STS Crane-Wharf Seismic Response and Design Considerations

Abstract: It has been 17 years (2007–2010) since Liftech presented to the industry how larger, modern cranes are expected to respond in large earthquakes, raising awareness about the increased risk to the crane structure for these larger cranes compared to their smaller predecessors. Since then, we have performed dozens of time history analyses for crane and wharf combinations with a variety of crane and wharf dynamic properties. These include wharves with short and long periods, including some that are similar to the crane’s dominant period of vibration.
This paper provides deeper insight into crane-wharf interaction based on the results of time history analysis, presents the expected crane and wharf response and performance during large earthquakes based on industry design practice, and evaluates the current crane and wharf design criteria used in the industry. It includes discussion of some of the state-of-the-art analysis tools and methods and the significance of the crane’s various dominant modes of vibration.
Most ports rely on the industry practice for crane seismic design requirements, but the Port of Oakland is an exception. The Port of Oakland maintains their own minimum seismic design criteria for cranes. We present a case study including these criteria, the effect on the port’s tenants for purchasing new cranes or modifying existing cranes, and the effect on the crane and the wharf designs.
Finally, we will present the latest recommendations regarding the crane seismic design criteria and the crane’s effect on the wharf structure.

How does this project / topic contribute to the advancement of the industry and profession?: This paper presents an update to recommendations for structural design, expected response of large STS cranes, and their effect on wharves during seismic events. Ships began increasing in size 25 years ago, requiring cranes to increase in size to meet the demands. When the cranes grew, the wharves changed, the crane and wharf response changed, and the crane-wharf seismic interaction changed. Twenty-five years later, the approach to seismic design has not evolved significantly but, over time, we have gathered a large set of analytical data, locations, and crane/wharf dynamic properties. We have drawn new conclusions from our recent work.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: This paper provides guidance for structural engineers for using state-of-the-art tools and methods for ship-to-shore crane-wharf interaction analysis. It also provides a novel set of recommendations for crane seismic design criteria, a topic which is not currently covered by any US code or standard.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The most challenging aspect of the topic is the significant variation of the dynamic properties of crane and wharf structure, diversity in data sets amassed over time, and drawing conclusions from the diverse data. Also, determining if the data are validated by actual seismic response performance is a challenge. To address these challenges, we collected the analysis results from many past projects and performed additional analysis to cover a large range of the crane and wharf dynamic properties. We compiled and compared the analysis results with the crane performance data we collected from seismic events.

Who is the target audience for this paper?: The target audience for this paper are crane, wharf structural designers/reviewers, and port authorities.