The Earthquake Engineering Online Archive

Cyclic inelastic behavior of steel offshore structures

Zayas, Victor A.; Mahin, Stephen A.; Popov, Egor P.

UCB/EERC-80/27, Earthquake Engineering Research Center, University of California, Berkeley, 1980-08, 339 pages (530/Z32/1980C)

In this report, experimental results are presented of the cyclic inelastic behavior of two one-sixth scale frame models of a representative southern California offshore platform designed according to American Petroleum Inst. wave and earthquake criteria. The primary objective of the research effort is to improve the understanding of the behavior of braced structural systems subjected to damaging earthquake motions. The 29.5 ft tall frame models consist of three braced panels which comprise a complete bent from the prototype X-braced platform. The displacement history imposed at the deck level with the base held stationary on both specimens is representative of severe seismic excitations. Two types of detailing representative of current practice are investigated. Observations are presented as to when the primary buckling of the braces occurred, which members were affected, and the extent of damage as it progressed through the structure. Data from frame lateral force versus lateral displacement hysteretic loops are examined as is the deterioration of the frame strength and stiffness. Energy dissipation and the effect of D/t ratio on the commencement of local buckling and the deterioration of strength are accorded special attention. The axial force-displacement response of frame bracing members is compared to those of bracing members with idealized pinned and fixed end conditions. The frame and brace experimental results are examined with respect to the American Petroleum Inst.'s recommended design criteria. Data and general observations regarding the inelastic behavior of tubular frames and braces are offered as a means to extend the state of knowledge of the seismic response of offshore structures.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-80-27.pdf (24 MB)