A strain criterion for pull-through failures in crest-fixed steel claddings

Crest-fixed steel claddings made of thin, high strength steel often suffer from local pull-through failures at their screw connections during high wind events such as storms and hurricanes. Adequate design provisions are not available for these cladding systems except for the expensive testing provisions. Since the local pull-through failures in the less ductile steel claddings are initiated by transverse splitting at the fastener holes, numerical studies have not been able to determine the pull-through failure loads. Numerical studies could be used if a reliable splitting criterion is available. Therefore, a series of two-span cladding and small scale tests was conducted on a range of crest-fixed steel cladding systems under simulated wind uplift loads. The strains in the sheeting around the critical central support screw fastener holes were measured until the pull-through failure occurred. This paper presents the details of the experimental investigation and the results including a strain criterion for the local pull-through failures in crest-fixed steel claddings.     

Safety against formation of through cracks of profiled fibre-reinforced cement sheets for roofing

Loads due to wind, snow or traffic on a roof determine the requirements to the strength and stiffness properties of profiled sheets for roofing. Apart from these loads, locked-in stresses can occur due to differences in temperature and moisture strains in the profiled sheets and the wooden laths supporting the sheets. These tensile and compressive stresses are induced in the sheets if they are firmly fastened to the laths with fastening screws.The purpose of this investigation was to analyse the safety of the profiled sheets in transmitting these loads without the formation of through cracks.The analysis is based on an experimental and a theoretical investigation of the strength and stiffness properties of unexposed profiled fibre-reinforced cement sheets and of sheets that had been exposed on a roof in three years.     

Wind uplift strength of trapezoidal steel cladding with closely spaced ribs

When crest-fixed thin trapezoidal steel cladding with closely spaced ribs is subjected to wind uplift/suction forces, local dimpling or pull-through failures occur prematurely at their screw connections because of the large stress concentrations in the cladding under the screw heads. Currently, the design of crest-fixed profiled steel cladding is mainly based on time consuming and expensive laboratory tests due to the lack of adequate design rules. In this research, a shell finite element model of crest-fixed trapezoidal steel cladding with closely spaced ribs was developed and validated using experimental results. The finite element model included a recently developed splitting criterion and other advanced features including geometric imperfections, buckling effects, contact modelling and hyperelastic behaviour of neoprene washers, and was used in a detailed parametric study to develop suitable design formulae for local failures. This paper presents the details of the finite element analyses, large scale experiments and their results including the new wind uplift design strength formulae for trapezoidal steel cladding with closely spaced ribs. The new design formulae can be used to achieve both safe and optimised solutions.     

Schubsteifigkeit zweiseitig gelagerter Stahltrapezbleche

Shear stiffness of trapezoidal steel sheets with two edges fastened. Profiled sheeting is often fastened only at the two edges which are normal to the span of the profiles according to its uniaxial load bearing behaviour for transverse loading and due to high effort in achieving all‐sided fastening. According to available design codes it is not possible to use the shear stiffness of this kind of diaphragms to stabilise beams against lateral torsional buckling. Therefore the effect of unsupported edges parallel to the span is investigated numerically and experimentally. This nonlinear investigation includes the flexibility of the fasteners. The numerical results agree well with the test results up to failure load. A knock‐down‐factor depending upon the a/b‐ratio and the shear stiffness of the diaphragm supported along 4 edges is obtained from the parametric investigations. The application of this knock‐down‐factor to the shear stiffness of the diaphragm supported along 4 edges gives that for the diaphragm supported along 2 edges. All this applies for the design load according to [6]. The ultimate loads of the diaphragms are much higher than these design loads.     

Response of pierced fixed corrugated steel roofing systems subjected to wind loads

The low-cycle fatigue response of corrugated metal roof cladding to fluctuating wind loads was studied by subjecting cladding specimens to a series of static, cyclic and simulated “real” cyclonic wind loads using a Pressure Loading Actuator (PLA), and measuring fastener response using a x–y–z load cell. The overall performance of cladding including crack initiation, propagation and patterns, and cycles to failure was found to be similar to previous tests that used line-loads to simulate wind pressure. The reaction at a fastener to spatially varying pressures was assessed by analysing the influence coefficients, to show that it is predominantly influenced by local loads acting along the screwed crest. In addition, the response of roofing specimens subjected to fluctuating cyclonic wind pressures replicated failures observed in the field. The fastener response varied with the load level and the response spectrum followed the wind load spectrum up to 5 Hz even with deformation and cracking of the cladding showing that these higher frequency wind “load cycles” were transferred into the supporting structure via the fastener.     

