The increase in vessel sizes in recent years and the need for deeper berths, in particular in the LNG/LPG industry, has meant that jetties are constructed in deep water and, as a result, in exposed locations, often extending several kilometres offshore.

In some cases, jetty decks have to be constructed close to the water surface, often dictated by operational requirement such as vessel loading and offloading at berth. In these scenarios, there is a risk of the jetty structure being exposed to wave forces under extreme wave conditions.

The research project developed as a result of feedback from industry that there was a need for clear design guidance for calculating wave forces on jetty and pier decks. While there are existing methods in the literature for calculating wave forces, often deriving from the offshore industry, guidance on their use is limited and difficult to apply.

The key aim of the project was therefore to develop practical engineering guidance for predicting wave forces. A project steering group, comprising consultants, contractors and owners of jetty facilities contributed to the project.

A major component of the project was a comprehensive series of physical model tests, undertaken to measure wave-induced forces on a typical jetty structure, constructed a scale of 1:25. Tests were undertaken in a 2-D random wave flume at Wallingford.

Force transducers were fitted to the jetty beams and deck elements to measure forces for a range of wave conditions and water levels. Test measurements were compared with values predicted using available methods, which tended to under-predict the forces acting on the structure.

Test results were then analysed and presented in graphical format. A set of prediction formulae were then derived which can be used to predict wave forces on jetties and piers.

The studies also gave guidance on short duration impact forces, which can be important for the design of some structure elements. The methods were tested out on a series of case studies provided by the project steering committee.

The project results and guidance are due to be published in early 2004 by Thomas Telford in a document titled 'Piers, jetties and related structures exposed to waves: Guidelines for hydraulic loadings.' The report also includes guidance on design wave conditions, prediction of scour around piles and mooring forces.

For further information on the project, contact Kirsty McConnell at HR Wallingford. Telephone:

01491 822304, email: kmcc@hrwallingford.co.uk