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CONTENTS
Volume 9, Number 3, June 2009
 

Abstract
Observations from experiments and real fire indicate that restrained steel beams have better fire-resistant capability than isolated beams. Due to the effects of restraints, a steel beam in fire condition can undergo very large deflections and the run away damage may be avoided. However disgusting damages may occur in the beam-to-column connections, which is considered to be mainly caused by the enormous axial tensile forces in steel beams resulted from temperature decreasing after fire dies out. Over the past ten years, the behaviour of restrained steel beams subjected to fire during heating has been experimentally and theoretically investigated in detail, and some simplified analytical approaches have been proposed. While the performance of restrained steel beams during cooling has not been so deeply studied. For the safety evaluation and repair of steel structures against fire, more detailed investigation on the behaviour of restrained steel beams subjected to fire during cooling is necessary. When the temperature decreases, the elastic modulus and yield strength of steel recover, and the contraction force in restrained steel beams will be produced. In this paper, an incremental method is proposed for analyzing the behaviour of restrained steel beams subjected to cooling. In each temperature decrement, the development of deformation and internal forces of a restrained beam is divided into four steps, in order to consider the effect of the recovery of the elastic modulus and strength of steel and the contraction force generated by temperature decrease in the beam respectively. At last, the proposed approach is validated by FE method.

Key Words
steel structure; restrained beam; fire resistance; cooling.

Address
Guo-Qiang Li; Department of Structural Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, PR China; State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, PR China
Shi-Xiong Guo; Department of Structural Engineering, Tongji University, 1239 Siping Road, Shanghai, 200092, PR China

Abstract
Heating correction, through heating and flattening a structure with a pressing machine, is the in-situ method used to repair buckled steel structures. The primary purpose of this investigation is to develop an FEM model which can predict the mechanical response of heat-corrected plates accurately. Our model clarifies several unsolved problems. In previous research, the location of the imperfection was limited to the center of the specimen although the mechanical behavior is strongly affected by the location of the imperfection. Our research clarifies the relationship between the location of the imperfection and the mechanical behavior. In addition, we propose further reinforcement methods and validate their effectiveness. Our research concludes that the strength of a buckled specimen can be recovered by heating correction and the use of an adequate stiffener.

Key Words
heating correction; residual imperfection; buckling analysis; finite element analysis.

Address
Pang-jo Chun; Wayne State University, Civil Engineering Department, 5200 Anthony Wayne Dr.,Detroit, MI, 48202, U.S.A.
Junya Inoue; The University of Tokyo, Material Engineering Department, 7-3-1 Hongo, Bunkyoku,Tokyo 113-8656, Japan

Abstract
The present research aims to develop a methodology to rapidly assess bridges with damage to the superstructure, caused by overheight trucks or lower-than-average overhead clearance. Terrestrial laser scanning and image processing techniques are combined with the finite element method to arrive at an analytical model which is more accurate, with respect to the complex geometrical aspects of the bridge in its damaged configuration.

Key Words
truck strikes; bridge damage; laser scanning.

Address
C.J. Stull and C.J. Earls; Cornell University, School of Civil and Environmental Engineering, 352 Hollister Hall, Ithaca, New York 14853, U.S.A.

Abstract
This paper reviews the concept of tensegrity structures and proposes a new type of dismountable steel tensegrity grids for possible deployment as light-weight roof structures. It covers the fabrication of the prototype structures followed by their instrumentation, destructive testing and numerical analysis. First, a single module, measuring 1 m ?1 m in size, is fabricated based on half-cuboctahedron configuration using galvanised iron (GI) pipes as struts and high tensile stranded cables as tensile elements. Detailed instrumentation of the structure is carried out right at the fabrication stage. The structure is thereafter subjected to destructive test during which the strain and the displacement responses are carefully monitored. The structure is modelled and analyzed using finite element method (FEM) and the model generated is updated with the experimental results. The investigations are then extended to a 2 ?2 grid, measuring 2 m ?2 m in size, fabricated uniquely by the cohesive integration of four single tensegrity modules. After updating and validating on the 2 ?2 grid, the finite element model is extended to a 8 ?8 grid (consisting of 64 units and measuring 8 m ?8 m) whose behaviour is studied in detail for various load combinations expected to act on the structure. The results demonstrate that the proposed tensegrity grid structures are not only dismountable but also exhibit satisfactory behaviour from strength and serviceability point of view.

Key Words
tensegrity; dismountable; finite element method (FEM); strain; monitoring.

Address
Ramakanta Panigrahi, Ashok Gupta and Suresh Bhalla; Civil Engineering Department, IIT Delhi, India

Abstract
This paper presents an experimental study of a newly developed composite floor system, built up from thin-walled C-profiles and upper concrete deck. Trapezoidal sheeting provides the formwork and the fastening of the sheet transmits the shear forces between the C-profiles and the deck. The modified formation of the standard self-drilling screw in the beam-to-sheet connection is applied as shear connector. Push-out tests are completed to study the composite behaviour of the different connection arrangements. On the basis of the test results the behaviour is characterized by the observed failure modes. The design values of the connection stiffness and strength are calculated by the recommendation of Eurocode 4. In the next phase of the experimental study six full-scale composite beams are tested. The global geometry is based on the proposed geometry of the developed floor system. The applied shear connections are selected as the most efficient arrangements obtained from the push-out tests. The experimental behaviour of the composite beams are discussed and evaluated. As a conclusion of the experimental study the Eurocode 4 plastic design method is validated for the developed composite floor.

Key Words
light-gauge composite floor; self-drilling screw; push-out test; full-scale beam test; failure modes; relative slip; design values.

Address
Szilvia Erdelyi and Laszlo Dunai : Department of Structural Mechanics, Budapest University of Technology and Economics, Hungary


Abstract
The long-term behaviour of simply supported composite steel-concrete beams with deformable connectors subjected to skew bending and torsion is presented. The problem is dealt with by recurring to the displacement method, assuming the bending and torsional curvatures and the longitudinal deformations of each sectional part as unknowns and obtaining a system of differential and integro-differential equations. Some solving methods are presented, in order to obtain exact and approximate solutions and evaluate the precision of the approximate ones. A case study is then presented. For the sake of clearness, the responses of the composite beam under loads applied in different directions are studied separately, in order to correctly evaluate the effects of each load condition.

Key Words
creep; composite steel-concrete beams; deformable connectors; skew bending; torsion; thin-walled section.

Address
Francesca Giussani and Franco Mola; Department of Structural Engineering, Milan University of Technology (Politecnico), P.za L. da Vinci, 32, 20133 Milan, Italy


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