自攻螺钉、拉铆钉连接的受力蒙皮抗剪性能试验研究

本文对111个自攻螺钉、拉铆钉连接及14块由这种连接件连接的蒙皮板进行了抗剪性能试验,并分析了其抗剪强度、抗剪刚度、工作特点、破坏模式以及变更连接件布置方式、压型板跨度对受力蒙皮性能的影响。试验结果与国外的试验和理论分析结果符合较好。文中还提出了将压型钢板等效为正交各向异性板,用有限元法分析蒙皮的抗剪性能,所得蒙皮连接件内力分布规律,有助于进一步研究建立我国的蒙皮设计计算方法。     

基于ANSYS的自攻螺钉波峰连接的抗剪性能有限元分析

为了满足防水要求,目前许多轻钢结构的屋面体系采用在压型钢板波峰处与构件连接的形式。由于波峰连接形式中,压型钢板和檩条不是紧密接触,因此比波谷连接形式的受力情况更加复杂。本文利用ANSYS程序,采用实体建模,并引入接触非线性,对自攻螺钉波峰连接的抗剪性能进行有限元模拟分析,并与试验结果进行对比分析。分析结果表明:有限元模型可以精细模拟出真实试件的变形和荷载位移曲线的走势,与试验结果拟合很好,应力分布规律也符合其变形和破坏模式。因此,此有限元模型可以作为替代试验分析的理想模型。     

W-600压型钢板受力蒙皮用于工业厂房的抗剪性能

本文结合工程实例,进行了高波压型板屋面蒙皮作用的试验研究;并首次把蒙皮自身刚度和屋面横向支撑刚度进行了比较。高波压型板屋面具有显著的整体蒙皮效应,板侧连接件和高波板下的承托支架对蒙皮横向刚度的提高起有利影响。     

新型墙面压型钢板系统承载力试验研究和设计

对新型墙面压型钢板HV-156系统进行了足尺的承载力试验分析,试验结果表明,同一板型在相同构造条件下,风吸力作用下系统的承载力低于风压力作用,即风吸力是新型墙面压型钢板设计的控制因素;破坏形式是屋面板出现局部屈曲,针对试验结果提出了新型墙面压型钢板系统所能承受的基本风压及适用地区。     

A novel approach to estimate the wind uplift resistance of roofing systems

Roof wind design consist of three parts: determination of wind loads, evaluation of wind uplift resistance and correlating the resistance with the design load such that the resistance is higher than the load requirement. Wind uplift resistance of a system with its respective components is evaluated in laboratory testing. This paper presents a novel approach to estimate wind uplift resistance when components are substituted during field application. Wind dynamics, on a mechanically attached single-ply roofing assembly, lift the membrane and cause fluttering, introducing stresses at the attachment locations. In such assemblies, the fastener–deck interface is a critical design factor. First, by taking steel deck as a component this paper systematically characterizes the various steel decks that are commonly used in low slope application. Second component, namely the fasteners and its engagement strength with deck have been quantified for variations of its design, size and sources. Based on this component characterization, fastener pullout resistance (FPR) is identified as a verification factor for system wind resistance estimation. When variations occur in the fastener–deck interface between the proposed and the existing configurations, the present research through case studies has proved that: “as long as the FPR of the proposed configuration is higher than the existing configuration then wind uplift ratings can be maintained”. This is valid as long as both the configurations have all the remaining roofing components similar with comparable layout. Based on this verification, the study recommends that the testing lab should report the FPR along with the wind uplift resistance such that FPR can be used as a verification factor to accept design/field alternatives.     

