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PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Influence of the Location of Resistant Cores on the Seismic Response of a Reinforced Concrete Three-Dimensional Frame Equipped with HDRB Base Isolation Devices
M.T. Braz César1 and R.C. Barros2
1Polytechnic Institute of Bragança, Portugal
, "Influence of the Location of Resistant Cores on the Seismic Response of a Reinforced Concrete Three-Dimensional Frame Equipped with HDRB Base Isolation Devices", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 199, 2007. doi:10.4203/ccp.86.199
Keywords: seismic isolation, high-damping rubber bearings, seismic behaviour, asymmetric three-dimensional frames, parametric studies, earthquake design.
The present work addresses the structural behaviour of three-dimensional reinforced concrete buildings with concrete cores of resistant walls and seismic isolation. In this study a single asymmetric concrete core was placed in a ten floor three-dimensional building and then a set of numerical analyses were made for several geometric arrangements without and with high-damping rubber bearings (HDRB). This base isolation (BI) system is used in order to reduce the structural seismic response and its associated damage. In order to evaluate the importance of the basic location of these structural elements, a parametric study is carried out changing the in-plan core location associated with symmetrical and asymmetrical structural distribution of the in-plan stiff core. The buildings were modelled using the commercial package SAP-2000 and the seismic analyses were carried out in accordance with the new European Code for seismic analysis and design: Eurocode 8 (EC8); the national annex is used to define the Portuguese elastic spectra.
To achieve acceptable lateral stiffness and resistance in both the main in-plan directions, the buildings must have adequate torsional stiffness in order to limit torsion effects; otherwise, from such effects, a non-uniform distribution of seismic forces in the vertical resistant structural elements might be expected, which becomes detrimental to building behavior and performance. This means that the buildings vibration shapes should be preferentially translation mode shapes, preventing the appearance of twist or torsion modes associated with eccentricities. The importance of these modes in the structural response is ascertained through the evaluation of the modal participation mass ratios, normally expressed as a percentage of the total mass of the structure.
The buildings of the parametric study were modelled using the commercial package SAP 2000 , to understand the three-dimensional reinforced concrete frames behaviour and performance under elastic response spectrum analysis. It was verified that base isolation significantly improves the structural behavior, by shifting the main period range associated with the change in structural stiffness through the use of the isolation system . The torsional effect associated with the resistant concrete core location is quite reduced when using BI, becoming practically invariant for the parametric variations studied. Also the seismic forces, as measured by the base shears, are drastically decreased by the implementation of such devices designed according to available methodologies.
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