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CONTENTS
Volume 6, Number 1, January 2014
 

Abstract
The main focus of this paper is the analysis of the different components of the variability for strong ground motions recorded from earthquakes produced by the Vrancea subcrustal seismic source. The analysis is performed for two ground motion prediction equations: Youngs et al. (1997) and Zhao et al. (2006), recommended within the SHARE project for the Vrancea subcrustal seismic source and which are proposed in the work of Delavaud et al. (2012) and graded best in Vacareanu et al. (2013c). The first phase of the analysis procedure consists of a grading procedure. In the second phase, the single station sigma procedure is applied for both attenuation models in order to reduce some parts of ground motion models’ variability produced by the ergodic assumption. The strong ground motion database which is used throughout the study consists of over 400 accelerograms recorded from 9 Vrancea intermediate-depth seismic events. The results of the single station sigma analysis show significant reduction of the standard deviations, especially in the case of the Youngs et al. (1997) attenuation model, which is also graded better than the other selected GMPE.

Key Words
ground motion prediction equation; strong ground motion database; single station sigma; seismic hazard

Address
Florin Pavel, Radu Vacareanu, Cristian Arion and Cristian Neagu: Department of Reinforced Concrete Structures, Technical University of Civil Engineering Bucharest, Bd. Lacul Tei no. 122-124, Sector 2, 020396, Bucharest, Romania

Abstract
A risk assessment framework for evaluating building structures is implemented in this study. This framework allows considering sources of uncertainty both on structural capacity and seismic demand. In particular randomness on seismic load, incident angle, material properties, floor mass and structural damping are considered; in addition the choice of fibre modelling versus plastic hinge model is also considered as a source of uncertainty. The main objective of this work is to study the contribution of these sources of uncertainty on the fragilities of steel and steel-reinforced concrete composite 3D building structures. The fragility curves are expressed in the form of a two-parameter lognormal distribution where vertical statistics in conjunction with metaheuristic optimization are implemented for calculating the two parameters.

Key Words
aleatory and epistemic uncertainties; fragilities; fibre and plastic hinge modelling; multicomponent incremental dynamic analysis; steel and steel-concrete composite buildings

Address
Nikos D. Lagaros: Institute of Structural Analysis & Antiseismic Research, Department of Structural Engineering, School of Civil Engineering, National Technical University Athens, 9, Iroon Polytechniou Str., Zografou Campus, GR-15780 Athens, Greece

Abstract
The 2009 L’Aquila, Italy earthquake shook a high density area causing a wide spectrum of damage to reinforced concrete with infill buildings, one of the most common building types used in Italy. The earthquake has proven to be a “full-scale” laboratory to further understand building performance. This paper presents the first results of a joint research effort between the University of Bologna and Degenkolb Engineers, aimed at investigating the seismic behavior of an infilled frame building that collapsed during the earthquake. State-of-the-practice techniques were implemented as a way to determine the reliability of these modeling techniques in anticipating the observed building performance. The main results indicate that: (i) the state-of-the-practice techniques are able to predict the observed behavior of the buildings; (ii) the masonry infills have a great influence on the behavior of the building in terms of stiffness, strength and global ductility.

Key Words
seismic response; masonry infills; L’Aquila earthquake

Address
Michele Palermo and Tomaso Trombetti: Universitá di Bologna, Viale del Risorgimento 2, 40136 Bologna, Italy
Ricardo Rafael Hernandez: Degenkolb Engineers, 300 South Grand Ave, Suite 1115, Los Angeles, CA, 90071, USA
Silvia Mazzoni: Degenkolb Engineers, 235 Montgomery Street, Suite 500, San Francisco, CA 94104, USA

