The new Library of Birmingham offers the city a 35,000m² library, a new 300 seat auditorium, shared with the neighbouring Repertory Theatre, and urban plan for Centenary Square. Designed by the internationally renowned Dutch architects Mecanoo, the original design concept for the structure was for a steel frame with significant trusses at various levels to transfer the loads to the load bearing columns and core structures. Working closely with Consulting Engineers Matthew Consultants (part of the Walsh Group), A J Morrisroe & Sons Ltd proposed and developed an alternative design, utilising post-tensioned concrete floor slabs and post-tensioned concrete transfer walls and arches, which was accepted by the client. This concrete solution offered both programme and commercial savings over the original steel scheme.
The package, now valued at circa £18.5m, incorporates numerous unusual and technically complex elements to offer the facilities outlined above. The Library of Birmingham project is Britain’s largest public library. The new library adjacent to Centenary Square in the City Centre replaced the existing Central Library with a new state-of-the-art 21st century centre for knowledge, information, learning and culture. The new library is integrated with the existing adjoining Birmingham Repertory Theatre.
The 60 metre high building incorporates several unusual and technically challenging elements including:
The 1st, 2nd and 3rd floors project over Centenary Square with a 10 metre span cantilever. This enormous span is suspended from above using storey height post-tensioned concrete arches with a 14.4 metre backspan.
Several of the arches are connected to the slip-formed core structures with connections capable of transferring working loads up to 2500kN (250 tonnes). Each of these connections required up to 36 40mm diameter coupled steel dowels to be accurately cast-in to the core walls during slip-forming operations.
Central light well rotunda:
The library is served by a striking central atrium that penetrates through the full height of the building and is created from internal overlapping rotundas up to 21 metres in diameter. This feature is achieved using post-tensioned floor slabs cantilevering up to seven metres in places and utilising the three storey high book-wall on the 2nd, 3rd and 4th floors as an integral part of the structure.
High level hanging structure:
Storey height post-tensioned transfer walls are used to accommodate the high level hanging structure; these span up to 21.6 metres to support loads from the four no hanging floor slabs in addition to loads from up to 5 no floor slabs above the hanging structure. Significant temporary works comprising bespoke temporary steel props and hydraulic jacks were incorporated to allow bottom up construction of the hanging structure and to allow a smooth transition to slabs hanging from the high-level transfer structures in the permanent condition.
Archive facilities on the 2nd, 5th and 6th floors:
To accommodate public spaces on the lower floors the archive storage is located on the 2nd, 5th and 6th floors. This fundamentally shifts the loading on the structure, placing these heavily loaded floors further up the building and imposing live loads up to 17.5kN/m² (1.75 tonnes/m²). Structurally, this is achieved with 275mm thick post-tensioned concrete floor slabs, spanning 7.2 metres and 450mm deep post-tensioned concrete band beams spanning 9 metres.
The loads of the structure are concentrated in relatively few columns and the core structures. Slender columns supporting working loads up to 23000kN (2300 tonnes) are achieved with the use of composite columns, utilising high strength reinforced concrete combined with heavy structural steel UC sections.