Presentation Overview
To request a copy of the PowerPoint slides, please contact media@westmorlandandfurness.gov.uk
Background to half-joint bridges, Brigsteer and Underbarrow
Brigsteer and Underbarrow are reinforced concrete post-tensioned half-joint bridges built between 1970 and 1971.
Half-joint bridges were introduced into bridge decks as a way of simplifying design and construction operations. A central span rests on L shaped joints. This form of joint is to inspect, leading to concerns about their condition. There is worldwide concern about bridges of this construction type.
Half-joint bridges gone wrong
A recent example of a catastrophic failure of a half-joint bridge was De la Concorde Overpass in Laval, Canada, where the authorities failed to close the road over the bridge to traffic following structural concerns.
As a result 5 people lost their lives and six other people were seriously injured.
Our assessment process
In Westmorland and Furness, there are five half-joint bridges. All have been inspected biennially since construction.
In 2020 the authority commenced a programme of half-joint assessments following the introduction of National Standard CS 466 ‘Risk management and structural assessment of concrete half-joint deck structures’. A contract was let to assess Brigsteer and Underbarrow in 2022.
The risk management and assessments process includes six parts:
- Initial Review
- Risk assessment for structural assessment
- Structural Review
- Structural Assessment
- Risk assessment for Management
- Management Plan.
Following receipt of the structural assessments of half-joints of Brigsteer and Underbarrow bridges, the council instructed Jacobs to undertake a review of the bridges in accordance with National Standard CS470 ‘Management of sub-standard highway structures.’ This resulted in the two bridges being classed as ‘Immediate Risk Structures.
The decision to close both bridges was unavoidable for the safety of all road users.
Nothing in our past maintenance regime is likely to have prevented the need to close these bridges. The structural concerns relate to the design of the bridge, not their maintenance.
In 2022 we also commenced the process to check the post-tensioning in accordance with National Standard CS 465 ‘Management of post-tensioned bridges.’ To date we have not undertaken intrusive investigations of the post-tensioning, typically this would follow on from a PTSI inspection, as a further commission.
Key findings from Jacobs Assessment/Report
Brigsteer and Underbarrow bridges have sustained unrestricted highway loading over a period in excess of 50 years.
The CS 470 report recommended that, to reduce the risk posed by the half-joints both Brigsteer and Underbarrow bridges should be closed to all traffic (i.e. eliminate all live loads on the bridge) and that the half-joints should be monitored.
This includes preventing their use by pedestrians, cyclists, equestrians and vehicles.
Taking into account the condition of the bridges and with monitoring in place, the report recommended that the A591 can safely remain open whilst a more sophisticated assessment, with intrusive works, is undertaken.
The report is now available to access on our ‘Brigsteer and Underbarrow bridge closures, Kendal’ webpage.
Improvements to the diversion route
The diversion routes were risk assessed before the closure and are found to be safe. They are the most suitable option in the area for the traffic that is diverted from the bridges. It avoids the narrowest lanes in and around Brigsteer village and narrow points between Brigsteer and Levens.
Care operators and emergency services have been informed and are still able to access all villages and support residents in need.
A second risk assessment has been conducted where our Traffic Team have identified the following improvements that are being made:
- Replacing damaged or faded signage – signs have been ordered and will be erected in the next two to three weeks
- Laying new road markings – the programme is currently being confirmed
- Clearing vegetation on the verges where necessary to improve visibility – our contractor has started works to clear the verges to improve visibility.
We are also in the process of assessing the diversion route and how they can be maintained through winter as a part of our gritting programme.
The team is open to feedback on the diversion route that has been chosen. If residents know of an alternative route, please complete our highways enquiry form on the council’s website or call the Highways Hotline on 0300 373 3300.
Our short term plan
Our two short-term objectives are to:
- Restore links across the A591 at the bridge sites
- Minimise disruption to the A591
The Council has commissioned a consulting engineer to undertake a peer review (second opinion) on the findings of Jacobs assessment. WSP are world leading in half-joint and post-tensioned bridge assessments and have led on the production of the relevant National Standards referred to previously.
The Council are also appointing a specialist to project manage and conduct an options and feasibility study that will confirm the best short-term solution for restoring the link across the bridges.
The study will include structural assessment, highway layouts and tie-ins, outline designs of temporary works, impact on public utility apparatus, cost plans and programming.
Possible short term solution options are:
- Propping the bridge at half-joint locations.
- Demolition and installation of temporary bridges.
