Specification for the design of light gage cold-formed steel structural members.

Mode of access: Internet.

Multiobjective optimization of cold-formed steel columns

The optimal design of cold-formed steel columns is addressed in this paper, with two objectives: maximize the local-global buckling strength and maximize the distortional buckling strength. The design variables of the problem are the angles of orientation of cross-section wall elements the thickness and width of the steel sheet that forms the cross-section are fixed. The elastic local, distortional and global buckling loads are determined using Finite Strip Method (CUFSM) and the strength of cold-formed steel columns (with given length) is calculated using the Direct Strength Method (DSM). The bi-objective optimization problem is solved using the Direct MultiSearch (DMS) method, which does not use any derivatives of the objective functions. Trade-off Pareto optimal fronts are obtained separately for symmetric and anti-symmetric cross-section shapes. The results are analyzed and further discussed, and some interesting conclusions about the individual strengths (local-global and distortional) are found.

A theoretical and experimental analysis of cold-formed steel shapes subjected to bending - Channel and simple lipped channel

Cold-formed steel shapes have been widely employed in steel construction, where they frequently offer a lower cost solution than do traditional laminated shapes. A classic application of cold-formed steel shapes is purlins in the roof panel of industrial buildings, connected to the roof panel by means of screws. The combined effect of these two elements has been the subject of investigations in some countries. Design criteria were included in the AISI Code in 1991 and 1996. This paper presents and discusses the results obtained from bending tests carried out on shapes commonly used in Brazil, i.e., the channel and the simple lipped channel, Tests were carried out on double shapes with 4.5 and 6.0 meter spans, which were subjected to concentrated loads and braced against each other on the supports and at intermediary points in three different load situations. The panel shape was also analyzed experimentally, simulating the action of wind by means of a vacuum box designed specifically for this purpose. The test results were then compared to those obtained through the theoretical analysis, enabling us to extract important information upon which to base proposed design criteria for the new Brazilian code.

Effect of web holes on web crippling strength of cold-formed steel channel sections under end-one-flange loading condition – Part I: Tests and finite element analysis

Web openings could be used in cold-formed steel beam members, such as wall studs or floor joints, to facilitate ease of services in buildings. In this paper, a combination of tests and non-linear finite element analyses is used to investigate the effect of such holes on web crippling under end-one-flange (EOF) loading condition; the cases of both flanges fastened and unfastened to the bearing plates are considered. The results of 74 web crippling tests are presented, with 22 tests conducted on channel sections without web openings and 52 tests conducted on channel sections with web openings. In the case of the tests with web openings, the hole was either located centred above the bearing plates or having a horizontal clear distance to the near edge of the bearing plates. A good agreement between the tests and finite element analyses was obtained in term of both strength and failure modes.

Effect of web holes on web crippling strength of cold-formed steel channel sections under end-one-flange loading condition - Part II: Parametric study and proposed design equations

A parametric study of cold-formed steel sections with web openings subjected to web crippling under end-one-flange (EOF) loading condition is undertaken, using finite element analysis, to investigate the effects of web holes and cross-section sizes. The holes are located either centred above the bearing plates or with a horizontal clear distance to the near edge of the bearing plates. It was demonstrated that the main factors influencing the web crippling strength are the ratio of the hole depth to the depth of the web, the ratio of the length of bearing plates to the flat depth of the web and the location of the holes as defined by the distance of the hole from the edge of the bearing plate divided by the flat depth of web. In this study, design recommendations in the form of web crippling strength reduction factor equations are proposed, which are conservative when compared with the experimental and finite element results.

