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CONTENTS
Volume 14, Number 6, December 2014
 

Abstract
A rational estimation of moisture distribution in structural concrete is vital for predicting the possible extent and rate of progression of impending degradation processes. The paper proposes a numerical scheme for analysing the evolution of moisture distribution in concrete subjected to wetting-drying exposure caused by intermittent periods of rainfall. The proposed paradigm is based on the stage wise implementation of non-linear finite element (FE) analysis, with each stage representing a distinct phase of a typical wet-dry cycle. The associated boundary conditions have been constituted to realize the influence of various meteorological elements such as rain, wind, relative humidity and temperature on the exposed concrete surface. The reliability of the developed scheme has been demonstrated through its application for the simulation of experimentally recorded moisture profiles reported in published literature. A sensitivity analysis has also been carried out to study the influence of critical material properties on simulated results. The proposed scheme is vital to the service life modelling of concrete structures in tropical climates which largely remain exposed to the action of alternating rains.

Key Words
concrete; wetting-drying; moisture distribution; FE analysis

Address
Kaustav Sarkar and Bishwajit Bhattacharjee: Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi - 110016, India

Abstract
The purpose of this paper is to present a numerical procedure to analyse reinforced concrete columns subjected to combined axial loads and bending that rigorously considers nonlinear material and nonlinear geometric characteristics. Column design and stability analysis are simultaneously regarded. A finite element method is used for calculating displacements and the material and geometric nonlinearities are taken into account using an iterative process. A computer program is developed from the proposed numerical procedure, and the efficiency of the program is verified against available experimental data. The model applies to constant rectangular cross sectional columns with symmetric reinforcement distribution.

Key Words
reinforced concrete; slender columns; material nonlinearity; geometric nonlinearity

Address
Susana L. Pires and Maria Cecilia A.T. Silva: Department of Structural Engineering, University of Campinas, 13083-852 Campinas, SP, Brazil

Abstract
Annular and solid concrete specimens with different aspect ratios and static unconfined compressive strengths were studied for impact loading using SHPB test setup. Numerical simulations in LSDYNA were also carried out and results were validated. The stress-strain curves obtained under dynamic loading were also compared with static compressive tests. The mode of failure of concrete specimen was a typical ductile failure at high strain rates. In general, the dynamic increase factor (DIF) of thin solid specimens was higher than thick samples. In the numerical study, the variation of axial, hydrostatic and radial stresses for solid and annular samples was studied. The core phenomenon due to confinement was observed for solid samples wherein the applied loads were primarily borne by the innermost concrete zone rather than the outer peripheral zone. In the annular samples, especially with large diameter inside hole, the distribution of stresses was relatively uniform along the radial distance. Qualitatively, only a small change in the distribution of stresses for annular samples with different internal diameters studied was observed.

Key Words
concrete; confinement; SHPB; strain rate; impact

Address
Yousef Al-Salloum, Saleh Alsayed, Tarek Almusallam,
S.M. Ibrahim and H. Abbas: MMB Chair for Research and Studies in Strengthening and Rehabilitation of Structures, Department of Civil Engineering, King Saud University, Riyadh 11421, P.O. Box 800, Saudi Arabia

Abstract
This paper presents a theoretical and computational approach to solve inelastic structures subjected to overloads. Current practice in structural design is based on elastic analysis followed by limit strength design. Whereas this approach typically results in safe strength design, it does not always guarantee satisfactory performance at the service level because the internal stiffness distribution of the structure changes from the service to the ultimate strength state. A significant variation of relative stiffnesses between the two states may result in unwanted cracking at the service level with expensive repairs, while, under certain circumstances, early failure may occur due to unexpected internal moment reversals. To address these concerns, a new inelastic model is presented here that is based on the nonlinear material response and the interaction relation between axial forces and bending moments of a beam-column element. The model is simple, reasonably accurate, and computationally efficient. It is easy to implement in standard structural analysis codes, and avoids the complexities of expensive alternative analyses based on 2D and 3D finite-element computations using solid elements.

