Merchant Square Fan Bridge

Having worked with Martin Knight and his team at Knight Architects on several previous occasions it is always great to hear that they have another moving bridge project that they would like to work with us on.  The concept that Knight Architects had presented as their competition entry was striking but also potentially posed several technical challenges. The lift bridge design consists of five 300mm wide blades that form the deck when lowered. The pivot axes for the five blades are horizontally offset from each other which is what gives the bridge its unique appearance in the raised position

As part of the competition entry a method of operation had been proposed, however, my first task upon joining the design team was to discuss the potential options for lifting the bridge and consider in conjunction with the architect and structural engineer (AKTII) which method offered the optimum solution for all aspects of the design. As with any moving bridge the reliability of operation is key to its success and even though the Merchant Square bridge doesn’t open that frequently, when it does open there can be no delays or problems. Various standard and also unusual methods of operation were considered drawing on other industries that Eadon work in to offer alternative solutions and ensure that the best solution for this specific problem was found. Often the most obvious solution is the right one and in the end the most appropriate method of operation was a simple hydraulic cylinder under each blade to provide the actuating force.

As with many lift bridges counter weights are used to reduce the load on the mechanism. In this project the counter weights are not only functional but also give the bridge its unique identity when in the lowered position. The counter weights are segments of a sphere formed around the pivot axis. As part of the design of the mechanism myself and the other Eadon team members working on the project reviewed the counter weight masses and assisted with the fine tuning of these to optimise the loading on the lift cylinders and pivot arrangement.

One of the hardest challenges on the project was the design of the pivot arrangement. Due to the relatively narrow width of each blade and the fact that they each lift about a different axis of rotation the pivot arrangement had to fit within the 300mm width of each finger. Whilst the bridge isn’t required to lift in high winds, the pivots had to be designed to accommodate high wind loads in the unlikely event that a failure of the operating equipment meant the blade was stuck in the raised position. This wind loading generated high side loads on each blade which had to be resisted over a narrow space envelope. Using 3D software we were able to develop a design of the pivot and supporting structure to fit within this tight space envelope and also ensure that the equipment could be installed and maintained. The 3D model was then developed into 2D fabrication drawings for construction. The 2D construction drawings were accompanied by an electrical and hydraulic performance specification which detailed the requirements for the associated electrical and hydraulic equipment based on loadings and performance requirements generated by ourselves.

The project was completed in 2014 and has gone on to be recognised in nominations for both architectural and engineering awards.

This type of project is excellent to work on as it involves many different types of engineering and also brings in the more artistic nature of architecture directly to the design. It also allows us to work with internationally renowned architects and engineers. Each project is a new challenge and will require the use of both existing knowledge but also the development of new skills or expansion of knowledge in one or more areas. One further benefit is that moving bridge projects are accessible to the public and hence enormous satisfaction can be gained when family and friends can go and visit something you have been working on.