This paper summarizes a study performed to evaluate the seismic performance of aluminum structures. The effect of different stress-strain behavior between aluminum and steel material on the seismic performance of two functionally similar structures is the focus of this study. A one-story building archetype was chosen and the FEMAP695 approach was employed to study seismic performance factors for the building designed either from aluminum or steel. A geometric and material nonlinear model employing shell and beam finite elements, but excluding fracture, was developed to analyze the behavior of both buildings under earthquake ground motions. Incremental dynamic analysis was performed on the two archetypes and a fragility curve describing the probability of collapse versus the earthquake intensity was derived for each building. Finally, the performance of the two buildings was evaluated, showing that the aluminum building performed comparably to the steel building. It was observed in the models that the hysteresis behavior for the aluminum building develops primarily through interaction between buckling and yielding of the flanges at beam-column connections and at column supports.

The objective of this paper is to explore the impact of load combinations on the method used to assess the structural reliability of cold-formed steel components determined by testing. Chapter F of the AISI Specification (AISI-S100-07) provides a means to determined the resistance, ϕ or (safety, Ω) factor of cold-formed steel components by direct testing. The procedure uses the standard (United States) Load and Resistance Factor Design format, but simplifies the load side to a single load combination and single dead-to-live load ratio. The impact of this assumption on the resulting component reliability is the focus of this work. To complete the work the bias factors and variances for all loading conditions are established. In addition, a range of practical load ratios, for all loads, is assumed. Parametric studies are performed to explore load case and load ratio dependency for use in the determination of the resistance factor, ϕ; specifically, the pre-factor term Cϕ and the load variance term VQ. The parametric studies are simplified into a table that provides load case dependent Cϕ and VQ factors. Design examples demonstrating the impact of current methods and the load combination dependent solution are provided.

This paper explores an all-steel design philosophy for flexural bracing requirements in cold-formed steel stud walls that employ mechanical bridging alone without sheathing. The current cold-formed steel design specification requires the brace for a single compression member to have stiffness equal to twice the ideal brace stiffness, but related proposals for braces in multiple stud walls, including brace force accumulation and minimum brace stiffness, have not yet been adopted. Bracing strength and stiffness demands in cold-formed steel-framed walls must be adequate to ensure safety but not overly conservative so that the requirements cannot be practically met. Elastic critical load and second-order elastic analyses are conducted herein to determine an adequate level of stiffness for a single braced compression member and relationships between strength and stiffness for braced multiple studs to that of a single stud. Statistics of measured member imperfections are incorporated to provide an equivalent imperfection for multiple stud walls. Design by second-order analysis is utilized to determine how alternating the direction of studs affects strength and stiffness requirements. For a single-braced compression member, the impact of allowing a minimum of 1.33 times, instead of twice the ideal brace stiffness, is explored as an alternative to current requirements. New design expressions for brace stiffness and strength, incorporating the notion of a minimum brace stiffness, and the equivalent imperfection are provided. The new expressions provide the designer with greater flexibility in developing solutions that meet the necessary stiffness and strength requirements. (C) 2014 American Society of Civil Engineers.

The objective of this paper is to demonstrate how simple bar-spring models can illustrate elementary and advanced structural behavior, including stability, imperfection sensitivity, and plastic collapse. In addition, the same bar-spring models also provide a ready means for assessing structural reliability. Bar-spring models for a column (both post-buckling stable and unstable), a frame, and a plate are all developed. For each model the influence of geometric imperfections are explicitly introduced and the ultimate strength considering plastic collapse of the supporting springs derived. The developed expressions are compared to material and geometric nonlinear finite element analysis models of analogous continuous systems, using yield surface based plastic hinge beam elements (in MASTAN) for the column and frame and shell elements (in ABAQUS) for the plate. The results show excellent qualitative agreement, and surprisingly good quantitative agreement. The developed bar-spring models are used in Monte Carlo simulations and in the development of first order Taylor Series approximations to provide the statistics of the ultimate strength as used in structural reliability calculations. Good agreement between conventional first order second moment assumptions and the Monte Carlo simulations of the bar-spring models is demonstrated. It is intended that the developed models provide a useful illustration of basic concepts central to structural stability and structural reliability.