Fastener-Based Computational Models of Cold-Formed Steel Shear Walls

Cold-formed steel (CFS) combined with wood sheathing, such as oriented strand board (OSB), forms shear walls that can provide lateral resistance to seismic forces. The ability to accurately predict building deformations in damaged states under seismic excitations is a must for modern performance-based seismic design. However, few static or dynamic tests have been conducted on the non-linear behavior of CFS shear walls. Thus, the purpose of this research work is to provide and demonstrate a fastener-based computational model of CFS wall models that incorporates essential nonlinearities that may eventually lead to improvement of the current seismic design requirements. The approach is based on the understanding that complex interaction of the fasteners with the sheathing is an important factor in the non-linear behavior of the shear wall. The computational model consists of beam-column elements for the CFS framing and a rigid diaphragm for the sheathing. The framing and sheathing are connected with non-linear zero-length fastener elements to capture the OSB sheathing damage surrounding the fastener area. Employing computational programs such as OpenSees and MATLAB, 4 ft. x 9 ft., 8 ft. x 9 ft. and 12 ft. x 9 ft. shear wall models are created, and monotonic lateral forces are applied to the computer models. The output data are then compared and analyzed with the available results of physical testing. The results indicate that the OpenSees model can accurately capture the initial stiffness, strength and non-linear behavior of the shear walls.

Failure analysis of cold-formed steel sections

The purlin-sheeting system has been the subject of numerous theoretical and experimental investigations over the past 30 years, but the complexity of the problem has led to great difficulty in developing a sound and general model. The primary aim of the thesis is to investigate the failure behaviours of cold-formed zed and channel sections for use in purlin-sheeting systems. Both the energy method and finite strip method are used to develop an approach to investigate cold-formed zed and channel section beams with partial-lateral restraint from the metal sheeting when subjected to a uniformly distributed transverse load. The stress analysis of cold-formed zed and channel section beams with partially-lateral restraint from the metal sheeting when subjected to a uniformly distributed transverse load is investigated firstly by using the analytical model based on the energy method in which the restraint actions of the sheeting are modelled by using two springs representing the translational and rotational restraints. The numerical results have showed that the two springs have significantly different influences on the stresses of the beams. The influence of the two springs has also been found to depend on the anti-sag bar and the position of the loading line. A novel method is presented for analysing the elastic local buckling behaviour of cold-formed zed and channel section beams with partial-lateral restraint from metal sheeting when subjected to a uniformly distributed transverse load, which is carried out by inputting the cross sectional stresses with the largest compressive stress into the finite strip analysis. By using the presented novel method, individual influences of warning stress, partially lateral restraints from the sheeting and the dimensions of the cross section and position of the loading line on the buckling behaviour are investigated.

Global optimisation of cold-formed steel sections

In this thesis, standard algorithms are used to carry out the optimisation of cold-formed steel purlins such as zed, channel and sigma sections, which are assumed to be simply supported and subjected to a gravity load. For zed, channel and sigma section, the local buckling, distortional buckling and lateral-torsional buckling are considered respectively herein. Currently, the local buckling is based on the BS 5950-5:1998 and EN 1993-1-3:2006. The distortional buckling is calculated by the direct strength method employing the elastic distortional buckling which is calculated by three available approaches such as Hancock (1995), Schafer and Pekoz (1998), Yu (2005). In the optimisation program, the lateral-torsional buckling based on BS 5950-5:1998, AISI and analytical model of Li (2004) are investigated. For the optimisation program, the programming codes are written for optimisation of channel, zed and sigma beam. The full study has been coded into a computer-based analysis program (MATLAB).

Estudo da estabilidade e da capacidade resistente de painéis estruturais do sistema construtivo Light Steel Framing

Pós-graduação em Engenharia Civil - FEIS

An application of reliability-based robustness assessment of steel moment resisting frame structures under post-mainshock cascading events

The paper presented herein proposes a reliability-based framework for quantifying the structural robustness considering the occurrence of a major earthquake (mainshock) and subsequent cascading hazard events, such as aftershocks that are triggered by the mainshock. These events can significantly increase the probability of failure of buildings, especially for structures that are damaged during the mainshock. The application of the proposed framework is exemplified through three numerical case studies. The case studies correspond to three SAC steel moment frame buildings of 3-, 9-, and 20- stories, which were designed to pre-Northridge codes and standards. Twodimensional nonlinear finite element models of the buildings are developed using the Open System for Earthquake Engineering Simulation framework (OpenSees), using a finite-length plastic hinge beam model and a bilinear constitutive law with deterioration, and are subjected to multiple mainshock-aftershock seismic sequences. For the three buildings analyzed herein, it is shown that the structural reliability under a single seismic event can be significantly different from that under a sequence of seismic events. The reliability-based robustness indicator used shows that the structural robustness is influenced by the extent by which a structure can distribute damage.

