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CONTENTS
Volume 3, Number 2, April 2012
 

Abstract
The energy-transmitting boundary, which is used in the well-known finite element method (FEM) program FLUSH, is quite efficient for the earthquake response analysis of buildings considering soil-structure interaction. However, it is applicable only in the frequency domain. The author proposed methods for transforming frequency dependent impedance into the time domain, and studied the time domain transform of the boundary. In this paper, first, the estimation methods for both the halfspace condition under the bottom of the soil model and the pseudo three-dimensional effect were studied with the time domain transmitting boundary. Next, response behavior when using the boundary was studied in detail using a practical soil and building model. The response accuracy was compared with those using viscous boundary, and the boundary that considers the excavation force. Through these studies, the accuracy and efficiency of the proposed time domain transmitting boundary were confirmed.

Key Words
energy transmitting boundary; FEM; time domain; soil-structure interaction; viscous boundary; excavation force

Address
Naohiro Nakamura: Research & Development Institute, Takenaka Corporation, 1-5-1, Ohtsuka, Inzai, Chiba, 270-1395, Japan

Abstract
The proposed research includes a comprehensive study on the seismic vulnerability assessment of typical building types, representative of the structural materials, the seismic codes and the construction techniques of Southern Europe. A damage database is created after the elaboration of the results of the observational data obtained from post-earthquake surveys carried out in the area struck by the September 7, 1999 Athens earthquake, a near field seismic event in an extended urban region. The observational database comprises 180.945 buildings which developed damage of varying degree, type and extent. The dataset is elaborated in order to gather useful information about the structural parameters influence on the seismic vulnerability and their correlation to the type and degree of building damages in near field earthquakes. The damage calibration of the observational data was based on label - damage provided by Earthquake Planning and Protection Organization (EPPO) in Greece and referred to the qualitative characterization for the recording of damage in post-earthquake surveys. Important conclusions are drawn on the parameters that influence the seismic response based on the wide homogeneous database which adds to the reliability of the collected information and reduces the scatter on the produced results.

Key Words
seismic vulnerability; observational earthquake damage; damage statistics; post-earthquake surveys; Athens earthquake; existing buildings

Address
Anastasia K. Eleftheriadou and Athanasios I. Karabinis: Laboratory of RC, Department of Civil Engineering, Democritus University of Thrace, B.Sofias 12, Xanthi 67100, Greece

Abstract
The Retrofit Yield Spectrum (RYS) is a new spectrum-based device that relates seismic demand of a retrofitted structure with the fundamental design parameters of the retrofit. This is obtained from superposition of Yield Point Spectra with design charts that summarize in pertinent spectrumcompatible coordinates the attributes of a number of alternative retrofit scenarios. Therefore, once the requirements for upgrading a given structure have been determined, the RYS enable direct insight of the sensitivity of the seismic response of the upgraded structure to the preliminary design decisions made while establishing the retrofit plan. By virtue of their spectrum-based origin, RYS are derived with reference to a single mode of structural vibration; a primary objective is to control the contribution of this mode in the retrofit design so as to produce a desirable distribution of damage at the ultimate limit state by removing soft storey formations and engaging the maximum number of structural members in deformation, in response to the input motion. Calculations are performed with reference to the yield-point, where secant stiffness is proportional to the flexural strength of reinforced concrete members. Derivation and use of the Retrofit Yield Spectra (RYS) refers to the seismic demand expressed either in terms of spectral acceleration, spectral displacement or interstory drift, at yield of the first storey. A reinforced concrete building that has been tested in full scale to a sequence of simulated earthquake excitations is used in the paper as a demonstration case study to examine the effectiveness of the proposed methodology.

Key Words
retrofit; spectra; seismic upgrading; yielding; ductility

Address
G.E. Thermou: Department of Civil Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
A.S. Elnashai: Department of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign,
2129e Newmark Lab., 205 N. Mathews Ave, Urbana, IL 61801, USA
S.J. Pantazopoulou: Department of Civil and Environmental Engineering, University of Cyprus, 1678 Nicosia, Cyprus
(on unpaid leave from D.U.Th., Greece)

Abstract
The performance of pure friction isolation system with respect to the frequency bandwidth of excitation and the predominant frequency is investigated. A set of earthquake ground motions (artificial as well as recorded [with different combinations of magnitude-distance and local site geology]) is considered for investigating effectiveness of pure friction isolators. The results indicate the performance of pure friction base isolated system does not only depend upon coefficient of friction and mass ratio but the stick-slip behaviour depends upon the frequency content of the excitation as well. Slippage prevails if the excitation frequency lies in a suitable frequency range. This range widens with increasing mass ratio. For larger mass ratios, the sliding effect is more pronounced and the maximum acceleration response is further reduced in the neighbourhood of frequency ratio (w/wn) of unity. The pure friction isolation system is effective in the case of broadband excitations only and that too, in the acceleration sensitive range of periods. The pure friction system is not effective for protection against narrow band motions for which the system response is quasi-periodic.

Key Words
band-limited excitation; earthquake; ground motion characteristics; friction isolation; frequency content; shape factor

Address
Radhikesh P. Nanda: Department of Civil Engineering, NIT Durgapur, Durgapur, 713209, India
Manish Shrikhande and Pankaj Agarwal: Department of Earthquake Engineering, IIT Roorkee, Roorkee, 247667, India

Abstract
The benchmark on the ASCE cable-stayed bridge has gathered since its proposal the interest of many specialists in the field of the structural control and the dynamic response of long span bridges. Starting from the original benchmark statement in the MATLAB framework, a refined version of the bridge model is developed in the ANSYS commercial finite element environment. A passive structural control system is studied through non linear numerical analyses carried out in time domain for several seismic realizations in a multiple support framework. An innovative electro-inductive device is considered. Its positive performance is compared with an alternative version considering traditional metallic dampers.

Key Words
cable-stayed; bridge; passive; control; user-element; earthquakes

Address
Marco Domaneschi and Luca Martinelli: Department of Structural Engineering, Politecnico di Milano, Milano, Italy


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