Strength Reduction Factor (R-Factor), often referred to as Response Modification Factor, is commonly used in the design of lateral force resisting systems under seismic loading. R-Factors allow for a reduction in design base shear demands, leading to more economical designs. The reduction of strength is remedied with ductile behavior in members of proper detailing. Modern seismic codes and provisions recommend R-Factors for many types of lateral force resisting systems. However these factors are independent of the system fundamental frequency and many other important system properties, resulting in factors that may result in an unfavorable seismic response. To evaluate the validity of prescribed R-Factors an extensive analytical parameter study was conducted using a FEM single degree-of-freedom Concentrically Braced Frame (CBF) under incremental dynamic analysis over a suite of ground motions. Parameters of the study include brace slenderness, fundamental frequency, increment resolution, FEM mesh refinement, effects of leaning columns, and effects of low-cycle fatigue. Results suggest that R-Factor can vary drastically for CBF systems with differing properties.

<p> A research programme is presented to more fully understand the behaviour of Round Hollow Structural Sections subjected to inelastic strain reversals. An attempt is made to establish a preliminary guideline for choosing a reasonable value for the slenderness ratio (D/t) that qualifies the Round HSS for cyclic loading. </p> <p> An experimental programme on nine sections was performed to evaluate the loss in load capacity due to inelastic cyclic loading and to construct the load-deflection hysteresis loops. </p> <p> Three different limiting cyclic deflections were imposed to the smallest D/t section and a comparison was made between the performance of the tube in each case. </p> <p> Prasad's computer program was used to select the strain value at which local buckling will appear and to calculate the half buckle wave-length. The results were compared to the experimental results obtained by the author. </p> <p> A comparison is made between two Round HSS having different diameters and thicknesses but the same D/t ratio. </p> <p> A comparison is made between the behaviour of Round HSS and Square HSS subjected to the same cyclic loading programme. </p> <p> An attempt is made to suggest a reasonable curve relating the number of cycles to failure and the D/t ratio. </p> / Thesis / Master of Engineering (ME)

This paper presents the experimental results and observation of elliptical concrete filled tube (CFT) columns subjected to axial compressive load. A total of twenty-six elliptical CFT specimens including both stub and slender composite columns are tested to failure to investigate the axial compressive behaviour. Various column lengths, sectional sizes and infill concrete strength are used to quantify the influence of member geometry and constituent material properties on the structural behaviour of elliptical CFT columns. As there is no design guidance currently available in any Code of Practice, this study provides a review of the current design rules for concrete filled circular hollow sections in Eurocode 4 (EC4). New equations based on the Eurocode 4 provisions for concrete filled circular hollow sections were proposed and used to predict the capacities of elliptical CFT columns.