Optimización y propuesta de sistema opaco de cerramiento multicapa ligero con estructura de light steel frame como alternativa competitiva a los sistemas de cerramientos tradicionales

En la actualidad, el crecimiento de la población y el desarrollo tecnológico de nuestros tiempos han originado novedosas formas de confort para los habitantes, lo cual a su vez se traduce en una demanda creciente de energía. No obstante, el concepto energético está llegando a la conciencia y es necesario adaptarse a la nueva situación, por lo tanto, es imprescindible el estudio y el aprovechamiento de nuevos sistemas constructivos de cerramientos, como pueden ser los cerramientos multicapas ligeros, que presentan características favorables para el ahorro en el consumo energético, y a su vez pueden ser industrializados, obteniendo beneficios, como la mejora de la calidad, el acortamiento de plazos constructivos, mayor seguridad, altas prestaciones, mayor ligereza, más espacio habitable, entre otros. El desarrollo de esta tesis doctoral esta centrado en definir tres propuestas de Cerramientos Multicapas Ligeros (CML) con estructura de light steel frame, analizando el comportamiento térmico y acústico, así como también el coste económico de las mismas, con el objetivo de demostrar que este tipo de sistema constructivo es una alternativa competitiva a los sistemas de Cerramientos Tradicionales y, que a su vez se puedan implementar en cualquier sistema constructivo y se puedan adaptar a los distintos ambientes climáticos que existen en España. Por otro lado, se han seleccionado tres Cerramientos Tradicionales, para llevar a cabo las distintas comparativas propuestas. La investigación se desarrolla en cinco grandes partes: La primera parte está formada por la justificación de la investigación y el planteamiento de los objetivos, así como también la hipótesis de partida y la metodología empleada. En la segunda parte se definen los antecedentes teóricos, divididos en tres temas: el cerramiento ? la fachada, la transmisión del calor y la transmisión del sonido en los cerramientos. También se realiza una síntesis del trabajo de investigación previo que he realizado ?Caracterización del comportamiento térmico de fachadas multicapas ligeras?, el cual sirve de base de partida para el desarrollo de esta tesis. Y por último, se desarrollan distintos temas relacionados con el Light Steel Frame (LSF), en donde se lleva a cabo una búsqueda de la documentación disponible sobre las investigaciones científico-tecnológicas, desde distintos puntos de vista: térmico, acústico, económico, estructural, en caso de incendio, industrialización y medioambiental ? sostenibilidad. Una vez realizados todos los puntos anteriores y para sintetizar la información, se lleva a cabo una clasificación de los sistemas de cerramientos que tienen como estructura el light steel frame, se analizan las ventajas e inconvenientes de cada uno de estos sistemas de la clasificación, llegando a unas conclusiones que sirven de base para definir las propuestas de Cerramientos Multicapas Ligeros. En la tercera parte, se definen los tres cerramientos tradicionales que se utilizan para realizar las comparativas con los cerramientos multicapas ligeros, definiendo las características de cada uno de los materiales y, también se desarrollan los criterios de diseño que deben cumplir los cerramientos multicapas ligeros, definiendo cada una de las tres muestras de ensayo de cerramientos multicapas ligeros. En la cuarta parte se lleva a cabo el análisis teórico ? experimental de las seis muestras de estudio, en donde, se realiza una investigación térmica basada en simulaciones y experimentaciones en células de ensayo e implementación de la termografía infrarroja. Por otro lado, se realiza también una investigación acústica desarrollando ensayos en laboratorio de aislamiento a ruido aéreo e intensimetría sonora. Y por último, se hace un análisis económico, tomando en cuenta las variables del coste de construcción, el consumo energético, el ahorro que supone la masa a la estructura y el espacio adicional que aporta este tipo de sistema constructivo a la superficie útil, para ello se plantean distintos escenarios de estudio. Una vez obtenidos los resultados de las diferentes investigaciones (térmica, acústica y económica), se llevan a cabo una serie de comparativas entre los cerramientos multicapas ligeros y los cerramientos tradicionales, y los cerramientos multicapas ligeros entre sí. En la quinta parte, se exponen las conclusiones derivadas de las distintas investigaciones y se realiza la comprobación de los objetivos propuestos y de la hipótesis de partida, destacando los hallazgos principales para cada situación y se presentan las líneas futuras de investigación que han ido surgiendo en el desarrollo de la tesis doctoral.

