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CONTENTS
Volume 6, Number 3, June 2006
 

Abstract
The behavior of steel-concrete composite beams is strongly influenced by the type of shear connection between the steel beam and the concrete slab. For accurate analytical predictions, the structural model must account for the interlayer slip between these two components. This paper focuses on a procedure for response sensitivity analysis using state-of-the-art finite elements for composite beams with deformable shear connection. Monotonic and cyclic loading cases are considered. Realistic cyclic uniaxial constitutive laws are adopted for the steel and concrete materials as well as for the shear connection. The finite element response sensitivity analysis is performed according to the Direct Differentiation Method (DDM); its analytical derivation and computer implementation are validated through Forward Finite Difference (FFD) analysis. Sensitivity analysis results are used to gain insight into the effect and relative importance of the various material parameters in regards to the nonlinear monotonic and cyclic response of continuous composite beams, which are commonly used in bridge construction.

Key Words
steel-concrete composite beams; beam elements; finite element method; nonlinear analysis; response sensitivity analysis; material parameters.

Address
Alessandro Zona; Department PROCAM, University of Camerino, Viale della Rimembranza, Ascoli Piceno 63100, ItalyrnMichele Barbato and Joel P. Conte; Department of Structural Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0085, USA

Abstract
One of the most promising ways through which a steel moment frame may attain high energy dissipating capability is to trim off a portion of the beam flanges near the column face. This type of moment connection, known as Reduced Beam Section (RBS) connection, has notable superiority in comparison with other moment connection types. As the result of the advantages of RBS moment connection, it has widely being used in practice. In spite of the good hysteretic behaviour, an RBS beam suffers from an undesirable drawback, which is local and lateral instability of the beam. The instability in the RBS beam reduces beam load-carrying capacity. This paper aims to investigate key issues influencing cyclic behaviour of RBS beams. To this end, a numerical analysis was conducted on a series of steel subassemblies with various geometric properties. The obtained results together with the existing experimental data are used to study the instability of RBS beams. A new slenderness concept is presented to control an RBS beam for combined local and lateral instability. This concept is in good agreement with the numerical and experimental results. Finally, a model is developed for the prediction of the magnitude of moment degradation owing to the instability of an RBS beam.

Key Words
steel structures; RBS moment connection; panel zone; instability; cyclic loading; ductility.

Address
Department of Civil Engineering, Amirkabir University of Technology, P. O. Box 15815-3537, Tehran, Iran

Abstract
The objective of this work is to describe the main steps involved in the derivation of a GBT (Generalised Beam Theory) formulation to analyse the vibration behaviour of loaded cold-formed steel members and also to illustrate the application and capabilities of this formulation. In particular, the paper presents and discusses the results of a detailed investigation about the local and global free vibration behaviour of lipped channel simply supported columns. After reporting some relevant earlier GBT-based results dealing with the buckling and vibration behaviours of columns and load-free members, the paper addresses mostly issues concerning the variation of the column fundamental frequency and vibration mode nature/shape with its length and axial compression level. For validation purposes, some GBT-based results are also compared with values obtained by means of 4-node shell finite element analyses performed in the code ABAQUS.

Key Words
eneralised beam theory (GBT); vibration analysis; buckling analysis; channel columns; column vibration; fundamental frequency; distortional modes; local-plate modes.

Address
Department of Civil Engineering, IST/ICIST, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

Abstract
This paper presents a novel analytical formulation for the analysis of composite beams with partial shear interaction stiffened by a bolted longitudinal plate accounting for time effects, such as creep and shrinkage. The model is derived by means of the principle of virtual work using a displacement-based formulation. The particularity of this approach is that the partial interaction behaviour is assumed to exist between the top slab and the joist as well as between the joist and the bolted longitudinal stiffening plate, therefore leading to a three-layered structural representation. For this purpose, a novel finite element is derived and presented. Its accuracy is validated based on short-and long-term analyses for the particular cases of full shear interaction and partial shear interaction of two layers for which solutions in closed form are available in the literature. A parametric study is carried out considering different stiffening arrangements to investigate the influence on the short-and long-term behaviour of the composite beam of the shear connection stiffness between the concrete slab and the steel joist, the stiffness of the plate-to-beam connection, the properties of the longitudinal plate and the concrete properties. The values of the deflection obtained from the finite element simulations are compared against those calculated using the effective flexural rigidity in accordance with EC5 guidelines for the behaviour of elastic multi-layered beams with flexible connection and it is shown how the latter well predicts the structural response. The proposed numerical examples highlight the ease of use of the proposed approach in determining the effectiveness of different retrofitting solutions at service conditions.

Key Words
composite beams; finite element method; partial interaction; stiffening; time effects.

Address
School of Civil Engineering, The University of Sydney, NSW 2006, Australia

Abstract
The behaviour of hollow structural steel (HSS) stub columns and beams filled with normal concrete and recycled aggregate concrete (RAC) under instantaneous loading was investigated experimentally. A total of 40 specimens, including 30 stub columns and 10 beams, were tested. The main parameters varied in the tests were: (1) recycled coarse aggregate (RCA) replacement ratio, from 0 to 50%, (2) sectional type, circular and square. The main objectives of these tests were threefold: first, to describe a series of tests on new composite columns; second, to analyze the influence of RCA replacement ratio on the compressive and flexural behaviour of recycled aggregate concrete filled steel tubes (RACFST), and finally, to compare the accuracy of the predicted ultimate strength, bending moment capacity and flexural stiffness of the composite specimens by using the recommendations of ACI318-99 (1999), AIJ (1997), AISC-LRFD (1999), BS5400 (1979), DBJ13-51-2003 (2003) and EC4 (1994).

Key Words
recycled aggregate concrete filled steel tubes (RACFST); recycled aggregate concrete (RAC); recycled coarse aggregate (RCA); stub columns; beams; confinement factor; composite actions; member capacity.

Address
You-Fu Yang; College of Civil Engineering, Fuzhou University, Gongye Road 523, Fuzhou, Fujian Province 350002, P. R. ChinarnLin-Hai Han; Department of Civil Engineering, Tsinghua University, Beijing, 100084, P. R. China


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