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CONTENTS
Volume 32, Number 6, August20 2009
 

Abstract
The two major widely used building design code documents of reinforced concrete structures are the ACI 318-05 and Eurocode for the Design of Concrete Structures EC2. Therefore, a thorough comparative analysis of the provisions of these codes is required to confirm their validity and identify discrepancies in either code. In this context, provisions of flexural computations would be particularly attractive for detailed comparison. The provisions of safety concepts, design assumptions, cross-sectional moment capacity, ductility, minimum and maximum reinforcement ratios, and load safety factors of both the ACI 318-05 and EC2 is conducted with parametric analysis. In order to conduct the comparison successfully, the parameters and procedures of EC2 were reformatted and defined in terms of those of ACI 318-05. This paper concluded that although the adopted rationale and methodology of computing the design strength is significantly different between the two codes, the overall EC2 flexural provisions are slightly more conservative with a little of practical difference than those of ACI 318-05. In addition, for the limit of maximum reinforcement ratio, EC2 assures higher sectional ductility than ACI 318-05. Overall, EC2 provisions provide a higher safety factor than those of ACI 318-05 for low values of Live/ Dead load ratios. As the ratio increases the difference between the two codes decreases and becomes almost negligible for ratios higher than 4.

Key Words
ACI 318-05; EC2-94; Reinforced Concrete; Flexural Design; reinforcement ratio; ductility; safety concepts.

Address
Rami A. Hawileh: Department of Civil Engineering, American University of Sharjah, P.O. Box 26666,
Sharjah, United Arab Emirates
Faris A. Malhas: Depratment of Civil Engineering and Environmental Engineering and Engineering Mechanics,
University of Dayton, Dayton, OH, USA
Adeeb Rahman: Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, Milwaukee, WI, USA

Abstract
A new simple relation for the estimation of modal correlation coefficients is presented. It is obtained from the decomposition of covariances of modal responses into background and resonant contributions, as it is commonly done for the variances. Thanks to appropriate assumptions, the modal correlation coefficients are estimated as weighted sums of two limit values, corresponding to the background and resonant responses respectively. The weighting coefficients are expressed as functions of the background-to-resonant ratios, which makes the proposed formulation convenient and easily accessible. The simplicity of the mathematical formulation facilitates the physical interpretation. It is for example proved that modal correlation coefficients can be non negligable even in case of well separated natural frequencies, which is sometimes unclear in the litterature. The new relation is mainly efficient in case of large finite element models. It is applied and validated on a finite element buffeting analysis of the Viaduct of Millau, the highest bridge deck ever built so far.

Key Words
modal correlation; correlation coefficient; CQC; SRSS; buffeting analysis; background response; resonant response; Viaduct of Millau.

Address
National Fund for Scientific Research, University of Liege, Department of Architecture, Geology,
Environment and Construction, Chemin des Chevreuils, 1, Bat. B52/3, B-4000 Liege 1, Belgium

Abstract
Excessive cable vibrations are detrimental to cable-stayed bridges. Increasing the system damping of cables is a key solution to resolve this severe problem. Equations representing the dynamic characteristics of an inclined cable with a Deck-Anchored Damper (DAD) or with a Clipped Tuned Mass Dampers (CTMD) are reviewed. A theoretical comparison on the performance of cable vibration reduction between the cable-DAD system and the cable-CTMD systems is thoroughly discussed. Optimal system modal damping for the free vibration and transfer functions for the forced vibration for the two cabledamper systems are addressed and compared in detail. Design examples for these two different dampers are also provided.

Key Words


Address
W. J. Wu: Mustang Engineering, 16001 Park Ten Place, Houston, TX, 77084, USA
C. S. Cai: Department of Civil and Environmental Engineering, Louisiana State University,
Baton Rouge, LA, 70803, USA

Abstract
This study proposes a new smart base isolation system that employs Magneto-Rheological Elastomers (MREs), a class of smart materials whose elastic modulus or stiffness can be varied depending on the magnitude of an applied magnetic field. It also evaluates the dynamic performance of the MREbased isolation system in reducing vibrations in structures subject to various seismic excitations. As controllable stiffness elements, MREs can increase the dynamic control bandwidth of the isolation system, improving its vibration reduction capability. To study the effectiveness of the MRE-based isolation system, this paper compares its dynamic performance in reducing vibration responses of a base-isolated singlestory structure (i.e., 2DOF) with that of a conventional base-isolation system. Moreover, two control algorithms (linear quadratic regulator (LQR)-based control and state-switched control) are considered for regulating the stiffness of MREs. The simulation results show that the MRE-based isolation system out performed the conventional system in suppressing the maximum base drift, acceleration, and displacement of the structure.

