Zaha Hadid Architects
Watson Steel Structures Ltd (Severfield-Rowen Plc)
BAM-HBG Construction Ltd
Glasgow City Council
The Riverside Museum provides a new exciting environment in which to showcase Glasgow’s rich and varied transport heritage.
The form of the roof structure is roughly z-shaped in plan with structural mullions at each end that not only support the roof, but also allow the glazed end façades to be supported without the need for any secondary members. In section the roof is a series of continuous ridges and valleys that constantly vary in height and width from one gable to the other with no two lines of rafters being geometrically the same. Generally the cross section is a pitched portal frame with a multi pitched rafter spanning between the portal and a perimeter column. There are also curved transition areas where the roof changes direction in plan.
The rafters themselves are not straight in plan but a series of facets that change direction in each valley. To accommodate these changes in line and to facilitate the connection of any incoming bracing and other members, the rafters at the ridges and valleys are joined at the surface of a cylindrical ‘can’. The majority of these ‘cans’ were truly vertical in the preset geometry of the roof, however where the relative slopes either side of the ridge or valley would have generated inordinately long oblique cuts the ‘cans’ were inclined to bisect the angle between adjacent rafters.
The diameter of most of the ‘cans’ was able to be standardised but, in cases of extreme geometry or where the sheer number of incoming members dictated, a larger diameter had to be used to allow all the incoming members to be welded directly to the ‘can’ wall. The most complicated valley connection had 10 incoming members that necessitated the use of a 1.0m diameter ‘can’ over 1.5m tall.
By using vertical ‘cans’ in the valley positions a standard connection between the tops of the tubular support props and the roof structure was designed. This consisted of a thick circular base plate to the ‘can’ with a blind M24 tapped hole in its centre, thus allowing an 80mm diameter tapered shear pin to be bolted directly to the base of the ‘can’.
The accuracy of fabrication was achieved by using a combination of shop jigs and EDM setting out techniques. All the complex rafter members were assembled in shop jigs whilst the geometry of the more simple members was set using EDM’s that were able to set the positions of certain critical splice connection holes. This was made possible by adding virtual “wires” through the centres of some of the holes during the X-Steel modelling. These wires allowed the EDM operator to check its end position in space when a circular prism was placed in the hole. Using this technology it was possible to accurately position the remote end of a steel member to ± 2mm in any direction.
The more complex members were assembled using shop jigs. These jigs were created by extracting a single member (assembly) from the X-Steel model, rotating it in space to create a single reference plane and then modelling in a secondary steelwork “frame” that the individual pieces (fittings) of the assembly could either be supported on or bolted to.
The whole of the building structure is supported on piles with none of the slabs having been designed as ground bearing. The columns are generally founded on individual pile caps with the slab spanning between individual piles so to allow the erection of the roof to be carried out from within the footprint of the building. The ground floor slab was designed to accommodate multiple 10.0 tonne loads at a minimum of 1.8m centres.
A prominent site by the River Clyde, and an unusual building form, make this project unmissable.
The technical challenges overcome by the steelwork designers and steelwork contractors were formidable, and it is a pity that the large structure will be mainly concealed. Nevertheless the contribution to the building is both crucial and praiseworthy.