Finite element modelling of stress concentrations in a reinforced concrete offshore structure
Finite element modelling of stress concentrations in a reinforced concrete offshore structure
This research describes the finite element modelling of a hybrid supporting tower for an offshore aerogenerator. The hybrid structure consisting of a steel tower mounted on a concrete tripod offers the best compromise between minimum weight and maximum stability. This combination also provides good durability and ease of construction. Earlier studies showed most economic geometry for the tripod support to be a small platform on which the steel tower can be mounted, with legs inclined at about 60o founded at positions determined by overall stability. The main emphasis has been to explore the areas of high stress concentrations which were anticipated to be at the concrete tripod joints. The research, therefore, concentrated initially on the overall modelling of the entire structure. Overall analysis has been carried out under both STATIC and DYNAMIC conditions. Every part of the aerogenerator, including the soil-structure interaction and various structural components were included in the overall model. The overall analysis was subsequently used to model the tripod joints in more detail. Detailed modelling of the joints provided an insight to better understanding of local stress development within the tripod joints. Close resemblance between the actual structure and the F.E. model proved to be crucial during the analysis. Soil-structure interactions were represented in the overall model by means of springs and dashpots. The stiffness of the springs was determined from a separate F.E. modelling of pile-soil medium. A guideline is established to show that the ratio of the number of master degrees of freedom to the active degrees of freedom in the overall model should not be less than a threshold which is different for modal analysis and forced vibration analysis. It is demonstrated that the use of automatic master degrees of freedom selection procedure seriously undermines the accuracy of the local stress analysis in the numerical models. Standard practice in applying finite element analysis to such a hybrid structure has been shown to give good predictions of static and dynamic response, but to underestimate seriously the stresses developed. Response to overall analysis was used to indicate how local stresses can develop. Local stresses have been shown to exceed those predicted by simpler methods, particularly in the areas of combined shear and bending where columns frame into the platform.
University of Southampton
1991
Parsa, Arash
(1991)
Finite element modelling of stress concentrations in a reinforced concrete offshore structure.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This research describes the finite element modelling of a hybrid supporting tower for an offshore aerogenerator. The hybrid structure consisting of a steel tower mounted on a concrete tripod offers the best compromise between minimum weight and maximum stability. This combination also provides good durability and ease of construction. Earlier studies showed most economic geometry for the tripod support to be a small platform on which the steel tower can be mounted, with legs inclined at about 60o founded at positions determined by overall stability. The main emphasis has been to explore the areas of high stress concentrations which were anticipated to be at the concrete tripod joints. The research, therefore, concentrated initially on the overall modelling of the entire structure. Overall analysis has been carried out under both STATIC and DYNAMIC conditions. Every part of the aerogenerator, including the soil-structure interaction and various structural components were included in the overall model. The overall analysis was subsequently used to model the tripod joints in more detail. Detailed modelling of the joints provided an insight to better understanding of local stress development within the tripod joints. Close resemblance between the actual structure and the F.E. model proved to be crucial during the analysis. Soil-structure interactions were represented in the overall model by means of springs and dashpots. The stiffness of the springs was determined from a separate F.E. modelling of pile-soil medium. A guideline is established to show that the ratio of the number of master degrees of freedom to the active degrees of freedom in the overall model should not be less than a threshold which is different for modal analysis and forced vibration analysis. It is demonstrated that the use of automatic master degrees of freedom selection procedure seriously undermines the accuracy of the local stress analysis in the numerical models. Standard practice in applying finite element analysis to such a hybrid structure has been shown to give good predictions of static and dynamic response, but to underestimate seriously the stresses developed. Response to overall analysis was used to indicate how local stresses can develop. Local stresses have been shown to exceed those predicted by simpler methods, particularly in the areas of combined shear and bending where columns frame into the platform.
This record has no associated files available for download.
More information
Published date: 1991
Identifiers
Local EPrints ID: 458266
URI: http://eprints.soton.ac.uk/id/eprint/458266
PURE UUID: f88ac16c-febb-4fb7-9cf1-20ad41c214e6
Catalogue record
Date deposited: 04 Jul 2022 16:45
Last modified: 04 Jul 2022 16:45
Export record
Contributors
Author:
Arash Parsa
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics