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CONTENTS
Volume 5, Number 6, December 2005
 

Abstract
The present work reports on a numerical simulation of a compartment fire. The fire was modeled using a simplified approach, where combustion is simulated as a volumetric heat release. Computations were performed with the commercial code CFX 5.6. Radiation was modeled with a differential approximation (P1 model), while turbulence effects upon the mean gas flow were dealt with a SST turbulence model. Simulations were carried out using a transient approach, starting at the onset of ignition. Results are provided for the temperature field time evolution, thus allowing a direct comparison with the analytical and experimental data. The high spatial resolution available for the results proved to be of great utility for a more detailed analysis of the thermal impact on the steel structure.

Key Words
compartment fire; experimental fire tests; fire safety engineering; numerical simulation; temperature distribution.

Address
Antonio M G. Lopes; Department of Mechanical Engineering, University of Coimbra, Polo II - Pinhal de Marrocos, 3030-290 Coimbra, PortugalrnGilberto C. Vaz; Department of Mechanical Engineering, ISEC, Polytechnic Institute of Coimbra, Rua Pedro Nunes, 3030-199 Coimbra, PortugalrnAldina Santiago; Department of Civil Engineering, University of Coimbra, Polo II - Pinhal de Marrocos, 3030-290 Coimbra, Portugal

Abstract
Steel angles are widely used in roof trusses as web and chord members and in lattice towers. Very often angle members are connected eccentrically. As a result, not only an angle member is under an axial force, but it is also subject to a pair of end eccentric moments. Moreover, the connection at each end provides some fixity so neither pinned nor the fixed end represents the reality. Many national design codes allow for the effects due to eccentricities by modifying the slenderness ratio and reducing the compressive strength of the member. However, in practice, it is difficult to determine accurately the effective length. The concept behind this method is inconsistent with strength design of members of other cross-sectional types such as I or box sections of which the buckling strength is controlled by the Perry constant or the initial imperfection parameters. This paper proposes a method for design of angle frames and trusses by the second-order analysis. The equivalent initial imperfection-to-length ratios for equal and unequal angles to compensate the negligence of initial curvatures, load eccentricities and residual stresses are determined in this paper. From the obtained results, the values of imperfection-to-length ratios are suggested for design and analysis of angle steel trusses allowing for member buckling strength based on the Perry-Robertson formula.

Key Words
angles; buckling; eccentricities; initial imperfections.

Address
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China

Abstract
In recent years, the use of steel tube confined concrete (STCC) columns has been the interests of many structural engineers. The present study is an attempt to study the monotonic and cyclic behaviours of STCC columns. For the monotonic behaviours, a series of tests on STCC stub columns (twenty one), and beam-columns (twenty) were carried out. The main parameters varied in the tests are: (1) column section types, circular and square; (2) tube diameter (or width) to thickness ratio, from 40 to 162, and (3) load eccentricity ratio (e/r), from 0 to 0.5. For the cyclic behaviours, the test parameters included the sectional types and the axial load level (n). Twelve STCC column specimens, including 6 specimens with circular sections and 6 specimens with square sections were tested under constant axial load and cyclically increasing flexural loading. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes. It was found that STCC columns exhibit very high levels of energy dissipation and ductility, particularly when subjected to high axial loads. Generally, the energy dissipation ability of the columns with circular sections was much higher than those of the specimens with square sections. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes such as AIJ-1997, AISC- LRFD-1994, BS5400-1979 and EC4-1994.

Key Words
composite columns; confined concrete; beam columns; design; concrete; hollow sections; seismic design; cyclic load; flexural stiffness; ductility.

Address
Lin-Hai Han; Department of Civil Engineering, Tsinghua University, Beijing, 100084, P. R. ChinarnGuo-Huang Yao and Zhi-Bo Chen; College of Civil Engineering and Architecture, Fuzhou University, Gongye Road 523, Fuzhou, Fujian Province, 350002, P. R. ChinarnQing Yu; Institute of International Engineering Project Management, Tsinghua University, Beijing, 100084, P. R. China

Abstract
This paper presents a state-of-the-art on the behaviour of steel joints under fire loading and some recent developments in this field, currently being carried out by the authors. Firstly, a review of the experimental research work on steel joints is presented, subdivided into isolated member tests, sub-structure tests and tests on complete building structures. Special emphasis is placed on the seventh Cardington test, carried out by the authors within a collaborative research project led by the Czech Technical University in Prague. Secondly, a brief review of various temperature distributions within a joint is presented, followed by a discussion of the behaviour of isolated joints at elevated temperature, focussing on failure modes and analytical procedures for predicting the moment-rotation behaviour of joints at elevated temperature. Finally, a description of the coupled behaviour of joints as part of complete structures is presented, describing previous work and investigations on real fire (including heating and cooling phases) currently being carried out by the authors.

Key Words
axial restraint; component method; composite joints; experimental tests; fire engineering; steel joints; temperature.

Address
Luis Simoes da Silva and Aldina Santiago; Department of Civil Engineering, University of Coimbra, Polo II - Pinhal de Marrocos, 3030-290 Coimbra, PortugalrnPaulo Vila Real; Department of Civil Engineering, University of Aveiro, 3810 Aveiro, PortugalrnDavid Moore; BCSA - British Constructional Steelwork Association, London, U.K.

Abstract
Buckling and post-buckling of cold-formed steel members are rather difficult to predict due to material and geometrical non-linearity. However, numerical techniques have reached a level of maturity such that many are now successfully undertaking ultimate strength analysis of cold-formed steel members. In numerical non-linear analysis, both geometrical and material imperfections, have to be estimated and properly used. They must be codified in terms of shape and magnitude. The presented paper represents a state-of-art report, including relevant results obtained by the authors and collected from literature, on that problem.

Key Words
thin-walled cold-formed members; material and geometrical imperfections; numerical modelling; codification.

Address
Dan Dubina; Dept. of Steel Structures and Structural Mechanics, Faculty of Civil Eng., \"Politehnica\" University of Timisoara, I. Curea 1, Timisoara, 300224, RomaniarnViorel Ungureanu; Laboratory of Steel Structures, Romanian Academy, Timisoara Branch, M. Viteazul 24, 300223, RomaniarnJacques Rondal; Department of Mechanics of Materials and Structures, University of Liege, Chemin des Chevreuils 1, B-4000, Liege, Belgium


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