Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Stability of Tubes Under External Pressure and Structural Loads

Prinicipal Investigators:

John Tassoulas

Sponsor:

Shell Oil Company

Completion Date:

November, 1993

Final Report ID#

B51(Click to view final report abstract)

The present work is aimed at developing a rigorous analytical technique in order to investigate the stability of tubular unstiffened and stiffened beam-columns under structural loads and the external pressure.  The first goal is to establish the validity of the technique by comparison with the experimental data of CBI and SwRI.  A point of particular interest in this study is the effect of residual stresses and initial imperfections on member stability. 

A tube element, which combines the cross-sectional ovalization with the longitudinal deformation, has been developed for the purposes of this analysis.  In addition, the nine-node isoparametric shell element, introduced elsewhere for nonlinear analysis, is also used in this study.  A very important contribution of this research is the development and use of an analytical technique for the ultimate capacity prediction of ring-stiffened tubes under combined loading.  The available literature on this topic is entirely experimental and limited to the case of pressure-axial load interaction.  For the rigorous analysis of such tubes, a special element, referred to as stiffener element, has been developed as an additional layer of the tube element.  The basic ideas concerning implementation of the finite element technique are presented in the next chapter.

Finally, this work examines the accuracy of the existing design formulas.  Analytical results and experimental data are compared with the new API-LRFD Draft specification as well as with several other design equations.  Particular emphasis is given to the effects of pressure on the ultimate capacity of tubular beam-columns.  It is believed that the present research effort will contribute to safer and more efficient design of offshore compliant towers.

Related Publications: Karamanos, S.A. and Tassoulas, J.L., "Stability of Inelastic Tubes Under Combined Tension and Bending," Proceedings, Tenth Structures Congress, ASCE, San Antonio, Texas, April 13-15, 1992.

Karamanos, S.A. and Tassoulas, J.L., "Hydrostatic Effects in Tubular Member Design," Proceedings, Offshore Mechanics and Arctic Engineering Conference, Houston, Texas, February 27-March 3, 1994.

Karamanos, S.A. and Tassoulas, J.L., "Analysis of Unstiffened and Stiffened Tubular Members Under External Pressure and Structural Loads," Proceedings, ASCE Structures Congress XII, Atlanta, Georgia, April 24-28, 1994, Vol. 2, pp. 1520-1525.

Karamanos, S.A. and Tassoulas, J.L. “Hydrostatic Effects in Tubular Member Design,” Journal of Offshore Mechanics and Arctic Engineering, ASME, Vol. 116, No. 4, pp. 246-251, November 1994.

Karamanos, S.A. and Tassoulas, J.L., "Stability of Stiffened Tubular Members," Proceedings, ASCE Structures Congress XIII, Boston, Massachusetts, April 2-5, 1995.

Karamanos, S.A. and Tassoulas, J.L., "The Ultimate Capacity of Tubular Members under External Pressure," Proceedings, EUROSTEEL '95, First European Conference on Steel Structures, Athens, Greece, May 18-20, 1995.

Karamanos, S.A. and Tassoulas, J.L., "Computational Stability of Offshore Tubes," Proceedings, Fourth National Congress in Mechanics, Xanthi, Greece, June 26-29, 1995.

Karamanos, S.A. and Tassoulas, J.L. “Stability of Ring-Stiffened Tubular Members under External Pressure,” Journal of Pressure Vessel Technology, ASME, Vol. 117, No. 2, pp.150-155, May 1995.

Karamanos, S.A. and Tassoulas, J.L. “Tension Effects on Pressure Capacity of Tubular Members,” Journal of Structural Engineering, ASCE, Vol. 121, No. 6, pp.955-963, June 1995.

Karamanos, S.A. and Tassoulas, J.L., "Effects of External Pressure on the Capacity of Tubular Beam-Columns," Journal of Structural Engineering, American Society of Civil Engineers, Vol. 121, No. 11, pp. 1620-1628, November 1995.

Karamanos, S.A. and Tassoulas, J.L., "Tubular Members I: Stability Analysis and Preliminary Results," Journal of Engineering Mechanics, ASCE, Vol. 122, No. 1, pp. 64-71, January 1996.

Karamanos, S.A. and Tassoulas, J.L., "Tubular Members II: Local Buckling and Experimental Verification," Journal of Engineering Mechanics, ASCE, Vol. 122, No. 1, pp. 72-78, January 1996.

 

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