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CONTENTS
Volume 2, Number 5, October 2002
 

Abstract
This paper proposes a model for analysing the non-linear behaviour of steel concrete composite beams prestressed by external slipping cables, taking into account the deformability of the interface shear connection. By assuming a suitable admissible displacement field for the composite beam, the balance condition is obtained by the virtual work principle. The solution is numerically achieved by approximating the unknown displacement functions as series of shape functions according to the Ritz method. The model is applied to real cases by showing the consequences of different connection levels between the concrete slab and the steel beam. Particular attention is focused on the limited ductility of the shear connection that may be the cause of premature failure of the composite girder.

Key Words
external pre-stressing; composite beams; flexible shear connection; shear connection duc-tility; non-linear analysis; steel-concrete composite bridges.

Address
PROCAM, University of Camerino, Viale della Rimembranza, 63100, Ascoli Piceno, ItalyrnInstitute of Structural Engineering, University of Ancona, Via Brecce Bianche, 60131, Ancona, Italy

Abstract
Tethers of Tension Leg Platform (TLP) are a series structural system where fatigue is thernprincipal mode of failure. The present study is devoted to the fatigue and fatigue fracture reliability study of these tethers. For this purpose, two limit state functions have been derived. These limit state functions are based on S-N curve and fracture mechanics approaches. A detailed methodology for the reliability analysis has then been presented. A sensitivity analysis has been carried out to study the influence of various random variables on tether reliability. The design point, important for probabilistic design, is located on the failure surface. Effect of wind, water depth, service life and number of welded joints are investigated. The effect of uncertainties in various random variables on tether fatigue reliability is highlighted.

Key Words
series system; fatigue reliability; tension leg platform; offshore structures.

Address
Department of Civil Engineering, Aligarh Muslim University, Aligarh, -202 002, India

Abstract
Use of composite steel construction with precast hollow core slabs is now popular in the UK,rnbut the present knowledge in shear capacity of the headed shear studs for this type of composite construction is very limited. Currently, all the information is based on the results obtained from experimental push-off tests. A finite element model to simulate the behaviour of headed stud shear connection in composite beam with precast hollow core slabs is described. The model is based on finite element method and takes into account the linear and non-linear behaviour of all the materials. The model has been validated against the test results, for which the accuracy of the model used is demonstrated. Parametric studies showing the effect of the change in transverse gap size, transverse reinforcement diameter and in-situ concrete strength on the shear connection capacity are presented.

Key Words
headed stud; composite construction; precast hollow core slabs; finite element modelling.

Address
School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, U.K.

Abstract
The paper describes the mechanical behavior of short concrete-filled steel tube (CFT) columnsrnwith circular section. The efficiency of the steel tube in confining the concrete core depending on concrete strength and the steel tube thickness was examined. Fifteen columns were tested to failure under concentric axial loading. Furthermore, a mechanical model based on the interaction between the concrete core and the steel tube was developed. The model employs a volumetric strain history for the concrete, characterized by the level of applied confining stress. The situation of passive confinement is accounted for by an incremental procedure, which continuously updates the confining stress. The post-yield behavior of the columns is greatly influenced by the confinement level and is related to the efficiency of the steel tube in confining the concrete core. It is possible to classify the post-yield behavior into three categories: strain softening, perfectly plastic and strain hardening behavior. The softening behavior, which is due to a shear plane failure in the concrete core, was found for some of the CFT columns with high-strength concrete. Nevertheless, with a CFT column, it is possible to use high-strength concrete to obtain higher load resistance and still achieve a good ductile behavior.

Key Words
concrete-filled steel tubes; confined concrete; passive confinement; high-strength concrete;

Address
Department of Structural Engineering, Concrete Structures, Chalmers University of Technology, SE-412 96 G?teborg, Sweden

Abstract
The main aim of the present paper is to present the results of a full-scale experimentalrninvestigation to study the structural behaviour of composite steel beams. The composite beam was made of cold-formed steel section shapes filled with reinforced concrete. First a comprehensive description of the experimental results in terms of: deflections, deformations, slippage and stress levels on critical steps of the load path is presented. The experimental results were then compared to theoretical values obtained by the use of an analytical model based on ultimate limit state stress blocks. Finally, a practical application of the use of this structural solution is depicted.

Key Words
composite construction; cold-formed structures; experimental analysis; composite struc-tural design; structural behaviour; cold-formed composite structures.

Address
Civil Engineering Department, PUC, Rio de Janeiro, Brazil, Structural Engineering Department,rnUERJ, Rio de Janeiro, BrazilrnStructural Engineering Department, UERJ, Rio de Janeiro, BrazilrnCivil Engineering Department, UFOP, Minas Gerais, Brazil


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