Arup collaborated with Nicholas Grimshaw & Partners in the design competition held in 1996.The Grimshaw/Arup entry was the only one to fully exploit the use of the existing storm water tank on the site.Arup provided structural, building services and civil engineering services as well as strategic advice on communications and security.
The site of the exhibition facility is the existing buried storm water tank.
This was built in the 1920s and used as part of Leicester's wastewater strategy until it was decommissioned in the 1960s.The tank was renovated to provide the substructure for the new facility and the existing walls can be seen around the perimeter of the sunken courtyard.The existing pump house building has been converted to form an energy centre.Maximising the site's resources and minimising expensive remediation was a common theme of the engineering approach.
The site is next to the River Soar and the tank was originally covered in 3m of ballast from the original excavation to prevent flotation.The first engineering challenge was to develop a method of converting the tank into the substructure while preventing flotation.The solution was to use a pressure relief system during construction.This allowed the ballast to be removed and the alterations completed. In the permanent condition, the ballast has been transferred to the base of the tank and the need for a permanent pressure relief system negated.
The cocoon structure is formed using steel tubes attached to the concrete core.The tubes are the largest standard diameter available.The main steel legs curve from the tank over the volume to meet the top of the core.The ribs, which support the EFTE cladding pillows, span between the core and the main legs and between the main legs.Stability is provided by the eccentric concrete core acting in torsion.To allow artefacts to be moved, the lower ribs at the front of the tower are demountable.
The tower is designed to be a covered external space.A CFD analysis of the tower temperatures in summer was completed to estimate the levels of visitor comfort throughout the season.This demonstrated that a natural ventilation solution could be developed for the tower. Heating is provided to combat condensation only in periods of low winter temperatures.
The exhibition hall is fully air conditioned, with humidity control.Air is supplied from high level to maintain the maximum possible clear height and therefore maximum flexibility.To satisfy potential loan agreements for exhibits from other institutions, the 'Mecklenburg Conditions'were adopted as the environmental criteria in the exhibition building.These specify internal environment appropriate for a visitor experience with few sensitive artefacts.Detailed analysis enabled a practical working solution to be developed within the budget constraints, which will achieve these conditions most of the time.This proved to be an acceptable solution to all parties.