Tecnologia construtiva de fachada em chapas delgadas estruturadas em light steel framing.

Aumento da produtividade, melhorias na qualidade dos produtos, redução de custos e de impactos ambientais são essenciais para a capacidade competitiva das empresas. A execução da fachada faz parte do caminho crítico da obra, por ser um subsistema que associa as funções de fechamento, acabamento, iluminação e ventilação e ainda por incorporar sistemas prediais; apresenta, por isso também, um alto custo direto em relação aos outros subsistemas do edifício. A tecnologia construtiva de fachadas em chapas delgadas com estrutura em Light Steel Framing (LSF) é uma alternativa viável para aumentar a produtividade e reduzir os prazos de obra, com qualidade e desempenho, e pode trazer benefícios em relação a atividades intensas em mão de obra como é o caso da alvenaria de vedação e de seus revestimentos. O presente trabalho tem por objetivo sistematizar e analisar o conhecimento relativo a essa tecnologia construtiva de fachada. O método adotado compreende revisão bibliográfica. Como contribuição, o trabalho reúne um conjunto organizado de informações sobre os principais sistemas disponíveis no mercado contemplando: a caracterização do sistema de fachada, de suas camadas e dos perfis leves de aço e a sistematização das principais avaliações técnicas de sistemas existentes em outros países, reunindo normas técnicas de produtos e de execução. Acredita-se que a reunião e organização das informações, antes dispersas em diversas referências, têm potencial para subsidiar o meio técnico para tomada de decisão quanto ao uso adequado da nova tecnologia.

Elementos de apoio ao dimensionamento de secções compostas em light steel framing

Dissertação de Mestrado, Engenharia Civil, Especialização em Estruturas, Instituto Superior de Engenharia, Universidade do Algarve, 2016

Risk optimization of a steel frame communications tower subject to tornado winds

The structural engineering community in Brazil faces new challenges with the recent occurrence of high intensity tornados. Satellite surveillance data shows that the area covering the south-east of Brazil, Uruguay and some of Argentina is one of the world most tornado-prone areas, second only to the infamous tornado alley in central United States. The design of structures subject to tornado winds is a typical example of decision making in the presence of uncertainty. Structural design involves finding a good balance between the competing goals of safety and economy. This paper presents a methodology to find the optimum balance between these goals in the presence of uncertainty. In this paper, reliability-based risk optimization is used to find the optimal safety coefficient that minimizes the total expected cost of a steel frame communications tower, subject to extreme storm and tornado wind loads. The technique is not new, but it is applied to a practical problem of increasing interest to Brazilian structural engineers. The problem is formulated in the partial safety factor format used in current design codes, with all additional partial factor introduced to serve as optimization variable. The expected cost of failure (or risk) is defined as the product of a. limit state exceedance probability by a limit state exceedance cost. These costs include costs of repairing, rebuilding, and paying compensation for injury and loss of life. The total expected failure cost is the sum of individual expected costs over all failure modes. The steel frame communications, tower subject of this study has become very common in Brazil due to increasing mobile phone coverage. The study shows that optimum reliability is strongly dependent on the cost (or consequences) of failure. Since failure consequences depend oil actual tower location, it turn,,; out that different optimum designs should be used in different locations. Failure consequences are also different for the different parties involved in the design, construction and operation of the tower. Hence, it is important that risk is well understood by the parties involved, so that proper contracts call be made. The investigation shows that when non-structural terms dominate design costs (e.g, in residential or office buildings) it is not too costly to over-design; this observation is in agreement with the observed practice for non-optimized structural systems. In this situation, is much easier to loose money by under-design. When by under-design. When structural material cost is a significant part of design cost (e.g. concrete dam or bridge), one is likely to lose significantmoney by over-design. In this situation, a cost-risk-benefit optimization analysis is highly recommended. Finally, the study also shows that under time-varying loads like tornados, the optimum reliability is strongly dependent on the selected design life.