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Temple Quay 2 Bridge, Bristol
Design
In 2003 Castlemore commissioned structural engineers Price & Myers, with the artist Martin Richman and Niall McLaughlin Architects, to build a competition winning 55m foot and cycle bridge across the old docks at their Temple Quay 2 development in Bristol.
Wanting to maximize the structural efficiency of the bridge by using a stressed skin approach, Price & Myers chose stainless steel as an efficient life cost solution and to avoid the need for frequent repainting. They decided to use GSA Analysis for all the static and dynamic forces on the bridge, covering both installation and service conditions.
Detail
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The unique feature of this pedestrian bridge is that the structural forces within the stressed skin panels are manifested in light. A pattern of over 20,000 holes of differing radii are plasma cut into the steel to represent the stress levels within: high levels of stress are made more solid with lower radius holes or none at all, while areas of low stress are punctured with larger diameter circles. This makes the invisible structural forces with the bridge explicit as a flowing pattern across the skin of the bridge.
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To create the pattern of holes, Price & Myers first generated high-resolution images from GSA. These images were black & white contour plots of all the principle modes of structural load (bending, torsion, frequency, lifting, shear, etc) superimposed over each other. As the bridge skins both twist and curve, they took both plan and elevation images. Using image manipulation software, the resulting images were corrected to account for the variation between the elevation and the warped 3D nature of the surface. As the bridge is symmetrical about both the centre line and mid span, they only needed to consider a quarter of the bridge. In the end, 16 images were needed to match the various panels on the bridge.
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To generate the holes in the bridge panels, each panel image was passed though a script to calculate the brightness of a 100x100 grid. The resulting in 10,000 data points were then imported into an Excel spreadsheet where the data was parsed into a series of brightness ranges with their corresponding hole sizes. For example, a brightness level of between 40 and 70 equated to a radius of 8mm. These radii were then read into a Catia 3D CAD model and distributed on an isoparametric grid (that is, a grid made of lines of equidistance) for each panel. Catia then produced the information that drove the CAD CAM / CNC plasma cutter that created the holes.
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One of the technical challenges faced by Price & Myers was ensuring that the holes were made in the correct location on each curved, twisting panel: the plasma cutter could only cut and punch flat panels. To achieve this, they used Catia to unfold the panel geometries so that they could transpose the GSA data driven holes onto the surface. The CAD model then refolded the panels to their original shape with the holes in place, mimicking the real-world procedure of the fabricator.
Installation
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As the installation was a major load case on the bridge, Price & Myers used GSA's stage analysis to check the bridge under the varying support and load conditions. As they could analyse these all in the same file, it eliminated the risk of trying to maintain several parallel models.
During the crane lift, everyone was very impressed that the predicted deflection across the 55m gap between the bridge legs was within 2mm of that predicted by GSA.
The crane installation caused such an interest that it was reported on the local BBC news. You can see the article here on the BBC web site: http://news.bbc.co.uk/1/hi/england/7522433.stm.
For further information please contact Tim Lucas: www.pricemyers.com