Made available in DSpace on 2014-07-29T15:03:35Z (GMT). No. of bitstreams: 1 pre-textuais Rodrigo Fernandes.pdf: 349523 bytes, checksum: 27a5e6d7df167303c662872391301d36 (MD5) Previous issue date: 2007-10-01 / This work contains a theoretical analysis of the behavior of plate girders. A plate girder has been calculated based on the criteria of the American standard Manual of Steel Construction Load and Resistance Factor Design (AISC, 1994), and checked by the Brazilian standard NBR 8800: Projeto e execução de estruturas de aço de edifícios (método dos estados limites) (ABNT, 1986), the revision project of the Brazilian standard Projeto de Revisão da NBR 8800: Projeto e execução de estruturas de aço e de estruturas mistas aço-concreto de edifícios (ABNT, 2003), the revision project of the Brazilian standard Projeto de Revisão da NBR 8800: Projeto de estruturas de aço e de estruturas mistas de aço e concreto de edifícios (ABNT, 2007) and the European standard Eurocode 3: Design of steel structures Part 1.1: General rules and rules for buildings (CEN, 1992). PFEIL (1989) has calculated a plate girder by using the Brazilian standard NBR 8800/86. The calculated dimension have been checked by the mentioned standards. NARAYANAN (1992 apud OWENS, KNOWLES E DOWLING, 1992) has dimensioned a plate girder by using the British standard BS 5950: Structural use of steelwork in building. Part 1: Code of practice for design in simple and continuous construction: hot rolled sections (BSI, 1990), which has also been checked by the mentioned standards. Furthermore, theoretical analyses related to the calculus of plate girders presented by many authors have been considered. The main goal is to assess the criteria utilized by the standards for the calculus of plate girders. From the obtained results, for the checked girders, by the standards and related theories, a comparative analysis among the utilized criteria by the standards has been made. The reached conclusion is that the Brazilian standard and its revision projects has identical criteria compared to the American standard for the calculus of plate girders. The European standard presents slightly different criteria compared to the American standard; however, both provide close results one compared to another. The theories utilized have also provided close results from those obtained by the standards. / Neste trabalho é feita uma análise teórica sobre o comportamento de vigas esbeltas. Uma viga esbelta foi dimensionada com base nos critérios da norma americana Manual of Steel Construction Load and Resistance Factor Design (AISC, 1994), e depois verificada pela norma brasileira NBR 8800: Projeto e execução de estruturas de aço de edifícios (método dos estados limites) (ABNT, 1986), pelo projeto de revisão da norma brasileira Projeto de Revisão da NBR 8800: Projeto e execução de estruturas de aço e de estruturas mistas aço-concreto de edifícios (ABNT, 2003), pelo projeto de revisão da norma brasileira Projeto de Revisão da NBR 8800: Projeto de estruturas de aço e de estruturas mistas de aço e concreto de edifícios (ABNT, 2007) e pela norma européia Eurocode 3: Design of steel structures Part 1.1: General rules and rules for buildings (CEN, 1992). PFEIL (1989) dimensionou uma viga esbelta utilizando a norma brasileira NBR 8800/86. As dimensões calculadas foram verificadas pelas normas citadas. NARAYANAN (1992 apud OWENS, KNOWLES E DOWLING, 1992) dimensionou uma viga esbelta utilizando a norma britânica BS 5950: Structural use of steelwork in building. Part 1: Code of practice for design in simple and continuous construction: hot rolled sections (BSI, 1990), a qual foi também verificada pelas normas citadas. Também foram consideradas análises teóricas relativas ao cálculo de vigas esbeltas apresentadas por diversos autores. O objetivo principal é avaliar os critérios utilizados pelas normas para o cálculo de vigas esbeltas. A partir dos resultados obtidos, para as vigas analisadas, pelas normas e pelas teorias existentes, foi feita uma análise comparativa entre os critérios utilizados pelas normas. A conclusão a que se pôde chegar é que a norma brasileira e seus projetos de revisão apresentam critérios idênticos aos da norma americana para o cálculo de vigas esbeltas. A norma européia apresenta critérios um pouco diferenciados dos critérios da norma americana, mas fornecem resultados aproximados entre si. As teorias utilizadas também forneceram resultados aproximados dos resultados obtidos pelas normas.

Esta tese discute as análises teórica e experimental de pilares de seção retangular, esbeltos, confinados por estribos, de concreto de alta resistência, sujeitos à flexo-compressão, considerando os estados limites últimos de ruptura do concreto ou por deformação excessiva das barras da armadura ou por instabilidade. Foram ensaiados 12 modelos de pilares com esbeltez mecânica igual a 92, compondo três séries de 4 pilares cada uma; os parâmetros estudados foram a excentricidade da força, a taxa volumétrica de armadura transversal e a resistência do concreto. Em uma segunda fase, foram analisados 9 pilares curtos de seção quadrada à compressão concêntrica com o objetivo de avaliar a ductilidade e obter as propriedades do concreto confinado. Para a realização dos ensaios foram empregadas rótulas unidirecionais, que permitiram transferir a força excêntrica ao pilar. Para a obtenção das resistências dos concretos, foram realizados ensaios para a determinação da composição dos materiais e foram traçadas curvas de dosagem. Os resultados experimentais foram comparados com os obtidos com o método exato que considera a não linearidade física e geométrica por meio de programas computacionais elaborados pelo autor. Observou-se que os resultados experimentais se aproximaram dos resultados teóricos. As ruínas dos pilares esbeltos foram por instabilidade, sendo que todos eles atingiram o ponto limite. Foi verificado que a capacidade resistente dos pilares é muito sensível para pequenas variações da excentricidade da força. Nos modelos analíticos foram incorporadas formulações de várias normas que contemplam concretos de alta resistência e o critério de confinamento indicadas pela literatura técnica com algumas modificações. Foi verificada uma pequena melhora na ductilidade ao incrementar a taxa de armadura transversal dos modelos ensaiados. Com os resultados obtidos e com as formulações analisadas, sugere-se uma forma alternativa de projeto de pilares esbeltos. / This thesis discusses the theoretical and experimental analyses of slender high-strength concrete rectangular columns confinement by lateral reinforcement, subjected to combined axial load and bending, considering the ultimate limit states of concrete crushing at the compressive face or the longitudinal bars excessive deformation or the column instability. Twelve column models were tested with 92 mechanical slenderness. These models included three series of four columns each; the parameters studied were axial load eccentricity, volumetric lateral reinforcement ratio and concrete strength. In a second step, nine square cross section short columns under concentric compression were tested to evaluate ductility and to obtain the confined concrete properties. A pair of unidirectional hinges was used to transfer the eccentric load to the columns. Tests were carried out for material\'s composition determination and dosage curves were drawn to obtain concrete strengths. The experimental results were compared with those obtained using the exact method that considers physical and geometrical nonlinearities through computational programs prepared by the author. There is not a significant difference between experimental and theoretical results. The instability failure was reach in all columns because of high slenderness, all of they reached the limit point. It was observed that the column ultimate strength is very sensitive for small axial load eccentricity variations. The formulations of several standards codes that consider the high-strength concrete and technical literature confinement criterion with some modifications have been incorporated in the analytical models. A small ductility improvement was observed considering the tests volumetric lateral reinforcement ratio increase. There is an alternative method suggested for slender columns design, based on the obtained results.

