Collapse Analysis Of Framed Offshore Structures

Abstract

The paper presents new approaches for nonlinear system analysis of trusswork platforms. The main idea behind the technique is.to minimize the cost of the nonlinear analysis by reducing the number of parameters and the size of element model. A brief description is given on the theoretical basis of the computer program including the formulation of incremental stiffness with modifications for plastic hinges. Special emphasis is given to the choice of adequate interpolation functions and to the evaluation of nonlinear element characteristics.The solution strategy follows the conventional incrementation procedure with special algorithms for handling stability problems and load reversal. The numerical procedure is demonstrated on buckling analysis of simple columns and_ frames.Comparison with experiments and alternative numerical computations proves the accuracy and efficiency of the procedure. Practical design examples are given on progressive collapse analysis of a jacket structure, a deep water tripod typer of platform and a module support frame.

Collapse analysis of steel jacket structures for offshore oil exploitation

“…Fig. 7 also compares the results obtained by the present analysis with the experimental results presented by Soreide et al [34]. The three points of the experimental curve that cross the x-axis may be understood as loading/unloading cycles during the experiment.…”

“…It is of particular interest because it includes all the basic difficulties for collapse analysis, such as a sharp nonlinear response with snap-back after the limit load, column buckling, and formation of several plastic hinges. Moreover, experimental results are available, presented by Soreide et al [34].…”

“…4, including Moan et al [33], Soreide et al [34], and Waegter et al [35]. It is of particular interest because it includes all the basic difficulties for collapse analysis, such as a sharp nonlinear response with snap-back after the limit load, column buckling, and formation of several plastic hinges.…”

Assessment of Existing Structures and Repairs

“…The collapse analysis for a similar platform was performed by USFOS pushover analysis, as per Soreide et al (1986), and it was found that the minimum RSR was equal to 2.19 at collapse and 1.76 at first failure in the leg joints at −9.0 m elevation below the mean seal level, i.e., an environmental load from the northwest 119% greater than maximum wave height (H max ) combined with wind speed equal to 15.6 m/s. The pushover analysis revealed an RSR equal to 1.13 at first failure due to pile yield for example increasing environmental load 25% greater than maximum wave 7.8 | Case Study: Platform Failure height with the associated wind speed.…”

Adaptive Space Frame Analysis. Part Ii: A Distributed Plasticity Approach.

“…K-frameIn this example, comparison is made between the prediction of ADAPTIC, using the plastic hinge and distributed plasticity approaches, and the analytical and experimental results reported by Soreide et al6 on the K-frame set-up shown in Figure 7. Although Soreide et al did not include any information regarding the level of imperfections, it was found that ADAPTIC provides best comparison with the experimental ultimate capacity if parabolic imperfections of (L/1000) are assumed in the diagonal members.…”