- Propping the current bridges and installing temporary bridges.
- Support the structure from above the bridge.
- More sophisticated analysis of the bridges.
Timeline
A Traffic Regulation Order is in place on both bridges for 18 months until 2026 and is the standard duration one can be in place. This is not confirmation of the length of closure which has not yet been determined.
The Peer Review by WSP is anticipated to be complete by early August 2024.
We have been in discussion with a consulting engineer to act as Lead Consultant who will be responsible for project management and feasibility assessments of chosen options. Once formally appointed, we anticipate the process for confirming a solution will take around three months.
Keeping residents updated
All the latest information on the closures can be found on our dedicated ‘Brigsteer and Underbarrow bridge closures’ webpage on westmorlandandfurness.gov.uk.
We will:
- Set up a monthly email newsletter - first issue planned for Friday 26 July 2024
- Share updates across the Westmorland and Furness social media pages
- Provide updates in the community via the local Parish and Town Councils.
Question and answer session
Safety of the A591
By acting on the findings and recommendations in the specialist report, including removing all applied load from the bridges, the safety of the A591 is not compromised and can remain open at this time.
People sighted walking on the A591
We have publicised alternative pedestrian routes which avoids the public right of way over the A591.
We are aware people are still using this route and to warn of this, we are erecting permanent signage to encourage road users to slow down.
Unfortunately much of the temporary signage encouraging use of alternative, safe pedestrian routes has been severely vandalised. Permanent signage will be erected in appropriate places in due course and we will promote them via our council channels.
An option of a roundabout
The possibility of a roundabout is a long term solution we will explore.
Our two short-term objectives are to:
- Restore links across the A591 at the bridge sites
- Minimise disruption to the A591
To do so, we are exploring the following possible options for a short term solution, amongst others:
- Propping the bridge at half-joint locations.
- Demolition and installation of temporary bridges.
- Propping the current bridges and installing temporary bridges.
- Support the structure from above the bridge.
- More sophisticated analysis of the bridges.
Accountability of the Councils project team
The assessment work undertaken by Jacobs was subject to a Category 3 check in accordance with National Standard CG 300 Technical Approval of Highway Structures, this included an independent check by another consulting engineer.
Because the structures are post tension, we have to commission an external specialist consultant to assess these bridges. Council-employed bridge engineers involved in the project are professionally qualified with up to 40 years experience in the construction industry. They keep senior officers informed of any important developments in their work.
Reports of dangerous driving on the diversion route
It is Cumbria Police’s jurisdiction to enforce excessive speeds and dangerous driving which we will work with them to explore potential solutions for this.
The Council will explore the option of introducing temporary lower speed limits and adding additional signage on parts of the diversion route to promote road users to drive slower.
Improvements to surrounding roads to relieve pressure on the diversion
The chosen diversion route has been risk assessed and has been found to be the most appropriate and safe route.
We are aware of roads, like Whetstone Lane, that those with local knowledge choose as their route, but we have deliberately chosen not to include as a part of the signed diversion as they is not currently suitable.
We will explore improvements options for surrounding roads.
Diversion times increased due to Kendal utility works
We will take this away and explore options to reduce the impact utility works are having on the diversion routes.
Emergency Service access to impacted villages
Care operators and emergency services have been informed of the official (and unofficial) diversion route and have this in their control rooms.
They are all still able to access the villages and support residents in need.
Following the claim an Ambulance did not follow the diversion and ended up at the bridge site unable to cross, we will recontact affected services and ensure they are aware of the route they need to follow.
Delivery of signage and concrete barriers
Officers involved in erecting the signage and laying concrete barriers at the closure sites followed the signed diversions and did not attempt to cross the unsafe structure as advised by the specialist report.
Quality of improvements to the diversion route
We have commissioned works to replace damaged or faded signs, laying road markings and clearing vegetation on verges where necessary to improve visibility.
Based on feedback raised regarding ‘low quality’ verge clearance works, we will follow up with out contractor to understand what has been delivered and how further improvements can be made.
We also recognise the skill set in the village regarding verge and hedge maintenance.
Traffic lights to reduce volume of road users on the bridges
The specialist report found structural concerns, requiring the Council to remove all applied load by closing the bridges to pedestrians, equestrians, cyclists and vehicles.
It is not possible to introduce traffic lights and allow any access to the bridges. This action would compromise the safety of those travelling over the bridges, and under on the A591.
