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CONTENTS
Volume 33, Number 3, October20 2009
 

Abstract
The seismic behavior of a framed structure with chevron-type buckling restrained braces was investigated and their behavior factors, such as overstrength, ductility, and response modification factors, were evaluated. Two types of structures, building frame systems and dual systems, with 4, 8, 12, and 16 stories were designed per the IBC 2003, the AISC LRFD and the AISC Seismic Provisions. Nonlinear static pushover analyses using two different loading patterns and incremental dynamic analysis using 20 earthquake records were carried out to compute behavior factors. Time history analyses were also conducted with another 20 earthquakes to obtain dynamic responses. According to the analysis results, the response modification factors turned out to be larger than what is proposed in the provision in low-rise structures, and a little smaller than the code-values in the medium-rise structures. The dual systems, even though designed with smaller seismic load, showed superior static and dynamic performances.

Key Words
buckling restrained braces; behavior factors; response modification factors; seismic design; building systems.

Address
Jinkoo Kim and Junhee Park: Dept. of Architectural Engineering, Sungkyunkwan University, Suwon, Korea
Sang-Dae Kim: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, Korea

Abstract
In the literature the problem of the topology optimization of the structure is usually solved for one, clearly described from the mechanical point of view material. Generally the topology optimization answers the question of the distribution of this mentioned above material within the design domain. Finally, material-voids distribution it is obtained. In this paper, for the structure mainly strengthened or sometimes weakened by the inclusions, the variation approach of the topology optimization problem is formulated. This multi material approach may be useful for the design process of various mechanical or civil engineering structures which need to be more

Key Words
topology optimization; minimum compliance approach; strengthened structure; multi material structure; mass constraints; FEM.

Address
Ryszard Kutylowski: Civil Engineering Institute (I-14), Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland

Abstract
This article presents the differential system that governs the mechanical behaviour of a curved-beam element, with varying cross-section area, subjected to generalized load. This system is solved by an exact procedure or by the application of a new numerical recurrence scheme relating the internal forces and displacements at the two end-points of an increase in its centroid-line. This solution has a transfer matrix structure. Both the stiffness matrix and the equivalent load vector are obtained arranging the transfer matrix. New structural matrices have been defined, which permit to determine directly the unknown values of internal forces and displacements at the two supported ends of the curved-beam element. Examples are included for verification.

Key Words
curved beam; differential system; transfer matrix; stiffness matrix; numerical method.

Address
F.N. Gimena, P. Gonzaga and L. Gimena: Dept. of Projects Engineering, Campus Arrosadia C.P. 31006, University Public of Navarre, Pamplona, Navarra, Spain

Abstract
Structural damage detection, damage localization and severity estimation of jacket platforms, based on calculating modal strain energy is presented in this paper. In the structure, damage often causes a loss of stiffness in some elements, so modal parameters; mode shapes and natural frequencies, in the damaged structure are different from the undamaged state. Geometrical location of damage is detected by computing modal strain energy change ratio (MSECR) for each structural element, which elements with higher MSECR are suspected to be damaged. For each suspected damaged element, by computing crossmodal strain energy (CMSE), damage severity as the stiffness reduction factor -that represented the ratios between the element stiffness changes to the undamaged element stiffness- is estimated. Numerical studies are demonstrated for a three dimensional, single bay, four stories frame of the existing jacket platform, based on the synthetic data that generated from finite element model. It is observed that this method can be used for damage detection of this kind of structures.

Key Words
damage detection; modal analysis; strain energy; jacket platforms.

Address
B. Asgarian and M. Amiri: K.N. Toosi University of Technology, Civil Engineering Department, Tehran, Iran
A. Ghafooripour: Islamic Azad University, Tehran Central Branch, Tehran, Iran

Abstract
The sealed, tuned liquid column gas damper (TLCGD) with gas-spring effect extends the frequency range of application up to about 5 Hz and efficiently increases the modal structural damping. In this paper the influence of several TLCGDs to reduce coupled translational and rotational vibrations of plan-asymmetric buildings under wind or seismic loads is investigated. The locations of the modal centers of velocity of rigidly assumed floors are crucial to select the design and the optimal position of the liquid absorbers. TLCGD

Key Words
asymmetric building; Bernoulli

Address
Chuan Fu: College of Architecture, North China University of Technology, Beijing 100144, China
Center of Mechanics and Structural Dynamics, Vienna University of Technology, Vienna 1040, Austria-Europe

Abstract
Test results of thirteen reinforced concrete corbels with shear span-to-depth ratio greater than unity are reported. The main variables studied were compressive strength of concrete, shear span-todepth ratio and parameter of vertical stirrups. The test results indicate that the shear strengths of corbels increase with an increase in compressive strength of concrete and parameter of vertical stirrups. The shear strengths of corbels also increase with a decrease in shear span-to-depth ratio. The smaller the shear span-to-depth ratio of corbel, the larger the stiffness and the shear strength of corbel are. The higher the concrete strength of corbel, the higher the stiffness and the shear strength of corbel are. The larger the parameter of vertical stirrups, the larger the stiffness and the shear strength of corbel are. The softened strut-and-tie model for determining the shear strengths of reinforced concrete corbels is modified appropriately in this paper. The shear strengths predicted by the proposed model and the approach of ACI Code are compared with available test results. The comparison shows that the proposed model can predict more accurately the shear strengths of reinforced concrete corbels than the approach of ACI Code.

Key Words
reinforced concrete corbels; shear strength; strut-and-tie model.

Address
Wen-Yao Lu: Dept. of Interior Design, China University of Technology, No. 56, Section 3, Xinglong Rd, Taipei, 11695 Taiwan
Ing-Jaung Lin: Dept. of Construction Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10672, Taiwan

Abstract
The purpose of this paper is to study shear locking-free parametric earthquake analysis of thick and thin plates using Mindlin\'s theory, to determine the effects of the thickness/span ratio, the aspect ratio and the boundary conditions on the linear responses of thick and thin plates subjected to earthquake excitations. In the analysis, finite element method is used for spatial integration and the Newmark-B method is used for the time integration. Finite element formulation of the equations of the thick plate theory is derived by using higher order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates clamped or simply supported along all four edges. In the analysis, 17-noded finite element is used. Graphs are presented that should help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that 17-noded finite element can be effectively used in the earthquake analysis of thick and thin plates. It is also concluded that, in general, the changes in the thickness/span ratio are more effective on the maximum responses considered in this study than the changes in the aspect ratio.

Key Words
shear locking-free parametric earthquake analysis; thick plate, Mindlin

Address
Y. I. Ozdemir and Y. Ayvaz: Civil Engineering, Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey

Abstract
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Key Words
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Address
Griengsak Kaewkulchai and Sdhabhon Bhokha: Faculty of Engineering, UbonRatchathani University, Thailand


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