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CONTENTS
Volume 13, Number 2, February 2014
 

Abstract
This study presents the mathematical model for predicting chloride penetration into saturated concrete under non-isothermal condition. The model considers not only diffusion mechanism but also migration process of chloride ions and other chemical species in concrete pore solution such as sodium, potassium, and hydroxyl ions. The coupled multi-ionic transport in concrete is described by the Nernst-Planck equation associated with electro-neutrality condition. The coupling parameter taken into account the effect of temperature on ion diffusion obtained from available test data is proposed and explicitly incorporated in the governing equations. The coupled transport equations are solved using the finite element method. The numerical results are validated with available experimental data and the comparison shows a good agreement.

Key Words
chloride; concrete; temperature effect; Nernst-Planck equation; ionic diffusion

Address
Nattapong Damrongwiriyanupap: Civil Engineering Program, School of Engineering, University of Phayao, Phayao 56000, Thailand
Linyuan Li: Department of Mathematics and Statistics, University of New Hampshire, Durham, NH 03824, United States
Suchart Limkatanyu: Department of Civil Engineering, Faculty of Engineering, Prince of Songkla University, Songkla 90112, Thailand
Yunping Xi: Department of Civil, Environmental, and Architectural Engineering, University of Colorado at Boulder, Boulder, CO 80309, United States

Abstract
Multivariate analysis is a statistical technique that investigates relationship between multiple predictor variables and response variable and it is a very commonly used statistical approach in cement and concrete industry. During model building stage, however, many predictor variables are included in the model and possible collinearity problems between these predictors are generally ignored. In this study, use of partial least squares (PLS) analysis for evaluating the relationships among the cement and concrete properties is investigated. This regression method is known to decrease the model complexity by reducing the number of predictor variables as well as to result in accurate and reliable predictions. The experimental studies showed that the method can be used in the multivariate problems of cement and concrete industry effectively.

Key Words
concrete; PLS; regression; slump flow; blaine

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

Abstract
This paper mainly discusses the influence of the aggregate properties including grading, shape, content and distribution on the chloride diffusion coefficient, as well as the initiation time of steel corrosion from a probabilistic point of view. Towards this goal, a simulation method of random aggregate structure (RAS) based on elliptical particles and a procedure of finite element analysis (FEA) at meso-scale are firstly developed to perform the analysis. Next, the chloride diffusion coefficient ratio between concrete and cement paste 𝐷app𝐷cp is chosen as the index to represent the effect of aggregates on the chloride diffusion process. Identification of the random distribution of this index demonstrates that it can be viewed as actually having a normal distribution. After that, the effect of aggregates on 𝐷app𝐷cp is comprehensively studied, showing that the appropriate properties of aggregates should be decided by both of the average and the deviation of 𝐷app𝐷cp . Finally, a case study is conducted to demonstrate the application of this mesoscopic method in predicting the initiation time of steel corrosion in reinforced concrete (RC) structures. The mesoscopic probabilistic method developed in this paper can not only provide more reliable evidences on the proper grading and shape of aggregates, but also play an important role in the probability-based design method.

Key Words
concrete structures; durability; mathematical modeling; uncertainty

Address
Zichao Pan: Department of Bridge Engineering, Tongji University, Shanghai, 200092, China
Xin Ruan and Airong Chen: Department of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
Vibration based damage detection is very popular in the civil engineering area. Especially, special structures like dams, long-span bridges and high-rise buildings, need continues monitoring in terms of mechanical properties of material, static and dynamic behavior. It has been stated in the International Commission on Large Dams that more than half of the large concrete dams were constructed more than 50 years ago and the old dams have subjected to repeating loads such as earthquake, overflow, blast, etc.,. So, some unexpected failures may occur and catastrophic damages may be taken place because of theloss of strength, stiffness and other physical properties of concrete. Therefore, these dams need repairs provided with global damage evaluation in order to preserve structural integrity. The paper aims to show the effectiveness of the model updating method for global damage detection on a laboratory arch dam model. Ambient vibration test is used in order to determine the experimental dynamic characteristics. The initial finite element model is updated according to the experimentally determined natural frequencies and mode shapes. The web thickness is selected as updating parameter in the damage evaluation. It is observed from the study that the damage case is revealed with high accuracy and a good match is attained between the estimated and the real damage cases by model updating method.

Key Words
concrete arch dam; damage detection, finite element modeling, modal testing, model calibration, modelupdating.

