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Forensic Engineering: Weigh up the evidence for Tay

Updated Wednesday, 23rd April 2008

Evaluating the evidence as to why the Tay Bridge collapsed, part of the BBC/OU's programme website for Forensic Engineering

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A selection of evidence from the Tay Bridge inquiry is listed below. The evidence is arranged in sections according to what subject area it relates to: condition of the bridge, strength of the wind, bridge design weakness, manufacture/construction defects, maintenance, speed of train over the bridge, fracture surfaces.

After viewing each piece of the evidence, decide which of the three proposed theories you think it supports. Then consider if the piece of evidence strongly disproves one of the theories.

For a list of the characters involved in the inquiry, have a look at the Who’s Who section. If you need a reminder of the three theories, have a look at the theory section for a summary.

Evidence relating to: Conditon of the bridge

Evidence given to Inquiry by John Cochrane on 27th April

MR TRAYNER: Did you notice that on some of the piers the lower tier of columns had been forced to the westward? - I did.

The great mass of the superstructure we know went over to the east? - Yes.

In your opinion what led to the forcing of those columns westward? - At No 5 pier the eastern set of columns is underneath the eastern girder crushed up.

The eastern set of columns are under the eastern girder? - Yes, as it lies on its side, or as it did lie on its side at the bottom. The western columns are lying over the top of the western girder, and that renders it absolutely clear to my mind that the three eastern columns gave way first, that the structure went over sufficiently quickly, and that then the three outer columns or western columns fell over on to the top of the girder, and so they are found.

THE COMMISSIONER: The eastern columns are under the girder? - Yes.

Showing that the eastern columns fell first? - Yes.

MR BARLOW: Showing that the eastern and western parts separated from each other? - That they are separated from each other. I think the probability is that the separation would not have taken place had the angle girders or L-girders at the top been connected together so as to have brought the whole six columns in unison.

Evidence given to Inquiry by Charles Meik whilst being questioned by Mr Bidder on 3rd May

Did you also find upon those portions of the girder any peculiar marks or scorings? - Yes, I found scores in several places.

Are those horizontal lines marks of something abrading the girder in a horizontal direction? - There appears to have been some body scraping over the struts and ties.

Those you also show upon the plan with red lines? - I have shown them with red marks.

They are horizontal, that is to say, lines in a horizontal direction, and I believe their height upon the girder corresponds with the height of the roof of the carriage? - Some of them, and some of them are lower.

Further on towards the north they get lower, but at the first they correspond accurately with the height of the roof of the carriage? - Yes.

THE COMMISSIONER: Do you mean the roof of the carriages in an upright position?

MR BIDDER: As they canted over, one mark corresponds with the roof of the second-class carriage, and the other with the roof of the guard’s van.

MR TRAYNER: All that Mr Bidder is entitled to get from the witness is that he has given us exactly what he saw, and that the measurements are correct but to say that those marks correspond with the roofs of the carriages is assuming heights which he has before him.

MR BIDDER: You do not know of your own knowledge what the height of the carriages was? - I have some idea of it.

At the first place at which those abrasions occurred, the southernmost of these abrasions, do you find that a rivet has been struck out? - Yes, in this corner (pointing to the plan).

MR TRAYNER: You mean that the rivet is not there.

MR BIDDER: Is it that the rivet has never been put in? - The rivet has been struck out; the cover has been lifted up.

The cover has been lifted up by something forcibly parting it? - By something forcibly parting it.

Did you find anything between the cover and the lattice? - I found splinters of wood.

THE COMMISSIONER: Where did you find those splinters of wood? - Between the cover and the tie. This is the cover on the tie (pointing to the plan). There are two covers, and between this inner cover and the tie there were splinters of wood.

MR BIDDER: This is the southernmost place where the abrasions occur? - Yes.

That cover and tie would be riveted up close together in the ordinary state of things? - The cover would be close on the tie.

With regard to those splinters, do they appear to have been driven in with considerable force? - Very considerable force indeed.

Evidence given to Inquiry by Thomas Napier Armit under examination by Mr Bidder on 4th May

Did you see the marks upon the girder, which are indicated upon the plan by red lines? - I was the first to observe them.

My friend tells me that you said you thought it so important, that you went into Dundee to have it photographed? - Yes.

Will you just describe those marks - are they distinct upon the girder? - They are black, and in passing your finger over them you can feel that there is more than the paint - that even the iron bears a graze, there are hard grazes, the heads of the rivets are very hardly rubbed, in passing your finger over you can feel a distinct hollow, and over the heads of the rivets there has been a very hard graze indeed.

Did you notice what Mr Meik described as one corner of the covering-plate being turned up and the rivet gone? - Yes, I assisted him to pick out some of the pieces.

Have you formed any opinion, from the appearances which you saw there, of how that could have been caused? - Yes, I have.

What is your opinion? - That the rear of the train must have done that, I should imagine the second-class carriage.

Mr Armit was examined by the Commissioner, Mr Rothery, later the same day

You have told us that you discovered some marks on the eastern side of the girder, at about 6 or 7 feet above the permanent way, which you supposed had been done by a portion of the second-class carriage? - Yes.

Of course you know what a second-class carriage is? - Yes.

What do you think would be the effect of its coming in contact with the girder? - It would be smashed all to pieces.

These marks are at the fifth bay? - Yes.

That is at the height of 11 feet 2 inches from the permanent way. How do you account for that? - I cannot tell how it was. Perhaps the train jumped up. I believe in any eccentricities in a train.

