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CONTENTS
Volume 1, Number 3, September 2010
 

Abstract
Previous research on pounding between seismically isolated buildings during earthquakes has been focused on impacts at the bases of structures and the effect of simultaneous interactions at the bases and at the superstructures has not been studied in details. In this paper, the seismic responses of adjacent buildings supported on different or similar base systems considering impacts between bases and superstructures are numerically investigated. The study is carried out in three parts for the two types of adjacent buildings: (i) both structures have fixed bases; (ii) one structure has fixed base and the other is seismically isolated and (iii) both structures have base isolation systems. The results of the study indicate that the pounding-involved responses of the buildings depend mainly on the type of structural base systems and on the structural parameters of both buildings. For the base-isolated building, the variation of the peak accelerations and displacements of the storeys have been found to be relatively low. On the other hand, significant differences have been observed for the fixed base building. The results of the parametric study conducted for different values of the gap size between colliding structures show the reduction in the peak base displacements as the gap distance decreases.

Key Words
structural pounding; earthquakes; seismic isolation; nonlinear modelling.

Address
Sayed Mahmoud: Faculty of Engineering at Mataria, Helwan University, 11718 Cairo, Egypt
Robert Jankowski: Faculty of Civil and Environmental Engineering, Gdansk University of Technology
ul. Narutowicza 11/12, 80-233 Gdansk, Poland

Abstract
A novel simple approach is presented for the seismic analysis of continuous buried pipelines subject to fault ruptures. The method is based on the minimization of the total dissipated energy during faulting, taking into account the basic factors that affect the problem, namely: a) the pipe yielding under axial and bending load, through the formation of plastic hinges and axial slip; b) the longitudinal friction across the pipe-soil interface; c) the lateral resistance of soil. The advantages and drawbacks of the proposed method are highlighted through a comparison with previous approaches, as well as with finite element calculations accounting for the 3D kinematics of the pipe-soil-fault systems under large deformations. Parametric analyses are also provided to assess the relative influence of the various parameters affecting the problem.

Key Words
buried pipeline; fault rupture; seismic design; finite element simulations.

Address
Roberto Paolucci: Department of Structural Engineering, Politecnico di Milano, P.za Leonardo da Vinci 32, 20133 Milano, Italy
Stefano Griffini: SOIL srl, v. Pestalozzi 10, Milano, Italy
Stefano Mariani: Department of Structural Engineering, Politecnico di Milano, P.za Leonardo da Vinci 32, 20133 Milano, Italy

Abstract
High-strength concrete (HSC) is becoming more popular in the construction of beams and columns of tall buildings because of its higher stiffness and strength-to-weight ratio. However, as HSC is more brittle than normal-strength concrete (NSC), it may adversely affect the flexural ductility and deformability of concrete members. Extended from a series of theoretical study conducted on flexural ductility of concrete beams, the authors would in this paper investigate the effects of some critical factors including the degree of reinforcement, confining pressure, concrete and steel yield strength on the flexural deformability of NSC and HSC beams. The deformability, expressed herein in terms of normalised rotation capacity defined as the product of ultimate curvature and effective depth, is investigated by a parametric study using nonlinear moment-curvature analysis. From the results, it is evident that the deformability of concrete beams increases as the degree of reinforcement decreases and/or confining pressure increases. However, the effects of concrete and steel yield strength are more complicated and dependent on other factors. Quantitative analysis of all these effects on deformability of beams has been carried out and formulas for direct deformability evaluation are developed. Lastly, the proposed formulas are compared with available test results to verify its applicability.

Key Words
beams; curvature; deformability; high-strength concrete; reinforced concrete; rotation capacity.

Address
K.J.H. Zhou, J.C.M. Ho and R.K.L. Su: Department of Civil Engineering, The University of Hong Kong, Hong Kong

Abstract
A gradient-based evolutionary optimization methodology is presented for finding the optimal design of viscous dampers to minimize an objective function defined for a linear multi-storey structure. The maximum value along height of the transfer function amplitudes for the interstorey drifts is taken as the objective function. Since the ground motion includes various uncertainties, the optimal damper placement may be different depending on the ground motion used for design. Furthermore, the transfer function treated as the objective function depends on the properties of structural parameters and added dampers. This implies that a more robust damper design is desired. A reliable and robust damping design system against any unpredictable ground motions can be provided by minimizing the maximum transfer function. Such design system is proposed in this paper.

Key Words
optimal damper placement; transfer function; evolutionary optimization; gradient-based method; earthquake response.

Address
Kohei Fujita, Kaoru Yamamoto and Izuru Takewaki: Department of Urban and Environmental Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan

Abstract
This paper is concerned with the optimal seismic design of added viscous dampers in yielding plane frames. The total added damping is minimized for allowable values of local performance indices under the excitation of an ensemble of ground motions in both regular and irregular structures. The local performance indices are taken as the maximal inter-story drift of each story and/or the normalized hysteretic energy dissipated at each of the plastic hinges. Gradients of the constraints with respect to the design variables (damping coefficients) are derived, via optimal control theory, to enable an efficient first order optimization scheme to be used for the solution of the problem. An example of a ten story three bay frame is presented. This example reveals the following

Key Words
supplemental viscous damping; passive control; irregular structures; yielding frames; optimal damper placement.

Address
O. Lavan: Faculty of Civil and Environmental Engineering, Technion . Israel Institute of Technology, Haifa, Israel
R. Levy: Department of Structural Engineering, Faculty of Engineering Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel


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