Optimum design of cold-formed steel beams subject to bending, shear and web crippling

Recently, cold-formed steel (CFS) members have become more prevalent within the construction industry. CFS beams can be optimised to increase their load carrying capacity. In this research, shape optimisation method is developed to obtain high structural resistance of cold-formed steel beams by taking into account the bending, shear and web crippling actions. First, the flexural strengths of the sections are determined based on the effective width method adopted in EC3, while the optimisation process is performed using the Particle Swarm Optimisation (PSO). Five different CFS channel cross-section are considered in the optimisation process. The flexural strengths of the optimised sections are then verified using detailed nonlinear finite element analysis. The results indicated that the optimised CFS beams provide a bending capacity which is up to 50% higher than the conventional CFS channel sections with the same amount of material. Shear, web crippling behaviours of five optimisedCFS beams were then investigated. Finally, innovative optimised CFS beam was proposed for lightweight forms of buildings and modular building systems to obtain high structural resistance

Numerical studies of steel channels with staggered slotted perforations subject to combined bending and shear actions

Cold-formed steel studs and purlins with staggered slotted perforations in webs are used in construction to improve thermal performance of the profiles and energy efficiency of structures. On the other hand, the web perforations adversely affect structural performance of the members, especially their shear, bending and combined bending and shear strengths. Relatively little research has been reported on this subject despite its importance. Many research studies have been carried out to evaluate the combined bending and shear behaviour of conventional cold-formed channel beams. To date, however, no investigation has been conducted into the strength of cold-formed steel channels with staggered slotted perforations under combined bending and shear actions. Finite element models of cold-formed steel channels with staggered slotted perforations were developed to simulate their combined bending and shear behaviour and strength. They were then validated by comparing the results with available experimental test results and used in a detailed parametric study. This paper presents the details of the numerical studies of cold-formed steel channels with staggered slotted perforations and the results

Barriers to the Effective Adhesion of High-Density Hardwood Timbers for Glue-Laminated Beams in Australia

A number of international timbers of high commercial importance are extremely difficult to glue, which is significantly hindering access to global market opportunities for engineered wood products, especially for heavily demanded structural products. Some particularly problematic timbers in Australia are the dominant commercial hardwood species, including spotted gum (Corymbia spp.) and Darwin stringybark (Eucalyptus tetrodonta). These species are renowned for their very high mechanical properties, natural durability and attractive aesthetic appeal. However, they are notoriously difficult to glue, especially for sawn laminate-based engineered wood products, such as structural glue-laminated beams. Despite considerable effort and testing of diverse internationally established best-practice approaches to improve adhesion, glue-laminated beam samples of these timbers still frequently fail to meet the requirements of the relevant standard, mainly due to excessive glue line delamination. This paper discusses the key barriers to effective adhesion of these high-density timbers and particularly emphasises the necessity of achieving greater adhesive penetration. Greater adhesive penetration is required to enhance mechanical interlocking, entanglement and molecular interactions between the adhesive and the wood to achieve stronger and more durable bonds. Potential solutions to enhance adhesive penetration, as well as to improve gluability in general, are discussed in terms of their likelihood to satisfactorily prevent delamination and the potential to be applied at an industrial scale. This new fundamental understanding will assist the development of solutions, allowing industry to commercialise newly engineered wood products made from high-density timbers

Shear Capacity of Cold-Formed Stainless Steel Beam with Elliptical Web Openings: Numerical Analyses

Cold-formed stainless-steel sections are increasingly being used in the construction industry, for both architectural and structural applications. The excellent combination of mechan-ical properties and corrosion resistance makes stainless steel a very good material for structural applications. Due to the lack of design rules for stainless steel, the design rules for carbon steel have been generally adopted in the stainless-steel design. However, the prominent non-linear be-haviour of stainless steel, which is the main difference with carbon steel, makes the standards for carbon steel not always accurate in the stainless-steel design. The provision of web openings at appropriate locations in such sections is also important to avoid cutting holes at an inappropriate location during the implementation stage. The type of section and the shape of opening were primarily chosen based on the application. The scope of this study is however limited to stainless steel Lipped Channel Beams (LCB) with elliptical web openings. The provision of openings in web affects the shear behaviour and shear capacity of LCB sections, but only very limited re-searches have been conducted so far. Hence, a numerical analysis was undertaken to investigate the shear behaviour and strength of cold-formed stainless steel LCB section with elliptical web openings. Finite element models of cold-formed ferritic stainless steel LCB with centered web openings were developed under the simply supported loading condition. They were validated with currently available shear test results and a detailed parametric study was undertaken to develop an extensive shear strength database. Numerical results showed that the currently available reduc-tion factor equations of circular web opening are either conservative or unsafe to use for the non-circular openings. Hence, numerical results were then used to develop a reduction factor to the shear capacities of cold-formed stainless steel LCBs with elliptical web opening

