Experimental testing and elastic buckling studies were performed on 68 C-section cold-formed steel joists with unstiffened rectangular web holes. Four Steel Stud Manufacturers Association (SSMA) cross-section types; 800S200-33, 800S200-43, 1000S162-54, and 1200S162-97, were evaluated to explore the influence of holes on local, distortional, and global bucking failure modes. Hole depth was varied in the tests to identify trends in ultimate strength. Ultimate strength was observed to decrease with increasing hole depth for 800S200-33, 1200S162-97 cross-sections. Due to small number of specimen and unidentified behavior of the beams, a more in depth study of the behavior of 800S200-43 and 1000S162-54 beams are necessary. Local buckling of the unstiffened strip above the hole was observed to accompany distortional buckling at the hole for the locally slender 800S200-33 and 1000S162-54 cross-sections. Thin shell finite element eigen-buckling analysis of each joist specimen, including measured cross-section dimensions and tested boundary and loading conditions, were conducted in parallel with the experiments to identify those elastic buckling mode shapes which influence load-deformation response. The distortional and lateral-torsional buckling moments were observed to decrease with increasing hole depth while a contrasting behavior was captured for local buckling modes. A modification to the AISI Direct Strength Method equations for beams with slotted web-holes was compared against the experimental results with predictions lower than tested strength. Initial cross-section imperfections led to inclined webs which decreased the capacity of the beams. The use of a water-jet cutting process was employed successfully to produce accurate holes sizes and locations in each joist specimen and is recommended for researchers and manufacturers as a method for custom fabrication of cold-formed steel members. / Master of Science

This research investigates if the LRFD strength reduction factor for cold-formed steel compression members can be increased above its current value of Ï c = 0.85, which was established by the LRFD Cold-Formed Steel Design Manual (1991) on the basis of 264 column tests. The resistance factor in the Canadian code for cold-formed steel compression members is also evaluated. A total of 675 concentrically loaded plain and lipped C-section columns, plain and lipped Z-section columns, hat and angle columns, including members with holes, are considered in the study. The predicted strengths are calculated with the AISI-S100-07 Main Specification and the AISI Direct Strength Method. The test-to-predicted strength statistics are employed with the first order second moment reliability approach in AISI-S100-07 Chapter F as well as a higher order method to calculate the resistance factor per cross-section type, ultimate limit state, and considering partially and fully effective columns. The observed trends support a higher resistance factor for columns buckling in a distortional buckling limit state and an expansion of the current DSM prequalified limits. The results also show that DSM predicts the column capacity more accurately than the Main Specification. The test-to-predicted ratios for plain and lipped angle columns exhibit a high coefficient of variation and become more and more conservative as global slenderness increases. It is concluded that fundamental research on the mechanics of angle compression members is needed to improve existing design methods. / Master of Science

The AISI (1996) Specification for the Design of Cold-Formed Steel Structural Members provisions for web-crippling are believed to be conservative for multi-web deck sections. They are based on unfastened specimens and are limited to the use of decks with certain geometric parameters. The unified web crippling equation of the North American (2002) Specification for the Design of Cold-Formed Steel Structural Members (adopted from Canadian S136-94 Specification) is also limited to certain geometric parameters. Although it has new web crippling coefficients for different load cases and different end conditions, in the End One Flange (EOF) loading case, coefficients for the unfastened configuration were used as a conservative solution for the fastened case because there was no directly applicable test data available in the literature. This thesis presents the results of an experimental study on web-crippling strength of multiple-web cold-formed steel deck sections subjected to End One Flange (EOF) loading. Seventy-eight tests were conducted at Virginia Tech. Test specimens lying inside and outside of certain geometric parameters of the specifications were tested with both unrestrained and restrained end conditions. Test specimens lying inside the specification parameters have revealed conservative results in the prediction of web crippling capacity using both AISI (1996) and North American (2002) equations. Using the unified web-crippling equation of North American Specification, a nonlinear regression analysis was performed to update the unfastened case coefficients and derive new fastened case coefficients. Also, the calibration of these coefficients is done for both Canadian S136 (1994) and AISI (1996) specifications. / Master of Science

