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CONTENTS
Volume 6, Number 2, April 2009
 

Abstract
In the current research, a displacement-based seismic design scheme to retrofit reinforced concrete columns using FRP composite materials has been proposed. An accurate prediction for the nonlinear flexural analysis of FRP jacketed concrete members has been presented under multiaxial constitutive laws of concrete and composite materials. Through modification of the displacement coefficient method (DCM) and the direct displacement-based design method (DDM) of reinforced concrete structures, two algorithms for a performance-based seismic retrofit design of reinforced concrete columns with a FRP jacket have been newly introduced. From applications to retrofit design it is known that two methods are easy to apply in retrofit design and the DCM procedure underestimates the target displacement to compare with the DDM procedure.

Key Words
displacement-based design; nonlinear flexural model; concrete column; FRP jacket; multi-axial constitutive law; seismic retrofit.

Address
Chang-Geun Cho : School of Architecture, Chosun University, Gwangju, Korea
Hee-Cheon Yun and Yun-Yong Kim : Dept. of Civil Engineering, Chungnam National University, Daejeon, Korea

Abstract
This paper presents finite element impact analysis for the design of Structurally Dissipating Rock-shed (SDR), an innovative design of reinforced concrete rock-shed. By using an appropriate finite element impact algorithm, the SDR structure is modelled in a simplified but efficient way. The numerical results are firstly verified through comparisons with the results of the experiments recently realized by ESIGEC and TONELLO I.C. It is shown that, using this impact algorithm, it is possible to correctly predict the SDR structural behaviour under different rock-fall impact conditions. Moreover, the numerical results show that the slab centre is the critical impact location for reinforced concrete slab design. The impact analyses have thus been focused on the impacts at the slab centre for the SDR structural optimization. Several series of parametric studies have been carried out with respect to load cases and engineering parameters choices. These numerical results support the robustness of the new SDR concept, and serve to optimize SDR structure and improve its conventional engineering design, especially for ensuring the slab punching shear resistance.

Key Words
structurally dissipating rock-shed; rock-fall impact; finite element impact analysis; structural; design; structure sensitivity study; punching shear.

Address
Yi Zhang : Technical Direction, Spie batignolles TPCI, 11 rue Lazare Hoche,92774 Boulogne-Billancourt Cedex, France
Francois Toutlemonde : Universite Paris Est-LCPC (Laboratoire Central des Ponts et Chaussees),58 bd. Lefebvre, 75732 Paris Cedex 15, France
Philippe Lussou : Lafarge Centre de Recherche, 95 rue du Montmurier 38070 Saint-Quentin-Fallavier Cedex, France
Universite Paris Est-LCPC (Laboratoire Central des Ponts et Chaussees),58 bd. Lefebvre, 75732 Paris Cedex 15, France

Abstract
Discrete element modeling (DEM) in concrete technology is concerned with design and use of models that constitute a schematization of reality with operational potentials. This paper discusses the material science principles governing the design of DEM systems and evaluates the consequences for their operational potentials. It surveys the two families in physical discrete element modeling in concrete technology, only touching upon probabilistic DEM concepts as alternatives. Many common DEM systems are based on random sequential addition (RSA) procedures; their operational potentials are limited to low configuration-sensitivity features of material structure, underlying material performance characteristics of low structure-sensitivity. The second family of DEM systems employs concurrent algorithms, involving particle interaction mechanisms. Static and dynamic solutions are realized to solve particle overlap. This second family offers a far more realistic schematization of reality as to particle configuration. The operational potentials of this family involve valid approaches to structure-sensitive mechanical or durability properties. Illustrative 2D examples of fresh cement particle packing and pore formation during maturation are elaborated to demonstrate this. Mainstream fields of present day and expected application of DEM are sketched. Violation of the scientific knowledge of to day underlying these operational potentials will give rise to unreliable solutions.

Key Words
concrete; concurrent-algorithm; dispersion; microstructure; discrete element modeling.

Address
P. Stroeven, J. Hu and M. Stroeven : Faculty of Civil Engineering & Geosciences, Delft University of Technology, Stevinweg 1, 2628 CN Delft, the Netherlands

Abstract
Splitting tensile strength (STS) of high-performance concrete (HPC) is one of the important mechanical properties for structural design. This property is related to compressive strength (CS), water/ binder (W/B) ratio and concrete age. This paper presents a clustering-based fuzzy model for the prediction of STS based on the CS and (W/B) at a fixed age (28 days). The data driven fuzzy model consists of three main steps: fuzzy clustering, inference system, and prediction. The system can be analyzed directly by the model from measured data. The performance evaluations showed that the fuzzy model is more accurate than the other prediction models concerned.

Key Words
compressive strength; splitting tensile strength; water/binder ratio; fuzzy clustering; modelling.

Address
Bulent Tutmez: School of Engineering, Inonu University, 44280 Malatya, Turkey

Abstract
Reinforced concrete floors constructed between movement restraints often crack seriously due to shrinkage after completion. One common mitigation measure is to construct the concrete floors in stages to allow part of the shrinkage movement to take place before completion. However, shrinkage movement analysis of concrete floors constructed in stages is quite cumbersome, as the structural configuration changes during construction, thus necessitating reanalysis of the partially completed structure at each stage. Herein, a finite element method for shrinkage movement analysis of concrete floors constructed in stages is developed. It analyses the whole structure, including the completed and uncompleted portions, at all stages. The same mesh is used all the time and therefore re-meshing and location matching are no longer necessary. This is achieved by giving negligibly small stiffness to the uncompleted portions, which in reality do not exist yet. In the analysis, the locked-in strains due to increase in elastic modulus as the concrete hardens and the creep of the hardened concrete are taken into account. Most important of all, this method would enable fully automatic shrinkage movement analysis for the purpose of construction control.

Key Words
concrete floor, construction control, creep, finite element, shrinkage.

Address
A.K.H. Kwan and P.L. Ng : Dept. of Civil Engineering The University of Hong Kong, Hong Kong, China


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