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
Hybrid masonry is an innovative technology for seismic design of buildings. The system uses reinforced masonry panels within a steel-framed structure, where steel connector plates link the steel frame to the masonry panels. The system has been used for construction of low-rise buildings in the low-seismic regions of the eastern and midwestern United States but has not been implemented in regions of moderate or high seismicity yet. Current research is underway to extend the application of hybrid masonry for use in high-seismic regions. In this paper, the overall approach for seismic design of one type of hybrid masonry systems is studied, and the steps of a capacity design process are presented, where two favorable ductile modes of behavior may be exploited: steel connector plates behaving as fuses or flexural yielding of the masonry panels. Moreover, this research applies the two design options for 3-, 6-, and 9-story prototype buildings located in a high seismic region and evaluates viability of hybrid masonry as a new seismic lateral-load resisting system. On the basis of this design framework and the exploratory studies, both approaches are shown to be feasible for developing realistic system configurations. Nevertheless, for the case of flexural yielding of the masonry panels, the steel connector plates must carry significant shear force demands. The structural system then requires more hybrid panels compared with corresponding systems when plasticity is concentrated in the steel connector plates. DOI: 10.1061/(ASCE)ST.1943-541X.0000672. (C) 2013 American Society of Civil Engineers.
In this paper, a set of simplified design equations for an unbonded posttensioned (PT) precast split hybrid shear wall system is developed. Such a system was proposed by the Precast Seismic Structural Systems (PRESSS) and can be used as a bearing wall or a special reinforced concrete wall for building frames, as defined in ASCE/SEI 7, for eliminating residual drift after seismic events. The panels are anchored to the foundation with unbonded PT tendons located at the panel center; adjacent panels are connected with uniformly distributed energy dissipating coupling devices. An iterative design procedure to calculate the required area of the PT reinforcement and the total yield force of all shear connectors in one vertical joint was proposed by PRESSS. This iterative procedure is exact, but tedious and lengthy. A simpler nondimensional chart-based design procedure was proposed by the writers. This procedure is efficient, but has limitations. A noniterative procedure adopted by ACI ITG-5.2, although simple, does not yield the optimum combination of the shear connectors force and PT force. The set of simplified design equations proposed in this study overcomes the shortcomings of these three procedures. It is simple, direct (noniterative), general, and yields the optimum design in fewer number of steps. The proposed design equations predicted values are accurate and are normally within +/- 2% of the exact optimum solution. DOI: 10.1061/(ASCE)ST.1943-541X.0000631. (C) 2013 American Society of Civil Engineers.
A Rayleigh quotient is developed to calculate estimates of the fundamental frequencies of tall slender buildings. The quotient provides simple analytical frequency estimates that agree well with results reported using a more detailed beam model and finite-element analyses. It is also shown that the fundamental frequency varies inversely with the height H of the building being modeled, and that the additional stiffening provided by one model of an outrigger appears not to appreciably alter the fundamental frequency. DOI: 10.1061/(ASCE)ST.1943541X.0000656. (C) 2013 American Society of Civil Engineers.
This paper presents a finite-element formulation for the dynamic analysis of I-beams curved in-plan, in which geometric nonlinearities owing to large deflections and inelastic material behavior are taken into account. The developed finite element is based on the total Lagrangian formulation. Wagner and warping effects are considered in the analysis. The nonlinear dynamic equilibrium equations are solved by using Newmark's step by step numerical integration procedure. The von Mises associative isotropic hardening model is used to formulate the metal plasticity. The elastic predictor-radial corrector algorithm is used to consider gradual yielding on the cross section and along the beam. Simpler finite-element formulations are also developed by excluding the effects of geometric and material nonlinearities. Numerical examples are provided to illustrate the significance of the effects of geometric and material nonlinearities on the dynamic behavior of I-beams that are curved in-plan. DOI: 10.1061/(ASCE)ST.1943-541X.0000383. (C) 2011 American Society of Civil Engineers.