Web Crippling Behaviour of Cold-Formed Stainless Steel LCB with Non-Circular Web Opening Under ETF Load Case

Cold-formed stainless steel beams are often subjected to concentrated, localised loads or reactions. These concentrated forces acting on flexural members cause localised bearing failures. This bearing failure, generally known as web crippling, is one of the critical failure modes of cold-formed stainless steel members. The provision of web opening at an appropriate location in such section is also important to avoid holes being cut at an inappropriate location during the construction stage. Different shapes and sizes of web openings are made on the web panel of such sections to facilitate building services. The scope of this study is however limited to stainless steel Lipped Channel Beams (LCB) with square and rectangular web openings. Presence of opening in the web directly influences the web crippling behaviour and also considerably reduces web crippling strength of stainless steel LCBs, but very limited researches have been undertaken to predict the web crippling capacity of stainless steel LCBs. Hence, a detailed finite element analysis was undertaken to investigate the web crippling behaviour and web crippling strength of cold-formed stainless steel LCBs with centered non-circular web opening under the exterior-two-flange (ETF) loading condition. Finite element models of cold-formed stainless steel beams with web opening under web crippling actions were developed to investigate the ultimate web crippling strength behaviour of cold-formed stainless steel beams with web opening including their elastic and post-buckling characteristics. They were validated with currently available web crippling test results. A detailed parametric study based on validated finite element model was undertaken to develop an extensive web crippling strength database and were then used to develop the new design equations for the reduction factor of web crippling capacities of cold-formed stainless steel beams with non-circular (i.e. Square or rectangle) web opening. Appropriate web crippling design rules within the framework of European and International Standards were developed based on obtained FEA results

Flexural Behaviour of optimised cold-formed steel beams with sleeve stiffened web openings

CFS beams are often provided with web openings to accommodate building services. However, the area reduction in the web affects their load-bearing capacities. The reduction of bending capacity can be regained through providing suitable stiffeners in the vicinity of the web openings and through providing the web openings to the optimised CFS beams. Many research studies have been conducted for the former but no research studies have been reported for the latter. This paper presents an investigation on providing reinforced web openings to optimised CFS beams to restore the original flexural capacity. A computational analysis was carried out. The Finite Element (FE) elements were validated against experimental data from the literature and then used in conducting detailed parametric studies (80 FE models). The influence of the rectangular openings with four different sizes (hole height-to-web depth ratios: 0.2, 0.4, 0.6 and 0.8) and four different sleeve stiffening lengths (5, 10, 15 and 20 mm) on the bending capacity subject to distortional buckling was investigated in the parametric study. The results indicated that introducing web openings to the optmised CFS along with sleeve stiffening arrangement is a satisfactory approach to restore the original bending capacity. In addition, the optimum sleeve length was found and updated direct strength-based design equations are proposed to predict the bending capacity of the CFS beams with sleeve stiffened rectangular web openings subject to distortional buckling

Optimised and slotted cold-formed steel channels: a solution for modular buidling systems

The steel construction industry has recently put a lot of effort to better understand Modular Building Systems (MBS) and replaced, where possible, conventional construction methods. MBS claims promising advantages including speed of erection, improved quality, reduced cost, and flexibility. Therefore, research efforts are tuned to the structural, social, and safety evaluations of MBS while it is recognised that there are challenges associated with their use, yet to be addressed. The main challenges are improving structural, fire, and energy performances, need for lightweight materials, more access space during renovation and transportation difficulties. This paper investigates how the use of optimised Cold-Formed Steel (CFS) members with slotted web can address such challenges. The optimisation was performed using Particle Swarm Optimisation (PSO) method and subsequently, slotted perforations were added to enhance the structural, fire and energy performances, respectively. Finite Element (FE) analysis was employed to assess the performance of optimised innovative CFS beams with slotted perforations. As a result, the optimisation and FE analyses resulted in a 30-65% of flexural capacity enhancements along with notable performance improvement in fire and energy performances over conventional Lipped Channel Beam (LCB). Using such optimised innovative sections a conceptual design of a corner-post module was also developed. Hence, the optimised CFS channels with slotted perforations would be a convenient tool to overcome the reported challenges related to MBS, result in more cost-effective and efficient building solutions