The study presents the results of an experimental and analytical investigation aimed at examining the lateral stability of rectangular reinforced concrete slender beams. In the experimental part of the investigation, a total of eleven reinforced concrete beams having a depth to width ratio between 10.20 and 12.45 and a length to width ratio between 96 and 156 were tested. Beam thickness, depth and unbraced length were 1.5 to 3.0 in., 18 to 44 in., and 12 to 39.75 ft, respectively. Each beam was subjected to a single concentrated load applied at midspan by means of a gravity load simulator that allowed the load to always remain vertical when the section displaces out of plane. The loading mechanism minimized the lateral translational and rotational restraints at the load application point to simulate the nature of gravity load. Each beam was simply-supported in and out of plane at the ends. The supports allowed warping deformations, yet prevented twisting rotations at the beam ends. In the analytical part of the study, a formula was developed for determining the critical loads of lateral torsional buckling of rectangular reinforced concrete beams free from initial geometric imperfections. The influences of shrinkage cracking and inelastic stress-strain properties of concrete and the contribution of longitudinal reinforcement to the lateral stability are accounted for in the critical load formula. The experiments showed that the limit load of a concrete beam with initial geometric imperfections can be significantly lower than the critical load corresponding to its geometrically perfect configuration. Accordingly, a second formula was developed for the estimation of limit loads of reinforced concrete beams with initial lateral imperfections, by introducing the destabilizing effect of sweep to the critical load formula. The experimental results were compared to the proposed analytical solution and to various lateral torsional buckling solutions in the literature. The formulation proposed in the present study was found to agree well with the experimental results. The incorporation of the geometric and material nonlinearities into the formula makes the proposed solution superior to the previous lateral torsional buckling solutions for rectangular reinforced concrete beams.

Feasible span-to-depth ratios for many modern bridge systems have been identified and documented in literature. No such parameters have been adequately identified in terms of proportioning bridge piers. This thesis includes a study of 22 existing reinforced concrete highway bridges and their respective pier systems to determine the state-of-the-art in design. The effect of different geometric and material parameters such as concrete strength, reinforcement ratio and slenderness ratio on the structural behavior of individual piers and multiple pier systems was examined. Approximate methods, which may be used for the purposes of preliminary design are discussed and reviewed. Serviceability and ultimate limit states design aids that can be used to identify appropriate preliminary cross-sectional pier dimensions and reinforcement ratios for individual piers given various slenderness ratios were developed. The structural behavior as well as an approach to the preliminary design of multiple pier bridge systems is presented.

Feasible span-to-depth ratios for many modern bridge systems have been identified and documented in literature. No such parameters have been adequately identified in terms of proportioning bridge piers. This thesis includes a study of 22 existing reinforced concrete highway bridges and their respective pier systems to determine the state-of-the-art in design. The effect of different geometric and material parameters such as concrete strength, reinforcement ratio and slenderness ratio on the structural behavior of individual piers and multiple pier systems was examined. Approximate methods, which may be used for the purposes of preliminary design are discussed and reviewed. Serviceability and ultimate limit states design aids that can be used to identify appropriate preliminary cross-sectional pier dimensions and reinforcement ratios for individual piers given various slenderness ratios were developed. The structural behavior as well as an approach to the preliminary design of multiple pier bridge systems is presented.

