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CONTENTS
Volume 36, Number 3, October20 2010
 

Abstract
The study of the seismic vulnerability of masonry buildings requires structural properties of walls such as stiffness, ultimate load capacity, etc. In this article, a method is suggested for modeling the masonry walls under in-plane loading. At the outset, a set of analytical equations was established for determining the elastic properties of an equivalent homogeneous material of masonry. The results for homogenized unreinforced brick walls through detailed modeling were compared in different manners such as solid and perforated walls, in-plane and out-of-plane loading, etc, and it was found that this method provides suitable accuracy in estimation of the wall linear properties. Furthermore, comparison of the results of proposed modeling with experimental out coming indicated that this model considers the non linear properties of the wall such as failure pattern, performance curve and ultimate strength, and would be appropriate to establish a parametric study on those prone factors. The proposed model is complicated; therefore, efforts need to be made in order to overcome the convergency problems which will be included in this study. The nonlinear model is basically semi-macro but through a series of actions, it can be simplified to a macro model.

Key Words
unreinforced brick walls; micro modeling; macro modeling; homogenization; analysis; stiffness; strength; failure pattern.

Address
Arsalan Kalali: Department of Civil Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
Mohammad Zaman Kabir: Department of Civil Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

Abstract
A methodology on application of the discrete singular convolution (DSC) technique to the free vibration analysis of thin plates with curvilinear quadrilateral platforms is developed. In the proposed approach, irregular physical domain is transformed into a rectangular domain by using geometric coordinate transformation. The DSC procedures are then applied to discretization of the transformed set of governing equations and boundary conditions. For demonstration of the accuracy and convergence of the method, some numerical examples are provided on plates with different geometry such as elliptic, trapezoidal having straight and parabolic sides, sectorial, annular sectorial, and plates with four curved edges. The results obtained by the DSC method are compared with those obtained by other numerical and analytical methods. The method is suitable for the problem considered due to its generality, simplicity, and potential for further development.

Key Words
discrete singular convolution; natural frequency; plates; numerical models; curvilinear domain.

Address
Omer Civalek: Akdeniz University, Faculty of Engineering, Civil Engineering Department, Division of Mechanics, Antalya, Turkiye
Baki Ozturk: Nigde University, Faculty of Engineering, Civil Engineering Department, Division of Mechanics, Ni de, Turkiye

Abstract
The paper seeks to explore some aspects of the current state of knowledge on progressive collapse in the technical literature covering blast loads and structural analysis procedure applicable to reinforced concrete (RC) buildings. The paper describes the progressive collapse analysis of a commercial RC building located in the city of Riyadh and subjected to different blast scenarios. A 3-D finite element model of the structure was created using LS-DYNA, which uses explicit time integration algorithms for solution. Blast loads were treated as dynamic pressure-time history curves applied to the exterior elements. The inherent shortcomings of notional member removal have been taken care of in the present paper by simulating the damage of structural elements through the use of solid elements with the provision of element erosion. Effects of erosion and cratering are studied for different scenarios of the blast.

Key Words
progressive collapse; blast pressure; finite element analysis; RC building.

Address
T.H. Almusallam: Specialty Unit for Safety and Preservation of Structures, King Saud University, Saudi Arabia
H.M. Elsanadedy: Specialty Unit for Safety and Preservation of Structures, King Saud University, Saudi Arabia
H. Abbas: Specialty Unit for Safety and Preservation of Structures, King Saud University, Saudi Arabia
S.H. Alsayed: Specialty Unit for Safety and Preservation of Structures, King Saud University, Saudi Arabia
Y.A. Al-Salloum: Specialty Unit for Safety and Preservation of Structures, King Saud University, Saudi Arabia

Abstract
The seismic-induced failure of a dam could have catastrophic consequences associated with the sudden release of the impounded reservoir. Depending on the severity of the seismic hazard, the characteristics and size of the dam-reservoir system, preventing such a failure scenario could be a problem of critical importance. In many cases, the release of water is controlled through a reinforced-concrete intake tower. This paper describes the application of a static nonlinear procedure known as the Capacity Spectrum Method (CSM) to evaluate the structural integrity of intake towers subject to seismic ground motion. Three variants of the CSM are considered: a multimodal pushover scheme, which uses the idea proposed by Chopra and Goel (2002); an adaptive pushover variant, in which the change in the stiffness of the structure is considered; and a combination of both approaches. The effects caused by the water surrounding the intake tower, as well as any water contained inside the hollow structure, are accounted for by added hydrodynamic masses. A typical structure is used as a case study, and the accuracy of the CSM analyses is assessed with time history analyses performed using commercial and structural analysis programs developed in Matlab.