Address
Temel Türker, Alemdar Bayraktar: Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Turkey


Abstract
A nonlinear finite element analysis using ANSYS is used to evaluate the seismic behavior of reinforced concrete exterior beam-column joints. The behavior of the finite element models under cyclic loading is compared with the experimental results. Two beam-column joint specimens (SH and SHD) with square hoop confinement in joint and throughout the column with detailing as per IS 13920 are studied. The specimen SHD was provided with additional diagonal bars from column to beam to relocate the plastic hinge formation from beam-column interface. The load-displacement relationship, joint shear stress and strain in beam obtained from numerical study showed good agreement with the experimental results. This investigation proves that seismic behaviour of reinforced concrete beam-column joints under reversed cyclic loading can be evaluated successfully using finite element modeling and analysis.

Key Words
reinforced concrete; confinement; beam-column joint; finite element modeling; shear stress

Address
P. Asha: Dept. of Civil Engineering, St. Peter\'s University, Avadi, Chennai – 54, Tamilnadu, India
R.Sundararajan: Government College of Technology, Coimbatore – 13, Tamilnadu, India

Abstract
The theoretical basis and the main results of a design procedure, which attempts to provide the optimal layout of ordinary reinforcement in prestressed concrete beams, subjected to bending moment and shear force are presented. The difficulties encountered in simulating the actual behaviour of prestressed concrete beam in presence of coupled forces bending moment - shear force are discussed; particular emphasis is put on plastic models and stress fields approaches. A unified model for reinforced and prestressed concrete beams under axial force - bending moment - shear force interaction is provided. This analytical model is validated against both experimental results collected in literature and nonlinear numerical analyses. Finally, for illustrating the applicability of the proposed procedure, an example of design for a full-scale prestressed concrete beam is shown.

Key Words
shear, flexure, prestressed concrete, design, plasticity

Address
Piero Colajanni, Antonino Recupero and Nino Spinella: Dipartimento di Ingegneria Civile, Informatica, Edile, Ambientale e Matematica Applicata, Università di Messina, Messina, Italy

Abstract
Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber (Vf = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

Key Words
fiber reinforcement; high-performance steel fiber reinforced concrete; mechanical properties; impact resistance; toughness; modeling

Address
Ramadoss Perumal: Department of Civil Engineering, Pondicherry Engineering College, Puducherry- 605014, India

Abstract
In this study, structural irregularities in plan, which has a considerable effect on earthquake behavior of buildings, have been investigated in detail based on Turkish Earthquake Code 2007. The study consists of six main parametric models and a total of 144 sub-models that are grouped based on RC structural systems such as frame, frame + rigid core, frame with shear wall, and frame with shear wall + rigid core. All models are designed to have both symmetrical plan geometry and regular rigidity distribution. Changes in the earthquake behavior of buildings were evaluated according to the number of storeys, number of axes and the configuration of structural elements. Many findings are obtained and assessed as a result of the analysis for each structural irregularity. The study shows that structural irregularities can be observed in completely symmetric buildings in terms of plan geometry and rigidity distribution.

Key Words
earthquake; architectural form; structural irregularities; RC buildings

Address
Tugba Inan: Department of Architecture, Izmir Institute of Technology, Izmir, Turkey
Koray Korkma: Department of Architecture, Izmir Institute of Technology, Izmir, Turkey
H. Cagatay: Department of Civil Engineering, University of Cukurova, Adana, Turkey

Abstract
A nonlinear, three-dimensional finite element analysis was conducted on six intermediate L-shaped spandrel beams using the \"ANSYS Civil FEM\" program. The beams were constructed and tested in the laboratory under eccentric concentrated load at mid-span to obtain a combined loading case: torsion, bending, and shear. The reinforcement case parameters were as follows: without reinforcement, with longitudinal reinforcement only, and reinforced with steel bars and stirrups. All beams were tested under two different combined loading conditions: T/V = 545 mm (high eccentricity) and T/V = 145 mm (low eccentricity). The failure of the plain beams was brittle, and the addition of longitudinal steel bars increased beam strength, particularly under low eccentricity. Transverse reinforcement significantly affected the strength at high eccentricities, that is, at high torque. A program can predict accurately the behavior of these beams under different reinforcement cases, as well as under different ratios of combined loadings. The ANSYS model accurately predicted the loads and deflections for various types of reinforcements in spandrel beams, and captured the critical crack regions of these beams.

Key Words
spandrelbeam, reinforced concrete, combined loading, finite element analysis

Address
O.F. Ibraheem, B.H. Abu Bakar and I. Johari: Department of Civil Engineering, University Sains Malaysia (USM), Penang, Malaysia


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