Reconstruction of the grandstand and realignment of the track has been driven by the racing schedule.
Demolition of the old stand started last October and the newly reconfigured Ascot has to be up and running ready for Royal Ascot in June next year.
To speed construction a prefabricated, modular structure has been adopted.
The shell and core are costing £85M and fit out will add another £45M. Buro Happold project leader Tim Page estimates that use of precast concrete elements will shave about six months off total construction time compared to conventional cast-insitu construction.
From the ground up, the stand is founded on 700, 14m deep, 650mm diameter CFA piles. Four shear cores, evenly spaced along the rear of the building, anchor the entire structure, the rest of which is a grid of slender columns and floor slabs.
Cores were cast insitu up to half height, and have been constructed of precast boxes between that point and full height. Columns are at 10.8m centres and support beams run front to back. Precast concrete Bison floor planks are laid between these, and the whole is topped with a concrete screed that stitches the planks together. Total floor depth is just over 200mm.
This lightweight structure has little moment frame capacity and has to be tied back to the shear cores for stability. Between the structure and the front of the central galleria, anchorage is achieved with shallow steel girder bridges that take 'hundreds of tons of shear load. They're very stiff in plan, ' says Page.
Laing O'Rourke is using temporary bracing to keep the grillage of columns and floors stable until the bridges can be stitched into place.
Work started at the west end of the building and has advanced east in a sort of Mexican wave. The westernmost portion of the precast structure was fully assembled at the start of this month ready for installation of the first steel roof trusses.
These were prefabricated in small sections in Slovakia and transported to site where they have been assembled into 14t-16t modules by roofi ng subcontractor Wagner Biro. They will be placed in single tower crane lifts, says Page.
Although their dimensions change as the building bellies out and tapers along its length, the roof structure essentially consists of two repeated elements.
Modules sitting on the rear of the structure have six points of contact, while front modules have three, one of which is the rear module. As soon as one front-back truss connection has been made that section is structurally stable, says Page, allowing erection of the adjacent front-back pair. Every fourth truss is tied to one of the shear cores.
After the concrete structure and roof have been erected the 13m cantilevered viewing terraces will be brought in under the roof canopy with crawler cranes.
The new grandstand is a highly serviced structure.
Of the 300 private boxes, every pair is served by one finishing kitchen, each requiring electricity, water, waste and gas. As with structural components, these have been prefabricated and come pre-installed in the core units. Plant is housed in the building's basement.
Three dimensional modelling was required to avoid potential clashes between services and structure.