Nottingham’s engineering library is being completely transformed thanks to a complex jacking and underpinning solution.
Project: George Green Library of Science & Engineering, University of Nottingham
Client: University of Nottingham
Contract value: £14m
Region: East Midlands
Main contractor: Galliford Try
Architect: Hopkins Architects
Structural engineer: Arup
Work to revamp and extend the science and engineering library currently underway at the University of Nottingham would have fascinated British mathematical physician George Green, after whom the library is named.
The Georgian miller turned academic would doubtless have been enthralled by the curving geometry of the building’s new extension, wondering at the applied physics that are enabling contractor Galliford Try to engineer the link between the original 1960s built concrete structure and the latest addition to it.
Project manager Richard Blythe is overseeing the library’s transformation under a £14m deal that will see the site team build the new 7,300 sq m three-storey extension.
It will feature split-floor mezzanine levels at each storey and be linked to the existing four-storey reinforced concrete structure, which will be refurbished both internally and externally.
The new addition will double the library space and also provide study spaces, work rooms, work stations and catering.
Old and new connected
“It is a very interesting reinforced concrete building originally constructed in the early 1960s but extended in the late 1960s and early 1970s to match the original structure,” Mr Blythe says.
“We are breaking into that original structure and connecting it to the newly built extension through a glazed entrance atrium.”
It’s a tricky task, not helped by the fact the library and its huge resource of books and academic papers has to remain open and available to university staff and students throughout the construction period.
“It is a very interesting reinforced concrete building originally constructed in the early 1960s but extended in the late 1960s and early 1970s to match the original structure”
Richard Blythe, Galliford Try
“It is an extra concern but it is one which we knew we would have to deal with,” Mr Blythe says.
“That requirement has always been there and we have been able to work round it.
“By keeping the university informed of our work schedule and tailoring it to suit, we have been able to minimise any disruption.”
To the naked eye, the existing library looks as though it was built in one phase rather than the two phases featuring the 1970s extension.
The original reinforced concrete building was designed as an all-concrete-frame structure featuring load-bearing ‘fins’ that run down its elevations.
These structural fins are supported on existing pad foundations at the base of the walls.
The 1970s extension to the library also features these fins but they are there for aesthetic purposes only and are non-load-bearing; the structure is actually supported from the cantilevered floor slab that stretches from the original building.
As part of the scheme, the project team will be excavating and deepening the original basement to the building, creating another level to the library from an existing storage area.
To do this, the team has underpinned around the north-west and north-east elevations of the existing building to depths of 1.5 m, enabling them to lower the ground level throughout the basement and cast a new slab.
The building will be jacked up around the rest of the basement perimeter to allow the new slabs to be installed.
The move is a significant design change from the initial plan which called for jacking the building all the way around its perimeter but the advantages of the underpinned solution proved too much to ignore.
“It is quite a change but there are so many advantages,” Mr Blythe says.
“Underpinning is quicker and quieter than a jacked solution, operationally it worked better for us and it is far more economic.”
In fact, with around four months initially timetabled in the project programme to carry out the jacking work by using the underpinning solution around part of the building’s periphery, the team managed to cut that time back to less than 10 weeks.
“Predrilling the reinforced concrete fins took a few weeks,” he adds.
“There was a lot of small steel bar reinforcement that we had to avoid. Ground conditions have been good with a clay/silt/sand layer overlying the hard sandstone bedrock.”
“We have weekly, fortnightly and monthly planning meetings to keep them informed of the sort of work we will be doing and how it might impact them”
Richard Blythe, Galliford Try
The existing library is built around a nominal 2 m grid with the tie-in point to the new extension at grid-line 5. Here the team is breaking through the existing walls at various points at each level to create new access bridges linking the old library to the new extension.
These sections are broken out while the library is still being occupied. Sections are cordoned off locally to the breakthrough point, with work carried out during weekends or later in the evening.
“Obviously where we are working so close to a live study environment there will be some disruption, but this is carefully managed between us and the university,” Mr Blythe says.
“We have weekly, fortnightly and monthly planning meetings to keep them informed of the sort of work we will be doing and how it might impact them.”
Two buildings into one
The new link building and library extension is being built directly alongside the existing library building as a new structure butting up against the existing.
But instead of leaving it as two separate structures with a connection joint, the team is tying the two together, physically connecting the two buildings and stitching them together by recessing steel bars into each of them.
“We felt it was a better solution than to have the two separate buildings,” he explains.
“We built the new reinforced-concrete wall and tied it into the existing. It is a more homogenous structure.”
With a BREEAM Excellent rating to hit as part of the university’s contract requirements, the team is installing rainwater harvesting units as well as a photovoltaic array.
These, coupled with the sedum roof, high-efficiency air-handling units, and connection to the university’s own district heating system, are all assessed by the independent engineer.
“We are on target to meet those requirements,” Mr Blythe says.
“Connecting to the district heating will be awkward because it is being kept live as we do it, but we will manage that.”
With just a few months to go, the Galliford Try team is on course to complete the scheme before the library is handed over for the University of Nottingham’s next intake of science and engineering students.
The library that jacks built
The decision to underpin around the north-west and north-east elevations of the library building helped shave precious weeks from the programme timetable, but in other areas the initial plan to jack the building, enabling the team to create the extended basement space, has remained.
Here, the initial plan was to create a pressure pad beneath the concrete slab where the columns are located and place steel beams either side of the column at the slab soffit.
The team would then jack against the steel beams from temporary pad foundations.
But there were fears that this would create a danger of shear failure of the slab either side of the steel beams and pressure pad, so an alternative jacking system has been introduced.
The team has scabbled out part of the concrete column itself and placed the steel beams within that scabbled section.
This enables the steel beams to sit within the columns and transfer the loading directly to them, negating any fear of shear.
The columns can then be extended and new pads cast.
“The existing columns are fine; structurally there is no problem with them,” Mr Blythe says.
“The whole process takes around two weeks per column, but we think we will be able trim that down to one and a half weeks.”
End of the line for a distinctive façade
The reinforced-concrete fins that dominate the façade of the science and engineering library offer a sound structural use.
But under the design created by architect Hopkins, of London 2012 Velodrome fame, they will also be covered by a façade that will match the high-specification curtain walling system that envelopes the rest of the building.
Originally the cladding was to be a broken curtain walling and rainscreen clad system, but this has evolved into the energy efficient system which is bracket-fixed top and bottom around the curves of the new library extension and around its existing section.
“It was to be a more common curtain walling type installation, but over time has developed into this extremely efficient system which gives 3.5 times the acoustic and air tightness rating of other systems,” Mr Blythe says.