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Agenda item 2 is for the committee to continue its inquiry into the circumstances surrounding the closure of the Forth road bridge. We will hear this morning from independent bridge experts. I welcome John Evans, who is a consultant at Flint & Neill Ltd, Richard Fish, who is an independent engineering consultant, and Peter Hill, who is general manager and bridgemaster with the Humber Bridge Board. Good morning, gentlemen. We go straight to questions, with Alex Johnstone to kick-off.
Please correct me if I am wrong, but I understand that the panel members have expertise on the Humber, Tamar and Severn bridges. We have heard from experts from whom we previously took evidence that rather than follow Department of Transport recommendations, the Forth bridge took a risk-based approach to inspections that often resulted in the frequency of inspections being higher than would have been recommended. Can you explain to us what the frequency of inspections is at the Humber, Tamar and Severn bridges and whether you, too, have adopted a risk-based approach?
I will kick off. I believe that it is correct to say that the first very formal attempt at using a risk-based approach was done on the Severn bridge. In my opinion, the reason for that was largely commercial rather than its being purely an engineering reason. The Severn bridge was going to become part of the concession agreement for construction of the second crossing and operation and maintenance of both bridges throughout the concession period. You can imagine that the concessionaires were very interested in knowing, among other things, what kind of moneys and resource they would have to expend on inspecting and maintaining the new bridge that was under their control and the—by that time—40-year-old bridge that they were taking over to run, as well.
On timing, the approach came at the end of a series of contracts for strengthening and uprating the Severn bridge. That work was undertaken by our firm on behalf the Department for Transport and, originally, the then Highways Agency. For that reason, we were deemed to know as much about the structure as probably anybody would. It was part of my individual personal duty to develop the maintenance manual for the Severn bridge, which became volume 12—I think—of the concession agreement, so it was very much a contractual document.
To go back to your question, the concepts of vulnerability and criticality were built into that inspection regime and a number of different periods of inspection were allocated to different elements of the structure. They were based largely on engineering—in other words, what the structure would suffer in terms of stressing, straining, movement and so on. However, the inspection periods were also based on the experience of operating the bridge up to that point.
Have I answered your question sufficiently?
Yes, I think that we have got that answer.
10:45
I will extend that point with regard to matters on the Humber bridge.
Commercial aspects play a part, but there are also practicalities in relation to such huge structures. The risk-based approach makes it practical to ensure that we have a sustainable system for inspection that does not overload the organisation by demanding unnecessary resources or providing unnecessary data.
As the committee may be aware, the standard format for inspection includes two-yearly general inspections and six-yearly principal inspections. Those levels were set by the Department of Transport. They are set in general for owners of large stocks of bridges, but we are the owners of a large bridge at the Humber, rather than a large stock of bridges. We therefore also found that a risk-based approach is more appropriate through its looking at both the risk of failure of any element and the consequences of the failure.
In certain areas, such as the abutments, which take the load from the cables at either end and are big blocks of concrete, intensive inspection is perhaps not practical or sensible—in 10 years they will still be big blocks of concrete—whereas other more flexible elements on the bridge require greater monitoring and more frequent inspection. That is also why we have adopted a risk-based approach.
For the record, I no longer have direct responsibility for the Tamar bridge; sadly that ended in about 2008, when I left the public sector and moved into the private sector. Since that time I have developed my own business working in bridge management and bridge maintenance. I can give my answers to the question drawing on both my experience at Tamar and my more recent experience.
In the old days of the Tamar bridge, the frequency of inspections was just as Peter Hill has described—general inspections every two years and principal inspections every six years. The concept of risk-based inspections was first introduced at the time of the changes around the United Kingdom Bridges Board having developed a code of practice for highway structures. In the interim, the Tamar bridge has moved towards a risk-based approach.
It is important that inspections should not just be prescriptive. The risk in that is that you just end up ticking a lot of boxes—saying to yourself, “What bits do I have to look at today? Yes, I’ve done that. Tick, tick.” It is necessary to be more reactive to the behaviour of the bridge and how it is performing. If there are areas of concern—little hotspots—that you think need to be looked at more in detail, you would instinctively want to increase the inspection frequency. That has, at the same time, to be recorded and regulated.
That is the shift to a risk-based approach in which the idea is developed that some parts of the structures will not change over decades—as Peter Hill has described—whereas others may change over months and years, which is where inspections are targeted. That is a more efficient and—dare I say it?—safer way to approach inspection.
Mr Fish, could you explain for the benefit of laypeople—on the committee and elsewhere, watching our proceedings—what the difference is between general inspections and principal inspections?
Yes. As you might expect, a general inspection means—I hesitate to use the word “superficial”—that you have only to look at elements of the structure from a distance, although if you can get up close that is all to the good.
There are two issues around principal inspections. First, they should be carried out by a chartered civil or structural engineer. Secondly, every part of the bridge should be accessed within touching distance.
That is very helpful.
Big bridges, even if they have similar designs, are all unique structures. We are focusing on the truss end links, which have been shown to be the weak link in this case. I presume that each of the bridges that we have talked about has components that are similar to the truss end link. Is that the case?
I think that the Tamar bridge is the closest, in that it and the Forth bridge both have stiffening trusses, whereas the Severn and Humber bridges have aerofoil section boxes, which is a slightly different arrangement.
The Tamar bridge is very similar to the Forth bridge in that at the end of the trusses, where they arrive at the tower, there are vertical connections—pintles with the pins—that do the same job as on the Forth bridge.
Under the risk-based approach, how often would you expect critical components of the bridge to be inspected and how often would you inspect a component such as a truss end link?
As a general statement, I think that the pintles are perhaps the most overlooked part of a traditional truss-type suspension bridge. Everyone focuses on cables, hangers, towers and the steelwork of the trusses, but the pintles tend to get overlooked, which is not to say that they are not inspected. At Tamar, I have personally gone down and accessed them and checked for movement, but they are very difficult to inspect, especially because you are relying on the movement for articulation of the bridge.
I spoke to the bridge manager at Tamar the other day and he said that as soon as the news about Forth came out, the first thing that he went to look at was the pintles on Tamar.
At Humber, we have elements that move in the same way—they are not truss end links, but they are structural elements that rotate on a bearing point. We have very recently replaced them because they were inspected and found to have failed. However, the mechanism of failure was excessive wear, which becomes quite apparent over time. Even a general inspection—or a superficial inspection, which is more of a walk past—could identify that type of failure in the case of the Humber. However, such inspections would not identify whether an element had seized. With our pins, the bearings had formed an oval, rather than a circle, for the pin to move in due to wear, so it became visually apparent. That is perhaps the difference.
I am talking about the Humber but, coincidentally, I was talking to the bridge manager of the Tamar yesterday when we had one of our annual meetings of bridge managers. They have a similar issue with similar elements at the Tamar bridge, which is again being observed through wear.
Severn is slightly different again. During the assessment for the new loadings, it was discovered that the original end props from the 1960s design, which are much shorter with a shallower box, were overloaded for the new system. Part of the strengthening process involved replacing those props completely with bigger props that were more outboard. As part of the replacement process, we refurbished the inner ones and provided them with a jacking facility so that, in a planned operation, we could come back and jack again and inspect the outer ones more carefully; we could check the loads as well as making a visual inspection. For that reason, by 1990 the equivalent system on Severn had been completely renovated. The original problem was twofold: it was overloaded and there was wear.
There was wear rather than seizing.
Yes.
Are you aware of any examples of a similar mechanism seizing in any other bridge?
We had a little talk just before we came here; I think that the closest example that I can identify is some bridges in America that had a suspended middle span. They hung on links and I believe that there were problems with those. There was one catastrophic collapse. They were a family of bridges on an interstate road so they were all refurbished. It is possible that the M50 bridge is not dissimilar, but I have never worked on it so I do not know.
Do you know of any bridges where special inspection or monitoring techniques are used to check whether the pins are moving correctly? If so, what methods are used?
I do not know of any system that checks whether the pins are moving. There are systems that check the movement of the bridge by checking the whole link. As I think Richard Hornby told you, the forces that are involved are enormous, so there is more likely to be damage if there is a jammed pin. However, I do not know of anything that checks whether the pins are turning. As the committee has discovered, we cannot see the pins.
Is it an easy thing to check? I imagine that, although flexibility is essential in the element, the movement must be extremely small.
The rotation on the pin is a small movement. However, if that movement is not taking place, the structure will still move. As it moves, strains develop and material becomes stressed and potentially overstressed against its original designed loads.
I echo John Evans’s point: I am not aware of anything that can specifically detect movement—
In normal weather conditions, if we stood beside the pin and looked at it, there would not usually be much movement. Is that right?
It would be difficult to discern the movement visually.
What may well come out of all of this is that the people who do structural health monitoring and so on will devise something to help to detect movement, or the lack of it, but we would not want to sit in front of a pin all the time trying to see whether it is moving. I am sure that a remote sensor can be developed, but at present structural health monitoring—or, as I like to think of it, structural performance monitoring—is more geared to the performance of the whole structure, including how it is working and articulating and what the deflections are compared with the loads. We get a picture of everything that is going on, but small issues cannot be diagnosed with a global structural performance system.
As I think has been discussed, the movement of elements of the structure away from the pin bearing may be of the order of tens of millimetres, but once movement is transferred back to the pin mechanism, it is remarkably small. However, in the absence of that movement, the forces that are transmitted can be very large.
We installed a replacement system at the Humber that monitors the stresses not in the pin bearing but in adjacent materials, to ensure that we are not overloading the structure. However, we have not monitored the pin bearing.
The committee has inevitably focused a lot of attention on the truss end link member and the seizure of the pin. Given that you have all outlined the limitations of structural health monitoring, I ask you the question that I put last week to Barry Colford, who is a former bridgemaster of the Forth road bridge. Do you believe that the issue could have been foreseen?
I refer back to what was said at the start of the questions about a risk-based inspection. If we monitored every single element and joint, it is possible that a detailed analysis of the information from every point of the bridge could give some indication of some trouble in some part of the bridge, but that would be a huge exercise.
Suspension bridges have a web of elements; that is particularly the case with the Forth road bridge trusses. If the action of one part of the web was restrained or slightly different from what it was designed to do, it would be an enormous task to monitor that and to determine what the results might be.
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I am not sure whether that was a yes, a no or a maybe. [Laughter.] You can come back to that, if you like.
I am having difficulty in answering the question with a definitive yes or no. The amount of data mining that would be necessary to give the information that would point us to a specific element causing distress would require a very large team of people looking at the results 24 hours a day. That might be possible, but it is probably not practical or economically viable.
I put the same question to Mr Fish.
It is difficult to divorce hindsight from all this, because we know what happened and are trying to wind the clock back a couple of months to assess whether what happened could have been anticipated and avoided. The structural performance monitoring on the Forth bridge is mostly geared at the cables, but it also gives an indication of deflections in the main truss. That could have been used to describe what was going on with the articulation at the bridge. If the conclusion was that the pintles and the linkages were, as I described earlier, a potential hotspot for a problem, an inspection regime would say only that there was potentially an issue with the whole element; it would not necessarily conclude that a failure involving a fracture in the metal above the pin would be the outcome.
