Design Awards: 2016: Merit

Leeds Station Southern Entrance

Leeds Station Southern Entrance

Architect
AHR Architects

Structural Engineer
Mott MacDonald

Steelwork Contractor
William Hare

Main Contractor
Carillion Rail Ltd

Client
Network Rail Infrastructure Ltd and West Yorkshire Combined Authority

The Leeds Station Southern Entrance (LSSE) has created a landmark structure to relieve congestion to the existing northern entrance, future-proof ticket gate line capacity and encourage growth in the south of the city by improving pedestrian access.

Located in a prominent yet challenging environment, straddling the River Aire and a busy railway, the concept design envisaged an architectural curved form, utilising glass and gold shingles to create a signature building of the highest aesthetic quality.

The project team rationalised the architectural surface into a steel diagrid structure, comprising repetitive RHS arches of known radii, connected out of plane by SHS diagonal members. This efficient solution reduced the number of radii used to form each arch by a third whilst achieving the original geometry +/-10mm. The framing solution also reduced the structural zone from 700mm to 400mm, freeing up internal space, and shared vertical load to a transfer deck whilst providing an inherently stable structure.

The shallow 600mm steel transfer deck carries the superstructure loads back to concrete piers aligned with the existing viaduct piers within the river. This was quickly erected above the river without the need for temporary works and provides the required clearance above the 1:200 year + 20% climate change flood level.

Steel construction provided the flexibility to span the new ticket concourse above the electrified railway via 25m trusses with the concourse floorplate slung beneath, and modularisation facilitated construction above the railway in 10-hour possessions without disruption to train services. Such offsite fabrication brought health and safety benefits in terms of minimising work above a river, adjacent to an operational railway and in a congested city centre.

At river deck level, access bridges and 50% of the river deck concourse have been erected within the confined space of the existing Victorian viaduct arches. This required the adoption of innovative construction techniques and the fabrication of bespoke lifting frames to hoist structural elements from barges located in the river up into the arches to tight tolerances.

Tight tolerances were also needed for the primary structure, which directly supports the cladding in lieu of a secondary support zone. The width of the building is also constrained to accommodate two lifts, four escalators and a stair within a width of only 12.5m. This resulted in a 25mm allowable erection tolerance across the building width.

Leeds station now boasts an iconic gateway, reducing journey times to the Southbank by up to 10 minutes for the estimated 20,000 people that will use the new entrance each day.

Judges’ Comment

This new gateway to the station provides a route from the fast-growing south side of Leeds, relieving pressure on the busy north entrance. The structure interfaces with the existing Victorian viaduct, station roof and concourses being directly over the River Aire.

The judges were impressed by the team’s planning and execution of the erection above the river and within a live station environment.

Energy from Waste Facility, Ardley

Energy from Waste Facility Ardley

Architect
Architecture & Planning Solutions and TSP Projects

Structural Engineer
TSP Projects

Steelwork Contractor
Bourne Steel Ltd

Main Contractor
Clugston Construction

Client
Viridor

The facility has been constructed to treat 300,000 tonnes of non-recyclable waste each year, diverting at least 95% of Oxfordshire’s residual municipal waste away from landfill and generating enough electricity to power 38,000 homes.

The completed building structure is up to 229m long varying from 38m to 70m wide and between 15m and 35m high. Steel was the natural choice for the main frame due to the convex and concave shapes in both plan and elevation, together with clear height and internal space requirements.

Although the structure looks like one building, internally under the cladding it is split into several zones incorporating different designs and resulting in over 2,000 tonnes of structural steelwork being used. With the processing plant taking up most of the internal areas, the use of models was crucial to make sure there were no clashes between key plant, equipment and their secondary supports and the main frame.

Within the waste bunker, cranes operate at high speeds with high acceleration and breaking forces, together with a grab swing with large pick-up loads. In this area the crane beams and all connected steel members had to be designed and fabricated to comply with Execution Class 3 requirements due to the high fatigue requirements. These areas were located on top of an 18m high concrete structure which limited access for connections to alongside one elevation only. To overcome this, a removable MEWP platform was designed and constructed to fit on the top of the concrete structure so connections could be accessed.

As the internal process plant and associated secondary steelwork for access and support were constructed in advance of the main frame enclosure, the use of modular roof assemblies, some weighing 40 tonnes, had to be used so that the 35m high roof could be infilled with steelwork to allow support for the cladding systems. These modular assemblies were installed using 800 tonne mobile cranes due to having to work over the constructed plant and metalwork areas, and also only having access along one side of the building.

The majority of steelwork was hot-dip galvanized to provide the necessary corrosion resistance and low maintenance requirements due to the difficulties in accessing the members whilst the building is in operation. Other areas, mainly accommodation areas or rooms with daily occupancy, were painted with intumescent coatings to achieve the specific fire resistance requirements.

The project was delivered on programme and to budget.

Judges’ Comment

A large and highly complex industrial plant has been enclosed by an undulating structural steelwork envelope. Site logistics and difficult construction phasing resulted in great challenges to the fabrication and erection which required modularisation and bold management.

The construction above column-free spaces to such a complex timetable was impressive.