How to Stabilise Existing Structures during Temporary Works

A growing use for Helifix masonry repair and reinforcement systems is to stabilise existing buildings during a new construction phase, enabling major structural works to be undertaken safely and cost-effectively.

There are a wide variety of situations for which Helifix can provide structural stabilisation. Some of the more common temporary requirements are:

• To allow the removal and replacement of significant structural elements
• To reinforce against heavy drilling or piling vibrations
• To allow the creation of new openings and reduce the loadings on other elements
• To open up work space by reducing or eliminating the need for traditional temporary mechanical props
• To reinforce party walls during demolition and development of neighbouring properties

Unlike traditional masonry repairs where Helifix products are installed to provide a permanent structural solution, here, once the construction work is complete the function of the Helifix system is typically superseded. However, the products still remain in place, are fully concealed and continue to provide additional structural support.

The benefits of using Helifix during temporary works are best illustrated through case studies. In the following projects, Helifix engineers have designed solutions that quickly, easily and economically overcome difficult temporary situations which could otherwise have proven dangerous, time consuming and costly to the planned developments.

BRISTOL

A project in Bristol involved the conversion of a five storey town house into self-contained flats with access being provided by a new stair tower to be constructed at the rear of the property. This meant that new doorway openings had to be created at each floor level and window openings had to be relocated.

The initial proposal had been to use traditional needle and prop methods to support the rear elevation during the conversion work but the main contractor, the design team and the project H&S officer, all had strong concerns about the overall stability of the rear elevation. Constructed from random rubble-filled stone walls, its height and thickness equated to a massive load that could become potentially unstable during the creation of the new openings. Also, due to the height at which the openings were to be created, the only available support for the props would be from the scaffold which was not designed to withstand such loading.

Helifix engineers devised a scheme to stabilise the stone walls and improve the load distribution around the position of the openings. Grouted CemTies were installed through the masonry to consolidate the rubble-filled walls above and around each opening position and the elevation was also tied into the internal cross walls to increase lateral support and stability. Lengths of twin HeliBars were bonded into the mortar beds across the entire elevation at all levels, both externally and internally, to tie the stone construction laterally and to assist the temporary props. To provide continuity of HeliBars, existing window openings were blocked and the reinforcement was continued though the blockwork.

Having overcome concerns regarding structural stability, the Helifix system enabled the conversion works to go ahead safely and on schedule, remaining concealed and in situ to assist with long term structural stability.

LLANELLI

Llanelly House, a 300 year old domestic building in Llanelli was to be completely restored and turned into a Genealogy Heritage Centre. This required the repair of a large timber beam, running above the shop front window and door on the front elevation, which provided support for two storeys of 650mm thick rubble-filled wall above. It was in very poor condition and large sections of decaying timber needed to be removed.

To secure the wall and provide support, pairs of stainless steel HeliBars were bonded into the masonry at two levels above the timber beam, both internally and externally, to form a deep masonry beam using the existing brickwork. Within the area of the Helibeam the rubble-filled wall was consolidated by cross pinning with fully grouted CemTies in a lattice arrangement.

The Helifix system reinforced and stabilised the masonry, working in conjunction with traditional temporary support props to carry the load of the two storey structure and enabling the safe removal of decayed timber and the reconstruction of the beam.

LIVERPOOL

 

A number of dilapidated Victorian three storey buildings in Williamson Square were to be demolished to make way for new retail units.

A laser survey identified that the adjacent concrete frame building, constructed in the 1970’s, had been built into the gable end of the properties to be demolished.

The survey and site investigations showed that the gable end comprised two adjacent 9” walls, now forming one party wall. Helifix devised a solution comprising grouted CemTies and SockFix grouted sock anchors to retain this wall, cost-effectively and reliably tying the two leaves together and securing it to the adjacent property.

Approximately 1,000 8mm stainless steel CemTies of varying lengths, bonded with HeliBond cementitious grout, were installed in the gable end in a 450mm x 450mm staggered formation.

Some 60 SockFix grouted anchors, 1,500mm long, were then installed at 600mm horizontal centres into the hollow concrete floor slab of the adjacent building at each floor level. As they were pumped full of grout the socks expanded into the voids of the floor slab, securing the retained gable wall to the main structure of the adjacent building allowing demolition to proceed without any major contract delays.

TROON

The collapse of a Victorian watercourse tunnel had caused major subsidence damage to the front elevation walls and party wall between  two terraced properties which, combined with a deep geological fissure, necessitated extensive traditional piling and excavation work. This operation was likely to cause vibration damage and potential destabilisation of the walls during the process.

To prevent this from happening, the Helibeam System was used to strengthen the walls to resist vibration and movement damage whilst at the same time address the major cracking that had been caused by the original subsidence. Mortar beds were channelled out at predetermined levels and stainless steel HeliBars were bonded into the slots with HeliBond cementitious grout. These formed deep masonry beams, using the existing masonry, which secured and reinforced the brickwork, stitched the cracks, provided restraint and spread the structural loads.

NEWCASTLE

 

A cinema, demolished some 10 years ago, shared a party wall with the adjacent public house. As this party wall had not been designed to be an exposed gable, steel shoring was erected to provide additional lateral restraint to support the wall. When the site was to be redeveloped with new offices, the steel shoring needed to be removed. To ensure that it was structurally safe to do so, various Helifix products were installed to fully secure the wall to the neighbouring structure.

BowTie HDs were installed across the full width of the wall into the upper storey floor and ceiling joists while BowTies were used to connect the brickwork gable rafters. Grouted CemTies were installed at the building’s corners to secure the delaminated gable end to the front and rear walls and ResiTies were used to connect the wall to internal cross walls. Once the stabilisation work was complete, the additional lateral restraint allowed the shoring to be safely removed leaving the site clear for re-development.

Contact us for further information on how our products can prevent structural damage, reduce propping requirements, open up work space and reduce cost during temporary works.