Key Words
intake towers; capacity spectrum method; dams; nonlinear static analysis; seismic behavior.

Address
Leonardo Cocco: Department of Structures, School of Engineering, National University of Cordoba, Cordoba 5000, Argentina
Luis E. Suarez: Department of Civil Engineering and Surveying, University of Puerto Rico, Mayaguez, Puerto Rico 00681-9000
Enrique E. Matheu: Office of Infrastructure Protection, US Department of Homeland Security, Arlington, Virginia 22201, USA

Abstract
The Discrete Element Method adopting particles for the domain discretization has recently been adopted in fracture studies of non-homogeneous continuous media such as concrete and rock. A model is proposed in which the reinforcement is modelled by 1D rigid-spring discrete elements. The rigid bars interact with the rigid circular particles that simulate the concrete through contact interfaces. The DEM enhanced model with reinforcement capabilities is evaluated using three point bending and four point bending tests on reinforced concrete beams without stirrups. Under three point bending, the model is shown to reproduce the expected final crack pattern, the crack propagation and the load displacement diagram. Under four point bending, the model is shown to match the experimental ultimate load, the size effect and the crack propagation and localization.

Key Words
discrete-element; reinforced-concrete; fracture.

Address
N. Monteiro Azevedo: LNEC, Av. Brasil 101, 1700-066 Lisboa, Portugal
J.V. Lemos: LNEC, Av. Brasil 101, 1700-066 Lisboa, Portugal
J.R. Almeida: Department of Civil Engineering, Faculdade de Ciencias e Tecnologia, UNL, 1700 Monte de Caparica, Portugal

Abstract
Materials which exhibit different elastic moduli in tension and compression are known as bimodular materials. The bimodular materials model, which is founded on the criterion of positivenegative signs of principal stress, is important for the structural analysis and design. However, due to the inherent complexity of the constitutive relation, it is difficult to obtain an analytical solution of a bimodular bending components except in particular simple problems. Based on the existent simplified model, this paper solves analytically bending thin plates with different moduli in tension and compression. By using the continuity conditions of stress components in unknown neutral layer, we determine the location of the neutral layer, and derive the governing differential equation for deflection, the flexural rigidity, and the internal forces in the thin plate. We also use a circular thin plate with bimodulus to illustrate the application of this solution derived in this paper. The results show that the introduction of different moduli has influences on the flexural stiffness of the bending thin plate.

Key Words
bimodulus; tension and compression; thin plate; bending; continuity.

Address
Xiao-ting He: College of Civil Engineering, Chongqing University, Chongqing 400045, PR China; Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, PRC, Chongqing 400045, PR China
Xing-jian Hu: College of Civil Engineering, Chongqing University, Chongqing 400045, PR China
Jun-yi Sun: College of Civil Engineering, Chongqing University, Chongqing 400045, PR China; Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, PRC, Chongqing 400045, PR China
Zhou-lian Zheng: College of Civil Engineering, Chongqing University, Chongqing 400045, PR China; Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, PRC, Chongqing 400045, PR China

Abstract
A fuzzy hybrid control technique using a semi-active tuned mass damper (STMD) has been proposed in this study for mitigation of wind induced motion of a tall building. For numerical simulation, a third generation benchmark is employed for a wind-excited 76-story building. A magnetorheological (MR) damper is used to compose an STMD. The proposed control technique employs a hierarchical structure consisting of two lower-level semi-active controllers (sub-controllers) and a higher-level fuzzy hybrid controller. Skyhook and groundhook control algorithms are used as sub-controllers. When a wind load is applied to the benchmark building, each sub-controller provides different control commands for the STMD. These control commands are appropriately combined by the fuzzy hybrid controller during realtime control. Results from numerical simulations demonstrate that the proposed fuzzy hybrid control technique can effectively reduce the STMD motion as well as building responses compared to the conventional hybrid controller. In addition, it is shown that the control performance of the STMD is superior to that of the sample TMD and comparable to an active TMD, but with a significant reduction in power consumption.

Key Words
fuzzy logic controller; hybrid control; semi-active tuned mass damper; skyhook; groundhook; wind-excited tall building.

Address
Joowon Kang: School of Architecture, Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, Korea
Hyun-Su Kim: Division of Architecture, Sunmoon University, Asan-si, Chungnam 336-708, Korea


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