Key Words
magneto-rheological elastomer (MRE); base isolation; linear quadratic regulator (LQR); state-switched control.

Address
Jeong-Hoi Koo: Department of Mechanical and Manufacturing Engineering, Miami University, Oxford, Ohio 45056, USA
Dong-Doo Jang, Muhammad Usman and Hyung-Jo Jung: department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea

Abstract
In the past few decades, effects of natural hazards, such as earthquakes and wind, on existing structures have attracted the attention of researchers and designers. More recently, however, the phenomenon of progressive collapse is becoming more recognized in the field of structural engineering. In practice, the phenomenon can result from a number of abnormal loading events, such as bomb explosions, car bombs, accidental fires, accidental blast loadings, natural hazards, faulty design and construction practices, and premeditated terrorist acts. Progressive collapse can result not only in disproportionate structural failure, but also disproportionate loss of life and injuries. This paper provides an up-to-date comprehensive review of this phenomenon and its momentousness in structural engineering communities. The literature reveals that although the phenomenon of progressive collapse of buildings is receiving considerable attention in the professional engineering community, more research work is still needed in this field to develop a new methodology for efficient and inexpensive design to better protect buildings against progressive collapse.

Key Words
progressive collapse; failure; blast loading; damage; building codes.

Address
O. Yagob and K. Galal : Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Quebec, Canada H3G 1M8
N. Naumoski : Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5

Abstract
Recent interest in the use of wireless sensor networks for structural health monitoring (SHM)is mainly due to their low implementation costs and potential to measure the responses of a structure at unprecedented spatial resolution. Approaches capable of detecting damage using distributed processing must be developed in parallel with this technology to significantly reduce the power consumption and communication bandwidth requirements of the sensor platforms. In this investigation, a damage detection system based on a distributed processing approach is proposed and experimentally validated using a wireless sensor network deployed on two laboratory structures. In this distributed approach, on-board processing capabilities of the wireless sensor are exploited to significantly reduce the communication load and power consumption. The Damage Location Assurance Criterion (DLAC) is used for localizing damage. Processing of the raw data is conducted at the sensor level, and a reduced data set is transmitted to the base station for decision-making. The results indicate that this distributed implementation can be used to successfully detect and localize regions of damage in a structure. To further support the experimental results obtained, the capabilities of the proposed system were tested through a series of numerical simulations with an expanded set of damage scenarios.

Key Words
structural health monitoring; smart sensors; DLAC.

Address
Nestor E. Castaneda and Shirley Dyke: Department of Mechanical, Aerospace and Structural Engineering washington University in St. Louis, St. Louis, Missouri 63130, USA
Chenyang Lu, Fei Sun and Greg Hackmann: Department of Computer Science and Engineering Washington University in St. Louis, St. Louis, Missouri 63130, USA

Abstract
In the present article bending, buckling and vibration analyses of tapered beams using Eringen non-local elasticity theory are being carried out. The associated governing differential equations are solved employing Rayleigh-Ritz method. Both Euler-Bernoulli and Timoshenko beam theories are considered in the analyses. Present results are in good agreement with those reported in literature. Beam material is considered to be made up of functionally graded materials (fgms). Non-local analyses for tapered beam with simply supported - simply supported, clamped - simply supported and clamped - free boundary conditions are carried out and discussed. Further, effect of length to height ratio on maximum deflections,vibration frequencies and critical buckling loads are studied.

Key Words
non local theory; Rayleigh-Ritz method; tapered beam; bending; buckling; vibration and boundary conditions.

Address
S. C. Pradhan and A. Sarkar: Department of Aerospace Engineering, Indian Institute of Technology Kharagpur
West Bengal, India – 721 302


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