Salford City Council
Engineering Design Section
30th July 2004
Duncan Street- Gable Wall – Structural Considerations
Introduction.
The subject wall is in a state of disrepair such that the adjacent landowner was
concerned for the safety of his workforce and equipment that has to work close to the
wall. The matter was brought to the attention of the City Council’s Building Control
Section.
As it was not possible to access the wall internally, the wall was inspected externally
only. Visual indications are that the wall has been exposed following the removal of
an adjacent building and this has left old steelwork and evidence of other structural
features.
The gable wall was not designed to be exposed in this way and the level of observed
deterioration is of concern.
A wall of these proportions would, even in good condition, be unstable unless
properly restrained in order to provide resistance to wind and self-weight buckling
forces. The old building, now demolished, may have originally provided this restraint.
A wall of this type would, in addition to being constructed of sound brick with mortar
filled horizontal and vertical bed joints, would be required to be tied back to the
structure not only by bonding with the side walls but also through mechanical fixing
to the roof, walls and floors and by intermediate steel or concrete columns.
The gable is visually unsatisfactory and contains serious bulges and voids. There is no
way of determining whether there is any adequate support provided as an internal wall
has been constructed internally to improve the appearance of the building at this end.
This adds weight to the view that the wall may be equally poor internally such that it
was required to be concealed.
There is an absence of an appropriate and robust basement retaining structure at
ground level.
Safety
Safety is an important consideration, not only for the current situation, but also at
various stages throughout the repair operation including inspection, propping,
demolition and repair.
It is currently unsafe to work close to the wall as there is no means of knowing
whether a small disturbance could trigger a collapse. It is therefore important that the
work is carried out in a methodical manner in accordance with detailed method
statements designed to minimise risk to unsuspecting workers employed to carry out
any repair work. Deterioration to the gable is now so advanced that it would not,
without careful investigation providing evidence to the contrary, be considered safe to
allow operatives and tradesmen close to the wall to effect patch repairs
Design Issues
Professional structural engineers acting on behalf of the City Council will insist upon
the work being carried out in accordance with British Standards, design codes and to
current good practice guides. Although in the past well executed patch repairs may
have had some minor beneficial effect it is now unlikely that any structural engineer
would underwrite such patching without first ensuring that the finished wall would
have the strength to meet modern design requirements.
Proposals
It is therefore envisaged that the following actions will be required; approximate
estimates of cost are shown against each activity in bold type.
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Clear building (£??? Loss of Business earnings).
Obtain access to wall internally (Say £1500 for contractors costs)
Review gable wall internally (£2000 access and fees)
Take down internal wall (£5000)
If deemed stable construct scaffold internally as access to wall and to prop
roof and sidewalls (£10,000)
If deemed unstable, construct scaffold at a safe distance and carefully roll in to
place. This to ensure personnel is not working below an unstable wall. Once in
place prop roof and support sidewalls. (£15,000)
All propping must allow for the situation when the wall is removed and the
building will be exposed to higher internal wind loading that could adversely
affect the roof and the remaining walls.
It should also be noted that support will be lost to the side wall masonry when
the gable wall is demolished.
When scaffold in place and roof is secure, measure roof structure and side
walls and carry out design of basement, supporting steelwork and masonry
gable in accordance with BS8110, BS5950, BS5268, BS5286 and the wind
code BS6399.(£7,000)
Following a detailed risk assessment and receipt of advice from specialist
demolition contractor, carefully take down the gable working from the
security of the scaffold internally and by using long reach hydraulic equipment
externally such that operatives are kept at a safe distance from any falling
masonry. (£12,000 includes legal access over private land).
Excavate basement area and construct new reinforced concrete or reinforced
masonry retaining walls. (£15,000)
Construct new concrete ground floor as required. (£2,000)
Install new steelwork wind posts and roof bracing as necessary. (£7,000)
Reconstruct new gable wall tying in to existing side walls and new steel wind
posts. (£20,000 including scaffold access externally)
Remove all internal temporary works (£2,000)
Building available for reuse.
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It is possible that the building will be out of use to the current business for a
period of 16 weeks.
Conclusions
The estimated cost of the above operations is therefore estimated to be circa £85,000 90,000 including fees but not including the cost of business closure for a period of up
to 16 weeks.
All the above figures are best guess estimates assuming the wall is inherently
unstable. They will be affected by factors that can be firmly established only when
safe access to the building has been achieved and outline design work completed.
These factors will include the following considerations:
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Can the wall be safely accessed internally and externally for inspection?
Will the adjacent landowner permit the wall to be demolished on to his land?
Is the wall robust enough to withstand demolition without uncontrolled
collapse?
When the wall is removed, will the remaining brickwork and structure be able
to withstand the increased wind forces caused by the large opening?
If not will additional prior strengthening be required?
The above comments are not provided as a structural report but as an indication of the
extent of the problems to which the various professionals should concentrate their
initial efforts in order to devise a safe and competent repair solution.
Max Griffiths
Engineering Design Section