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CONTENTS
Volume 41, Number 4, February25 2012
 

Abstract
The shear strength is an important factor in the design of prestressed concrete beams. Therefore, researchers have utilized various methods to determine the shear strength of these elements for the design purposes. To evaluate some of the proposed theoretical methods, numerous models of posttensioned beams with or without vertical prestressing are selected and analyzed using the finite element method and assuming nonlinear behavior for the materials. In this regard the validity of modeling is evaluated based on some tests results. In the second part of the study two beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. The analytical results consist of compressive strut slope and mid span load deflection are compared with some experimental results, and the results of some codes\' formulas. Finally comparing the results of nonlinear analysis with the experimental values, a new formula is proposed for determining strut slopes in prestressed concrete beams.

Key Words
shear strength; prestressed concrete; vertical prestressing; strut slope; crack pattern; testing; truss models

Address
Alireza Rahai and A. Shokoohfar: Department of Civil Engineering, Amir Kabir University of Technology, Tehran 1591634311, Iran

Abstract
This paper attempts to determine the inclination of the compression strut within variable angle truss models for RC beams loaded in shear-flexure through a proposed semi-analytical approach. A truss unit is used to analyze a reinforced concrete beam, by the principle of virtual work under the truss analogy. The inclination of the compression strut is then theoretically derived. The concrete contribution is addressed by utilizing the compatibility condition within each truss unit. Comparisons are made between the predicted and published experimental results of the seventy one RC beams with respect to the shear strength and the inclined angle of the compression strut at this state to investigate the adequacy of the proposed semi-analytical approach.

Key Words
inclination of strut; truss model; concrete contribution; shear strength

Address
Bing Li: School of Civil and Environment Engineering, Nanyang Technological University, 639798, Singapore
Cao Thanh Ngoc Tran: Department of Civil Engineering, International University, Vietnam National University, Ho Chi Minh City, Vietnam

Abstract
This study explores a coefficient-based seismic capacity assessment method with a special emphasis on low-rise masonry in-filled (MI) reinforced concrete (RC) buildings subjected to earthquake motion. The coefficient-based method without requiring any complicated finite element analysis is a simplified procedure to assess the maximum spectral acceleration capacity of buildings. This paper first compares the fundamental periods of MI RC structures obtained, respectively, from experimental period data and empirical period-height formulas. The coefficient-based method for low-rise masonry buildings is then calibrated by the published experimental results obtained from shaking table tests. The comparison of the experimental and estimated results indicates that the simplified coefficient-based method can provide good approximations of the maximum spectral accelerations at peak loads of the low-rise masonry reinforced concrete buildings if a proper set of drift factors and initial fundamental vibration periods of structures are used.

Key Words
seismic capacity; masonry; earthquake; inter-storey drift; shaking table tests

Address
R.K.L. Su and C.L. Lee: Department of Civil Engineering, The University of Hong Kong, Hong Kong, China
Y.P. Wang: Department of Civil Engineering, National Chiao-Tung University, Hsinchu, Taiwan

Abstract
The strength theory of concrete is significant to structure design and nonlinear finite element analysis of concrete structures because concrete utilized in engineering is usually subject to the action of multi-axial stress. Experimental results have revealed that lightweight aggregate (LWA) concrete exhibits plastic flow plateau under high compressive stress and most of the lightweight aggregates are crushed at this stage. For the purpose of safety, therefore, in the practical application the strength of LWA concrete at the plastic flow plateau stage should be regarded as the ultimate strength under multi-axial compressive stress state. With consideration of the strength criterion, the ultimate strength surface of LWA concrete under multi-axial stress intersects with the hydrostatic stress axis at two different points, which is completely different from that of the normal weight concrete as that the ultimate strength surface is openended. As a result, the strength criteria aimed at normal weight concrete do not fit LWA concrete. In the present paper, a multi-axial strength criterion for LWA concrete is proposed based on the Unified Twin-Shear Strength (UTSS) theory developed by Prof Yu (Yu et al. 1992), which takes into account the above strength characteristics of LWA under high compressive stress level. In this strength criterion model, the tensile and compressive meridians as well as the ultimate strength envelopes in deviatoric plane under different hydrostatic stress are established just in terms of a few characteristic stress states, i.e., the uniaxial tensile strength ft, the uniaxial compressive strength fc, and the equibiaxial compressive fbc. The developed model was confirmed to agree well with experimental data under different stress ratios of LWA concrete.

