Stability Analysis and Displacement Measurements of Graving Drydock Walls

Abstract

Maintenance and safety certification of the Navy's graving drydocks are essential in supporting fleet operation and readiness. Thus, structural analyses of graving drydocks are made regularly by the Naval Facilities Engineering Command using a finite element computer program. An analytical method is implemented to evaluate the structural adequacy of existing drydocks which are subjected to static and earthquake loads. The results of the analyses are used in certifying the safety of drydocks. Due to the complexity of the drydock structure, an analysis is begun by setting up structural models which can accurately include structural and geotechnical parameters for finite element numerical analysis. The accuracy of the results can then be checked through a comparison of the different models used in the analysis, and the comparison of field observations made from carefully monitored instrumentation. For example, in order to evaluate a mathematical analysis of the response of a drydock to static and earthquake loads, measurements of the movement of drydock walls in Charleston Naval Shipyard, South Carolina, were made by flooding and draining the drydock during a docking operation. A dial gauge instrument was used to measure the displacement of a wall and a laser electronic distance measuring instrument (EDM) was used to measure the displacement across the width of the dry-dock. The purpose of this paper is to present the drydock wall stability analysis method and to compare the analytical results with the observed wall displacement. Conclusions were derived from the results of the finite element analysis and the measured wall displacement. The results were useful in the structural analyses and safety certification of the graving drydocks.