We can say with hindsight that that should have been examined and that some analysis should have been done to assess the loads in the end posts on the truss. However, as I said to my fellow witnesses before the meeting, the irony is that the Forth bridge is one of the most well-managed bridges in the whole United Kingdom. I have a huge regard for Barry Colford, who had such a thorough understanding of the bridge. It seems unlikely that something would be overlooked and I would have thought that, at the very least, those issues would have been addressed.
I am sorry that that, too, was not a yes or no answer.
My experience of this sort of thing is that, when the joints begin to jam up, there is usually evidence from noise, which is always what we look for. As far as I can tell from all that has been said here, there was no evidence of creaking or groaning. For those who do not know, if that kind of thing happens on a bridge structure, it resonates through the whole structure and there are very loud noises. As far as I know, there has been no report of that in this case.
If the pin jams up and there are internal stresses on the connection between the fabricated bit and the pin, we get no evidence of that. What happens is that an imperfection—I will not call it a defect—becomes overstressed and we can get a sudden failure, which transfers quickly across the weld line and into the material. My experience is that we would not find such a failure until it was there.
That is a fairly definitive no.
My question on structural health monitoring has been covered, but I will look at the issue from a different angle. It is fair to say that structural health monitoring is not a silver bullet that will solve every problem that occurs on the bridge. Some witnesses have already identified the fact that it is expensive to do that and that it can take up a lot of staff time. You could well have staff monitoring screens 24 hours a day, at a huge cost to the organisation. Is that a fair point?
I think that it is. We have to add one other factor, which is that the people who are looking at the data have to be experienced enough to understand what they are seeing.
I agree. The big issue with what is got out of structural health monitoring concerns the translation from data to information. People can get bombarded with millions and millions of bits of data, but they have to be interpreted.
The more recent developments in structural performance monitoring have led to what is called post-processing. The structure is modelled from the point of view of structural analysis, and what is happening on the bridge is compared with what the computer model says. As soon as there is a difference between what is happening on the bridge and what is happening in the computer model, the lights flash and the bells ring. That provides people with the information so that they do not necessarily have to go through vast amounts of data.
That approach is at an embryonic stage. A lot of bridges are putting on new structural performance monitoring, but the post-processing is needed to turn data into information.
That seems to make a lot of sense. That would be some form of exceptions warning.
Exactly.
As you know, the new bridge will have some of that. However, the new bridge will have up-to-date design and will probably not need structural performance monitoring to the same extent as the bridge that was built in 1964. In terms of best practice around the world, are you aware of bridges that have put in structural health monitoring because of particular problems?
A lot of retrofitting has gone on. As you intimated, it is easier to put a system into a new bridge, as it can be designed in from the outset. A lot of structures that are being built have built-in structural health monitoring systems and a lot of data collection. It is not quite so easy to retrofit older bridges, because we do not really know what has gone on in their history. Some elements will have moved because of creep or shrinkage, and applying a new system after such movements have taken place means that we will not necessarily be getting the full picture. A lot of retrofitting is going on, but people are still falling into the trap of having a vast amount of data and not necessarily a lot of information.
That is a good point.
I can only reiterate what has been said. On a new bridge, it is sensible and worth while to install equipment that is capable of monitoring the structure, even if we do not have 100 per cent credible methods for analysing that data at the moment. There is a risk from data mining that we collect data but no one knows what to do with it. However, undoubtedly, the picture is always improving.
Mr Evans’s point about abnormal noise was interesting. As a non-engineer, my view is that you can have all the structural health monitoring you want, but you should not forget about the day-to-day, commonsense approach, which involves considering noise and conducting visual inspections, too.
That is why we have a range of inspection protocols. Even though, as is the case for the big bridges, we generally do not subscribe to the fixed general inspection and the principal inspection, we still expect our inspectors to report unusual noises. Having a team that is dedicated to the structure, with people who know the structure inside and out—which was the case with Barry Colford’s team—is essential.
I will stick with you for my next question, Mr Hill. The committee has been told that the truss end links at the Humber bridge have recently been replaced. Will you describe when the problem was identified, what the problem was and when the work was completed?
Certainly. They were not truss end links; they were called A frames, which were torsional and rotational members on the Humber bridge—
I am sorry to interrupt but, for the layman and woman watching the meeting, and for committee members, will you explain the difference between the two elements?
Suspension bridges do not have conventional bearings. The loads are not transferred from the deck down to supports under the bridge; they are transferred up to the cables. Nevertheless, if the ends of the bridge were left free to rotate, they could twist in mid-air horizontally, vertically and laterally. There needs to be a restraint to stop those movements. Theoretically, those do not take vertical load, but in reality, they do, because they are structural elements. Those are the elements that we replaced at the Humber bridge. However, the truss end links on the Forth bridge were expected to take load and to restrain the bridge in the different directions.
Our replacement was for the A frames, as they were called. It was first identified that they were wearing in around 2005 or a little before that. That was identified because they had been moving and they had worn. Without getting too technical, I will say that the pins travelled through bushes, which were specially machined to allow the rotation. The pins were grooved to allow grease to be forced in to facilitate that rotation.
So that we are clear, were the pins on the Humber bridge visible so that you could detect the issue with a visual inspection?
The ends of the pins could be made visible. They had cover plates, but we could remove them to see the pins. However, we still would not have detected any rotation by sitting looking at them, because it is microscopic.
It was subsequently found that the pins had locked into the bushes, which was perhaps a similar form of failure to that on the Forth bridge. The bushes themselves had then rotated within the A frames, which caused wear that became visible. That was the indication of the failure.
Was that picked up at one of the standard inspections or was it picked up because of an exceptional issue on the bridge?
The failure did not cause a significant issue for the bridge’s serviceability or operation. The visible wearing of the hole and the dropping of the A frame structure were picked up through inspection.
That is helpful.
