Impact tests and parametric impact studies on drive-in steel storage racks

Extensively used in the industry to store goods, steel storage racks are frequently subjected to accidental impact forces from operating forklift trucks. There is currently little understanding of the nature of these impact forces, leading to occasional catastrophic failures because of inadequate structural design. International racking design codes deal with impact but use an arbitrary value of impact force with no scientific justification. This paper focuses on an impact-sensitive type of storage rack, called “drive-in racks”. Contrary to classical “selective racks”, where pallets are stored on beams and where each single pallet is always accessible, “drive-in racks” allow the forklift truck to drive into the rack to store pallets on beam rails, one after the other, on the first-in, last-out principle. This type of design leads to slender uprights in the down-aisle direction, only restrained at the base and at the top. When subjected to an impact force, the bowing of the upright triggers progressive failure by allowing the pallets to drop through.This paper presents experimental results obtained from tests on a complete full-size drive-in rack structure subjected to the impact of a forklift truck. Parametric impact studies using finite element analysis are also presented. Factors affecting the sensitivity of drive-in racking structures to impact are investigated and conclusions are drawn about the parameters most significantly influencing the progressive collapse of this type of rack under impact.     

Bolted moment connections in drive-in and drive-through steel storage racks

The stability of steel storage racks, which are often unbraced, may depend solely on the pallet beam to upright connector and on the stiffness of the base plate to floor connection. This paper presents experimental results from cyclic tests performed on portal beam to upright bolted moment connections intended for cold-formed steel drive-in and drive-through storage racks. In storage racks, portal beams are typically connected to uprights by “tab connectors”, which are costly to manufacture and experience initial looseness. By simply bolting the portal beams to the uprights, bolted moment connections may represent a cost-effective alternative to “tab connectors”. A literature review shows that bolted moment connections between cold-formed steel members are economical and feasible. However, experimental results show a significant amount of looseness in the connection after an initial high moment-rotational stiffness. Being slender structures, storage racks are sensitive to the second-order P-Δ effect, and international racking specifications require the initial looseness of the tab connectors to be considered when analysing the stability of the rack in the down-aisle direction (sway motion). The non-linear cyclic behaviour of bolted moment connections is presented and explained herein. Based on finite element results, it is shown that, for drive-in and drive-through racks, the looseness in bolted moment connections can be ignored in ultimate limit states design. Finally, the paper concludes with proposing two methods, with different degree of complexity, for the design of drive-in and drive-through racks with bolted portal beam to upright bolted moment connections.     

组装式货架钢结构立柱性能研究现状

详细介绍了到目前为止,国内外有关货架钢结构立柱的性能研究,从立柱自身构造特点及边界条件两大方面分析了开孔开口冷弯薄壁立柱特有的力学性能和破坏模式等,强调了进一步研究的必要性。     

Determination of the base plate stiffness and strength of steel storage racks

This paper addresses the problem of determining the stiffness and strength of steel storage rack base plate assemblies. Base plate assemblies are usually bolted to an upright and to a concrete floor, and they are used to provide resistance against the flexural buckling of the upright and/or the overall down-aisle buckling of the frame. The semi-rigid stiffness is usually determined by means of a test of two pre-loaded uprights connected to a concrete block in a dual-actuator set-up. Guidance for conducting the test is provided in the European Standard EN 15512. However, several aspects of the test need clarification, notably the test set-up and the transducer arrangement for measuring the rotations of the base plate. This paper provides recommendations for how best to conduct the test, and proposes an alternative test method to that given in the EN 15512 Specification.The paper also identifies the contributions to the deformations of base plate assemblies, including the deformations of the supporting floor, the base plate assembly itself and the upright, and proposes simple expressions for calculating the stiffness associated with each contributing deformation where applicable. Furthermore, the paper proposes a deformation criterion for determining the ultimate design moment for base plate tests which do not attain a peak moment.     

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.     

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.     

Application of direct strength method to axially loaded perforated cold-formed steel studs: Longwave buckling

A study to develop methods of analyzing perforated, axially loaded, cold-formed steel studs using the provisions of the Direct Strength Method [3] was undertaken using the Finite Strip Method as the method for determining the elastic buckling stresses. Several different models were developed to represent the effect of the web perforations. The capacities predicted using the Direct Strength Method for the limit state of longwave buckling were compared to capacities calculated using the equations contained in the AISI Specification [3]. The limit states of local and distortional buckling are considered in a companion paper [12]. The validity of the results is discussed and recommendations are made for the use of the Direct Strength Method for these members.     

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.     

吕梁地区日光温室弧形钢架荷载分析

针对吕梁地区已修建的10 m跨度的弧形钢架砖墙型日光温室,结合我国最新的建筑结构荷载规范,确定了作用在弧形钢架上的各种荷载,重点计算了弧形钢架的自重、雪荷载、风荷载,并且根据日光温室的实际使用情况,抛开北风风压对日光温室的影响,确定了三种可能不利荷载组合。     

自复位钢框架钢板剪力墙性能化设计方法

基于“自复位”理念,提出了一种采用钢板剪力墙耗能的自复位钢框架钢板剪力墙结构,对其进行了受力机理分析,并给出了自复位钢框架钢板剪力墙的复位条件。依据GB 50011—2010《建筑抗震设计规范》设定了自复位钢框架钢板剪力墙基于性能的设计目标,基于性能目标提出了自复位钢框架钢板剪力墙的设计流程,从构件的实际受力状态出发对该设计方法进行了研究,并推导出构件的设计公式。以某传统钢框架为例,对其进行了由钢板剪力墙耗能的自复位结构边缘构件设计,并采用有限元软件ABAQUS对其中单榀单跨进行了Pushover分析。结果表明：当层间位移角达到2%时,结构的残余变形量控制在0.2%以内,主体结构边缘构件仍处于弹性工作状态,推覆过程中钢板墙耗散了大量能量;推覆结束后,结构余留少量残余变形,这主要是由于梁柱节点绕梁上下翼缘转动时梁上下翼缘角部受到挤压引起,可通过适当设置翼缘加强板减少甚至消除残余变形。     

An efficient method for computation of effective length factor of columns in a steel gabled frame with tapered members

The concept of effective length is the only available common method for column design without non-linear structural analysis. Researches conducted for determination of effective length of members are mainly related to a constant moment of inertia. In many investigations related to members with variable moment of inertia, finite element and approximation methods are used. In this article, a method for quick calculation of the effective length factor of columns in steel gabled frames with tapered members is proposed. The method is based on two-dimensionless design-oriented charts relating the critical load of columns to frame characteristics and boundary conditions. Since I-sections are usually used for gabled frames members, the variation of moment of inertia along the length of members (beams or columns) is approximated as a parabolic function. As is demonstrated in the Numerical studies, these calculations can yield, in a very efficient way, accurate results for gabled frames consisting of tapered elements.     

浅谈建筑物粘钢加固施工要点

结合工作经验,叙述了粘钢加固法的施工流程及操作要点,通过分析某工业厂房结构破损原因,针对其受损部位、受损程度分别提出不同的加固方案,经试验证明粘钢加固法对于厂房梁柱的加固是一种实用的加固方法。     

Behaviour,failure and DSM design of cold-formed steel beams: Influence of the load point of application

This work presents and discusses the results of an ongoing numerical investigation on the buckling, post-buckling, collapse and design of cold-formed steel beams subjected to non-uniform bending due to transverse loadings acting away from the shear centre (either at the top or bottom flange). These results consist of (i) elastic buckling loads and modes, obtained through analyses based on Generalised Beam Theory (GBT), and (ii) elastic–plastic equilibrium paths and collapse loads, yielded by Ansys geometrically and materially non-linear shell finite element analyses. The numerical ultimate strength values are compared with their estimates provided by the current Direct Strength Method (DSM) strength curves and, on the basis of this comparison, it is possible to assess the merits of the DSM approach to design beams subjected to transverse loadings acting away from the shear centre – moreover, novel features that may improve the performance of this approach are identified.     

