Abstract The current advanced analysis techniques for steel frames generally use structural analyses with geometric and material nonlinearities to capture the collapse strength of the steel frame. Unfortunately, the true strength of a steel frame cannot be predicted with accuracy because of the uncertainties of the most significant design variables. Building codes of steel structures apply a resistance factor to account for the uncertainties present in the design variables and thus ensure a target level of structural reliability. This article examines the reliability of planar steel frames subject to gravitational loads by advanced structural analysis (second-order inelastic analysis). To calculate the collapse probability of planar steel frames, we utilized the first-order reliability method (FORM). The advanced analyses were performed using the program MASTAN2 and considered the geometric nonlinearities and inelasticity of the steel. The collapse probabilities of planar steel frames were evaluated and the adequacy of the resistance factor applied was discussed. The current inelastic design procedure of ANSI 360 reduces the yield strength and stiffness of all members by a factor of 0.90. Thus, the present study suggests that the adopted resistance factor must be equal to 0.85 for the target reliability index equal to 3.0, or it must be equal to 0.69 for the target reliability index equal to 3.8. Unfortunately secondorder second order analysis. . analysis) firstorder first FORM. FORM (FORM) MASTAN discussed 36 090 0 90 0.90 Thus 085 85 0.8 30 3 3.0 069 69 0.6 38 8 3.8 (FORM 09 9 0.9 08 0. 3. 06 6

Abstract This article presents a procedure for the reliability assessment of cold-formed steel beams based on the Direct Strength Method (DSM) and the Effective Section Method (ESM). Using a comprehensive database, a statistical analysis of the test results was performed to determine the statistical properties of the professional factor random variable. The statistical parameters related to material strength, geometric properties and load effects were obtained from established references for reliability analysis. Safety levels compatible with the North American and the Brazilian codes relating to structural design of cold-formed steel members have been established. The first-order reliability method (FORM) was used to calculate resistance factors φ for usual nominal live-dead ratios. The results of the reliability analysis showed that the DSM and ESM design methods have similar levels of reliability. The same resistance factor as the DSM can be used for the ESM, without compromising the minimum level of reliability established. The results obtained with the LRFD calibration data, presented a good approximation with the load factor φ = 0.90, except for the distortional mode. With the LSD calibration data, values well below the specified were required in order to achieve the required level of reliability. It was also found that the load factor γ = 1.25, in the format of the Brazilian standard, could reach the safety requirements established for all buckling modes.

Abstract This article reports the results of an investigation on the effects of internal moments on the vibration behavior of thin-walled steel members. The analyses are based on the Generalized Beam Theory (GBT), a thin-walled bar theory accounting for cross-section in-plane deformations - its main distinctive feature is the representation of the member deformed configuration by means of a linear combination of cross-section deformation modes, multiplied by their longitudinal amplitude functions. The study concerns a simply supported T-section (with unequal flanges) members exhibiting a wide range of lengths and subjected to uniform internal moment diagrams - their magnitudes are specified as percentages of the corresponding critical buckling values. After providing a brief overview of the main concepts and procedures involved in performing a GBT-based structural analysis, the vibration behavior of load-free and loaded T-section members is addressed - the influence of the applied loadings is assessed in terms of (i) the fundamental frequency difference and (ii) the change in the corresponding vibration mode shape. For validation purposes, some GBT results are compared with values yielded by shell finite element analysis performed in the code ABAQUS (Simulia, 2008).

Nesse trabalho, é apresentado um estudo de ligações soldadas dos tipos K e KT, com barras afastadas, formadas por perfis tubulares de aço estrutural, sem costura, de seção transversal retangular no banzo e circular para demais membros. Para esse estudo, foram desenvolvidas análise analítica e análise numérica das ligações. Também foram desenvolvidos ensaios experimentais em protótipos em escala real e ensaios de tensões residuais no perfil retangular do banzo. Os ensaios dos protótipos das ligações visaram à obtenção do comportamento, carga última e modo de colapso da ligação. A análise numérica em elementos finitos envolveu a geração, a análise e a calibração, a partir dos resultados obtidos nos ensaios experimentais. O modelo foi constituído de forma que representasse o comportamento e a capacidade de carga das ligações ensaiadas experimentalmente. Os resultados foram apresentados de modo a comparar os dados obtidos experimentalmente com os diversos modelos numéricos gerados, com e sem o cordão de solda e sem as imperfeições geométricas. As análises realizadas apresentam boa correlação com os resultados experimentais.

This work presents a study of welded T and KT gap joints, formed by a seamless hollow section with rectangular hollow chord sections and circular hollow sections for the members. The developed study considers theoretical and numerical analyses for the joints, experimental tests in full scale prototypes, and tests for residual stress in the rectangular hollow section. The experimental results were used in order to obtain the overall joint behavior, ultimate load, and collapse mode. The numerical analysis using finite elements methods involved the generation, testing and calibration of the experimental results. The model represents the behavior and load capacity of the tested joints. The numerical models considered or not the welding and geometric imperfections and the results were compared with the experimental data. The accomplished analyses present good correlation with the experimental results.