Twenty cantilever diaphragm tests were performed in the Structures and Materials Laboratory at Virginia Tech. The tests included both deep deck and cellular deck profiles with varying structural and side-lap connections. The tests were conducted with three different structural connections: screws, pins and welds and two different side-lap connections: screws and button punch. The tests were conducted and both load and deflection of the diaphragms were recorded. The current International Code Council, ICC, evaluation procedure shows that there are two different methods for measuring diaphragm deflection. The first method was by measuring specific corner displacements and making corrections to remove any rigid body motion. The second method is by measuring the deflection of the diagonals of the diaphragm. In this study both measurements were taken to do a comparison of the results that were obtained. Both strength and stiffness values were calculated based on the Steel Deck Institute (SDI) Diaphragm Design Manual (2004) and modifications described by Luttrell (2005). The paper by Luttrell (2005) only recommends modifications for the calculation of diaphragm stiffness. The data obtained from the tests were compared to the SDI calculations to distinguish any noticeable trends. Modifications are recommended regarding diaphragm strength and further research is suggested to create a better stiffness prediction of diaphragms. / Master of Science

Currently, ASHRAE has determined the zone method and modified zone method are appropriate calculation methods for materials with a high difference in conductivity, such as cold-formed steel (CFS) walls. Because there is currently no standard U-Factor calculation method for CFS walls, designers and code officials alike tend to resort to the zone method. However, the zone method is restricted to larger span assemblies because the zone factor coefficient is 2.0. This tends to overestimate the amount of surface area influenced by CFS. The modified zone method is restricted to C-shaped stud, clear wall assemblies with framing factors between 9 and 15%. The objective of the research is to narrow the gap of knowledge by re-examining the modified zone method in order to more accurately determine R-Values and U-Factors for CFS wall assemblies with whole wall framing factor percentages of 22% and above.

Utmattning av stålmaterial är ett fenomen som varit känt i närmare 190 år men trots det är det fortfarande långt ifrån helt utforskat. Utmattningsegenskaper hos grundmaterial och svetsar är idag relativt utforskat, medan områden som utmattningsegenskaper hos kallformade stålprofiler fortfarande mer eller mindre är outforskat. Med utforskningen av utmattningsegenskaper hos kallformade stålprofiler som huvudsyfte delades examensarbetet upp i två delar. En överliggande kranbomsoptimering med huvudmålet att sänka vikten så mycket som möjligt med hjälp av materialbyte till ett mer höghållfast stål och optimal användning av material med avseende på utmattning. Den andra delen av examensarbetet är en framtagning av en provkropp med huvudmålet att kunna testa utmattningsegenskaper för kallformade stålprofiler samt att ge dimensionerande värden till kranbomsoptimeringen. Provstavsframtagningen resulterade i tre versioner av provkroppar som i teorin ska ge utmattningsegenskaper i longitudinell riktning för kallformade stålprofiler. Eftersom provstavarna inte kunde prövas på grund av tidsbrist baserades kranbomsoptimeringen på teoretiska värden. Resultatet av kranbomsoptimeringen var att vikten kunde sänkas från 1027 kg till 435 kg utan att påverka andra beaktade kranegenskaper. / Even though fatigue in steel structures is a phenomenon that was discovered almost 190 years ago it is still far from fully explored. The fatigue properties of base materials and welded materials are currently relatively well known, but the fatigue properties of cold-formed steel profiles are still more or less unknown. With the investigation of fatigue properties of cold-formed steel profiles as the main purpose, this master thesis was divided into two parts. An overhead optimization of a crane with the main goal of reducing weight as much as possible with the help of upgrading materials to higher strength steels and using the materials in an optimal way with respect to fatigue. The second part of the master thesis is the development of a test specimen with the main goal of testing the fatigue properties of cold-formed steel profiles and to provide dimensioning values for the optimization of the crane. The development of test specimen resulted in three versions of specimens which in theory will provide fatigue properties in the longitudinal direction for cold-formed steel profiles. Since the test specimens could not be tested because of shortage of time, the optimization of the crane had to be based on theoretical values. The results of the optimization were that the weight could be lowered from 1027 kg to 435 kg without affecting any other consideration characteristics of the crane.

