Analysis and Design of Steel-Concrete Composite Frame Systems
The lack of clear guidance regarding the value of elastic flexural rigidity (EI) that should be used in the analysis of steel-concrete composite columns is a significant unresolved issue that hinders the design of frame systems that include these members. The common approach of utilizing the rigidity of either the steel or the concrete only tends to be overly conservative. Other approaches that combine the rigidities have not been fully validated for use in strength and stability design procedures or for the determination of lateral deflections. To address this issue, research has been conducted to develop comprehensive recommendations for the elastic flexural rigidity of composite columns. A complimentary goal has been to validate common strength design procedures, including interaction diagrams, axial compression and bending moment anchor points, and analysis procedures to determine required strengths. In this paper, an assessment of current strength design methodologies is presented along with recommendations for potential improvements. Both the AISC Direct Analysis method and the ACI elastic second-order analysis method are investigated. INTRODUCTION The wide availability of structural analysis software packages that perform accurate geometric nonlinear analyses has made second-order elastic analysis design approaches very common in practice. Such design provisions exist for steel-concrete composite members in both the AISC Specification (AISC 2010b), as the Direct Analysis method, and the ACI Code (2011), as the second-order analysis method. However, neither methodology has yet been comprehensively assessed for validity and accuracy, as has been done in the past for structural steel (Kanchanalai 1977; Surovek-Maleck and White 2004) and for reinforced concrete (Hage and MacGregor 1974). This paper presents the results of a large parametric study that has been conducted to assess the current design methodologies with a particular emphasis on the elastic flexural rigidity (EI) recommended for analysis. 2605 Structures Congress 2014 © ASCE 2014
ALTERNATIVE APPROACHES FOR ELASTIC ANALYSIS AND DESIGN OF STEEL FRAMES. I: OVERVIEW
Two methods for analysis and design of steel framing systems are outlined and compared to the current American Institute of Steel Construction (AISC) load and resistance factor design (LRFD) buckling solution or effective length based procedure: an AISC LRFD based notional load approach and a modified elastic approach. Both methods provide a rational means of accounting for the key phenomena that affect system strength, specifically residual stresses (i.e., member inelasticity) and initial geometric imperfections. By accounting for these factors directly within a second-order elastic analysis, the need for effective length factors or buckling solutions is eliminated. Also, these methods provide a more accurate estimate of required internal system forces than current methods. Examples of solutions for a stability critical industrial-type frame are presented to illustrate the application of these methods, and to compare and contrast their results with solutions from both the current AISC LRFD procedures and from rigorous distributed plasticity analysis.
Multilayer high density flex technology
The industrial trend of shrinking microelectronic devices while increasing the density of interconnections places great demands on the substrates upon which these devices are packaged. Multilayer flex circuits will provide the interconnection densities needed to meet these demands in a wide range of packaging and interconnection technologies. This paper discusses the development of ultra-high density flexible circuits. Processes and materials to fabricate fine line pitches from 12.5 /spl mu/m to 40 /spl mu/m are examined. Various microvia structures, through hole and blind via, are demonstrated. A test vehicle was designed and built for BGA packages to illustrate the density capability. A four-layer structure is demonstrated by using Z-connection to connect two layer pairs. Electrical, mechanical, and reliability test results are presented to show the selection of flex substrate material, Z-connection methodology and fabrication processes. A cost comparison of high-density flex to alternative substrates is discussed to identify potential.