Case Study

Falkirk Wheel

• unique steel rotating boat lift
• linear and nonlinear analysis
• solid element modelling of movement sensitive connections

LUSAS Bridge analysis software was used as the primary analysis tool by Tony Gee and Partners (TGP) for preliminary and subsequent detailed design work on the Falkirk Wheel. The Wheel (as it is known) is a unique lifting bridge designed to reconnect the Forth & Clyde and Union canals between Glasgow and Edinburgh in Scotland. It is the world’s first rotating boat lift and the first boat lift to be built in the UK since 1875.

The project is part of a £78m British Waterways scheme to restore the two canals to their former glory. Construction of the interchange section, which comprises the Wheel, an elevated aqueduct at its upper end and a holding basin at its lower, is being led by a joint venture of Morrison and Bachy-Soletanche. Butterley Engineering, designers and manufacturers of the wheel, Tony Gee and Partners, structural engineering specialists and Bennett Associates, M&E engineering specialists and architects RMJM Scotland Ltd. complete the team.

The Wheel has an outside diameter of 35m, and comprises two 1.4m wide steel, clawed arms rotating on a 3.5 m diameter axle. A pair of 25m long, 300 m3 water filled caissons (or "gondolas") act as containers for boats which are lifted through the 24m vertical distance between the two canals. Drive is provided at one end of the axle through a system of hydraulic planetary gear units, with stability of the caissons ensured by a network of synchronised gears. It is capable of carrying a total payload of 600 tonnes in winds of Beaufort Force 6 (25-31 miles per hour). Boat transfer time will be about 15 minutes.

The uniqueness of the structure required TGP to employ some innovative and unconventional design methods. UK design codes for bridges, buildings and floating vessels were utilised, as well as Norwegian, German and American codes for such criteria as thin walled cylinder behaviour and constrained ice loading. A 1:50 scale model was used in a wind-tunnel for testing aerodynamic effects. Finite element analysis using LUSAS Bridge aided the structural design and included nonlinear solid continuum modelling of movement sensitive connections.

Detailed analysis made use of three separate LUSAS models. A 3D linear elastic shell element model allowed for analysing the axle and arms of the main structure. A 3D linear elastic model using a combination of shell and beam elements modelled one of the gondolas . Both these models, as well as being the basis of the material design (via the stress outputs), were particularly useful in estimating deflected shapes and displacements, which can have a critical influence on the moving parts of the structure.

A 3D nonlinear solid continuum model was used to analyse a small part of a joint in the main axle situated just inside the clawed arm. Richard Prosser, project engineer of Tony Gee and Partners, said "we needed assurance that the axially loaded joint would not prise apart, and the results from the LUSAS model formed a vital part of this assurance".

Construction of the 100m long viaduct section and the turning basin is well underway and the project is on course for the Wheel to help turn a dream into reality and re-connect the the Forth & Clyde and Union canals in the spring of 2002.