I turn to Mr Fish and Mr Evans. Has similar work been carried out at the Tamar and Severn bridges?
The Tamar bridge went through quite an elaborate strengthening and widening project in the late 1990s and early 2000s. That involved a lot of work with supplementary cables and replacing a concrete deck with a steel orthotropic plate. During that process, the analysis looked at the existing linkages—the pintles—and it was deemed that no work was required. That work was a major milestone in the history of the Tamar bridge and, if other work had been needed, it would have been done at that point. Nothing has been done subsequent to that.
I touched on what was done at the Severn bridge. To follow the train of thought, the structural analysis indicated that the inner links would be overstressed under the new loadings. That meant that we designed the outer links to a new standard, so we did not suffer problems, but when we took them apart, we found wear in the bushes.
I am not absolutely sure about this, but I think that they were a kind of self-lubricating bush—I think that it is called sintered bronze. The bushes were definitely wearing.
11:15
Based on their engineering experience, would the witnesses like to make any comments on the specific failure on the Forth road bridge?
As I said earlier, I suspect that the failure happened between the two inspections—the inspection in May and the inspection when it was picked up, in early December. Because of the nature of steel, when an imperfection starts to grow, it grows very quickly.
I support what John Evans just said. Another point to remember is that, when the steel for the Forth bridge was being fabricated, steel quality was not of the same quality as it is now. The Tamar bridge was finished a bit earlier—it was finished in 1961—and the Forth bridge was finished in 1964. When we did the recent work on the Tamar bridge, we could see that the quality of the existing steel was mixed. There were some areas where there were a lot of impurities—holes and thin blowpipes—in the steel. The quality of the steel cannot be guaranteed. I am not saying that that was a factor, but it should be recognised that, in the 1960s, steel quality was not the same as it is now.
In simple terms, will you explain why there has been such a change in steel quality since the 1960s?
I think that that is largely because the industry was being built up in the post-war period. Levels of quality control increased through the 1970s and the 1980s. There was a demand for steel after the war, and it was perhaps more important to produce quantity than it was to produce quality.
Is that not necessarily just a UK thing? I know that a lot of the steel for the new Forth crossing is from China.
Yes—do not get me started on Chinese steel.
We are building a bridge with it.
On the basis of that, we could certainly have done with more domestic steel being used.
That probably falls outwith the remit of our present inquiry, although it would be an interesting diversion.
I agree that such a failure—if it happened in the way that I believe that it did—would occur very quickly, particularly in a material of unknown quality.
Do you echo Mr Fish’s comments about variable steel quality?
That was certainly the case in the past in the UK, but we believe that even the Chinese steel is now manufactured to a much better standard than was perhaps the case in the past.
I do not want to get told off by the convener for pursuing a steel inquiry, so I will leave it there.
I will talk about the response to the failure. As Mr Evans pointed out, the truss end link was seen to have failed on 1 December. The bridge was closed and it reopened to all traffic except heavy goods vehicles on 22 December. Was that a reasonable length of time to take to carry out the emergency work? From what you know about the repair work, was the solution appropriate?
I am absolutely confident that the work was a remarkable achievement. I have come into this only since the event, and I have been following what has been going on. The fact that all 16 end links were dealt with in that time, in difficult conditions in the middle of winter in the middle of the Forth, given the problems with the old steel that we have discussed, makes it a remarkable achievement.
Do you think that an appropriate solution was engineered?
Yes. One of my disciplines is welding and I would have been nervous about welding on the steels involved. We have discussed their age and quality. I might have gone for a bolted solution, but the people involved appear to have achieved what they set out to do.
I echo John Evans’s comments entirely. We were sent some outline drawings of the solution, which I thought was innovative, practical and easy to build. The time that it has taken has been exemplary. I have absolutely no criticism of the outcome or the time taken to deliver it.
This needs to be tempered by the fact that the solution may not prove to be permanent—I do not know. However, the team working on the problem seems to have come up with an excellent solution and installed it promptly. I was certainly impressed.
Thank you for those observations. Has any of you ever closed a bridge that you were responsible for—the Humber, the Tamar or the Severn—to all traffic?
About 12 hours ago, actually. [Laughter.] Due to the high winds on Monday night, I was on the Humber bridge at half past 10 with a full closure in place. That was not for a structural issue, though; it was because, unfortunately, a vehicle had overturned.
Yes, for operational reasons I have had to close a bridge. However, that has not been for structural reasons; it has been because of suicide incidents, or vehicles turning over or breaking down.
My experience is that we managed to strengthen the whole of the Severn crossing—not just the Severn but the Wye bridge—with only two four-hour complete closures in the middle of one night. We, too, have had wind incidents.
The committee will be aware of the time when the Erskine bridge was hit by an oil rig. I spent the next six weeks on site with emergency repairs. For the first week, we had to close the bridge until we were satisfied that we were not going to get a complete failure—a catastrophic collapse of the structure. That led to all the difficulties of controlling the traffic. You might remember that that went on for quite a few months.
Yes, I remember that.
Therefore, in summary, a closure such as the one on the Forth road bridge would be a very rare event. It begs the question whether, in your opinion, it could have been foreseen and prevented.
As we have discussed, I do not think that it was possible to have foreseen the particular failure. However, the idea of having contingency measures in place for when something catastrophic happens might be looked at in future. The obvious thing straight away was to stop the heavies, because it is very difficult to control heavy goods. They tend to go in gaggles, which is the very thing that we do not want on the loading of bridges. Pre-planned diversion routes and that kind of thing are not uncommon these days. They lessen the impact, but they would not have prevented the problem.
There is a cause-and-effect issue here. As we discussed, the cause would have been very difficult to predict, and the effect—the closure of the bridge—is a decision that was not taken lightly.
