A Damage Mechanics Approach to Fatigue Assessment in Offshore Structures

This article is intended to describe the development of a fatigue damage model capable of assessing fatigue damage in offshore structures. This is achieved by for mulating a set of damage coupled constitutive and evolution equations which make the for mulation of a unified approach possible under both low and high cycle fatigue damage and consistent with the structural dynamic response of the changing/deteriorating material be haviors. The structural analysis for the whole designed period, say about 30 years, can be carried out with the aid of the proposed analytical procedure, in which the fundamental characteristics of sea wave statistics responsible for the structural dynamic response can be sufficiently considered. An offshore structure subject to complex ocean environment is described by a general stochastic system which embeds a group of stochastic subsystems, each characterizing a duty cycle. An effective analytical method is established by introduc ing the concept of duty strain range with a clear mathematical definition and its analytical solution which covers all possible spectral parameters. The history-dependent damage is also included in the damage model so that the overload effects can be analyzed. It should be pointed out that the whole procedure can be fully computerized such that the practical or engineering significance of varying design variables can be readily highlighted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67255/2/10.1177_105678959300200405.pd

Discrete-time modal control for seismic structures with active bracing system

[[abstract]]In this study, a shaking-table test was performed to verify a proposed discrete-time modal control method that is suitable for seismic control of structural systems and also easy for digital control implementation. The computation of the feedback gain is formulated in a discrete-time domain and is given in a concise matrix form. A method for generating the best achievable eigenvectors that are most consistent with the target values is also proposed. The test involves a full-scale three-story building model that is actively controlled by an active bracing system. The test results show that the proposed discrete-time modal control can be a very efficient and promising method for mitigating the seismic response of building structures. For the building model tested, the performance of the proposed method with only two feedback signals can be as effective as that of full state feedback control