2020 Merits

Structural Steel Design Awards

The Gravity Bar, Guinness Storehouse, Dublin

PROJECT TEAM

Architect:
RKD

Structural Engineer:
Arup

Steelwork Contractor:
Steel & Roofing Systems

Main Contractor:
 P.J. Hegarty & Sons

Client:
Diageo

The Guinness Storehouse is Ireland’s number one tourist attraction and one of the most visited in Europe, with approximately 1.7 million visitors per year. The original storehouse structure dates back to 1902, with the circular Gravity Bar itself being built in 2000.

This project comprised the expansion of the Gravity Bar, to more than double the original size, together with strengthening works to the existing Storehouse and the development of a new three-storey Hub building providing office space for Diageo staff.

The Gravity Bar is located at seventh floor level with the existing roof of the Storehouse at fifth floor level. A series of strengthening works had to be carried out throughout the structure below before the new structure could be erected. A crash deck at sixth floor level over the full footprint of the new structure allowed construction to be safely carried out above, while the Storehouse remained open below, and provided a working platform for steel erection.

The steel frame for the new Gravity Bar is supported on four CHS columns which are located directly above existing columns in the Storehouse structure below. The floor structure is formed from a grillage of box girder beams and UB section infills.

All UB infills and several of the box girders were detailed with service penetrations to coordinate exactly with the MEP requirements. The downpipes from the roof were also integrated inside the CHS perimeter columns in several locations where required.

Nine box girders totalling approximately 110 tonnes formed the bulk of the steelwork for the Gravity Bar and were fabricated with 75mm-thick top and bottom flanges and 30mm-thick webs. A full trial erection of the box girders was completed offsite to ensure accuracy and avoid any issues during site erection.

The perimeter of the building at the seventh floor is formed from a curved PFC section, which was erected in discrete lengths and welded, with the welds ground flush, to produce one continuous member around the full bar. This was joined in with the existing bar’s PFC to form one seamless band around the bottom of the glazing. The roof level perimeter steelwork is also formed from curved PFC sections with a curved CHS welded to this all the way around the structure.

The Gravity Bar has been doubled in size, transformed into a figure of eight and is designed to give visitors maximum views across Dublin’s city skyline.

This popular bar sits above Dublin’s most visited tourist attraction and the works were carried out with the building remaining operational throughout. The challenging installation forms an extension to an existing rooftop structure that sits above the 1904 ‘Protected’ building. The new bar is supported on four steel columns that connect through the roof to the strengthened, historic structure, below.

Judges’ comment

Scarborough Footbridge, York

PROJECT TEAM

Architect:
Network Rail

Structural Engineer:
AECOM

Main Contractor:
AmcoGiffen

Client:
City of York Council

Scarborough Footbridge provides a new pedestrian and cycle shared-use facility which spans the River Ouse approximately 50m north of York Station. The existing narrow lattice U-frame superstructure and steep step access has been replaced with a widened architectural weathering steel pedestrian bridge with step-free approaches. The new crossing has greatly improved access for all users, promoting sustainable travel between the station and key parts of the city centre, and is now attracting approximately 4,000 users per day.

The overall structural form and approach parapets are reminiscent of Viking longships, providing a fitting aesthetic appearance for the centre of York. The bridge comprises two main river spans of 22m, formed of prefabricated box girders with integral curved parapets and cantilevered deck plates. The west side of the deck also incorporates an ornate painted parapet to match the existing. The two 10m side spans spanning over the existing river footpath are formed of prefabricated U-troughs with integral parapets and deck plate to match the main river spans.

Stability of the cantilevered main spans was met by provision of mechanical uplift bearings. Tensioned straining wires run through integral eyelets on the parapets and are anchored into masonry-clad anchor blocks at either end of the structure.

The approach ramps and stairs at either end of the structure are flanked by bespoke fabricated painted steel curved parapet panels with a stainless steel top rail and integrated handrail lighting. The steelwork elements of the scheme are complemented by masonry blocks and stone cladding providing a mix of modern and historic elements enhancing the local conservation area.               

The main river spans were erected from the adjacent rail bridge using a rail-mounted crane. Use of finite element analysis was incorporated into the steelwork design from an early stage to refine steelwork plate sizes and provide a cost-effective and lightweight solution to ensure stability of the lifting plant and existing substructure. This ensured the main river spans could be erected in one lift per span, under the 24-tonne weight limit imposed on the crane. The FE analysis also provided an accurate centre of gravity for the lifted spans giving the contractor confidence in erection of complex unsymmetrical girders within a geometrically constrained site and limited rail possession time.

The replacement Scarborough Footbridge is unique in its appearance and structural form and wholly fulfils the brief to promote sustainable transport for all users and improve access through the City of York.

The replacement footbridge expands pedestrian and cycle access between York Station and key parts of the City addressing existing access and capacity issues. The project used its location, adjacent to Scarborough Rail Bridge, to enable delivery and installation of large preassembled units using the railway. The bridge wholly fulfils the brief, promoting sustainable transport for all users through the City.

Judges’ comment