The safety of the travelling public is absolutely paramount. I would not question the decision made by the engineers who were at the sharp end and faced with the issue. I do not have the evidence to ask, “Could the bridge have been kept open with just two lanes running instead of four?” I do not know. However, a decision had to be taken around public safety.
I can only say that, knowing the competencies of Barry Colford’s team, I cannot see that the incident could have been predicted or determined in any other practical way. The subsequent action of the team that reacted to the emergency and is currently looking after the bridge seems to have been entirely appropriate.
Thank you, gentlemen.
I turn to consideration of future maintenance, repair and strengthening works. Are there lessons to be learned elsewhere from the experience on the Forth?
We have a strong, international community that shares information, and most of our maintenance programmes are based on information that is shared around the world.
I believe that the Forth bridge had a type of forward maintenance plan similar to ours. I have a 60-year major maintenance programme, which is informed by the experience of similar structures throughout the world. Of course, 60 years is an impossible time to look ahead at maintenance. The intention is to ensure that we identify the areas of risk and the elements that we know have had to be maintained on similar structures around the world and to ensure that they are in the programme to be addressed at an appropriate time.
The key point is linking the inspections to the maintenance, so that you determine when to intervene.
This is not a strict comparison, but let us compare the Forth bridge to a formula 1 car. The ideal for a formula 1 car is that, as soon as it crosses the finishing line, all the components fail. That is the design life and that is what is intended for such a car. Every component of a formula 1 car is given a design life, and structures and bridges are exactly the same—except that you want to have some sort of contingency and reassurance.
You can look at the results of inspections and structural performance monitoring and come up with a regime of maintenance intervention. It might say that, at this point, it would be sensible to replace cable band bolts because you do not want them to fail—I give that example because I know that that has been done on the Forth bridge. There is an intervention point somewhere ahead of failure.
On lessons to be learned, there is an international suspension bridge conference this June and I hope that the lessons of the Forth bridge will be able to be learned at that. I assume that that is down to Transport Scotland and whether it is willing to release the information. There are only four big suspension bridges in the UK, but there may be about 400 in the United States and around the world. It is vital for those owners to learn lessons from the Forth, as well as for those of us in the UK.
The one lesson that I would take from the events is that the end links are an element for which one could provide an alternative load path, as we did on the Severn bridge. We did it on Severn for a different reason, and we were lucky to be able to do it. It might be an idea to have in mind a way of dealing with the failure of any one link.
Thank you.
Good morning. I want to ask about the capital planning for the bridge and how you capital plan in your areas. We have heard certain terms during evidence to the committee: the engineers mentioned a wish list that they always had, the Forth Estuary Transport Authority provided an indicative capital plan, and there are also committed projects at any one time. Can you shed some light on those terms and tell us your understanding of them? How long do you have a capital plan in place for your bridges?
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I know that Barry Colford would not refer to such a plan as a wish list. We all recognise that there are financial constraints on maintenance. We do not have an infinite pot, but we need to look to the future and identify projects that may or may not, subject to inspection, require to be undertaken.
My maintenance plan is over 60 years. The plan for the Humber bridge has such a long extent because we are still working to repay the capital debt for its construction, which has around 30 years to run, and I was looking at a programme of maintenance to at least double that timescale. That is why I am working on 60 years.
A more reasonable return period from maintenance for a structure without that kind of constraint is probably around 20 years. It is still impossible to look into the future for 20 years to determine what will be necessary. However, it is important for operational and serviceability reasons—to keep the bridge safe and fit for purpose—to ensure that we are aware of the projects that are likely to become necessary to at least consider based on experience from the global community. It is also important to plan appropriately for those projects to ensure that we do not end up with a huge amount of work all to do in one year but that we are able to space it out and to plan for the financial outlay that is necessary for it.
At the Tamar bridge, we used to work to horizons of five, 10 and 15 years, but that was fluid because, if an issue was discovered during an inspection, the programme had to change.
It is broadly possible to separate work into essential and desirable projects. Some interventions can be put off. The obvious one is painting. If we put a painting scheme off for two, three or five years, the bridge will not collapse but the intervention that we will have to make at the future point is likely to be more expensive, so there is a fine balancing act between setting the priorities and determining the most efficient way of managing and maintaining the bridge.
Smaller structures are treated as a bridge stock rather than individual bridges but, for every structure of any size, it is necessary to have a long-term capital plan. It would have to be fairly fluid and linked to the optimum time for maintenance interventions.
That is how the budget would be planned. The big question, which is clearly as much a political one as an engineering one, is whether the budget drives the maintenance or the maintenance drives the budget. I know which way round I would want it to be, but I am in the real world as well.
My experience is slightly different. I cannot tell what happened with the Severn bridge between the end of the construction in 1966 and when the strengthening started in the 1980s. It was in the hands of a local authority during that period, and I do not know how the authority budgeted. However, the strengthening works were all costed. They were done through competitive tendering, so the funds were provided by Government.
Once the bridge moved into the concession period, there was another set of considerations. The key consideration that Clare Adamson is talking about is that, at the end of the concession period, whenever that is—it is either temporal or financial—the bridge is to be handed back to the owner, which is the Government, in the condition that it was intended to be in. Therefore, it starts its life again.
Whoever takes over after that—we do not know at the moment who that will be—will have to have some financial plan and budget. There will be the usual financial constraints on that, but I hope that they will know more clearly what they will have to allow for in the way of inspection and maintenance.
In terms of your annual budget for running the bridges, do you have any capital reserves or contingency funds in case the unforeseen happens? Can you give me an idea of the level of those reserves in an annual budget?
