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The article presents the background on the step-by-step procedures available in the 2005 American Institute of Steel Construction (AISC) Specification for Structural Steel Buildings for computing composite column and beam-column strength, including accounting for stability effects on members subjected to biaxial flexure plus axial compression. The new processes highlighted in the AISC Specification are discussed, including the use of a plastic stress distribution method that accounts for the beneficial effects of the concrete to the strength of the cross-section. Several examples are provided for calculating the design strength of encased composite sections as well as filled composite sections, both rectangular and circular.

The article discusses the behavior of steel joist girder structures with PR column bases. The section reports on a combined analytical/experimental investigation aimed at: assessing the frame behavior of joist girder frames with different column base fixities; evaluating the stiffness and strength of column bases by means of both experimental and analytical approaches; and developing seismic design procedures that account for the real column base conditions. It also reflects on a companion paper, discussing in detail other design aspects and provides an example design for type of structure.

A full-scale two-story unreinforced masonry (URM) building was tested in a quasistatic fashion to investigate the nonlinear properties of existing URM structures and to assess the efficiency of several common retrofit techniques. This paper presents the main experimental findings associated with the nonlinear properties of the original URM structure. The test structure exhibited large initial stiffness and its damage was characterized by large, discrete cracks that developed in masonry walls. Significant global behavior such as global rocking of an entire wall, and local responses such as rocking and sliding of each individual pier were observed in the masonry walls with different configurations. In addition, formation of flanges in perpendicular walls and overturning moments had significant effects on the behavior of the test structure. A comparison between the experimental observations and the predictions of FEMA 356 provisions shows that major improvements are needed for this latter methodology. [ABSTRACT FROM AUTHOR]

A variety of elastic and inelastic analytical approaches were used to investigate the response of a full-scale unreinforced masonry (URM) structure tested in the laboratory. Elastic analyses, employing a three-dimensional finite element model, revealed little coupling between parallel walls, and pointed to the appropriateness of two-dimensional analytical tools for further simulation of the test structure. The nonlinear analytical methods employed included, in order of increasing complexity, a rigid body analysis, a two-dimensional nonlinear pushover analysis, and a three-dimensional nonlinear finite element analysis. All methods considered important structural characteristics such as failure modes of perforated walls, flange effects, and global overturning moment effect. All methods predicted the experimental behavior fairly well. Strengths and weaknesses of these analytical approaches are discussed, and recommendations for analyzing old URM buildings are presented. [ABSTRACT FROM AUTHOR]

Based on the results of a full-scale lateral load test of a two-story unreinforced masonry (URM) structure, modifications are suggested for the model implied by FEMA 356 for the in-plane analysis of perforated URM walls. These modifications allow the model to address global issues such as flange participation, overturning effects, and global rocking. In addition, changes are proposed to the pier model as well as to the definition of effective pier height. Following a description of each modification, the analysis results obtained using the proposed model and FEMA 356 are compared with experimental results. In terms of base shear resistance, the proposed model displayed an average error (absolute value) of 13% compared with an average error of 21% from FEMA 356. In addition, the proposed model also provided more accurate representation of failure modes. The improved accuracy of the proposed model is primarily attributed to the consideration of global issues. The results of a parametric analysis are also presented to provide insight into the relative influence of each modification proposed. [ABSTRACT FROM AUTHOR]

The commentary to the AISC-LRFD Specification addresses the design of framing systems containing partially restrained (PR) connections, but it does not provide specific guidance on how to analyze these types of systems to determine appropriate internal forces for design. In addition, it provides little information on how to select an appropriate connection stiffnesses for design calculations, such as the calculation of effective length factors. This paper presents an approach that allows for the consideration of nonlinear connection response using commonly available elastic analysis software. In addition, the application of the direct analysis approach to PR framing systems is presented in the context of the proposed method for handling the connection nonlinearity. The direct analysis approach allows for stability to be assessed using the AISC-LRFD beam-column interaction equations with the axial strength term Pn determined based on the actual member length. This eliminates the complexity of determining effective length factors for partially restrained framing. [ABSTRACT FROM AUTHOR]