Whittle Arch and Glass Bridge, Coventry

• Landmark steel structures in regeneration area

• Displacement assessment of arches due to self weight

• Eigenmode assessment of bridge structure

As part of Coventry's Phoenix Project, which totally regenerated a previously neglected part of the city, gardens, housing, retail outlets, and two new public spaces were created. One of these spaces, Millennium Place, incorporates two unique steel structures: the Whittle Arch and the Glass Bridge. Whitbybird (now Ramboll) used LUSAS finite element analysis software to assist with the design of the structures on behalf of its client Coventry City Council.

Whittle Arch

The Whittle Arch is a dramatic twin-arch tubular structure that provides a focal point to the whole Millennium Place development. It is named after and commemorates Sir Frank Whittle, the pioneer of the jet engine, who was born in Coventry. Spanning 60m across a service road, the arches are formed of aerofoil section tubular lattices, clad with perforated stainless steel sheathing. The arches are fabricated from standard circular hollow steel sections that span between plated diaphragms. One set of tubes span directly between the diaphragms to carry the axial thrusts and bending moments, another forms a series of spirals between the diaphragms and these carry the shear forces and torsions that exist under the different loadcases. The arches lean together supporting each other through a single connection point at the crown approximately 15m above the ground. At night the structure is illuminated from within the steel mesh cladding.

The arch follows in the footsteps of Frank Whittle by pushing the use of technology. Arch geometry was initially set up using a 3D computer drafting package before being imported into LUSAS for a finite element analysis analysis to be carried out. Structural deflections obtained from LUSAS were transferred directly back into the CAD software package so the pre-cambered form of the structure could be made available to the steelwork contractor.

Constructed adjacent to Coventry's Transport Museum and just a few metres from the Whittle Arch, the Glass Bridge rises in a spiral to take pedestrians up and over a medieval city wall and across the restored Lady Herbert Garden before arriving in the garden of International Friendship. The bridge takes its name from the glass fins which envelope the parapets but the structure is actually predominantly constructed of steel. 

The bridge and ramp structure is formed of a simple 762mm diameter tube that is pre-bent to the various radii needed to form the profile of the bridge. Tubular steel columns, irregularly positioned to avoid features beneath the bridge, support the tube. An intricate steel deck and balustrade system with coloured glass fins guides pedestrians to their destination.

The 15m diameter spiral ramp is a good example of a complex torsion structure and whilst it forms only 50m of the bridges total length of 130m, it is the main engineering feature.  Ramboll used LUSAS finite element analysis to investigate the response of the structure and in particular to ascertain the modes of vibration for the 40m long unsupported length of the spiral section. Three tuned mass dampers, sized to deal with the first principal mode of vibration, are housed within the steel tube to prevent any potential excitation of the structure by vandals.

Awards

• British Urban Regeneration Association Award (The Phoenix Initiative) best practice in regeneration 2006
• Civic Trust Award commendation 2004
• Regeneration Award best mixed-use project 2004
• RIBA Award regional 2004
• Structural Steel Design Award commendation 2004

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