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
Experimental investigation of slab joints between existing buildings and new frames for vertical expansion; [Part I]
Vertical additions can be made to existing buildings to provide more residences while avoiding the need to fully dismantle and reconstruct the buildings. Super‐structural frames consisting of shallow composite beams and steel columns can be prefabricated as modular units, replacing the wall frames that are conventionally constructed in existing bearing wall buildings. A lightweight modular construction introduced in this study minimizes the needed structural reinforcement of frames below, enabling quicker and safer assembly of frames relative to traditional wall frame construction. This paper introduces joint details between added steel columns and existing slabs. Extensive experimental investigations were performed to study the structural behavior of the suggested joints. Eight full‐scale specimens were loaded to failure to evaluate the structural applicability and reliability of the connecting methods introduced in this study, and to identify any problems with the vertical additions. The present work was also intended to find effective design procedures to those issues, and to provide test data for use in detailed analytical investigation of the structural behavior. Regardless of the connection method and the failure mode, all specimens demonstrated stable structural performance within the range of loadings that are expected during the service life of vertically extended buildings.
Applications of nanocomposite hydrogels for biomedical engineering and environmental protection
Nanocomposite hydrogels are polymeric networks that possess a unique property of hydration. The presence of alcohols, carboxylic acids and amides as hydrophilic moieties in structure of nanocomposite hydrogels enhances their stiffness and water-absorbing capacity. Addition of cross-linker in the synthesis of hydrogels increases their stability under extreme conditions of temperature, pH and pressure. Natural polymer-based nanocomposite hydrogels are biodegradable, highly hydrophilic and possess good mechanical strength. Gelatin, chitin, cellulose, pectin, carrageenan, starch and alginate are natural polymers commonly used to fabricate nanocomposite hydrogels. Nanocomposite hydrogels have special characteristics such as high swelling rate, selectivity and stimuli-sensitive nature. Here we review nanocomposite hydrogels for environmental protection and biomedical engineering. Applications in biomedical engineering include drug delivery agents, wound dressing, tissue engineering and antibacterials. Applications in environmental protection include ion exchangers, adsorption, photocatalysis and soil conditioning. Many nanocomposite hydrogels show excellent adsorption selectivity for heavy metal ions: Cu2+ up to 30.35 mg/g, Pb2+ up to 35.94 mg/g, and Zn2+ and Fe3+ up to 94.34 mg/g. Xanthan gum-based nanocomposite hydrogel has removed 96% dye from industrial effluent as reported. In addition, most of the nanocomposite hydrogels showed better adsorption capacity for pollutants in the pH range from 5 to 7. The nanocomposite hydrogels could also be regenerated and successfully utilized for several times. Nanocomposite hydrogels are therefore good bio-absorbent materials for environmental detoxification.