轻型门式刚架结构设计研究

说明了轻型门式刚架的主要特点,简要介绍了目前门式刚架应用的状况,总结了门式刚架结构形式,对其材料的选用,梁、柱、檩条设计及其荷载计算、侧位移计算进行了详细的研究和分析,以便于轻型门式刚架的推广。     

基于MC随机有限元法高层钢框架结构抗风可靠性分析

从可靠度理论出发,基于概率理论探讨蒙特卡罗(Monte Carlo)随机有限元法的基本原理,采用有限元分析软件AN-SYS提供的APDL语言,将结构分析与其PDS模块的统计分析能力相结合,编写基于拉丁超立方抽样法的蒙特卡罗随机有限元法程序,对某高层钢框架结构工程进行风载作用下的可靠性分析。计算结果表明,本文采用的方法具有较高的计算精度和效率,适于解决结构可靠性分析问题。     

LNG储罐预应力钢绞线束伸长值计算方法探讨

通过对16万m3LNG储罐预应力钢绞线束的计算,详细介绍了国外预应力钢束理论伸长值的分段计算方法,并经过与国内算法比较,得出了精确计算预应力钢束伸长值对预应力施工控制的重要性。     

Review: The Direct Strength Method of cold-formed steel member design

The objective of this paper is to provide a review of the development and current progress in the Direct Strength Method for cold-formed steel member design. A brief comparison of the Direct Strength Method with the Effective Width Method is provided. The advantage of methods that integrate computational stability analysis into the design process, such as the Direct Strength Method, is highlighted. The development of the Direct Strength Method for beams and columns, including the reliability of the method is provided. Current and ongoing research to extend the Direct Strength Method is reviewed and complete references provided. The Direct Strength Method was formally adopted in North American cold-formed steel design specifications in 2004 as an alternative to the traditional Effective Width Method. The appendices of this paper provide the Direct Strength Method equations for the design of columns and beams as developed by the author and adopted in the North American Specification.     

钢管混凝土柱极限承载力的统一算法研究

介绍国内外各设计规程关于钢管混凝土柱极限承载力的计算方法并进行比较分析。钢管混凝土单肢柱、哑铃形柱、格构柱的受力性能具有共性,即长细比和偏心率对柱面内整体极限承载力的影响基本上是独立的。基于上述规律,在分析评价国内外各规程计算方法的基础上,对钢管混凝土柱极限承载力的统一算法开展研究。分别进行钢管混凝土单肢柱、哑铃形柱、格构柱的算例分析,研究结果表明,计算值与试验值吻合良好。最后提出适合工程应用的钢管混凝土柱极限承载力的统一算法,为钢管混凝土计算理论的进一步完善和规程修订提供参考。     

Experimental and numerical investigations of cold-formed stainless steel tubular sections subjected to concentrated bearing load

Experimental and numerical investigations of cold-formed stainless steel square and rectangular hollow sections subjected to concentrated bearing load are presented in this paper. A total of 124 data are presented that include 64 test results and 60 numerical results. The tests were performed on austenitic stainless steel type 304, high strength austenitic and duplex material. The measured web slenderness value of the tubular sections ranged from comparatively stocky webs of 6.2 to relatively more slender webs of 61.4. The tests were carried out under end and interior loading conditions. A non-linear finite element model is developed and verified against experimental results. Geometric and material non-linearities were included in the finite element model. The material nonlinearity of the flat and corner portions of the specimen sections were carefully incorporated in the model. It was shown that the finite element model closely predicted the web crippling strengths and failure modes of the tested specimens. Hence, the model was used for an extensive parametric study of cross-section geometries, and the web slenderness value ranged from 52.0 to 206.7. The test results and the web crippling strengths predicted from the finite element analysis were compared with the design strengths obtained using the American, Australian/New Zealand and European specifications for stainless steel structures. A unified web crippling equation with new coefficients for cold-formed stainless steel square and rectangular hollow sections subjected to concentrated bearing load is proposed. It is demonstrated that the proposed web crippling equation is safe and reliable using reliability analysis.     

Effective Width Method for determining distortional buckling strength of cold-formed steel flexural C and Z sections

This paper proposes a design method, based on the Effective Width Method, for determining the nominal distortional buckling strength of typical cold-formed steel C and Z sections subjected to bending. The method can be integrated into the classic effective width design provisions specified in AISI S100, and it allows the conventional design approach to cover more comprehensive limit states. The proposed method is calibrated by the flexural distortional buckling strength predicted by the Direct Strength Method. Comparison with experimental results indicates that the proposed method yields reasonable predictions for the flexural distortional buckling strength of industrial standard C and Z sections. The method offers the same level of accuracy and reliability as the Direct Strength Method.