PARS installation: reducing collateral damage risk and improving safety whilst saving costs on parapet strengthening
Parapet strengthening of Bishopsford Bridge in the London Borough of Merton
Bishopsford Bridge parapet already had a sufficient mass to give it the required level of vehicular containment. The problem, however, was that vehicle impact could spray debris onto the adjacent pavement and injure or kill pedestrians. We therefore designed the PARS System to significantly reduce the risk of flying debris. The System was designed to meet the requirements of the Department for Transport.
Working from the inside – cheaper, quicker and safer
Working on the exterior face of a bridge is logistically difficult and is generally what makes any remedial work very expensive due to the likelihood of needing possessions or of road, rail or waterway closures and often complicated and costly scaffolding access.
The PARS parapet strengthening work is undertaken safely from the bridge deck and therefore during the installation ensures no risk to trains, vehicles or boats below. Our video shows our specially designed prototype safety gantry which allows the work to proceed whilst protecting the workforce and the area below the bridge from falling debris or tools. This gantry can be easily and rapidly installed, moved along the parapet and removed. The cost savings of this method are thus significant.
We invited members of LoBEG (London Bridges Engineering Group) as well as engineers from Network Rail to view the installation process and finished product of our PARS parapet strengthening System at Bishopsford Road Bridge.
The contract for Merton allowed us to analyse the project costs accurately. Excluding the traffic management costs the contract work for the single parapet strengthening took less than two weeks of steady work to complete and cost approximately £1,360 excluding VAT per linear metre.
Bishopsford Road Bridge built in 1882
TFL recognises the importance of maintaining all parts of the historic bridge stock and instructed Goldhawk to undertake the rehabilitation and strengthening of the bridge parapet.
Rebar installation in progress
Horizontal slots are cut into the face of the parapet every two courses and twin HeliBars are installed as shown.
Installing the Helifix CemTies
Hooked CemTies are then installed to form a mechanical connection with the longitudinal reinforcement.
Encapsulating the reinforcement
After the HeliBar and CemTie reinforcing system is installed, it is encapsulated in MARFLEX, a solvent free thixotropic epoxy/urethane resin that bonds it to the masonry.
The MARFLEX is over-pointed with lime mortar to provide a matching finish to the parapet.
Prototype mobile scaffold access to the top of the parapet
An innovative prototype mobile scaffolding platform is used to work above the parapet whilst demonstrating and maintaining safe operation of potential rail, road and access to vehicles, trains, boats the public below.
The bespoke twin length sock anchors are grouted in in two distinct operations. The first to anchor the bottom section. This will allow the anchor to be tensioned to compress the brickwork. The second injection to grout the tensioned anchor fully into the parapet.
Injecting the grout
Helifix SockFix high capacity anchors were installed at pre-defined centres and pressure grouted into the parapet.
The Helifix SockFix Anchor being tensioned
The SockFix anchor is tensioned to a predetermined load to vertically compress the masonry of the parapet.
Careful finishing of the SockFix Anchor installation
The SockFix anchor installation is neatly pointed to leave a neat appearance to the masonry and maintain the bridge’s aesthetic appeal.
Members of LoBEG and Network Rail viewing the installation works. The photo shows Dave Kitching, our MD, giving a talk on the installation.