Esta tese discute as análises teórica e experimental de pilares de seção retangular, esbeltos, confinados por estribos, de concreto de alta resistência, sujeitos à flexo-compressão, considerando os estados limites últimos de ruptura do concreto ou por deformação excessiva das barras da armadura ou por instabilidade. Foram ensaiados 12 modelos de pilares com esbeltez mecânica igual a 92, compondo três séries de 4 pilares cada uma; os parâmetros estudados foram a excentricidade da força, a taxa volumétrica de armadura transversal e a resistência do concreto. Em uma segunda fase, foram analisados 9 pilares curtos de seção quadrada à compressão concêntrica com o objetivo de avaliar a ductilidade e obter as propriedades do concreto confinado. Para a realização dos ensaios foram empregadas rótulas unidirecionais, que permitiram transferir a força excêntrica ao pilar. Para a obtenção das resistências dos concretos, foram realizados ensaios para a determinação da composição dos materiais e foram traçadas curvas de dosagem. Os resultados experimentais foram comparados com os obtidos com o método exato que considera a não linearidade física e geométrica por meio de programas computacionais elaborados pelo autor. Observou-se que os resultados experimentais se aproximaram dos resultados teóricos. As ruínas dos pilares esbeltos foram por instabilidade, sendo que todos eles atingiram o ponto limite. Foi verificado que a capacidade resistente dos pilares é muito sensível para pequenas variações da excentricidade da força. Nos modelos analíticos foram incorporadas formulações de várias normas que contemplam concretos de alta resistência e o critério de confinamento indicadas pela literatura técnica com algumas modificações. Foi verificada uma pequena melhora na ductilidade ao incrementar a taxa de armadura transversal dos modelos ensaiados. Com os resultados obtidos e com as formulações analisadas, sugere-se uma forma alternativa de projeto de pilares esbeltos. / This thesis discusses the theoretical and experimental analyses of slender high-strength concrete rectangular columns confinement by lateral reinforcement, subjected to combined axial load and bending, considering the ultimate limit states of concrete crushing at the compressive face or the longitudinal bars excessive deformation or the column instability. Twelve column models were tested with 92 mechanical slenderness. These models included three series of four columns each; the parameters studied were axial load eccentricity, volumetric lateral reinforcement ratio and concrete strength. In a second step, nine square cross section short columns under concentric compression were tested to evaluate ductility and to obtain the confined concrete properties. A pair of unidirectional hinges was used to transfer the eccentric load to the columns. Tests were carried out for material\'s composition determination and dosage curves were drawn to obtain concrete strengths. The experimental results were compared with those obtained using the exact method that considers physical and geometrical nonlinearities through computational programs prepared by the author. There is not a significant difference between experimental and theoretical results. The instability failure was reach in all columns because of high slenderness, all of they reached the limit point. It was observed that the column ultimate strength is very sensitive for small axial load eccentricity variations. The formulations of several standards codes that consider the high-strength concrete and technical literature confinement criterion with some modifications have been incorporated in the analytical models. A small ductility improvement was observed considering the tests volumetric lateral reinforcement ratio increase. There is an alternative method suggested for slender columns design, based on the obtained results.

AASHTO LRFD requires the use of longitudinal stiffeners in plate girder webs when the web slenderness D/tw is greater than 150. This practice is intended to limit the lateral flexing of the web plate during construction and at service conditions. AASHTO accounts for an increase in the web bend buckling resistance due to the presence of a longitudinal stiffener. However, when the theoretical bend buckling capacity of the stiffened web is exceeded under strength load conditions, the Specifications do not consider any contribution from the longitudinal stiffener to the girder resistance. That is, the AASHTO LRFD web bend buckling strength reduction factor Rb applied in these cases is based on an idealization of the web neglecting the longitudinal stiffener. This deficiency can have significant impact on girder resistance in regions of negative flexure. This research is aimed at evaluating the improvements that may be achieved by fully considering the contribution of web longitudinal stiffeners to the girder flexural resistance. Based on refined FE test simulations, this research establishes that minimum size longitudinal stiffeners, per current AASHTO LRFD requirements, contribute significantly to the post buckling flexural resistance of plate girders, and can bring as much as a 60% increase in the flexural strength of the girder. A simple cross-section Rb model is proposed that can be used to calculate the girder flexural resistance at the yield limit state. This model is developed based on test simulations of straight homogenous girders subjected to pure bending, and is tested extensively and validated for hybrid girders and other limit states. It is found that there is a substantial deviation between the AISC/AASHTO LTB resistance equations and common FE test simulations. Research is conducted to determine the appropriate parameters to use in FE test simulations. Recommended parameters are identified that provide a best fit to the mean of experimental data. Based on FE simulations on unstiffened girders using these recommended parameters, a modified LTB resistance equation is proposed. This equation, used in conjunction with the proposed Rb model also provides an improved handling of combined web buckling and LTB of longitudinally stiffened plate girders. It is observed that the noncompact web slenderness limit in the Specifications, which is an approximation based on nearly rigid edge conditions for the buckling of the web plate in flexure is optimistic for certain cross-sections with narrow flanges. This research establishes that the degree of restraint at the edges of the web depend largely on the relative areas of the adjoining flanges and the area of the web. An improved equation for the noncompact web slenderness limit is proposed which leads to a better understanding and representation of the behavior of these types of members.