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Great Belt Bridge Cable Crawler Gantries

Following their success in designing Cable Crawler gantries for the Humber Bridge, Eadon were employed to carryout a similar task for the Great Belt Bridge in Denmark, the third largest suspension bridge in the world. A Cable Crawler gantry is a mobile working platform which straddles the main cable of a suspension bridge and can travel from bridge deck level all the way to the top of the main towers. For information about the Humber Bridge gantries click here.

By David Price

I had built up a good working relationship with the client on several similar access gantry projects since the formation of the company back in 2009 and so we were the natural choice to be asked to assist them with the tender for the Great Belt Bridge Dehumidification project. In particular we were employed to provide a concept design which would enhance the client’s tender quality submission, and also provide information to allow for accurate pricing of the four access gantries to be used.

At an early stage the client arranged a trip to the bridge in Denmark where we were given a tour around the bridge including the areas which are never seen by the public such as in the main cable anchorages, and particularly exciting, a trip up to the top of one of the main towers some 254m above sea level. We were able to talk with the bridge operators and discuss many things including access and traffic arrangements for working on the bridge.

My initial review of the bridge highlighted that the new gantries would need to be much bigger than the Humber Bridge gantries in all three dimensions. Additionally they would need to be stronger and more powerful in order to cater for the higher winds and steeper main cables due to the extra height of the towers, which are about 100m higher than on the Humber.

Prior to starting work I met with the client to discuss the requirements for the new gantries then using Solidworks I put together a 3d model of the structure for a draft gantry design using preliminary member sizes based on previous experience. I then carried out some basic hand calculations in Mathcad to establish the loads which the new gantry would need to withstand, particularly due to wind gusts of up to 130mph. Following this I used the Humber Bridge STAAD Pro analysis model as a basis to quickly produce a new analysis of the bigger, heavier gantry for the Great Belt. The STAAD Analysis showed which members were failing the code checks to BS EN 1993-1-1 and enabled new member sizes to be chosen such that we could be confident the structural design was adequate. The Solidworks model was then updated and the mechanical operating equipment roughly added sufficient for tender submission and pricing.

The client was successful in winning the dehumidification contract and hence we were awarded the work to produce the detailed design for the Cable Crawler gantries.  I was responsible for coordinating the team to carry out the detailed design which entailed finalising the preliminary gantry model, carrying out a full set of design calculations to justify the design to the appropriate codes, and producing a full set of manufacturing drawings. The final design of the gantry was 36m long, 3.5m wide, 4m high, and weighed 22 tonnes.

During the manufacturing period I carried out the work necessary to enable the gantries to be CE marked to the Machinery Directive putting together the technical file and coordinating the Notified Body necessary due to the hazardous nature of the equipment.

I put together the necessary documentation to carryout the load testing of the gantries and led the testing at the manufacturers works prior to them being shipped to Denmark for installation on the bridge. Once on site I inspected the gantries on the main cable to ensure they were set up and being used as intended, as well as carried out several training sessions for the operators based on the operation and maintenance manual I had produced.

The project was extremely enjoyable, encompassing several different fields of engineering and many different skills. To see the immense, impressive structures which I was responsible for designing, high up in the air on one of the world’s most iconic bridges gave me a tremendous amount of job satisfaction.

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