Les éléments séparatifs à base de plaques de plâtre (cloisons, bloc-porte…) sont d’abord destinés à délimiter les espaces à l’intérieur d’une construction. Ils contribuent aux exigences essentielles pesant sur l’ouvrage en termes de sécurité en cas d’incendie, d’isolation thermique et acoustique. La réglementation française stipule que la vérification de la résistance au feu des ces éléments doit être vérifiée par des essais en vraie grandeur menées selon des procédures normalisées et qui sont souvent onéreux pour les industriels. De plus, la limite du four (5 m de hauteur et 7 m de largeur actuellement) pose un problème pour les fabricants quand ils veulent valider des cloisons plus grandes. Par conséquent, la tendance industrielle est de développer une méthode prédictive du comportement au feu des éléments séparatifs. Cette thèse présente une étude dans le cadre du projet de recherche de EFECTIS France, ce qui conduit à l'élaboration d'un modèle numérique capable de prédire le comportement thermo-mécanique des cloisons en plaques de plâtre se composant d’une ossature métallique vissée sur des parements en plaques de plâtre, quand elles sont soumises à une action thermique normalisée de EN 1363-1 sur une face. Dans cette étude, on présente d’abord des programmes d’essais qui permettent d’une part, d’identifier les propriétés thermo-physiques et thermo-mécaniques de plaques de plâtre cartonné, à température ambiante et à haute température, et d’autre part de caractériser la liaison cinématique de la fixation par vissage des parements en plaques de plâtre sur les montants acier de l’ossature interne, à température ambiante. En suite, on présente le développement des modèles thermique et mécanique avec le logiciel CAST3M en utilisant les paramètres mesurés lors des programmes d’essais sur les matériaux et les assemblages. Les modèles développés permettent de prendre en compte : (i) les phénomènes de transfert thermique par conduction, rayonnement et convection au travers d’une cloison - (ii) la chute du parement exposé de la cloison pendant l’essai - (iii) le comportement mécanique de la cloison elle-même, c'est-à-dire le comportement thermo-mécanique de ses éléments constitutifs (plaques de plâtre cartonné et montants métalliques) ainsi que celui des assemblages vissés des plaques de parements sur les montants d’ossature. / The fire resistance of building elements (partition walls, door sets ...) by means of tests according to standard procedures is often expensive for manufacturers. In consequence, Efectis France is conducting a specific research project aiming to develop an efficient and economical tool in order to carry out the preliminary design of new products as well as their optimization and extend the application of experimental results to configurations different from those of the test (change of size, of component, of boundary conditions ...). This thesis presents a study in the scope of above research project, which led to the development of a numerical model capable of predicting the thermo-mechanical behavior of separating elements such as flexible partitions made with internal steel studs and plasterboard facings, when they are subjected to standard thermal action of EN 1363-1 on one side. This study is organized in three steps. The first one is an experimental investigation relative to the characterization of thermo-physical and of thermo-mechanical properties of plasterboards used in above mentioned partition walls. In the second step, a specific numerical model for the analysis of plasterboard partition fire behavior is developed. This model allows treating not only nonlinear heat transfer but also the nonlinear structural behavior of the partitions from thermal stresses taking into account the degradation of rigidities for the punctual screwing of plasterboards on the steel studs. In the third step, the prediction of the numerical model is compared with experimental results in terms of temperature and displacements of the partitions. The comparisons enable to show the validity of the numerical model to predict appropriately the fire behavior of plasterboard partitions.