Load carrying capacity enhancement of cold formed steel walls using shotcreted steel sheets

Recently worldwide cold formed steel buildings are recognized as viable alternatives to reinforced concrete buildings especially in seismic areas. This is because they are lightweight (easy to handle), fast constructed, energy efficient (green houses), economical, dimensionally stable and they do not need skilled worker. Under vertical loading the design principles of these buildings are well established and codified, however, under lateral loadings such as wind and earthquake loads efficiently design is needed. In this paper a new sheathing technique uses shotcreted ribbed steel sheets is proposed to improve the stability and increase the lateral load carrying capacities of the CFS walls in order to withstand earthquake and wind loads safely. The idea is to sheath the outer side of CFS structure external walls with thin ribbed steel sheets, then shotcreted the sheets with cement or gypsum mortars. To test the concept full size wall specimens were prepared in the laboratory and tested under monotonic vertical and lateral loads. Some of the specimens were sheathed with the traditional fiber cement boards or gypsum boards with mat reinforcement, while the others were sheathed with the proposed technique. Test results indicates that the lateral load carrying capacities of the walls sheathed with the proposed technique increases by about two times compared with the walls sheathed with traditional boards. And under ultimate loads they fail in local failure modes rather than overall buckling failure modes which commonly occur in the walls sheathed with traditional boards.     

Wind load resistance of modified bituminous roofing systems

Wind effects on roofing systems are dynamic, because of wind's fluctuation in time and space. Therefore a dynamic means of evaluating roofing systems is beneficial for identifying the component in a roofing system that has the weakest resistance against wind uplift forces. The Special Interest Group for Dynamic Evaluation of Roofing Systems (SIGDERS) commissioned a unique North American roofing facility, which has been used to evaluate a mechanically fastened modified bituminous membrane roof system under three different test methods: the Factory Mutual FM-4470 static test standard, the UEAtc (European Union of Agreement) procedure, and the SIGDERS-developed dynamic load cycle. Comparison of the results of these tests shows that UEAtc and SIGDERS tests produce failure modes similar to those observed in the field. The SIGDERS load cycle was completed in much less time than the UEAtc procedure.     

多跨连续压型钢板承载力的近似计算

提出了一个估算多跨连续压型钢板极限承载力的近似方法,即拟简单塑性铰方法。该方法考虑了连续压型钢板中的弯矩重分布,能够较为准确地估算多跨连续压型钢板的承载力。与已有文献中的试验相比,该方法估算的承载力是偏于安全的。由该法还得到了估算这种压型钢板在均布荷载下的承载力的显式,便于实际应用。     

Investigation of thermally-induced loads in modified bituminous roofing membranes

When exposed to various thermal conditions, installed roofing membrane experiences dimensional change, which creates induced, loads on the membrane material. These loads can cause a number of undesirable effects such as the membrane separating away from the parapet wall, seam components splitting, membrane tear at the vicinity of fasteners and membrane slag causing blistering. This paper deals with two kinds of thermally-induced loads, namely, reversible thermal expansion/contraction and irreversible stress releasing. The mechanisms for each type of induced load have been explored in detail on two membrane types of different internal structure. Thermal conditions are configured in the experiments to simulate typical Canadian summer and winter temperatures on a black roofing membrane surface. This study also explores the role of the membrane's length and pre-loading on the induced loads. Based on limited data, some practical recommendations are given, such as regarding the influence of the induced loads in the membrane and on the performance integrity of the roofing assembly constructions when subjected to various exposure conditions.     

受压轻型钢-加气混凝土-钢组合墙体的结构性能

由试验结果和分析结果介绍了一种由2层薄壁钢板中夹轻质加气混凝土(LFC)组成的墙体结构在轴向压力作用下的结构性能。试验中的试件尺寸为400mm×400mm×100mm,共制作了2组共12个试件。这些试件有6个不同的参数:不同钢板厚(0.4mm和0.8mm),三种边界条件。LFC的密度为1000kg/m3。试验结果包括破坏模式、最大荷载和沿垂直于力作用方向的应变反应。在分析中,假定钢板与LFC不产生相对滑移,并且LFC能有效阻止钢板的向内屈曲。对钢板运用了屈曲后有效宽度的方法计算试件的承载能力并与试验结果进行了对比。研究发现结合Uy和Bradford的板局部屈曲系数与Liang和Uy的有效宽度方程的计算结果与试验结果能良好地吻合。最后,对这种新型组合墙体在低层建筑中的适用性和局限性作了可行性研究。     