There were always reserves for contingencies with the Tamar maintenance budgets. I cannot recall what the level was as a proportion, but there would effectively be a revenue budget for the operation and management of the structure, and there would be a capital budget for planned maintenance. There would also need to be a budget for reactive maintenance. That may have been taken from the reserves, or it may have been at the expense of other planned maintenance. However, I am afraid that I do not know the detail about the level of the reserves in proportion to the overall budget.
At the Humber we hold a small reserve. Generally, that is incorporated within our major maintenance fund. Many of the projects on a bridge the size of the Humber bridge are big projects, just because of the size of the bridge. They cost significantly more than what we can collect in any one year.
We have a maintenance fund, which we build up in consideration of the major maintenance programme, so that it can be expended at the appropriate time. If any contingent works need undertaking, we will often take what is required from that fund and we will then increase payments over subsequent years to get back up to the level that we need for future projects.
What do you understand as the difference between work that is essential to maintain the long-term integrity of the bridge and safety-critical work? What would have happened if the work had been identified as safety critical?
The term “safety critical” is quite unusual. I would recognise safety as being one of the paramount elements that we consider in prioritising works. In any risk-based assessment, we obviously consider the risk and the consequences of failure, including the financial and operational consequences and the consequences of any failure for safety. That would help to prioritise work at the bridge.
I am not party to the concessionaires’ shareholdings, but I suspect that they are big enough not to specifically identify reserves. They will be big enough to provide anything that is necessary to meet their commercial obligations.
On long-term capital planning, was it reasonable to review the non-committed projects in light of the decision to build the new Forth crossing?
I say yes.
Knowing a little bit of the history around both the new and the old Forth road bridges, I would say that you had to consider the two in the round. The similarities with the Severn are fairly strong. There was an existing bridge, and a new one was built alongside it, although the process through which the project here is being delivered is very different.
You must take a couple of steps back and consider the future transport links across the Forth. You cannot separate the two.
I ought to clarify—and Richard Fish may not know this—that the strengthening of the Severn bridge was decided on before the second crossing was on the cards. The bridge was the only link at the time.
From a public governance of funding perspective, I am sure that it would be appropriate to consider the maintenance of one structure with an adjacent new structure. However, I would not like to say that that was actually done—basically, I do not know.
Finally, as a result of the review that it undertook, FETA identified a trial repair to the bit of the truss end link that it was worried about, which is not the bit that broke and closed the bridge. Have you been able to look at that repair and identify that that approach is a reasonable repair strategy for the future of the truss end links at that point?
Personally, I have very limited knowledge about that. I am aware of what was undertaken, but I do not know enough about the mechanism of loads there to comment on it.
I have seen the copies of the original drawing, so I understand how it worked, but I do not know anything about what was proposed as a repair.
Again, I have only superficial knowledge about that, but it is not unusual to do a trial when before adopting something, if it is possible to do a trial. I would have thought that it was reasonable to do the trial and find out all the bugs before lashing into the work.
I think that some of the questions I intended to ask have already been covered.
I will take you back a wee bit. I am quite interested in how you go about the inspection regime. In the absence of some of the high-tech solutions that are available now, it seems to me that you are talking primarily about a visual inspection. Mr Evans talked about sound, which makes sense to me. I know a mechanic who often diagnoses faults with an engine just by listening to it. Am I correct to say that, in the absence of any sound, you do a visual inspection, and that you are looking for defects such as stress cracks? If so, it would tend to be a binary thing, in which the element you are looking at either looks okay or does not look okay. Am I correct that that is the best outcome that that kind of inspection can deliver, as currently practised?
You are correct. A lot of it is down to the experience of the engineer or bridge inspector. The most useful tool that I take to bridge inspections is a hammer. That brings us back to the issue of sound. Whether it is a bit of masonry or a bit of metal, you tap it and there is a sound to it that gives you confidence that it is intact. Once you find an issue, you will be more intrusive and try to define the problem a bit more. At first sight, it is a visual inspection using the inspector’s experience and, occasionally, a bit of brute force.
That is very useful, thank you.
I go back to the tension between the budget—nobody has an absolutely open-ended budget—and on-going maintenance, repairs and so on. How do you prioritise projects when they cannot all be carried out within a budget?
We have touched on the concept of things being safety critical. Again, I am a bit nervous about using that term. To me, if something that is safety critical fails, the whole structure fails—it is not just an operational failure that might mean that you have to close the bridge. If you come across something that is truly safety critical, there is no option; you have to go in and do the work, and somebody has to find the money to sort it out. With other things, such as painting or surfacing, as Richard Fish says, you can put them off, although only up to a point—there are standards even in surfacing to do with road condition. However, with an element such as a jammed-up expansion joint that puts the structure out of operation, you just have to do something straight away and the money has to be found for it, whether from a commercial operation or from central funds.
11:45
That leads me very nicely into my final couple of questions. The committee has received written evidence from Mr Bob Hopewell, a retired engineer who looked after some bridges in North Ayrshire. Of course, those bridges were not on the same scale as the ones that we are talking about, but a number of similarities can be drawn. He said:
“No public bridge authority would refuse to fund essential maintenance that was considered to present an unacceptable risk to the travelling public.”
Do you regard that statement as being generally correct?
Yes.
Absolutely. The Humber bridge acts call on us to provide a safe method of crossing the Humber estuary for our customers.
Thank you. My final question—
I am sorry, Mr MacKenzie, but does Mr Fish want to answer that question?
No, convener. That is fine.
My apologies.
The same chap, Mr Hopewell, says:
“In my opinion, the integrity of a bridge manager would mean that it would be a resigning matter if funds were refused and the bridge were allowed to remain open against his/her recommendation.”
Do you agree with that statement?
I must admit that when I read Mr Hopewell’s submission that bit made me smile. However, what he is saying brings us back to the shift from an engineering decision to a political decision.