European example of a solution used to make half-joint bridges safe
We are not aware of the solution used on a bridge of this type in Italy, or if it will be suitable for our half-joint, post-tension structures.
We are willing to hear from those that are aware of different options that we could explore as a part of options and feasibility study. To get in touch, please complete the highways online reporting form found at westmorlandandfurness.gov.uk.
Consideration of a ‘plan B’
Although we were aware of the potential issues associated with half-joint bridges in 2020, it’s important to think about this in a national perspective.
We have followed National Guidance when completing out six step process and we are confident in our decision based on the findings of the report. On receiving the outcome of the assessment we acted immediately.
If we use the example of National Highways, they have been going through the same process, and have been since the last three to four years. They have been reassessing their bridges and are closing and replacing their bridges where issues have been identified.
We have dealt with the information we have received and put solutions in place to prevent catastrophic failure of the structure.
Funding the short term and long term solutions
We have funding within our existing budgets to deliver short-term solutions that will hopefully allow us to restore links across the A591 at the bridge sites in the short term.
We do not have the funds to rebuild both bridges at this time.
Westmorland and Furness Highways have met with the Department for Transport Official to seek support for funding for a permanent solution,
Opportunity for improving diversion route road surfaces
We are exploring the option to bring forward and accelerate our planned works road improvement works in the area. Any improvements will need to consider appropriate traffic management to ensure road users can still pass through the route.
Impact on businesses and lack of support
We recognise the impact these closures are having on local businesses. The Council’s Economic Development Team were in touch on Monday 15 July 2024 and will work with them to conduct an impact assessment.
Quick installation of temporary bridges for events
Event bridges that run over a road will have been designed well in advance of the event. We are looking at temporary bridges as a part of our options study that will take three to six months to complete.
Propping the bridge span using the space in the A591 central reservation
This is a complicated option due to the position of the half joints and the back spans that are post tensioned. The post tensioning is a system of extended cables that are anchored between the back of the abutments and tip of the cantilevers, which puts the top fibres of the cantilevers into compression and assists in the support of the heavy infill beams that form the bridge deck.
In the interests of safety and to allow an appropriate solution to be implemented it is necessary to fully understand the condition and quality of construction of this system. This will require intrusive investigations.
Propping the central span at the central reserve may compromise the structural behaviour of the bridge, possibly leading to cracking in the top of the beams, leading to catastrophic failure. The options and feasibility study will consider this option, although it is thought unlikely to be viable.
Snow fall impacting safety
It was questioned as to why pedestrians are not allowed to cross the bridge, yet the weight of snow could be more onerous. It was explained that the pedestrian loading in the assessment is actually more onerous than snow loading.
In the event that there is a significant build-up of snow that causes any concern the authority would take steps to protect the public from potential overload of the bridge, albeit this is considered unlikely.
Invasive or visual assessment
Our consultants have undertaken some borescope surveys at the half-joints, although this was limited by filler material within the joints.
We have not yet conducted invasive investigations to determine the concrete grade or reinforcement arrangement, bar sizes and numbers of bars. This is likely to require some form of propping so that it can be undertaken safely.
The assessment philosophy adopted has been based on a lower bound theorem, using Strut and Tie models, which is considered to be safe. The assessment code refers to upperbound theorems but warns about the dangers of using them because they may not yield a safe result.
We have scrutinised the report and interrogated the consultants, we are confident in the recommendations made by them, however the peer review by should provide us with assurances and possibly highlight any areas for improvement.
Actions from the meeting
The Council will complete the following actions:
- The Economic Development Team has had telephone conversations, or left voicemails with those who attended the meeting. Other businesses have been contacted by email and will be followed up with a telephone call. Businesses are gathering information on the impacts of the closures and a joint workshop will be arranged in the coming weeks.
- Follow up with the North West Ambulance Service, Cumbria Fire and Rescue, Cumbria Police and care providers to ensure they are clear on the diversion route.
- Work with Cumbria Police to tackle reports of dangerous driving and speeding vehicles on the diversion route
- Review the verge maintenance work that has been conducted on the diversion route which has been reported to be inadequate
- Introduce signage, where possible, to promote safe pedestrian routes avoiding the A591
- Explore the option of improving passing places and verge vegetation on surrounding roads
- Set up reoccurring meeting with local, impacted Parish and Town Councils
- Set up ‘Brigsteer and Underbarrow Bridge Closures’ mailing list for attendees who provided their email address and a newsletter every month starting on Friday 26 July.