Abstract
Interaction between closely-spaced buildings subject to earthquake induced strong ground motions, termed in the literature as “seismic pounding”, occurs commonly during major seismic events in contemporary congested urban environments. Seismic pounding is not taken into account by current codes of practice and is rarely considered in practice at the design stage of new buildings constructed “in contact” with existing ones. Thus far, limited research work has been devoted to quantify the influence of slab-to-slab pounding on the inelastic seismic demands at critical locations of structural members in adjacent structures that are not aligned in series. In this respect, this paper considers a typical case study of a “new” reinforced concrete (R/C) EC8-compliant, torsionally sensitive, 7-story corner building constructed within a block, in bi-lateral contact with two existing R/C 5-story structures with same height floors. A non-linear local plasticity numerical model is developed and a series of non-linear time-history analyses is undertaken considering the corner building “in isolation” from the existing ones (no-pounding case), and in combination with the existing ones (pounding case). Numerical results are reported in terms of averages of ratios of peak inelastic rotation demands at all structural elements (beams, columns, shear walls) at each storey. It is shown that seismic pounding reduces on average the inelastic demands of the structural members at the lower floors of the 7-story building. However, the discrepancy in structural response of the entire block due to torsion-induced, bi-directionally seismic pounding is substantial as a result of the complex nonlinear dynamics of the coupled building block system.

Key Words
seismic pounding; EC8 compliant buildings; three-dimensional model; ductility demand; spectrum compatible accelerograms; incremental dynamic analysis

Address
Paschalis Skrekas and Agathoklis Giaralis: Department of Civil Engineering, City University London, Northampton Square, EC1V 0HB, London, UK
Anastasios Sextos: Department of Civil Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece

Abstract
Nonlinear dynamic analyses are carried out to investigate the influence of the pinching hysteretic response of the exterior RC beam-column joints on the seismic behavior of multistory RC frame structures. The effect of the pinching on the local and global mechanisms of an 8-storey bare frame and an 8-storey pilotis type frame structure is evaluated. Further, an experimental data bank extracted from literature is used to acquire experimental experience of the range of the real levels that have to be considered for the pinching effect on the hysteretic response of the joints. Thus, three different cases for the hysteretic response of the joints are considered: (a) joints with strength and stiffness degradation characteristics but without pinching effect, (b) joints with strength degradation, stiffness degradation and low pinching effect and (c) joints with strength degradation, stiffness degradation and high pinching effect. For the simulation of the beam-column joints a special-purpose rotational spring element that incorporates the examined hysteretic options developed by the authors and implemented in a well-known nonlinear dynamic analysis program is employed for the analysis of the structural systems. The results of this study indicate that the effect of pinching on the local and global responses of the examined cases is not really significant at early stages of the seismic loading and especially in the cases when strength degradation in the core of exterior joint has occurred. Nevertheless in the cases when strength degradation does not occur in the joints the pinching may increase the demands for ductility and become critical for the columns at the base floor of the frame structures. Finally, as it was expected the ability for energy absorption was reduced due to pinching effect.

Key Words
hysteretic response; pinching; strength degradation; stiffness degradation; RC beam-column joints; energy dissipation; multistory RC frame structures; seismic responses

Address
Maria J. Favvata and Chris G. Karayannis: Department of Civil Engineering, Section of Structural Engineering, Democritus University of Thrace, 12 V. Sofias street, Xanthi, GR 67100, Greece

Abstract
Multiple level performance of seismically isolated elevated storage tank isolated with multi-phase friction pendulum bearing is investigated under totally 60 records developed for multiple level seismic hazard analysis (SLE, DBE and MCE). Mathematical formulations involving complex time history analysis have been proposed for analysis of typical storage tank by multi-phase friction pendulum bearing. Multi-phase friction pendulum bearing represent a new generation of adaptive friction isolation system to control super-structure demand in different hazard levels. This isolator incorporates four concave surfaces and three independent pendulum mechanisms. Pendulum stages can be set to address specific response criteria for moderate, severe and very severe events. The advantages of a Triple Pendulum Bearing for seismic isolation of elevated storage tanks are explored. To study seismic performance of isolated elevated storage tank with multi-phase friction pendulum, analytical simulations were performed with different friction coefficients, pendulum radii and slider displacement capacities.

Key Words
multi-phase friction pendulum; probabilistic analysis; seismically isolated elevated storage tank; demand parameter

Address
Hesamaldin Moeindarbari and Touraj Taghikhany: Department of Civil and Environmental Engineering, AmirKabir University of Technology (Polytechnic), Tehran, Iran
Masoud Malekzadeh: Department of Civil, Environmental and Construction Engineering, University of Central Florida, Orlando, Florida, USA


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