Mechanics and test study of flexible membranes ballooning in three dimensions

Numerous enclosure wall systems employ membranes that are not fully adhered, common examples being mechanically attached housewraps in screen-type exterior wall systems. Many roofing systems also incorporate membranes that are not fully adhered such as mechanically fastened single-ply membranes. Under a negative air pressure differential caused by wind suction, these wall and roof membranes can deform or balloon. Ballooning of the membrane affects many aspects of its performance. For instance, it changes the volume of the air chamber in screen-type wall systems and therefore, affects both the extent of screen pressure moderation and the nature of ventilation within the wall. In case of the single-ply roofing membrane, excessive ballooning can tear or rupture the membrane at the mechanical fastener location and therefore fail the membrane as the primary waterproofing component in the roofing system. This paper develops the structural mechanics for flexible membranes ballooning in three dimensions under a negative air pressure differential. The governing differential equation is derived and solved numerically. A second-order paraboloid of revolution is assumed to describe the ballooning shape. A series of physical tests were conducted to confirm that the ballooning shape follows the second-order paraboloid of revolution and compare the model predict with the test data.     

金属蒙皮板剪切性能的试验及有限元分析

结合蒙皮板在实际工程的做法,对压型钢板采用自攻螺丝连接的受力蒙皮进行剪切性能试验。通过对蒙皮的破坏模式和极限抗剪承载力的分析,对板型、檩条间距对蒙皮抗剪性能的影响进行研究。并采用ANSYS对蒙皮板进行有限元分析,考虑几何大变形、连接件的滑移等非线性因素。将试验数据与有限元结果进行比较,研究结果表明,采用ANSYS分析受力蒙皮是可行的,可以用有限元方法来代替大量重复性试验。     

Buckling behavior of cold-formed zed-purlins partially restrained by steel sheeting

This paper presents a study on the buckling behaviour of purlin-sheeting systems under wind uplift loading. The restraint provided by the sheeting to the purlin is modeled by using two springs representing the translational and rotational restraints. The analysis is performed using finite strip methods in which the pre-buckling stress is calculated based on the same model used for the buckling analysis rather than taken as the ‘pure bending’ stress. The results obtained from this study show that, for both local and distortional buckling, the restraints have significant influence on the critical loads through their influence on the pre-buckling stress rather than directly on the buckling modes. While for lateral-torsional buckling, the influence of the restraints on the critical loads is mainly due to their influence on the buckling modes rather than the pre-buckling stress.     

Structural performance of lightweight steel-foamed concrete–steel composite walling system under compression

This paper presents the results of an experimental and analytical investigation on the structural behaviour of a composite panel system consisting of two outer skins of profiled thin-walled steel plates with lightweight foamed concrete (LFC) core under axial compression. The gross dimensions of the test specimens were 400 mm×400 mm×100 mm. A total of 12 tests were carried out, composed of two duplicates of 6 variants which were distinguished by two steel sheeting thicknesses (0.4 mm and 0.8 mm) and three edge conditions of the sheeting. The density of LFC was 1000 kg/m³. Experimental results include failure modes, maximum loads and load-vertical strain responses. In analysis, full bond between the steel sheets and the concrete core was assumed and the LFC was considered effective in restraining inward buckling of the steel sheets. Using the effective width method for the steel sheets, the load carrying capacities of the test specimens were calculated and compared with the experimental results. It was found that a combination of the Uy and Bradford plate local buckling coefficients with the Liang and Uy effective width formulation produced calculation results in good agreement with the experimental results. Finally, a feasibility study was undertaken to demonstrate the applicability and limit of this new composite walling system in low rise construction.     

压型金属板屋面雨水排水设计应注意的问题

在厂房屋面设计中,对雨水排水设计重视不够,是造成屋面渗漏的重要原因之一。强调在屋面设计中应“排”与“防”并重,综合考虑,并提出压型金属板屋面雨水排水设计应注意的若干问题。