Key Words
lightweight aggregate (LWA) concrete; Unified Twin-Shear Strength (UTSS) theory; multiaxial strength criterion; ultimate strength envelope; tensile and compressive meridians

Address
Li-cheng Wang: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China

Abstract
In recent years, CFRP material usage in strengthening applications gradually became widespread. Especially, the studies on the strengthening of shear deficient reinforced concrete beams with CFRP strips are chosen as a subject to numerous experimental studies and research on this subject are increased rapidly. The most important variable, that is affected on the failure mode of CFRP strips and that is needed for determining the shear capacity of the strengthened reinforced concrete beams, is the strain distribution between CFRP strips and concrete. Numerous experimental studies are encountered in the literature about the determination of strain distribution between CFRP strips and concrete. However, these studies mainly focused on the CFRP strips under axial tension. There are very limited numbers of experimental and analytic studies examining the strain distribution between concrete and CFRP strips, which are under combined stresses due to the effects of shear force and bending moment. For this reason, existing experimental study in the literature is used as model for ANSYS finite element software. Nonlinear finite element analysis of RC beams strengthened against shear with CFRP strips under reverse cyclic loading is performed. The strain distributions between CFRP strips and concrete that is obtained from finite element analysis are compared with the results of experimental measurements. It is seen that the experimental results are consisted with the results derived from the finite element analysis and important findings on the strain distribution profile are reached by obtaining strain values of many points using finite element method.

Key Words
CFRP; Nonlinear Finite Element Analysis; ANSYS

Address
Ozgur Anil, Nalan Bulut and Murat Ayhan: Civil Engineering Department, Gazi University, Maltepe, Ankara, 06570, Turkey

Abstract
In seismic analyses of structures, additional eccentricity is introduced to take account for oscillations of random and unknown origins. In many codes of practice, the torsion about the vertical axis is considered through empirical accidental eccentricity formulation. Due to the random nature of structural systems, it is very difficult to evaluate the accidental eccentricity in a deterministic way and to specify its effect on the overall seismic response of structures. The aim of this study is to develop a procedure for the evaluation of the accidental eccentricity induced by uncertainties in stiffness and mass of structural members, using the neural network techniques coupled with Monte Carlo simulations. This method gives very interesting results for single story structures. For real structures, this method can be used as a tool to determine the accidental eccentricity in the seismic vulnerability studies of buildings.

Key Words
seismic design; accidental eccentricity; neural networks; Monte Carlo; uncertainty

Address
M. Badaoui: University of Djelfa, Cite Ain Chih, BP3117 Djelfa, Algeria
A. Chateauneuf: Clermont Universite, Universite Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand, France; CNRS, UMR 6602, Institut Pascal, F-63171 Aubiere, France
N. Bourahla and M. Bensaibi: University of Blida, Route De Soumaa, BP270 Blida, Algeria

Abstract
The diagnosis of bridge serviceability is carried out by a combination of in-situ visual inspection, static and dynamic loading tests and analyses. Structural health monitoring (SHM) using information technology and sensors is increasingly being used for providing a better estimate of structural performance characteristics rather than above traditional methods. Because the mechanical behavior of bridges with various kinds of damage can not be made clear, it is very difficult to estimate both the damage mode and degree of damage of existing bridges. In this paper, the sensitivity of both static and dynamic behaviors of bridges are studied as a measure of damage assessment through experiments on model bridges induced with some specified artificial damages. And, a method of damage assessment of bridges based on those behaviors is discussed in detail. Finally, based on the results, a possible application for structural health monitoring systems for existing bridges is also discussed.

Key Words
bridge; damage assessment; diagnosis; sensitivity analysis; static behavior; dynamic behavior

Address
Ayaho Miyamoto and Satoshi Isoda: Graduate School of Science & Engineering, Yamaguchi University, Ube, Japan

Abstract
An adaptive modeling and simulation technique is introduced for the effective and reliable fluid-structure interaction analysis using MSC/Dytran for large-scale complex pressurized liquid containment. The proposed method is composed of a series of the global rigid sloshing analysis and the locally detailed fluid-structure analysis. The critical time at which the system exhibits the severe liquid sloshing response is sought through the former analysis, while the fluid-structure interaction in the local region of interest at the critical time is analyzed by the latter analysis. Differing from the global coarse model, the local fine model considers not only the complex geometry and flexibility of structure but the effect of internal pressure. The locally detailed FSI problem is solved in terms of multi-material volume fractions and the flow and pressure fields obtained by the global analysis at the critical time are specified as the initial conditions. An in-house program for mapping the global analysis results onto the fine-scale local FSI model is developed. The validity and effectiveness of the proposed method are verified through an illustrative numerical experiment.

Key Words
large-scale liquid containment; fluid-structure interaction; Adaptive FSI Simulation; Multimaterial volume fractions; two-phase flow; coarse- and fine-scale models

Address
Sung-Woo Park: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea
Jin-Rae Cho: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea; Research and Development Institute of Midas IT, Gyeonggi 463-400, Korea

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