Cold-formed Steel Structural Systems Research Articles

A critical review of cold-formed steel seismic resistant systems: Recent developments, challenges and future directions

Cold-formed steel (CFS) systems have seen an increased application in the past few decades, especially in the construction of low- to mid-rise buildings. CFS members offer considerable structural and environmental advantages, such as low weight, ease and speed of construction, greater manufacturing flexibility, recyclability and low embodied carbon. Despite the significant potential offered by CFS structural systems, the seismic design of lateral force-resisting systems (LFRS) for CFS multi-story buildings is challenging. There are many different types of systems capable of providing the lateral load resistance capacity of the CFS framing, and this paper provides a comprehensive review of the research developments made in CFS braced-wall systems and moment-resisting frames, as the most conventional systems, to study their structural performance and identify the research gaps, challenges, and future directions. The major research developments are summarised in terms of load capacity, stiffness, energy dissipation capacity and failure mode. As an outcome of the crucial review, it was found that CFS LFRSs can generally offer more efficient design solutions regarding seismic characteristics such as high ductility and energy dissipation capacity. Despite a rather large body of research on CFS braced walls, it is necessary to assess the response of these systems in various aspects, such as developing an optimisation framework to withstand the combination of vertical and horizontal loading plus resist the impact of severe fire. With respect to moment-resisting frames, one of the main research needs is to develop systems suitable for multi-story buildings, especially in seismic regions.

Thermal Performance and Energy Efficiency of Lightweight Steel Buildings: a Case-Study

Steel façade systems follow the actual tendencies in construction offering robust and sustainable solutions, able to answer to actual conditions and to offer adequate interior thermal comfort. The modern sandwich panels provided by the current façade system producers combine the required thermal resistance by varying the thermal insulation material and its thickness with the required structural demands. In addition, the façade layer could be over-coated with different materials, thus offering the required architectural aspect. Other advantages of the systems rely on industrialized prefabrication, fast installation and adaptability. They could also be disassembled and reused. The study presents an analysis of some envelope solutions existing on the market for buildings made of thin-walled cold-formed steel structural systems. The study consists in an annual energetic analysis of Mineral Wool (MW)-based system and a more sustainable recycled-PET thermal wadding-system. The analysis includes for input the own-produced energy by power grids and additional national grid energy while for output heating / cooling and electric appliances are considered. The study is completed by a life-cycle environmental analysis. The study revealed that when the thermal insulations have nearly the same U-value, the environmental impact of the recycled-PET thermal wadding-based system is smaller than that of MW-based system. Although the environmental impact of the recycled-PET thermal wadding is higher in the production stage, the insulation quantity of the material needed for PET-recycled thermal wadding to accomplish the required thermal resistance is much smaller than that of MW. Moreover, the original material for the recycled-PET thermal wadding is 100% recycled which implies a certain benefit of circularity to the material. The study also proves that the glazing ratio has also an impact on the thermal performances of studied systems: by reducing the overall glazing ratio of the envelope, the solar gain drops significantly, which leads to an increased heating energy demand, in order to meet indoor thermal comfort.

Challenges and solutions associated with the simulation and design of cold-formed steel structural systems

The treatment of cold-formed steel sections in design codes is very largely restricted to individual members under ideal conditions. More efficient design is possible if the complexities of the structural response caused by the thin plating and complex shapes, together with the actual conditions of load introduction and restraint arising from practical situations can be recognised. Traditionally this has only been possible by resorting to full-scale testing. This is, of course, time consuming and expensive; moreover, the impossibility of covering all variations of all the important problem parameters means that developing a comprehensive understanding of all aspects of the physical behaviour is unlikely. Numerical analysis offers the promise of an alternative approach. However, for this to be reliable there must be confidence that it accurately models the physical situation. For the past decade a programme of research has been underway aimed at the provision of a more complete understanding of the structural behaviour of cold-formed steel sections when employed in particular practical situations. Three such cases are addressed herein: purlins as used in the roofs of industrial buildings, beams used to support floors and columns forming part of a stud wall framing system. In each case the process has been to firstly identify all the important structural components including fastening arrangements, then to develop numerical models using ABAQUS that represent each of these physical features to a sufficient degree of accuracy, then to validate the models by comparison with all available test data, then to conduct parametric studies covering the full range of variables found in practice and, finally, to use the pool of results and the improved insights into behaviour as the basis for improved design approaches that, by more accurately capturing the key physical features, provide better predictions of performance. An important feature of this has been to ensure that the resulting design procedures were the simplest possible consistent with reliable predictions.

Cross-sectional optimization of cold-formed steel channels to Eurocode 3

Cold-formed steel structural systems are widely used in modern construction. However, identifying optimal cross section geometries for cold-formed steel elements is a complex problem, since the strength of these members is controlled by combinations of local, distortional, and global buckling. This paper presents a procedure to obtain optimized steel channel cross-sections for use in compression or bending. A simple lipped C-shape is taken as a starting point, but the optimization process allows for the addition of double-fold (return) lips, inclined lips and triangular web stiffeners. The cross-sections are optimized with respect to their structural capacity, determined according to the relevant Eurocode (EN1993-1-3), using genetic algorithms. All plate slenderness limit values and all limits on the relative dimensions of the cross-sectional components, set by the Eurocode, are thereby taken into account as constraints on the optimization problem. The optimization for compression is carried out for different column lengths and includes the effects of the shift of the effective centroid induced by local buckling. Detailed finite element models are used to confirm the relative gains in capacity obtained through the optimization process.