Key Words
reinforced concrete; elastoplastic; softening; nonlinear analysis; finite element method; interaction diagrams

Address
Konstantinos Morfidis: Institute of Engineering Seismology and Earthquake Engineering (EPPO-ITSAK), 55535, Pylaia, Thessaloniki, Greece

Panos D. Kiousis: Colorado School of Mines, Department of Civil and Environmental Engineering, Golden CO 80401

Hariton Xenidis: Department of Civil Engineering, Aristotle University of Thessaloniki, Aristotle University campus, 54124, Thessaloniki, Greece

Abstract
The purpose of this study is to evaluate the behavior and the strength of SRG (Steel Reinforced Grout) externally strengthened Reinforced Concrete (RC) beams by using a nonlinear numerical analysis. The numerical simulation was carried out by using a three-dimensional (3D) finite element model. An interface element with a suitable damage model was used to model the connection between concrete surface and SRG reinforcing layer. The reliability of the finite element 3D-model was checked using experimental data obtained on a set of three RC beams. The parameters taken into consideration were the external configuration, with or without U-end anchorages, the concrete strength, the amount of internal tensile steel reinforcement. Conclusions were made concerning the strength and the ductility of the strengthened beams by varying the parameters and on the effectiveness of the SRG reinforcing system applied with two types of external strengthening configuration.

Key Words
inite element method; non-linear analysis; reinforced concrete; steel reinforced grout; strengthening

Address
Francesco Bencardino and Antonio Condello: Department of Civil Engineering, University of Calabria,
Via P. Bucci, Cubo 39B, 87036 Rende, Cosenza, Italy

Abstract
The management of existing concrete bridges has become a major social concern in many developed countries due to the large number of bridges exhibiting signs of significant deterioration. This problem has increased the demand for effective maintenance and renewal planning. In order to implement an appropriate management procedure for a structure, a wide array of corrective strategies must be evaluated with respect to not only the condition state of each defect but also safety, economy and sustainability. This paper describes a new performance evaluation system for existing concrete bridges. The system evaluates performance based on load carrying capability and durability from the results of a visual inspection and specification data, and describes the necessity of maintenance. It categorizes all girders and slabs as either unsafe, severe deterioration, moderate deterioration, mild deterioration, or safe. The technique employs an expert system with an appropriate knowledge base in the evaluation. A characteristic feature of the system is the use of neural networks to evaluate the performance and facilitate refinement of the knowledge base. The neural network proposed in the present study has the capability to prevent an inference process and knowledge base from becoming a black box. It is very important that the system is capable of detailing how the performance is calculated since the road network represents a huge investment. The effectiveness of the neural network and machine learning method is verified by comparing diagnostic results by bridge experts.

Key Words
performance evaluation; concrete bridge; load-carrying capability; durability; expert system; fuzzy set theory; machine learning; neural network

Address
Ayaho Miyamoto and Hisao Emoto: Graduate School of Science & Engineering, Yamaguchi University, Tokiwadai,Ube, 755-8611, Japan

Hiroyoshi Asano: Ube Industries Consultant Co., Ltd., Ube, 759-0206, Japan

Abstract
In this paper, it is aimed to determine the finite element model updating effects on the structural behavior of long span concrete highway bridges. Birecik Highway Bridge located on the 81stkm of Şanlurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The bridge consist of fourteen spans, each of span has a nearly 26m. The total bridge length is 380m and width of bridge is 10m. Firstly, the analytical dynamic characteristics such as natural frequencies and mode shapes are attained from finite element analyses using SAP2000 program. After, experimental dynamic characteristics are specified from field investigations using Operational Modal Analysis method. Enhanced Frequency Domain Decomposition method in the frequency domain is used to extract the dynamic characteristics such as natural frequencies, mode shapes and damping ratios. Analytically and experimentally identified dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, shear forces, bending moments and compressive stresses are reduced %28.6, %21.0, %19.22, and %33.3-20.0, respectively.

Key Words
dynamic characteristics; enhanced frequency domain decomposition; finite element model updating; long span concrete highway bridge; operational modal analysis

Address
A.C. Altunisikand A. Bayraktar: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
The use of composite materials to strengthen reinforced concrete (RC) structures against blast terror has great interests from engineering experts in structural retrofitting. The composite materials used in this study are rigid polyurethane foam (RPF) and aluminum foam (ALF). The aim of this study is to use the RPF and the ALF to strengthen the RC panels under blast load. The RC panel is considered to study the RPF and the ALF as structural retrofitting. Field blast test is conducted. The finite element analysis (FEA) is also used to model the RC panel under shock wave. The RC panel performance is studied based on detonating different TNT explosive charges. There is a good agreement between the results obtained by both the field blast test and the proposed numerical model. The composite materials improve the RC panel performance under the blast wave propagation.

Key Words
displacements; field blast test; finite element analysis; blast wave; composite materials; RC panels; TNT explosive charge

Address
Sherif A. Mazek: Civil Engineering Department, Military Technical College, Cairo, Egypt

Ashraf A. Mostafa: Egyptian Engineering Department, Cairo, Egypt


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