Incorporating Cyclic Degradation into Pile Design for the Gull Wing Bridge, Lowestoft

The paper presents the design analysis for the piled support for the rolling bascule Gull Wing Bridge in Lowestoft, England.  The nature of the rolling bascule bridge is that individual pile loads within the pile group vary significantly during each bridge opening event.  This results in the cyclic degradation of the pile shaft resistance, differing from a conventional static pile design where the resisted variable actions are normally only a small component of the total design actions. The approach has been developed using lessons learned from offshore pile design and modified to be appropriate for the design principles of Eurocodes. An additional capacity reduction factor, as a function of the mean and peak cyclic loading and their resulting cyclic degradation of resistances, has been developed and incorporated into the design process. Failure to consider cyclic degradation of the pile shaft capacity would have resulted in the risk of medium to long-term settlement being outside the operational limits for the bridge.