The complex scaffolding works to provide access to the entire bridge is progressing well with follow on works continuing all three spans.
Encapsulation has now been completed to both the North & South Spans with the Centre Span following on shortly. This encapsulation allows us to manage the correct climatic controls for application of the new protective coatings to the bridge. With the bridge encapsulated we will be able to control temperature, relative humidity, and other atmospheric conditions.
There is approximately 300km of scaffold tube, 75000 scaffold clips and 18000 13ft scaffold boards used on the bridge.
The Condition Led repairs, as their name suggests, are repairs to steelwork members that are in poor condition. We are currently repairing, and in some cases replacing these. As these steel members and connections transfer the load from the vehicles and people passing above, they must be removed and replaced in a particular sequence to ensure the stability of the bridge is maintained and that adjacent steel members do not become overloaded.
The condition led repairs are not isolated to any particular type of member, instead there are repairs required to bracing members, springing columns, longitudinal girders, and the main arch girders. Many of the defects are unique, therefore bespoke designs are being developed to resolve them.
As the bridge is a web of steelwork members and scaffolding, transporting heavy steel to and from each location is the greatest challenge.
Image to left: Condition Led Steelwork Repairs on the Springing Columns
Concrete Bridge Deck
Following completion of the testing on the existing bridge deck we have developed a repair methodology and a sequence for undertaking the same.
Large areas of the underside of the concrete deck have delaminated with concrete spalling off. This is primarily due to the ingress of water and through a process known as carbonation. Large sections of the underside of the underside of the deck will be removed using hydro demolition and the defective concrete replaced.
As we are breaking out large sections of the reinforced concrete bridge-deck from below, we need to remove the loading from vehicles above. Traffic management will be used to remove the vehicle loads – we cover the specifics of traffic management further on in this update.
Image to right: This photograph shows an area of the deck where investigations were carried out to develop the repair methodology.
Cast Iron Façade Works
The process to remove the existing façade has commenced under the guidance of specialists in this field.
This is an extremely complex process as the façade is made up of hundreds of individual components which have been installed and fixed together with hidden fixings to enhance the appearance of the structure. This, coupled with the fact that we are only removing partial sections of the cast, means these works have involved considerable thought to ensure the temporary stability of the remaining facade is maintained.
Once all the defective facade is removed, the process of recasting replacements will take place.
Grit Blasting & Painting Preparations
The purpose of the grit blasting is to efficiently remove any existing coatings and surface corrosion from the current steel and cast iron and to provide a roughened surface for the new paint to properly adhere. The grit blasting process involves mixing an abrasive material (Grit) with compressed air and projecting it towards the painted surface.
Over the past few months we have been mobilising the equipment required to undertake this blasting and painting operation and positioning this below the North Bridge at New Street Car Park.
From New Street Car Park, we are installing the blast hoses and waste lines to convey the new, and recover the spent grit, to and from the working face on the North Bridge.
We have also undertaken a trial to ensure that the proposed grit blasting equipment can remove the existing coatings. Grit Blasting and painting will commence in February 2020 and continue for approximately 14 months.
We have undertaken paint trials on the bridge to ensure that we are restoring the colour of the bridge back to its previous appearance.
You can see from the photo above that the existing colours have faded significantly since last painted in the early 1990’s.
Traffic Management & Roadworks on the North Bridge
Commencing on 17 February 2020 Balfour Beatty will implement traffic management on North Bridge. The traffic management will change and develop through 9 phases over a minimum 16-month period.
Each of the 9 phases will be split into works above and works below deck. Phase 1 will last a minimum of 10 weeks. Whilst the works are taking place below the deck, there will be weight restrictions within the traffic management enclosure so you may notice only minimal activity at road level.
The layout and location of the first phase of the works is indicated below. This is phase 1 of 9.
The traffic management will reduce the number of traffic lanes in each direction from the current two down to one. A pedestrian footpath in each direction will be maintained, however the width will be reduced to facilitate the works.
Bus stops will be removed from the bridge to ensure stopping buses do not cause a restriction to traffic flow – changes will be advertised locally at the current bus stops.
More information will follow in future updates.