Projects and Features
Industry solves technical challenge
Structural steelwork has played a prominent role in creating a technical college with an industrial identity.
Royal Greenwich University Technical College
Main client: Royal Borough of Greenwich
Architect: Walters & Cohen
Main contractor: BAM Construction
Structural engineer: Clarke Nicholls Marcel
Steelwork contractor: Bourne Special Projects (part of Bourne Group)
Steel tonnage: 234t
Project value: £9.5M
A brownfield site in Woolwich, south London, is being converted into a new University Technical College (UTC) backed by the University of Greenwich, Transport for London, Wates and the local authority, the Royal Borough of Greenwich.
UTCs are said to be a new concept in education, offering 14-19 year olds a full time, technically orientated curriculum and clear route into higher education, apprenticeships and careers.
As well as technical subjects, specialising in engineering and construction, students will also study GCSE and A-level subjects, so a mixture of classrooms and workshops are required for a UTC.
To highlight this technically aligned educational format an industrial feel to the college design has been achieved, most notably through the use of exposed structural steelwork and the retention of a steel framed 1950s warehouse.
This existing structure has had its original steelwork strengthened and the building will house workshops and classrooms. An adjacent new steel building with three floors will accommodate more classrooms and will feature plenty of exposed steel, enhancing the premises’ desired architectural feel.
As well as providing the project with the required aesthetic look, steelwork was chosen for its speed of construction. “The UTC will open in time for the autumn (2013) term,” says Kevin Stoney, BAM Construction Project Manager. “We only have a 12 month on site programme, so a quick steel erection process is vital for keeping us on schedule.”
Another important consideration was the poor ground conditions under the site. The new steel framed structure is supported on piled foundations and the lighter steel solution reduces the number and lengths of piles needed.
Bourne Special Projects completed the steel erection, which also included the installation of precast planks, in just six weeks.
“The site is quite constrained and having another contractor on site laying the precast planks would have meant us having to stop the steel erection programme intermittently,” says Chris Page, Bourne Special Projects Senior Site Manager. “By doing both tasks we were able to erect one floor along with the planks, and then move on to the next level using the lower floor as a safe working platform.”
In order to provide stability to the new three-storey high frame, Bourne initially installed a fully fabricated and braced lift shaft. Weighing 9.5t, the steel framed unit was brought to site in one piece and saved the overall programme nearly three days of assembly work. Once in place, the shaft – which is centrally positioned along one of the main elevations – allowed the rest of the steel frame to be erected around it.
The teaching block has a footprint of 58m × 18m and features a first floor entrance foyer leading onto the adjacent Woolwich Road. Steps will lead up to the main doors and then into the college. The first and second floors will accommodate classrooms, while the ground floor will house dining areas and a large open plan fitness suite.
Each of the three floors has a different wall alignment as the rooms on each level vary in size. This has made it difficult to align column positions within walls as grids vary between 3m and 9m throughout the structure. However the flexibility of a steel framed solution has worked successfully within these constraints.
In order to create a 17.2m × 19m ground floor fitness suite with no internal columns a transfer structure has been installed. This consists of two 16m long 1.11m-deep plate girders, and is positioned at roof level.
“Both the first and the second floors above the fitness suite are hung from these two girders, forming the open space at ground floor,” says John Matthews, Associate at Clarke Nicholls Marcel. “Putting the transfer structure at roof level was the most efficient solution. The only alternative was to place deep transfer beams at the underside of the first floor. The first floor could not be raised due to the adjacent street level, so this would have meant lowering the ground floor level to maintain the required clear height. The additional excavation costs meant this wasn’t an option.”
Positioning of the vertical bracing was also a challenge says Mr Matthews: “On a long narrow building most of the walls and partitions have windows, doors or teaching boards, so areas for bracing are at a premium. The lift shaft is heavily braced making it a primary core, while cross bracing has also been installed beside the stairwells and moment resisting frames used to maintain structural stability.”
Both the teaching block and the renovated workshop will form one large interlinked building, although each is structurally independent with a movement joint separating them.
The original steelwork frame for the workshop dates from the 1950s. Visual surveys confirmed it was in good condition with very little corrosion. The structure has been re-checked based on the original steel section values and design stresses including additional loading from the new roof covering. It has also been stiffened with new vertical and horizontal bracing and horizontal tie beams to allow existing internal masonry shear walls to be removed.
A steel framed canopy has been added to the rear (interior) elevation of the workshop. It is 50m long, 6m wide and supported on 10 × 4.2m high columns at varying centres. As well as providing external protection for students from inclement weather, it is another steel architectural feature adding to the overall industrial look.
Appraisal and reuse of existing buildings
Proposed changes in the planning system under current consultation are intended to promote sustainable development by making the best use of existing buildings. Changes of use between industry and warehouse classes to business/office use are expected to occur more often, leading to a greater need for structural appraisal of steel buildings
Amongst the available publications assisting in this process are the following:
- Historical Structural Steelwork Handbook, W Bates, BCSA Ltd, 1984;
- Appraisal of existing iron and steel structures, M Bussel, SCI Publication 138, 1997;
- Appraisal of existing structures (Second Edition), Institution of Structural Engineers, 1996.
The principal technical challenges in converting the workshop building for use by the Royal Greenwich UTC flowed from the slightly increased loads from the new roof and the change to the lateral stability system for the building.
Architectural requirements imposed limits on the width of bracing elements such that tension-compression bracing formed from tubes was too wide. New steel tension-only cross bracing in the form of 150mm x 30mm flats was therefore provided where allowed by the architectural layout. The bracing elements chosen are axially stiff to minimise the change in stiffness from the internal masonry walls. The lever arm of the braced panels is such that the uplift from the overturning moment is overcome by the column vertical load and work to the foundations has been avoided.
It is common for demolition and opening-up work to reveal unforeseen complications. It was discovered that on one grid intersection, the expected steel column was not present: the roof steelwork was supported on a brick pier. A new steel column was required to complete the bracing panel in this location.
The structure was re-analysed using proprietary software for vertical loads from the new roof and wind loads determined using BS6399 Part 2. Elements were hand-checked to BS 5950-1: 2000 using original section properties taken from the Historical Structural Steelwork Handbook. Existing elements were found to be adequate except for transfer beams supporting alternate trusses. The installation of pv panels was restricted to reduce the loading on the transfer beams to an acceptable level.
Checking the structural adequacy of steel elements using limit-state design codes is satisfactory; however this is not always so. The approach is unsuitable for the assessment of cast iron because failure in tension is always brittle and sudden. Cast iron elements should therefore be assessed using elastic section properties, service loads and permissible stresses.