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PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON THE DESIGN AND CONSTRUCTION OF NON-CONVENTIONAL STRUCTURES
Edited by: B.H.V. Topping
An Equivalent Damping Factor for Earthquake Response Analysis of Cooling Towers from Soil-Structure Interaction View Points
T. Sohri*, Y. Mukaiyama+, S. Kato* and P.L. Gould#
*Department of Regional Planning, Toyohashi University of Technology, Japan
T. Sohri, Y. Mukaiyama, S. Kato, P.L. Gould, "An Equivalent Damping Factor for Earthquake Response Analysis of Cooling Towers from Soil-Structure Interaction View Points", in B.H.V. Topping, (Editor), "Proceedings of the International Conference on the Design and Construction of Non-Conventional Structures", Civil-Comp Press, Edinburgh, UK, pp 123-132, 1987. doi:10.4203/ccp.7.16.7
The present paper discusses the effects of dynamic soil-structure interaction to the response of reinforced concrete cooling towers on a multi-layered soil column. The discussions of the results lead to a concept of "an EQUIVALENT DAMPING FACTOR heq" which is applied to a simplified/practical model, being a cooling tower fixed at the footing. The heq, if applied to the simplified model, is defined to give an almost same response for the tower resting on the soil layers.
The values of heq for various combinations between types of cooling towers and types of soil columns are obtained numerically by comparing the responses between two analytical models. One of them, being called an original model, considers a complete dynamic soil-structure interaction in its analysis. This model consists of a tower and a footing resting on a multi-layered soil column, the both of the structures and the soil layer being subjected to incident earthquake motions at its bedrock. The other is the fixed tower model, named as a simplified or practical model. The tower is assumed to be fixed at the footing at which the footing is supposed to be subjected to a free field earthquake motion. That is, the motion is the response at the top of the soil column without structures on it when the soil column receives the same incident earthquake motion as the original model at its bottom.
By using the present equivalent damping factor in the simplified model, the radiation of seismic energy into the surrounding soils under the structure can be approximately taken into account even when a usual engineering model, being often adopted in the engineering practices, is used to estimate the responses of cooling towers on soil layers. The estimated values of heq from various results for several combination between types of cooling towers and types of soil columns are summarized in tabular form, leading to an approximate guideline that an internal viscous damping factor for reinforced concrete towers may be raised by about 5 percent than the original material damping factor of concrete towers.
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