A method to carry out a Reliability-Based Optimization (RBO) of especially nonlinear structural systems is introduced. Statistical uncertainties involving both structural and loading properties are considered. The concept is based on the separation of structural reliability analyses and the optimization procedures. Two approaches are discussed, depending on the interaction of reliability analysis and mathematical programming and the way of representation of the limit state functions (LSF) of the structure. As, for cases of practical significance, the LSF is known only pointwise it is approximated by Response Surfaces (RS). For the response calculations Finite Element (FE) procedures are utilized. Failure probabilities are determined by applying variance reducing Monte Carlo simulation (MCS) techniques such as Importance Sampling (IS). Following the reliability analysis, the optimization procedure is controlled by the NLPQL algorithm. A numerical example in terms of a template ocean platform exemplifies the procedures.

Reliability-based optimization of structural systems

Wave-in-deck loads on coastal bridges and the role of air

II. EFFECTS OF FINE SEDIMENT RESUSPENSION IN ESTUARIES Maynard M. Nichols Virginia Institute of Marine Science School of Marine Science College of William and Mary Gloucester Point, Virginia 23062 Sediments supplied to an estuary undergo repeated cycles of resuspension and deposition prior to permanent accumulation or transport into the sea. A review of published literature and field observations of estuarine suspended sediment in the Chesapeake Bay region, indicate that sediment is resuspended in response to fluctuating energy over a wide range of time scales. The temporal variations of resuspension, therefore, inherit a hierarchy of scales following the scales of motion. Resuspension is a key process in the cycling of fine sediment in estuaries. The process enriches the suspended sediment load and stratifies the vertical gradients of suspensions. It increases the mean residence time of suspended sediment in the water column. Therefore, resuspension reinforces horizontal advective transport and enhances the turbidity maximum. Resuspension modifies the chemical composition of estuarine sediments by increasing the interaction time, sequestering or releasing chemicals and by mixing sediment from different sources, or from the same source but with a different geochemical history.

Estuarine Cohesive Sediment Dynamics

BRBF response modification factor

The slope stability of some offshore environments can be evaluated by using only conventional acoustic profiling and short-core sampling, followed by laboratory consolidation and strength testing. The test results are synthesized by using normalized-parameter techniques. The normalized data are then used to calculate the critical earthquake acceleration factors or the wave heights needed to initiate failure. These process-related parameters provide a quantitative measure of the relative stability for locations from which short cores were obtained. The method is most applicable to offshore environments of gentle relief and simple subsurface structure and is not considered a substitute for subsequent site-specific analysis. Four sites off California and Alaska contain acoustically defined sediment failures. Calculated critical earthquake factors in these failed areas are typically lower than in adjacent unfailed areas, a result lending credence to the method.

Regional Method to Assess Offshore Slope Stability

Wave-in-Deck Forces on Offshore Platforms

A nonlinear fiber element for the simulation of buckling, post buckling, and hysteric responses of tubular struts is formulated and implemented in the nonlinear program DRAIN-3DX . In this element both material and geometric nonlinearities are considered. The element is applied to simulate post buckling and hysteric response of pinned and fixed tubular struts subjected to cyclic loading. The results are in good agreement with available results, i.e., experiment and other analytical models data in terms of buckling load, load-deformation curve, strength, and stiffness degradation.

R. G. Bea

Papers

Wave-in-Deck Forces on Offshore Platforms

Inelastic Postbuckling and Cyclic Behavior of Tubular Braces

Soil Movements and Forces Developed by Wave-Induced Slides in the Mississippi Delta

Gulf of Mexico Hurricane Wave Heights

Performance Shaping Factors in Reliability Analysis of Design of Offshore Structures