The Earthquake Engineering Online Archive

Inelastic structural modeling of braced offshore platforms for seismic loading

Zayas, Victor A.; Shing, Pui-shum B.; Mahin, Stephen A.; Popov, Egor P.

UCB/EERC-81/04, Earthquake Engineering Research Center, University of California, Berkeley, 1981-01, 148 pages (530/Z32/1981)

A review is presented of state-of-the-art computer analysis of the inelastic structural response of braced steel offshore structures. Such analyses have recently been used in the offshore industry, but their reliability and limitations have not been verified against experimental data. In this report, analytical results are compared with experimental results obtained for two X-braced tubular steel frames in order to assess current modeling techniques. Several types of analytical brace models are reviewed, and comments on their theoretical bases, correlation with experimental results, and practicability are included. From these models, a particular phenomenological brace model is selected and implemented and the required input parameters are identified. Analytical and experimental results are compared. Differences in the internal distributions of member inelastic deformations are noted when the frame analyses are compared to the experimental results. These differences result in a different deterioration of frame lateral load capacities compared to those observed experimentally. Nonlinear solution schemes are evaluated and a step-by-step solution procedure with unbalanced load correction is adopted. Suggestions for improving frame and brace modeling are offered. An improved physical theory brace model employing plasticity theory is suggested, offering more realistic modeling of member deformations and depending less on empirical data.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-81-04.pdf (4 MB)