Os perfis de aço formados a frio apresentam, em geral, elevada relação largura/espessura, tornando-os suscetíveis à flambagem local, caracterizada por uma flambagem de chapa, mas que também pode ocasionar um outro modo de flambagem, denominado flambagem por distorção, desconsiderado no dimensionamento de perfis laminados, mas que pode resultar crítico principalmente nos perfis com enrijecedores de borda e constituídos por aço de elevada resistência mecânica. Tal fenômeno é caracterizado pela perda de estabilidade do conjunto formado pelo elemento comprimido e seu enrijecedor de borda, alterando a forma inicial da seção transversal. Portanto, as normas mais atuais têm apresentado procedimentos para avaliar a resistência de barras com base na flambagem por distorção, como o procedimento simplificado da norma australiana AS/NZS 4600:1996, proposto por HANCOCK e que foi também adotado pela recente norma brasileira NBR 14762:2001, o método direto de resistência, recentemente proposto para incorporação à especificação do AISI (American Iron and Steel Institute) e a GBT (Generalized Beam Theory).Nesse trabalho é feita uma abordagem dos procedimentos propostos para a avaliação da flambagem por distorção em barras submetidas à compressão centrada e à flexão, comparando-se os resultados obtidos pelo procedimento da norma brasileira, pela análise elástica via método das faixas finitas - MFF e pela análise via método dos elementos finitos - MEF, admitindo barras sem e com imperfeições iniciais. É feita também uma abordagem com relação aos outros procedimentos internacionais para a avaliação do fenômeno. / Cold-formed steel members present, in many cases, an elevated width/thickness ratio (thin-walled members), which probably lead up to the local buckling, which is characterized by a plate buckling, and also may lead up to another buckling mode, called distortional buckling, not considered on the design of hot-rolled members, but which may result critical in cold-formed members, specially in the ones with edge stiffeners and made with high strength steel. Such phenomena is characterized by the instability of the group formed by the compression flange and its stiffener, changing the initial shape of the cross section. Nowadays, codes present procedures to evaluate member’s resistance also due to distortional buckling, as the simplified method in the Australian code, AS/NZS 4600:1996, proposed by HANCOCK, which was adopted by the new Brazilian code, NBR 14762:2001, the Direct Strenght Method, recently proposed as an AISI (American Iron and Steel Institute) Draft, and the GBT (Generalilzed Beam Theory).This work talks about procedures proposed to evaluate distortional buckling in members under compression and bending, comparing results obtained by the method showed in the brazilian code, by numerical Finite Strip Method elastic analisys - FSM, and by Finite Element Method analisys – FEM, on members with and without initial imperfections. It is also done an explanation related to other international procedures to evaluate the phenomena.

No Brasil, o emprego de estruturas de aço constituídas por perfis formados a frio tem crescido consideravelmente, em virtude da ampla disponibilidade de laminados planos no mercado (chapas finas), bem como pela busca de soluções estruturais mais competitivas. Nesse cenário, pode-se destacar as estruturas mistas de aço e concreto destinadas aos edifícios habitacionais de pequeno porte, em que os tradicionais perfis laminados são substituídos por perfis formados a frio tanto nas vigas como nos pilares. Embora o sistema de vigas mistas possa ser considerado consolidado no campo dos perfis laminados e soldados, o comportamento estrutural no caso de perfis formados a frio necessita de investigação mais aprofundada, de modo a verificar os modos de ruína e a viabilidade do emprego dos modelos teóricos clássicos. Nesse trabalho foi desenvolvido um estudo teórico e experimental sobre as vigas mistas em perfis formados a frio duplo U enrijecido, focalizando a ligação mista (ligação viga-pilar) e consequentemente a resposta estrutural da região de momento fletor negativo. O programa experimental consistiu da análise de dois protótipos cruciformes para determinar a curva momento-rotação, o momento resistente, a rigidez, a capacidade de rotação e identificar modos de falha. Foi possível constatar maior capacidade de rotação da ligação com cantoneiras de assento e de alma quando comparada a uma ligação totalmente soldada. Comparando com o modelo experimental o método dos componentes avaliou de forma razoável a rigidez em serviço, já o método proposto por Leon et. al. superestimou muito esse parâmetro, a capacidade de rotação foi avaliada de forma satisfatória pelos dois métodos. O momento resistente negativo da viga mista obtido experimentalmente apresentou um valor intermediário entre os valores teóricos obtidos por processo plástico e elástico. / In Brazil, the cold-formed steel structures have been widely used justified by the large availability of steel sheets in the market (thin sheets) and the search for more competitive structural solutions. Thus as steel and concrete composite structures are applied in small constructions the traditional hot-rolled one is replaced by cold-formed members in the beams and columns. Even though the composite beams system is known in the hot-rolled and welded shapes field, the structural behavior of the cold-formed steel still needs more accurate investigation to verify the failure modes and the viability of the classic theoretical models. In this work a theoretical and experimental study about cold-formed steel and concrete composite beams was developed, focusing on the beam-to-column connection and the structural behavior on the region of hogging bending. For the experimental program two cruciform models of beam-column connections were analyzed to obtain the moment-rotation curves, the stiffness, and the rotation capacity. It was possible to verify the largest rotation capacity of the connection with the steel seat and web angle when compared with the totally welded connection. In the case of connection the method of the components estimates well the secant stiffness and the rotation capacity presenting a value closer to the ones obtained experimentally, Leon et al. procedures estimated well the initial stiffness and the rotation capacity, but the value of the secant stiffness is much larger than the experimental one. In the case of composite beam the ultimate strength (Mmax) experimentally obtained presented an intermediate value to the ones obtained by the plastic and elastic method.

