Title:
Behavior of Storage Cells in Condeep Structure under Hydrostatic Pressure
Author(s):
Amr I. I. Helmy and Michael P. Collins
Publication:
Structural Journal
Volume:
113
Issue:
4
Appears on pages(s):
839-850
Keywords:
offshore structures; shear strength; water pressure
DOI:
10.14359/51688824
Date:
7/1/2016
Abstract:
To investigate the structural safety of the storage cells of some existing Condeep concrete offshore oil and gas platforms built in the 1970s, a 1:13 scale model of a typical upper dome-cell wall junction of a storage cell of such a platform was loaded to failure by increasing the external water pressure in the Hydraulic Testing Facility at the University of Toronto, Toronto, ON, Canada. A number of the early Condeep platforms use an internal pressurization system to restrict the pressure differential to approximately a 50 m (164 ft) head of water at the critical dome-cell wall junction. If this internal pressure system fails, the pressure differential across the domes and walls of the cells will approximately double. The question then becomes whether this increase in differential pressure will result in the failure of the structure. In the experiment, the model resisted a maximum pressure differential equivalent to a 147 m (482 ft) head of sea water. Immediately prior to failure, radial cracks could be seen near the base of the dome and water was flowing into the specimen at a rate of 139 L/min (37 gal./min). The final failure was abrupt and involved a brittle shear failure encompassing one half of the circumference of the cell wall. At failure the dome displaced downwards approximately 25 mm (1 in.) and the top of the cell wall was pushed approximately 10 mm (3/8 in.) outwards.
Related References:
1. Lenschow, R., and Hofsoy, A., “Carrying Capacity of the Intersection between Dome and Cylinder Wall of a Reinforced Concrete Structure,” Proceedings, First International Conference on Behavior of Offshore Structures (BOSS 76), Norwegian Institute of Technology, Trondheim, Aug. 2-5, 1976, V. 2, pp. 174-233.
2. Kuchma, D. A.; Tamas, J.; and Collins, M. P., “Strength of Upper-Dome Cell-Wall Connection of Concrete Offshore Structures,” ACI Structural Journal, V. 96, No. 5, Sept.-Oct. 1999, pp. 683-692.
3. Helmy, A., “Behaviour of Offshore Reinforced Concrete Structures under Hydrostatic Pressure,” PhD thesis, Department of Civil Engineering, University of Toronto, Toronto, ON, Canada, 1998, 417 pp.
4. Polak, M. A., “Nonlinear Analysis of Reinforced Concrete Shells,” PhD thesis, Department of Civil Engineering, University of Toronto, Toronto, ON, Canada, 1992, 388 pp.
5. Vecchio, F. J., VecTor6, VecTor Software Suite, Toronto, ON, Canada, www.civ.utoronto.ca/vector/software.html. (last accessed June 8, 2016)
6. Vecchio, F. J., and Collins, M. P., “The Modified Compression Field Theory for Reinforced Concrete Elements Subjected to Shear,” ACI Journal Proceedings, V. 83, No. 2, Mar.-Apr. 1986, pp. 219-231.
7. Koltuniuk, R., “Investigating the Influence of High Water Pressure on Cracked Surfaces of Offshore Concrete Structures,” MASc thesis, Department of Civil Engineering, University of Toronto, Toronto, ON, Canada, 1990, 155 pp.
8. Helmy, A., “Behaviour of Reinforced Concrete Cylinders Subjected to External Hydrostatic Loading,” MASc thesis, Department of Civil Engineering, University of Toronto, Toronto, ON, Canada, 1993, 169 pp.
9. Neville, A. M., Properties of Concrete, third edition, Prentice-Hall, Upper Saddle River, NJ, 1991, 766 pp.