Development of Affordable Steel-Framed Modular Buildings for Emergency Situations (Covid-19)

This paper presents the development of novel affordable steel-framed modular units for construction with enhanced overall (healthcare, structural, fire, and lightweight) performance, which ideally suits for emergency response situation, such as current covid-19 pandemic. The nature of quick response and well-prepared strategies are essential to cope with the demand of quicker construction for emergency response structures and if similar situation continues or arises in the future as well. Off-site oriented modular construction is ideal to provide these requirements at very short notice for emergencies. Modular units made of steel components are a leading choice due to the exceptional strength and rigidity for lightweight construction. A new weight optimisation procedure was developed for Cold-Formed Steel (CFS) joists in varying shapes of and results show that weight for per unit length of the joists can be reduced up to 24% without compromising structural capacity. This was verified with validated Finite Element (FE) models. In order to improve the faster jointing method, a novel cut and bend intra-module connection was also introduced. In addition, strap bracing is used for the lateral stability of steel-framed modular buildings. Modular breathing panels are proposed to be employed in corner post modules as sidewalls to improve the indoor air quality and reduce the spread of disease. Based on the comprehensive assessment and numerical results conceptual design of performance improved steel-framed corner post modular unit was proposed to offer short-to-medium (in response to emergencies), as well as long-term solutions for the construction industry

Web crippling behaviour of cold-formed high-strength steel unlipped channel beams under End-One-Flange load case

High-strength Cold-Formed Steel (CFS) members are widely adopted as structural members in building structures due to its higher ultimate capacity. The flexural members are often subjected to concentrated transverse loads which may leads to buckling instabilities including web crippling. However, there is no appropriate design rules and studies are available to estimate the web crippling strength of high-strength CFS members. Hence, this paper presents a detailed numerical investigation on high-strength CFS unlipped channel sections subjected to End-One-Flange (EOF) loading condition with nominal yield strengths of 700 MPa, 900 MPa and 1000 MPa. For numerical simulation study, non-linear Finite Element (FE) models were developed and validated with the experimental results followed by an extensive parametric study using ABAQUS. In total, 243 FE models were developed with different geometric and material parameters including section thickness, material strength, web slenderness ratio, inside bent radius to thickness ratio and bearing length to thickness ratio. The ultimate web crippling strength results were compared with the available design guidelines to check their suitability and accuracy in terms of strength prediction. Then, new design rules to predict the web crippling capacity of high-strength CFS unlipped channel section under EOF condition based on unified and Direct Strength Method (DSM) approaches were proposed

Web crippling behaviour and design of aluminium lipped channel sections under two flange loading conditions

Aluminium alloys have recently drawn significant attention in structural applications due to its outstanding mechanical characteristics. Thin-walled members fabricated by aluminium alloys can be more competitive in construction industries than the conventional cold-formed steel sections, particularly in areas with high humidity and severe environmental conditions. Nevertheless, they are more vulnerable to various types of instability due to their relatively low elastic modulus compared to steel. Applying high concentrated load transversely on thin-walled members can cause critical damage to the web of the cross section called web crippling. Although a large number of studies has been performed to investigate the web crippling mechanisms on different types of sections, the existing studies are primarily of the empirical nature and thus merits further investigations. To fill the research gap, this study was thus performed based on our previously conducted experimental work to further comprehend the web crippling phenomenon of the roll-formed aluminium lipped channel (ALC) sections under the loading conditions of end-two-flange (ETF) and interior-two-flange (ITF). This was done through numerical investigations followed by a parametric study which are reported herein in details. A wide range of roll-formed ALC sections covering web slenderness ratios ranged from 28 to 130, inside bent radii ranging between 2 mm and 8 mm, bearing lengths ranged from 50 mm to 150 mm, and three sheeting aluminium alloy grades (5052-H32, 5052-H36 and 5052-H38) were considered in the parametric study. The acquired web crippling database was then used to assess the consistency and accuracy of the current design rules used in practice. It was found that the web crippling capacity determined by the current international specifications are unsafe and unreliable, whereas the predictions of the recently proposed equations agree very well. Furthermore, a Direct Strength Method (DSM)-based capacity prediction approach was proposed and then validated against the web crippling database acquired here as well as the experimental and numerical data for cold-formed steel lipped channel sections used in the literature