All buildings should be robust; designed and constructed so that in the event of the loss or damage to a single component this does not cause the collapse of the entire structure or a large part of it.
This is defined in the Eurocodes as designing and executing a structure in such a way that it will not be damaged by events, such as explosion, impact and the consequences of human error, to an extent disproportionate to the original cause.
This design consideration was initially introduced in the UK following the partial collapse in 1968 of Ronan Point, a recently constructed 22 storey east London tower block. A gas explosion in the kitchen of the 18th floor flat resulted in the collapse of the entire corner of the tower block, killing four people and injuring 17 others. An enquiry found that the tower was badly designed and poorly constructed which led to changes to building regulations in 1970 covering ‘Disproportionate Collapse’ that have since been extended and further modified.
These mandatory requirements are now covered by Building Regulation A3 and all buildings have been brought under its control so that, as well as new build design and construction, it also applies to existing buildings that are to undergo refurbishment or change of use.
Following a full structural survey and risk assessment, any areas of a building which are considered to be at risk of disproportionate collapse need to be strengthened.
Helifix structural wall ties, fixings and reinforcements, together with their specially developed concealed installation techniques, provide an ideal means of achieving the required levels of strengthening.
Case Study 1
The conversion of the former Wiltshire Police HQ into a new technical college, South Wiltshire UTC, provides a good example of the A3 rules being applied to enable this change of use.
After meeting with the design team at Jubb Consulting Engineers, four areas of the building were identified as being possible areas of risk, due to critical load conditions affecting the external corners, the front elevation and internal load bearing walls. Calculations were carried out by Helifix engineers to analyse the reinforcement requirements for these areas and a final programme of strengthening was agreed with the project engineers.
Around the entire exterior of the four storey building and along the internal load bearing central spine wall, high tensile stainless steel HeliBars were bonded into channelled-out mortar beds. These were installed at two different levels between all the windows with three 6mm diameter HeliBars being bonded into each slot, using HeliBond cementitious grout, with a total of 2,190m being used. These reinforced the existing brickwork and enabled it to act as continuous masonry beams, helping to support and spread the structural loads, particularly in the large masonry panels at the building’s corners.
Further HeliBars were used to secure the external elevations to the internal concrete floor slabs. The HeliBars were inserted through clearance holes in the masonry and bonded with HeliBond into channels cut into the concrete. The outer ends of the bars were then bent at right angles, with no loss of performance, and bonded into the external mortar beds.
In addition, SockFix grouted anchors were installed at the corners at a 45o angle through the mid depth of the wall to secure the panels and allow the corners to cantilever. These heavy duty, long series sock anchors were inserted into clearance holes and then pumped full of SockFix grout expanding the sleeve and bonding the assembly to the surrounding masonry. The outer brick was removed before the sock anchor was installed and replaced after installation to conceal the entry hole.
Once the building had met all its mandatory requirements, to avoid any risk of disproportionate collapse, it could be transferred from the Wiltshire police to become South Wiltshire UTC.
Case Study 2
A similar situation occurred when a former carpet warehouse was to be converted into a city academy for Birmingham Metropolitan College and Kidderminster College.
The Grade II listed ‘Piano Building’ was built in 1867 and gained its nickname because, when viewed from above, it resembles the shape of a grand piano. After standing empty for a number of years it was purchased in a joint venture by the two colleges. As part of its extensive refurbishment it had to comply with the strict Building Regulations governing disproportionate collapse.
The survey and risk assessment identified the areas of masonry between the windows on all storeys and elevations as needing to be strengthened. The project engineers specified Helifix reinforcement products and the contractor then undertook the installation of some 1,500 linear metres of stainless steel HeliBars.
Every other mortar joint was channelled-out on each masonry panel before 7m long x 8mm diameter HeliBars were bonded into the cut slots with high performance HeliBond cementitious grout. The HeliBars were overlapped by 500mm to ensure continuous reinforcement within the brickwork.
The fully concealed HeliBars provide non-disruptive masonry reinforcement while still being flexible enough to accommodate normal building movement and with no visible disturbance to the original fabric.
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