Evaluation of Marine Structures for Kinematic Effects

In performance-based seismic design, a marine structure is designed for inertial loading effects associated with the dynamic response of the structure. Some waterfront structures also experience seismically induced kinematic effects, associated with soil liquefaction and lateral spreading. This presentation explores some of the approaches for incorporating these kinematic effects into the seismic design and analysis of marine structures.

Although most performance-based design provisions for piers and wharves require that kinematic effects be considered in seismic design, there is generally not detailed guidance on how these effects should be considered analytically. In addition, there are various opinions and practices across the industry in accounting for these soil-structural demands. Considerable judgement is required by the design professional in deciding how to include the kinematic loads into the structural analysis.

Combination of inertial and kinematic earthquake effects is one of the major decisions that need to be made in the analysis and design process. This presentation will discuss the various theoretical design methodologies; including, superposition of results, simultaneous load combinations, post-inertial kinematic response, and post-kinematic inertial response. This presentation will provide commentary on how these approaches can be implemented as well as how these combinations correlate to observed earthquake response.

This presentation will also include a ˜how-to’ component for incorporating the kinematic loading into an analysis. Some of the inertial and kinematic combination methods are straight-forward, but they could overpredict lateral displacements due to their simplified nature. More refined approaches involve a complicated staging of restraint and loading parameters in the non-linear finite element analysis models. This presentation will address the more practical considerations for performing these evaluations. It will discuss lessons learned in the authors’ experiences of doing these analyses, and provide recommended tips for obtaining trust-worthy analytical results.

For owners and developers, this presentation will provide background information on seismic design parameters: what the difference is between inertial and kinematic loads, and why these loading schemes need to be carefully addressed. For engineers and design consultants, this presentation will provide insight into the practical implementation of these seismic demands: how to combine inertial and kinematic loads in the structural analysis, and tips for modeling the behavior in a finite element structural analysis model.

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