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CONTENTS
Volume 8, Number 6, December 2011
 

Abstract
In this investigation, reservoir sediment and municipal sewage sludge were sintered to form the artificial lightweight aggregates. The sintered aggregates were compared with the commercialized lightweight aggregates to in terms of potential alkali-silica reactivity and chemical stability based on analyses of their physical and chemical properties, leaching of heavy metal, alkali-silica reactivity, crystal phase species and microstructure. Experimental results demonstrated that the degree of sintering of an aggregate affected the chemical resistance more strongly than did its chemical composition. According to ASTM C289-94, all potential alkali-silica reactivity of artificial lightweight aggregates were in the harmless zone, while the potential reactivity of artificial lightweight aggregates made from reservoir sediment and municipal sewage sludge were much lower than those of traditional lightweight aggregates.

Key Words
sewage sludge; reservoir sediment; sintering; lightweight aggregate (LWA); potential alkalisilica reactivity.

Address
I.J. Chiou: Graduate School of Materials Applied Technology, Department of Civil and Environmental Engineering, Nanya Institute of Technology, No. 414, Sec.3,
Jhongshan E. Rd., Jhongli, Taoyuan 320, Taiwan, R.O.C.
C.H. Chen: Department of Social and Regional Development, National Taipei University of Education, No. 134, Sec. 2, Heping E. Rd., Taipei City 106, Taiwan, R.O.C.

Abstract
The capacity design rule for beam-column joints, as adopted by the EC8, forces the formation of the plastic hinges to be developed in beams rather than in columns. This is achieved by deriving the design moments of the columns of a joint from equilibrium conditions, assuming that plastic hinges with their possible overstrengths have been developed in the adjacent beams of the joint. In this equilibrium the parameters (dimensions, material properties, axial forces etc) are, in general, random variables. Hence, the capacity design is associated with a probability of non-compliance (probability of failure). In the present study the probability of non-compliance of the capacity design rule of joints is being calculated by assuming the basic variables as random variables. Parameters affecting this probability are examined and a modification of the capacity design rule for beam-column joints is proposed, in order to achieve uniformity of the safety level.

Key Words
reliability; capacity design; partial safety factors; concrete structures.

Address
George C. Thomos and Constantin G. Trezos: Laboratory of Reinforced Concrete, National Technical University of Athens, 5 Iroon Polytechniou, Zografou, Greece 157 73

Abstract
Our ability to predict hydration behavior is becoming increasingly relevant to the concrete community as modelers begin to link material performance to the dynamics of material properties and chemistry. At early ages, the properties of concrete are changing rapidly due to chemical transformations that affect mechanical, thermal and transport responses of the composite. At later ages, the resulting, nano-, micro-, meso- and macroscopic structure generated by hydration will control the life-cycle performance of the material in the field. Ultimately, creep, shrinkage, chemical and physical durability, and all manner of mechanical response are linked to hydration. As a way to enable the modeling community to better understand hydration, a review of hydration models is presented offering insights into their mathematical origins and relationships one-to-the-other. The quest for a universal model begins in the 1920

Key Words
modeling; portland cement; hydration; simulation; tricalcium silicate; alite.

Address
Tiantian Xie and Joseph J. Biernacki: Tennessee Technological University Cookeville, TN 38505, USA

Abstract
Particle packing on meso-level has a significant influence on workability of fresh concrete and also on the mechanical and durability properties of the matured material. It was demonstrated earlier that shape exerts but a marginal influence on the elastic properties of concrete provided being packed to the same density, which is not necessarily the case with different types of aggregate. Hence, elastic properties of concrete can be treated as approximately structure-insensitive parameters. However, fracture behaviour can be expected structure-sensitive. This is supported by the present study based on discrete element method (DEM) simulated three-phase concrete, namely aggregate, matrix and interfacial transition zones (ITZs). Fracture properties are assessed with the aid of a finite element method (FEM) based on the damage materials model. Effects on tensile strength due to grain shape and packing density are investigated. Shape differences are shown to have only modest influence. Significant effects are exerted by packing density and physicalmechanical properties of the phases, whereby the ITZ takes up a major position.

Key Words
particle packing; particle shape; fracture properties; FEM; DEM; ITZ; concrete.

Address
Huan He: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands;
Faculty of Applied Sciences, University of Liege, Liege, Belgium
Piet Stroeven, Martijn Stroeven and Lambertus Johannes Sluys: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands

Abstract
The main object of this study is to evaluate the seismic response effects on a reinforced concrete building isolated by triple concave friction pendulum (TCFP) bearings. The site-response effects arise from the difference in the local soil conditions at the support points of the buildings. The local soil conditions are, therefore, considered as soft, medium and firm; separately. The results on the responses of the isolated building are compared with those of the non-isolated. The building model used in the time history analysis, which is a two-dimensional and eight-storey reinforced concrete building with and without the seismic isolation bearings and/or the local soil conditions, is composed of two-dimensional moment resisting frames for superstructure and of plane elements featuring plane-stress for substructure. The TCFP bearings for isolating the building are modelled as of a series arrangement of the three single concave friction pendulum (SCFP) bearings. In order to investigate the efficiency of both the seismic isolation bearings and the site-response effects on the buildings, the time history analyses are elaborately conducted. It is noted that the site-response effects are important for the isolated building constructed on soft, medium or firm type local foundation soil. The results of the analysis demonstrate that the siteresponse has significant effects on the response values of the structure-seismic isolation-foundation soil system.

Key Words
seismic isolation; triple concave friction pendulum; gap elements; non-linear link element; site-response effects; series model; reinforced concrete building.

Address
Sevket Ates: Karadeniz Technical University, Department of Civil Engineering, Trabzon, Turkey
Muhammet Yurdakul: Bayburt University, Department of Civil Engineering, Bayburt, Turkey

Abstract
Strengthening of reinforced concrete (RC) members against shear that is one of the failure modes especially avoided by using carbon fiber reinforced polymer (CFRP) is widely used technique, which is studied at many experimental studies. However, conducting experimental studies are required more financial resources and laboratory facilities. In addition, along with financial resources, more time is needed in order to carry out comprehensive experimental studies. For these reasons, a verified finite element model that is tested with previous experimental studies can be used for reaching generalized results and investigating parameters that are not studied. For this purpose, previous experimental study results are used and

Key Words
ANSYS; finite element analysis; RC beam; strengthening; nonlinear analysis.

Address
Nalan Bulut, Ozgur Anil and Cagatay M. Belgin: Department of Civil Engineering, Gazi University, Maltepe, Ankara, Turkey, 06570

Abstract
The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a facade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

Key Words
smeared crack model; punching; shear softening diagram; material nonlinear analysis; steel fiber reinforced self-compacting concrete; inverse analysis.

Address
A. Ventura-Gouveia: Department of Civil Engineering, ISISE, School of Technology & Management, Polytechnic Institute of Viseu, Viseu, Portugal
Joaquim A.O. Barros: Department of Civil Engineering, ISISE, School of Engineering, University of Minho, Guimaraes, Portugal
Alvaro F.M. Azevedo: Department of Civil Engineering, Faculty of Engineering of the University of Porto,
University of Porto, Porto, Portugal


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