We know that there is honour among bridgemasters.
I, too, am an ex-local authority bridge engineer, and I recall situations in which, without wanting to put any pressure on elected members, I had to say to them, “You’ve got to realise the implications of any decision to slightly reduce or not have a maintenance regime.” I sympathise with Mr Hopewell’s sentiment, but I would never go so far as to say that it should be a resigning matter; it would be a case of the person in question having a bit of a tantrum. Given today’s financial climate, resignations would be taking place all over the country.
The point has obviously been made in an emotive way, but I would expect anyone in that position who identified what I would term a safety-critical event to ensure that no one was going to be put at risk. I would not consider it a resigning matter—I would simply close the bridge.
Thank you. That was very useful.
Do you wish to add anything, Mr Evans?
I tend to agree with what has been said. The difficulty with deciding to close the bridge is that you need to have that responsibility. Peter Hill has total responsibility, and I would say that the concessionaire of the Severn bridges has as good as total responsibility. However, unless the failure was actually a structural one, they would talk to the Department for Transport, the Welsh Government and so on before they said, “We’ve got to close the bridge.”
Thank you very much, gentlemen. That has been very useful.
If I heard you correctly, Mr Hill, I believe that you talked about the risks and consequences of failure.
I did, yes.
With regard to risk management, Mr Colford described in evidence to us last week what appeared to be a hierarchy of risk, with the most safety critical—and I know that people hesitate to use that phrase—being the safety of bridge users, by whom I mean the travelling public and the people who operate the bridge. After that comes the bridge’s long-term structural integrity and then operational safety. Is that a fair characterisation?
It is. If a situation that posed a significant danger to life and limb were to present itself, the consequences of that risk would obviously be uppermost in any consideration of what action should be taken.
On the long-term integrity of the bridge, we might come across something that was critical to the long-term viability of the structure. However, there is often more than one way to skin a cat in such a scenario, so it might be appropriate to pause. Certainly, if it is just a matter that inconveniences the public or the operator, that would be a lesser consequence.
I certainly agree that there is a hierarchy in risk management. Assessing both the likelihood of a risk occurring and its consequences presents an objective way of rationalising and prioritising risks. I agree that the sort of hierarchy that, as the convener said, Mr Colford described is appropriate.
I would add just one point, which is that we have also to take cognisance of the emergency services, because they come into the equation. They deal with the operation on the carriageway, as it were, which might not be particularly structurally important. However, they can certainly intervene and close the bridge to traffic.
Thank you for that. Clare Adamson spoke about the indicative capital plan and we have had a bit of a discussion about how you prioritise maintenance works given the budgetary constraints within which you operate. Clearly, part of the committee’s discussion and inquiry is around the postponement of a particular piece of work: the replacement of the entire truss end link assembly, which had been costed at an estimated £10 million to £15 million. Do you have a perspective, based on your own engineering experience and what you have learned about what happened at the Forth road bridge, on whether the decisions that were taken were consistent with the hierarchy of risk that we have just been discussing? In other words, were the decisions to postpone capital maintenance works correct?
As Barry Colford said, that is a fairly hypothetical question now. We know what failed, but I do not think that anybody at the time thought that those particular links were going to fail.
On the consequences of overloaded upper brackets, with my limited knowledge from reading and seeing what has happened in the past few days, I do not think that it was an unreasonable decision to go for the trial and then see what came out of that, in light of the £10 million to £15 million budget for the whole thing.
So there was a risk, but it was an operational risk. Is that a fair assessment?
In effect, yes.
I have certainly reprioritised work in the past by smoothing out not only the cost profile but the practicality of undertaking work when other works were going on at the same time on the bridge. We cannot start cutting several structural elements at once, so sometimes there is a need to reprioritise on that basis. If the consequences of the risk appear to be only to do with the serviceability of the bridge rather than being a critical risk to it, reprioritising is perfectly reasonable.
Mr Fish, do you have a perspective on that?
I endorse what the others have said. In any maintenance budget there will be pressures from the amount of money in the budget and from other maintenance needs and interventions that need to be carried out, which have to be balanced with one another. With hindsight, we can say that the work that has been referred to should not have been removed from the programme. However, given a reducing budget and increasing demands elsewhere, it is quite understandable that that decision was taken.
In your experience of your bridge, how involved would the board be in accessing money in order to prioritise work?
I assume that you are referring to the political dimension. The board would make the final decision on the recommendation of the engineer or the bridgemaster—whoever was taking a view. I do not really know what that relationship is. There needs to be an element of trust. The board cannot say that its priority is to maintain the bridge if it is not going to allocate funds to do that. The bridge manager also has to have implicit trust in the engineering side.
Is that your experience of your bridge?
Yes, very much so. It has almost become a joint decision. Both have to recognise the territory in which the other operates and, at the same time, there has to be a real will for the board to sign up to what the engineer says or we end up in the position that Mr Hopewell described.
Again, Severn crossings are slightly different. Let me try to draw the closest parallel. The concessionaire is ultimately responsible during the concession period, but there is a Government representative who oversees.
Somebody talked about taking a light touch. I hate the idea but I was Government representative for some years and, during that period, if the concessionaire wanted to do something that fell outwith the work envisaged in the maintenance and inspection manual and all the other volumes of the concession agreement, we were in a position to say no. However, we would do that only if we really felt that it was something that would be totally unwise for the bridge. Nonetheless, there was somebody just behind the board, overseeing it.
I suppose that, in that example, if there was critical work and the budget had not been guaranteed, that would be a resigning matter, as Mr Hopewell said.
When there are people who oversee the board, if the budget is not allocated for safety-critical work that comes up because the money for that year—or for the next three or five years or whatever—has been spent, who is ultimately responsible for allocating funds? How are those funds generated if safety has been impacted but there is no money? How does that work?
