18m All-Glass WalkwayEdit profile
150 Cheapside is a prestigious new office building close to St Paul’s Cathedral in the City of London, EC2. At 1st floor level, within the entrance foyer, users walk out onto a 18m long and 1.5m wide all-glass bridge. The bridge is constructed entirely of laminated glass and comprises triple laminate glass floor panels bonded to glass beams at 1.5m spacing. Glass to glass beam connections are made with a innovative structural connection. The bridge is supported by concrete walls on one side – with cast-in Halfen channels and T-shaped bolts – and suspension rods to the underside of 2nd floor slab that are pin fixed through the ends of the glass beams. The architect was inspired by recently completed glass structures but wanted to extend the boundaries further. The complex nature of this structure required a finite element analysis, to evaluate stresses, deformation as well as the natural frequency and dynamic response of a computer model of the structure. The safety of the structure is provided by a built in redundancy in the design of glass beams and other structural glass elements. The technique used to construct glass beams 18 metres long relied on load transfer through holes in the glass and to ensure that the bearing materials and areas were sufficient and accurately fabricated to prevent high stress concentrations which would cause premature failure. A series of laboratory tests were carried out on toughened and laminated toughened samples with a 40mm diameter hole in the glass. Results gave a mean failure load of the single toughened samples of 5,5 tonnes. For the laminate glass sample the mean failure load was double showing equal load sharing by both panes and reliability in the connection solution. To prove that our design assumptions and analysis were correct an extensive testing program was carried out on a full scale mock up. A live load of 5 KPa was applied equivalent to 4.5 layers of sandbags, followed by point load application and sharp object impact tests, using a 25kg steel impactor dropped from various heights. In the end the walkway was completed slightly ahead of the program in March 2009 and within the budget.