Terças de aço formadas a frio são muito utilizadas em sistemas de cobertura e fechamento. Para conferir continuidade entre tramos adjacentes e possibilitar um melhor aproveitamento de material, são empregadas ligações parafusadas por transpasse e com luva. O comportamento estrutural dessas ligações é muito dependente da sua configuração geométrica e do nível de carregamento. Com base em uma série de nove experimentos e análises teóricas, o comportamento estrutural dessas ligações foi investigado no tocante aos esforços resistentes e à rigidez. Observou-se que o modo de falha tem sempre uma componente distorcional significativa e uma resistência menor que a prevista pela metodologia atual de projeto. No caso do momento fletor resistente, a distribuição de tensões de flexão oblíqua é a que melhor se aproxima do comportamento real das terças, sendo possível a partir de uma análise de estabilidade elástica considerando tal comportamento, e, baseado no método da resistência direta e na curva de dimensionamento do modo distorcional, obter uma previsão segura do momento fletor resistente. Além disso, a rigidez da ligação, com relação aos deslocamentos verticais é bastante dependente do tipo de ligação, sendo que as terças com ligações por luva são mais deformáveis que terças sem ligações. Por outro lado, terças com ligações por transpasse são menos deformáveis que terças fisicamente contínuas. As parcelas de rigidez da ligação são apresentadas, e a componente de deformação do furo é a mais significativa. Uma expressão para deduzir a rigidez rotacional da ligação é apresentada, juntamente com um modelo de barras para modelagem da ligação. Os resultados teóricos se ajustam muito bem aos experimentais. Conclui-se em linhas gerais, que as ligações por transpasse podem ser consideradas plenamente satisfatórias do ponto de vista de comportamento estrutural, sendo que terças com essas ligações são mais resistentes e rígidas que terças com continuidade física. O mesmo não ocorre nas terças com ligações por luva, porém, dada a limitação no número de ensaios, tais ligações carecem mais estudos. / Cold-formed steel purlins are widely used in roofs and wall systems. The continuity of long runs of cold-formed steel purlins is guaranteed by sleeve and overlap bolted connections, which allows a better load distribution and material savings. The structural behavior of these connections is highly dependent on their geometric configuration and load level. The strength and stiffness of these connections were determined through a series of nine experiments, numerical and analytical analysis. Results have shown that distortional buckling has a major contribution on the stability analysis of the cold-formed steel purlin. To safely determine the flexural strength of the purlin, one must consider unrestrained bending stress distribution and distortional buckling. The connection type influences the rigidity of the purlin thus the vertical displacement. Purlins with overlapped connections are stiffer than physically continuous ones, although purlins with sleeved connections are not. The bearing deformation at the connection region is responsible for a reduction in the system stiffness. To account for the change in stiffness and determine the vertical displacement, an expression for the bearing stiffness and a beam model are proposed. The results of this model show good agreement with experimental data. The general conclusion of this research is: overlapped bolted connections enhance the structural response of the purlins when compared to physically continuous ones. The same does not hold true for purlins with sleeved connections.