Again, my experience is slightly unusual. The shareholders are very conscious of the safety of the travelling public so they would find the funds.
What would happen if it was a Government matter?
The Government would have to intervene or it would have to give us permission to borrow the funds.
Would local authorities be involved in that at any point?
Although it was similar to FETA in a way, the Tamar bridge was unusual because it was managed by a joint committee of two local authorities. In order to do the strengthening and widening work, we needed additional funds, and the two local authorities subsidised the work using their own reserves. That was the equivalent of going to central Government.
I was going to come on to that. How was that work budgeted for or prioritised at the beginning? Who were the partners?
I will try to keep a long story short. The bridge is a joint undertaking with a ferry operation that uses chain ferries across the Tamar. The local authorities had a reserve to replace those ferries. It was a classic decision about two crossings, and the decision was to defer the replacement of the ferries. The money was shifted to the bridge, which gave us a capital allowance.
The Tamar bridge was tolled both during and before the works, so we were able to source a fairly static toll income. Therefore, we started the strengthening work—I hesitate to say this—without enough money in the bank to finish it. We had to keep the bridge open to traffic during all the work so that we could collect the tolls. We went into the red to the tune of about £2 million for a period of about six months. As I said, that was funded by the two parent authorities under a fairly loose borrowing arrangement. Initially, we went to central Government for funding but their response was, “No. You charge tolls. There’s your income—use that to pay for the work.”
The structures are very similar, but they are all very different in terms of governance and funding.
12:00
It is certainly complicated.
Yes.
That is helpful. Thank you.
Do members have any further questions?
I am going to explore some dangerous territory. I went into this last week, but I will briefly do so again.
The work on the truss end links was deferred. That work was associated with the opposite end of the link, which has not failed. If that work had been carried out when it was originally mooted, would it have led either to the discovery of a problem in the area that failed or to maintenance to that area that would have prevented the problem?
I am afraid that, without a far more detailed understanding of the mechanism, it would be impossible to say whether that is the case.
The question that I intended to ask after that is: how often do you find yourself in a position in which planned maintenance work on a major structure leads to additional maintenance work that may immeasurably defer cost, or danger, in the longer term? How integrated is the process? Can it be separated into its individual parts?
In theory, it can be separated, but in practice it hardly ever is. It can almost certainly be separated.
When you decide to do some work, you undertake that work based on an assumption about what the problem is. Once you start, you find the reality of the problem. The Forth cable investigations is a classic example of that. Those investigations had to be done to determine the problem. They led to other maintenance interventions, such as the dehumidification to help to resolve the problem with the cable.
I think that the same process would have applied if the investigation had started at the tower connection rather than the truss connection. You cannot know where that might have led. It might have led to an analysis that said that the problem was not up there but down at the bottom. Who is to say? The one-word answer is “Possibly”.
I would suggest that it is fairly unusual for planned works to uncover unknowns, because we tend to plan such works over a significant period of time. We investigate what the impacts on other structural elements may be and we plan for those impacts. Therefore, it is quite rare that we start with one problem and find half a dozen others. In certain elements, we might not find what we were expecting, and that leads to a different solution, but we do not tend to find other things that we were not aware of.
Again, I might be able to give a parallel. At the beginning of the concession period, there was a joint inspection by the potential concessionaires and the Government’s representative staff—my staff. It was intended that that joint inspection would flag up anything that might need to be done during the concession period. After that, the only thing that could get extra money for the concession was something that could not have been found during that inspection. You might say that that is a kind of Government-backed reserve.
Equally, as far as the strengthening works were concerned—as I said, it was a competitive tender—there was a large contingency. That is to say, there was a contingency sum of 10 to 12 per cent, not all of which was spent. However, we knew that, once we got into the work in deep detail, we would find things that we had not seen before.
Is it in the nature of maintenance that the unforeseen will be found if you maintain something and that, as a consequence, if you defer maintenance, there is an element of risk?
I think that there is a larger element of risk if you defer maintenance.
The risk that results from keeping your head in the sand and not knowing what is going on is far greater than if you have a maintenance regime that can at least give you an indication of what is going on.
As an aside, when you do not really know the extent of the problem, the issue around some of the maintenance works is arriving at an estimate for budgetary purposes at the outset. As I understand it, that is why the estimate was—as I think the convener said—between £10 million and £15 million. People might say that that is a big range, but you just do not know the extent of the cost until you start work, which is why building in a contingency is a very sensible thing to do when you are developing budgets for maintenance.
Thank you for indulging me.
Not at all. I think that that was a very helpful line of questioning. Do members have any further questions?
Do any of our witnesses want to place any final points on the record?
I would like to reiterate what I said at the beginning. I am amazed at how much has been accomplished in such a short time. I know that a huge amount of resource was put in, but it was still a major effort and all involved are to be congratulated.
I endorse that statement.
It is very healthy that the committee is conducting this inquiry. I am sure that the impact was felt very hard among the travelling public in Scotland, but it was also national and international news among the bridge community. As John Evans described, a potential problem was very quickly turned into a success. Well done to those concerned, and to your committee for conducting this inquiry. Thank you for the invitation to come along and talk to the committee.
Thank you. It appears that you have the last word, Mr Hill.
I can only really build on what the other two have said and assure you that, internationally, this discussion will continue for quite some time. As Richard Fish mentioned, we will be attending the international cable supported bridge operators’ conference. I expect that Barry Colford will attend that as well, and I am sure that we will discuss the issue there.
On behalf of the committee, I thank our witnesses for making their considerable experience and expertise available to the committee this morning. Their contribution has been invaluable in informing our work on the inquiry.
12:08 Meeting suspended.Previous
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