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Civil-Comp Proceedings
ISSN 1759-3433 CCP: 76
PROCEEDINGS OF THE THIRD INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: B.H.V. Topping and Z. Bittnar
Paper 66
Optimal Design of Lead Rubber Bearing Seismic Isolators in Buildings C.P. Katsaras and V.K. Koumousis
Institute of Structural Analysis & Aseismic Research, Department of Civil Engineering, National Technical University of Athens, Athens, Greece Full Bibliographic Reference for this paper
C.P. Katsaras, V.K. Koumousis, "Optimal Design of Lead Rubber Bearing Seismic Isolators in Buildings", in B.H.V. Topping, Z. Bittnar, (Editors), "Proceedings of the Third International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 66, 2002. doi:10.4203/ccp.76.66
Keywords: base isolation, LRB systems, optimal design.
Summary
A method is proposed that determines the optimal design of Lead Rubber Bearing
(LRB) systems based on a systematic use of the interrelations that govern the
behaviour of a single LRB. This is based on the assumption of constant velocity
spectra and the analysis of a single degree of freedom system adopted by many
design codes. The optimal cost of the bearing that consists of the cost of rubber and
lead is determined by varying the external and the internal diameters together with
the total height of rubber. The constraints refer to the damping ratio and the
allowable shear strain as well as performance and capacity constraints. The optimal
solution corresponds to the maximum values for the damping ratio and shear strain
and is deduced systematically on a curve derived for every specific problem for the
critical capacity constraint that controls buckling. This simplification is extended to
problems having different groups of LRBs and the optimal solution is deduced
accordingly. Numerical results are presented which are compared with those
determined following a mathematical programming approach and their agreement is
established.
Seismic isolation constitutes a design strategy that attempts to separate the structure from the damaging effects of the earthquake ground motions [1]. One practical seismic isolation system that provides the necessary requirements in the form of a single elastomeric bearing unit is the Lead Rubber Bearing (LRB) [2]. The procedures suggested by various codes of practice for the evaluation of isolated structures are in increasing order of complexity, a) the equivalent static analysis, b) the response spectrum analysis and c) time-history analysis. The equivalent static method is based on the assumption of a rigid superstructure above the isolators and is suitable also for the cost optimization of the isolation system and its performance.
The constant velocity spectrum assumption implies that the displacement is
proportional to the period
The material cost is proportional to a constant The proposed algorithm for the optimal design of a single LRB system consists of the following steps:
The Single LRB optimization problem can be directly extended to cover the
design of LRB base isolation systems that consist of bearings having the same total
rubber thickness
From the analysis and results it becomes evident that the optimal material cost
solution of a single LRB system can be deduced systematically once the damping
coefficient and the allowable shear strain are set to their maximum values. This is
performed through the establishment of the curve of optimal cost in the
References
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