Numerical evaluation: AISI S400 steel-sheathed CFS framed shear wall seismic design method

Seismic design provisions for steel-sheathed cold-formed steel framed shear walls, specific to Canada, are not provided in the existing AISI S213 Standard “North American Standard for Cold-Formed Steel Framing – Lateral Design”. A multi-phase approach was adopted in order to develop appropriate seismic design provisions for inclusion in the new AISI S400 Standard “North American Standard for Seismic Design of Cold-Formed Steel Structural Systems”. The approach included the extensive displacement based testing and dynamic testing of shear walls, the analysis of the test data results, the development and calibration of dynamic numerical models in OpenSees, and lastly, the dynamic response history analyses of twelve archetype buildings designed for the seismic hazard in three cities; Halifax (low seismic), Montreal (medium seismic) and Vancouver (high seismic). It is this last phase of the study that is documented herein. Fragility curves were developed from the buildings' response to 44 scaled ground motion records following a method adapted from the FEMA P695 analysis methodology. The results showed that the design method is appropriate, including the seismic force modification factors of Rd=2 and Ro=1.3. Improvement to the predicted seismic response of CFS framed buildings could be forthcoming if one were to account for the contribution of the non-structural gypsum wall panels.

Special Issue on Cold-Formed Steel Structures

Because of the recent increase and diversity in commercial activity dealing with the usage of cold-formed steel structures in the construction industry, the research community workingwith this type of structure has been faced with new challenges. This has fostered a fairly large number of considerable advances in structural engineering topics related to cold-formed steel applications. The aim of this special issue of the Journal of Structural Engineering is to put together, in a single comprehensive issue, a representative sample of the newest and most relevant analytical, numerical, and experimental original research devoted to investigating the behavior and design of cold-formed steel structures around the world. Indeed, this issue includes contributions from researchers working in 13 countries, located on four continents. This special issue contains 18 technical papers and one technical note covering a wealth of topics concerning cold-formed steel structural systems. Without claiming to be exhaustive, it is possible to find papers dealing with members (columns and beams), panels, frames, walls, shear walls, and connections. Overall, the papers describe specific analytical, numerical, or experimental investigations that (1) address first-order buckling, postbuckling, or ductility problems; (2) involve static or dynamic (including seismic) analyses; (3) cover both carbon and stainless cold-formed steels, and (4) are concerned mainly with behavioral aspects or focus on design issues; namely, the development of rules for codes and specifications. For organizational purposes, the papers are divided into four groups, each one corresponding, as much as possible, to a given structural system type. The first group is comprised of eight papers on the analysis and design of isolated cold-formed steel structural elements, including seven papers on members and one on panels. The second group includes three papers that are concerned with the behavior and design of cold-formed steel connections, one aiming specifically at studying effects resulting from elevated temperatures. The technical note that closes the special issue also addresses a connection strength problem. Next, the third group consists of four papers that report investigations on the static behavior and design of cold-formed steel walls (one paper) and the cyclic/dynamic behavior and performance of shear walls (three papers). Finally, the last group contains the remaining three papers, all concerning cold-formed steel frames; two papers on buildings and one on storage racks. The content of each of the papers included in the special issue is succinctly outlined in the subsequent sections. Cold-Formed Steel Structural Elements

Cyclic Testing and Modeling of Cold-Formed Steel Special Bolted Moment Frame Connections

A cyclic testing of nine full-scale beam-to-column moment connection subassemblies was carried out to support the development of design provisions for a lateral load-resisting system in the AISI S110: Standard for Seismic Design of Cold-Formed Steel Structural Systems—Special Bolted Moment Frames. This type of one-story framing system features C-section beams connected to hollow structural section columns by bearing-type high-strength bolts and is commonly used in industrial platform construction. The test results showed that these specimens had an interstory drift capacity significantly larger than 0.04 rad. The cyclic behavior was characterized by a linear response, a slip range, and a significant hardening response due to bearing at bolt holes. The conventional strong column-weak beam design philosophy is not appropriate for this system. The inelastic action through the bolt slip and bearing in the connection is a ductile yielding mechanism. Beams and columns should be protected to remain elastic by the capacity design principles. Based on the concept of the instantaneous center of rotation of an eccentrically loaded bolt group, a model that can properly simulate the cyclic behavior of the bolted moment connection is presented.

Advances in Analysis and Design of Cold-Formed Steel Structures

This paper summarizes a number of recent experimental and numerical investigations into the structural behaviour of cold-formed steel structures with bolted connections conducted by the authors, and all of them focus on the efficient use of bolted moment connections between cold-formed steel sections. It aims to present the latest analysis and design techniques as well as some practical design guidance and considerations on the overall performance of cold-formed steel structural systems. Hence, researchers and designers are encouraged to exploit the structural benefits offered by cold-formed steel structures with practical and efficient moment framing in building construction.