剪力墙的受力机理,能够较准确地预测CTSRC剪力墙的受剪承载力。     

半刚性连接钢框架-钢板剪力墙结构抗震性能试验研究

通过对半刚性连接框架-钢板剪力墙结构在水平反复荷载作用下的试验研究,得到了结构的滞回曲线、延性指标、水平刚度、梁柱应变、转角及各关键部位的变形。从耗能能力、刚度退化、承载力、延性等方面分析该种结构的抗震性能和耗能机理;依据应力分布、梁柱转角研究半刚性节点与钢板剪力墙的相互影响效果;分析结构的内力转换和破坏模式。结果表明：该结构具有良好的延性和耗能性能;半刚性节点在反复荷载作用下没有明显变形,节点刚度退化小,框架和钢板剪力墙协同工作良好;梁柱半刚性连接弱化了结构的整体刚度,框架自身承担的水平荷载有限;破坏模式为内填钢板剪力墙局部撕裂,拉力带作用明显,钢框架柱脚及梁柱半刚性连接部位形成塑性铰,框架整体呈弯曲破坏模式。图12表4参10     

Large-scale test of symmetric cold-formed steel (CFS)-concrete composite beams with BTTST enhancement

A new connection device, based on bent-up tab shear transfer enhancement called bent-up triangular tab shear transfer (BTTST), has been studied through a symmetric cold-formed steel (CFS)-concrete composite beam subjected to a static bending test. BTTST provides an alternative connector system unique to CFS where CFS sections are usually thinner than hot-rolled sections and welding of headed-stud shear connectors is inapplicable. Coupled with the back-to-back arrangement of two CFS channels where symmetricity of the built-up section is restored, the resulting composite floor system has been proven to possess adequate strength and stiffness properties under static loads. The work has shown that the predicted values of the flexural capacities calculated using a new equation of shear capacity of BTTST agrees reasonably well with the experimental values.     

Behavior of steel-sheathed shear walls subjected to seismic and fire loads

A series of tests was conducted on six 2.7 m×3.7 m shear wall specimens consisting of cold-formed steel framing sheathed on one side with sheet steel adhered to gypsum board and on the opposite side with plain gypsum board. The specimens were subjected to various sequences of simulated seismic shear deformation and fire exposure to study the influence of multi-hazard interactions on the lateral load resistance of the walls. The test program was designed to complement a parallel effort at the University of California, San Diego to investigate a six-story building subjected to earthquakes and fires. The test results reported here indicate that the fire exposure caused a shift in the failure mode of the walls from local buckling of the sheet steel in cases without fire exposure, to global buckling of the sheet steel with an accompanying 35% reduction in lateral load capacity after the wall had been exposed to fire. This behavior appears to be predictable, which is encouraging from the standpoint of residual lateral load capacity under these severe multi-hazard actions.     

冷弯薄壁型钢组合墙体受剪性能研究综述

根据对冷弯薄壁型钢结构体系传力路径的分析,承受和传递水平、竖向荷载的组合墙体的受力性能对整个结构的抗震性能至关重要。按照从局部到整体的顺序,依次对国内外开展的墙体龙骨、墙面板连接件和组合墙体的抗震性能的研究进行综述。结合对国内外具有代表性的剪力墙受剪试验结果进行的统计分析,分别给出墙面板、墙面板连接件、钢龙骨框架、墙体高宽比、墙体开洞及加载类型对墙体受剪承载力的影响。部分墙体受剪试验结果与中国规范相应的设计参考值进行对比,指出按线性内插得到的由大间距连接件连接的墙体受剪承载力规范参考值趋保守。按照中国规范给出的抗力分项系数值进行可靠度计算,计算结果表明规范的设计参考值不能很好的符合目标可靠度为3.2的要求。按文献建议调整抗力分项系数后的计算结果与目标可靠度吻合良好,但应进行更多的研究寻求合理的抗力分项系数值。最后对该类结构体系抗震性能研究领域需要深入研究的问题提出了建议。     

高强冷弯型钢骨架墙体抗剪性能试验研究

对550MPaC型冷弯型钢立柱、550MPa带肋钢板和石膏板组成的高强冷弯型钢骨架墙体进行了16块足尺试件(宽2.4m,高3m)的抗剪试验研究。对带肋钢板+石膏板双面板、单面带肋钢板、单面石膏板和双面无板带交叉扁钢拉条支撑4类墙体试件进行了无竖向力水平单调加载、无竖向力水平低周反复加载和有竖向力水平低周反复加载的试验,得到了各类墙体试件的受剪承载力指标和位移延性系数μ等性能指标。试验结果表明:各类墙体单调加载试件抗剪强度均比反复加载试件高;单面石膏板墙体试件与0.8倍的单面带肋钢板墙体试件的承载力指标之和与双面板墙体试件承载力指标接近;双面无板带交叉扁钢拉条支撑墙体试件抗剪强度是双面板墙体试件的60%~67%;双面板墙体试件延性系数在1.731~2.384之间。     

冷弯薄壁型钢-钢板剪力墙抗震性能试验研究

为研究冷弯薄壁型钢-钢板剪力墙结构的抗震性能,对冷弯薄壁型钢边柱内置薄钢板剪力墙进行低周往复加载试验,对比不同边柱截面厚度及截面形式对其抗震性能的影响。试验中得到了冷弯薄壁型钢-钢板剪力墙的破坏形态、荷载-位移滞回曲线、骨架曲线、荷载及位移特征值,并对结构的破坏特征、延性、耗能能力、承载力及刚度退化进行分析。结果表明:冷弯薄壁型钢-钢板剪力墙具有良好的抗震性能;增加边柱截面厚度及选用帽形边柱均可提高剪力墙的承载力、刚度及耗能性能。计算3个试件受剪承载力设计值和弹性抗侧刚度,其值均高于常用冷弯薄壁组合墙体的;结合破坏特征提出冷弯薄壁型钢-钢板剪力墙3个受力阶段;边柱对剪力墙破坏起控制因素,工程设计中应保证边柱承载能力,宜采用"强边柱、弱钢板"的设计理念。