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Wijesundara K.K.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School | Nascimbene R.,European Center for Training and Research in Earthquake Engineering | Sullivan T.J.,University of Pavia
Bulletin of Earthquake Engineering | Year: 2011

The direct displacement based seismic design procedure utilises equivalent viscous damping expressions to represent the effect of energy dissipation of a structural system. Various expressions for the equivalent viscous damping of different structural systems are available in the literature, but the structural systems examined in the past have not included concentrically braced frame structures. Thus, this study describes the development of an equivalent viscous damping equation for concentrically braced frame structures based on the hysteretic response of 15 different single storey models. Initially, equivalent viscous damping is calculated based on the area based approach and then corrected for the earthquake excitation. An iterative procedure is adopted to calibrate the equivalent viscous damping expression to the results of inelastic time history analyses using a number of spectrum-compatible real accelerograms. From the results of this research, a new damping expression is developed as a function of the ductility and the non dimensional slenderness ratio. © 2011 Springer Science+Business Media B.V.

Franchin P.,University of Rome La Sapienza | Pinto P.E.,University of Rome La Sapienza | Rajeev P.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School
Journal of Earthquake Engineering | Year: 2010

Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In order to take into account the uncertainty in the knowledge of structural properties, EC8-3 defines, analogously to the ordinary material partial factors, an adjustment factor, called confidence factor (CF), whose value depends on the level of knowledge (KL) of properties such as geometry, reinforcement layout and detailing, and materials. This solution is plausible from a logical point of view but it cannot yet profit from the experience of its use in practice, hence it needs to be substantiated by a higher level probabilistic analysis accounting for and propagating epistemic uncertainty (i.e., incomplete knowledge of a structure) throughout the seismic assessment procedure. This article investigates the soundness of the format proposed in EC8-3. The approach taken rests on the simulation of the entire assessment procedure and the evaluation of the distribution of the assessment results (distance from the limit state of interest) conditional on the acquired knowledge. Based on this distribution, a criterion is employed to calibrate the CF values. The obtained values are then critically examined and compared with code-specified ones. The results pinpoint a number of deficiencies that appear to somewhat invalidate the approach. The methodological significance of the work extends beyond the assessment procedure in EC8-3, since similar factors appear in other international guidelines (e.g., the knowledge factor of FEMA356). Copyright © A.S. Elnashai & N.N. Ambraseys.

Adhikari G.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School | Petrini L.,Polytechnic of Milan | Calvi G.M.,University of Pavia
Bulletin of Earthquake Engineering | Year: 2010

The paper investigates the applicability of current direct displacement based seismic design (DDBD) procedure, developed by Priestley and his coworkers, for straight long span bridges under transverse seismic excitation synchronous to all supports. This category of bridges often possess some additional features such as massive tall piers, highly irregular distribution of mass and stiffness due to unequal superstructure spans and pier heights, large deformation capacity etc. that are absent in short-to-moderate span bridges for which DDBD has extensively been verified. It is shown that DDBD in its current form is unable to capture both displacement and base shear demand when compared with nonlinear dynamic analysis results. Accordingly, a simple mechanics based extension of the current procedure that takes into account the effect of pier mass while computing base shear demand as well as a modal combination rule for estimating displacement demand is proposed and validated using a series of parametric studies. The new procedure also allows engineer to allocate strength at the potential plastic hinge location in more general terms. © 2010 Springer Science+Business Media B.V.

Paksoy A.M.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School | Petrini L.,Polytechnic of Milan
Bridge Maintenance, Safety, Management, Resilience and Sustainability - Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management | Year: 2012

In Italy, as well as in other seismic countries, many viaducts along the highways were built in the Sixties without antiseismic criteria. Moreover, some of these bridges are fundamental after a seismic event for allowing the civil protection interventions and first aid organizations. Therefore, they are needed to be assessed against seismic risk. In this paper we present a displacement-based seismic assessment procedure for reinforced concrete multi-span bridges in transverse response which gives reliable results and, at the same time, is sufficiently simple to be applied on a large population of bridges in a short time thanks to an ad hoc developed numerical tool. © 2012 Taylor & Francis Group.

Masoudi M.,European School for Advanced Studies in Reduction of Seismic Risk ROSE School | Masoudi M.,International Institute of Earthquake Engineering and Seismology | Eshghi S.,International Institute of Earthquake Engineering and Seismology | Ghafory-Ashtiany M.,International Institute of Earthquake Engineering and Seismology
Engineering Structures | Year: 2012

This paper discusses the failure mechanism of elevated concrete tanks with shaft and frame staging (supporting system) along with seismic behavior of these construction types. In order to modify the current code-based seismic design methodology, computer models have been established to determine the response modification factors, R, of the shaft and frame staging elevated tanks. The computational models have been subjected to an ensemble of earthquake ground motions. The effects of multi-component earthquakes, fluid-structure interaction and the P-. Δ effects on the inelastic response of elevated tanks have been studied by conducting linear and nonlinear response history analyses. According to results of analyses and observed inelastic behavior during past earthquakes, the R factors for shaft and frame staging elevated concrete tanks have been evaluated regarding the seismicity of the site. Moreover, the shortcomings associated to the current simplified seismic analysis and design procedure have been addressed and a more rational modeling has been suggested especially for the shaft staging systems to enhance distribution of the ductility demand. © 2012 Elsevier Ltd.

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