Significant structural openings and alterations are being made to the 139 year old Royal Albert Memorial Museum in Exeter.
Refurbishing and extending the Royal Albert Memorial Museum in Exeter has provided contractors and engineers with some unexpected and complex challenges since work began on site last spring.
The main body of the two storey Grade II listed building, which faces out into Queen Street, was built in 1869 with additional wings being added through the late 1800s around a rear central courtyard. The museum features displays that range from local history to butterflies, geology and clocks. Now a £15M refurbishment programme is breathing new life into the Victorian structure.
The works, which started on site in April 2008, involve replacing three roofs, demolishing and rebuilding two 12m high masonry gable walls, making some significant holes in the load bearing masonry walls as well as installing a new roof and bridge structure across the central courtyard. A lift shaft and a new wing are also included in the programme. The new wing will be a pre‐fabricated timber panel building in the back left corner of the museum, on the site of the old Clocks Gallery, which was demolished in December last year.
“We’re giving it [the museum] a change in circulation,” says Building Design Partnership (BDP) project engineer Clare Harvey. BDP is the project’s structural engineer. “What was a series of galleries will be turned into meaningful circulation space. It means lots of structural openings in the existing fabric.”
Around 60 openings will be cut into the load bearing masonry walls. These vary between the removal of entire cross walls within the building (8m wide by 4m high) to the creation of openings within existing walls of various sizes – up to 2.5m wide by 2.5m high for pedestrian circulation to smaller openings to allow creation of new routes for building services. Temporary works figure prominently in efforts to support the upper sections of the wall and floors above while the wall openings are cut and secured.
Small holes are made above the level of each of the larger openings. Temporary steel beams known as needles are placed through the holes to transfer the load from above to temporary props either side. This then allows the opening to be made. Then, a lintel or permanent type of transfer system is installed in the plane of the wall, allowing the temporary works to be removed. Where large openings are being made, portal frames are being put in place, with large spread footings to ensure that the bearing pressure on the ground is not exceeded.
The main building, which was built in 1869, features load bearing basalt stone walls with loose rubble mortar and the wings that were added between 1882 and 1899 are made from clay brick.
“The initial building is made from large basalt stone with rocky road looking mortar,” says BDP senior engineer Steve Johnson. “We weren’t sure how [that type of wall construction] would react [to breaking a hole through]. Because of the large cobbles and mortar, we had to overbreak [and patch the wall up afterwards]. The walls are between 500mm and 600mm thick. We had to put scaffolding up just to get the huge stones down.”
The amount of information that could be gleaned from opening up works before the contract was awarded was limited as the museum was still open and operating. Limited construction information existed from the time of construction and when it came to carrying out the works, the building fabric was often found either to be in a poor condition or not as expected.
“Everything we touched had a different issue,” says main contractor BAM Construct senior site manager Clive Horsnell. “It wasn’t what you expected to find. The information available prior to tender was limited because it was a working museum. Inspection and appraisal has been ongoing.”
One such example was the removal of a ground floor wall at the back right hand corner of the 1899 wing. Above it sits the first floor store room which contains part of the museum collection.
Additional steel beams were discovered on opening up the ground floor wall and ceiling. These had been added at some point to support the extra load from the floor above when it had become a store room. These connected into extra steel beams in the wall which had acted as lintels at one time, but at some point, the door openings had been blocked up. These steel beams unfortunately were in the same plane in which the design team had originally planned to put temporary props.
Everything we touched had a different issue. Information prior to tender was limited as it was a working museum.
Clive Hornsell, BAM
“We had to prop the existing steel beams in order to drill holes through them, through which we could then put some needles,” says Harvey.
“We couldn’t needle above the beams because that’s where the storage was. We couldn’t needle below as that was where the permanent works were going. We had to go through it.”
The project team has found an extravaganza of oddities and surprises. BAM Construct has been working round a stuffed elephant and giraffe in one of the galleries, and the ceiling structure is being evaluated to see whether it can support a whale skeleton weighing several hundred tonnes.
The structure of the building also threw up a number of surprises “We found that the walls step out in the lift shaft,” says Horsnell. “Fat walls sit on top of thin walls. Also in some areas, the walls went straight down with no foundations.”
A Norman ditch running under the existing building has contributed to the challenges. Differential settlement has led to the museum’s local history gallery at the northern side of the building leaning towards the back of the building against the neighbouring Clocks Gallery. “The north end was collapsing into the ditch and the clocks gallery was holding it in place,” says Harvey. “The buildings were leaning towards each other and collapsing together. Contractor Uretek underpinned and improved the soil with resin injection, giving the impression of consolidated ground.”
The instability had produced major cracks with an average width of 35mm in the gallery walls. These were stitched together by inserting steel helical reinforcing bars into the masonry joints across the cracks.
The Clocks Gallery and the northernmost wall of the local history gallery have been demolished to make way for the new wing. A huge temporary works tower constructed from soldiers was installed to keep the flank walls of the gallery in place until the new wall could be built. Temporary works designer Mabey Hire used system 160 soldiers to form a framed modular structure, tied back into wall to keep the two flank walls from leaning into or out from each other.
“The temp works allowed you to remove the end of the building without compromising the structure or adding load to it,” says Harvey. Sequencing and design of temporary and permanent works were technically challenging and the interdependency meant that a close relationship was required between the permanent works and temporary works designers.
“Particularly with the advent of CDM, people no longer say that’s permanent works, that’s your job; that’s temporary works, that’s my job,” says Johnson. “Everyone works as a team.”
Together the design team and construction team have struggled through all the obstacles the eccentric old building has thrown at them, and are discussing the last few details , with client Exeter City Council. The museum is due to reopen in early 2011.
About the museum
The Devon and Exeter Albert Memorial, as it was originally known, was developed as a museum, art gallery, library, reading room, school of art and school of science.
It was originally conceived as a memorial to Prince Albert by Sir Stafford Northcote and was funded via a public appeal in 1860.
It was renamed the Royal Albert Memorial Museum in 1899 when the Duke and Duchess of Edinburgh opened the final section of the building.
The museum is a 19th century gothic masterpiece with ornate stonework exterior and split central staircase. It has changed little since the last gallery section opened, although the city library moved out of the museum in 1930.
The school of science ultimately developed into the University of Exeter and the school of art is now the University of Plymouth Faculty of Art & Education.
The Royal Albert Memorial Museum houses collections including clocks and natural history exhibits including a stuffed giraffe a whale and an elephant.
It also houses a local history gallery, a geology gallery and a Roman gallery.
Client: Exeter City Council
Main Contractor: BAM Construct
Structural engineer: Building Design Partnership
Architect: Allies & Morrison
Temporary works designer and supplie:r Mabey Hire
Temporary works installer: AWCS