You believe, therefore, that that mark on the fifth bay was due to some eccentricity of the train? - Yes.

And could not have been caused except by some eccentricity of the train? - I do not know of anything in our operations that could have caused those marks.

I am not asking you about your operations, I am asking you about the marks upon that fifth bay. You have told us that you believed that the mark on the fifth bay was caused by the second-class carriage coming into collision with the eastern girder, and you have told us that that would knock it all to pieces. I want to know what part of the second-class carriage could have caused that mark at a height of 11 feet 2 inches on the fifth bay? - It might not be the second-class carriage, it might be the carriage ahead of it.

How could it be the carriage ahead of it, if, as you say, you do not think any carriage ran more than its own length? - This is just about the length of a carriage ahead. The end of the first-class carriage was found here; 3 or 4 feet beyond the joint of No 3 and No 4 girders.

The theory would be first that the second-class carriage was smashed to pieces, and then that the guard’s van was blown off against the third span? - Yes.

THE COMMISSIONER: Knowing that the guard’s van was below the second-class carriage, can you account at all for those other markings? - It is very possible that the guard’s van caused them - very possible - I should say very likely.

MR TRAYNER (through the Court.): If the van was still on the rails, and tilted over by the wind, can you form any opinion as to how much that would diminish the height of the place at which it struck? - If it was on the rail and tilted over, it would very likely come below that, but, as I have said before, I should not be at all astonished if it jumped up.

THE COMMISSIONER: What you call the eccentricity of the train? - Yes.

THE COMMISSIONER: Will there be any other person called, besides these witnesses, who have seen the fragments since, because otherwise it may possibly be necessary either that Mr Law, or the Court itself, should look at them. Is there anybody on behalf of the company, under whose control all this is, who might be produced to give evidence about it?

MR BALFOUR: Mr Drummond, the locomotive superintendent, has seen all the carriages, and he can describe their condition accurately.

Duggald Drummond was recalled and examined further by Mr Trayner on 4th May

Supposing that the first-class carriage had been tilted by the lateral force of the wind, so as to bring its easternmost corner in contact with the lattice-work, how much must it have gone eastward to touch the lattice? - That is, how much it would have fallen below its natural level on the rails?

Just so? - I should think about 3 feet, it would have been lowered.

MR BIDDER: That is rather ambiguous; what do you mean when you say that “it” must have been lowered 3 feet? - The top edge of the carriage.

MR TRAYNER: The ambiguity was in your own mind, Mr Bidder, and not in the question. (To the witness.) If that carriage tilted over by lateral pressure, how much would that have reduced its height from what it would have been, if it had been standing perpendicularly on the rails? - From 2 to 3 feet, I think.

And therefore, if it did strike the latticework, it would have struck it, as you think, between 7 and 8 feet from the level of the rails? - That is so.

Can you conceive that carriage in any way not running alongside of the girder, but tilted over or thrown over from the rails, so that it could have struck the girder at a height of 11 feet above the rail? - I cannot understand it.

MR BARLOW: Will you tell us in what state you found the engine; was the steam shut off? - The steam was not shut off.

Were the brakes applied? - No, they were not.

Was there anything to indicate that there had been time to do anything after the appearance of the accident? - There was every indication that there was no time for acting. The reversing lever was standing at the third notch from the centre, or six notches from the full forward gear; the regulator was standing full open, and the brake screw on the tender was full off; the brake screw on the brake van in the rear of the train was also off.

Those would be indications of great suddenness in the character of the accident? - They would be indications of great suddenness. The first thing for a driver to do if there was anything wrong, would be to shut the regulator if he felt any jolting with his engine, and the next thing would be to apply the brake. They have to do it so often while the engines are slipping in wet weather that it is the first thing that they attempt to do; in fact, they do that before they attempt to put on the brake.

During Sir Thomas Bouch’s evidence on 30th April the Commissioner asked …

Will you give to the Court your opinion as to what did cause the accident that destroyed the Tay Bridge? - Well, I have thought a great deal about it very anxiously, and my own opinion if fixed now; that it was caused by the capsizing of one of the last or the two last carriages - that is to say, the second-class carriage and the van; that they canted over against the girder.

In your judgement, the thing which caused the destruction of the bridge was the capsizing by the wind of the second-class carriage, and I suppose that would take with it the van? - Yes.

Against the leeward girder? - Yes.

And so coming into collision with the girder? - I think so.

Extract from Rothery’s [Chairman] report

Condition after the Accident

(33.) Let us now see what was the condition of the bridge immediately after the accident

(34.) And, first, as regards the girders. These, it seems, were lying in the bed of the river to the east of, and at some distance from the base of the piers, having turned over on their sides, so that what had been the east side was now the bottom, the west side forming the top. It appears from a plan, which was put in by the railway company, that the girder did not lie in a straight line, but that the three sections, of which it was composed, formed three distinct arcs, with their concave sides towards the piers, being nearest to the piers at the expansion joints, and furthest from them at the fixed bearings. Thus at piers 28,33,37, and 41, where there were expansion joints, the distances of the girder from the piers were respectively 22 feet 6 inches, 21 feet, 25 feet 6 inches, and 23 feet; whilst piers 31, 35, and 39, where there were fixed bearings, the distances were respectively 42 feet 6 inches, 51 feet, and 44 feet 6 inches. At the intermediate roller bearings the distances were something between the two, the only exception being opposite to pier 29, where the distance from the pier was only 16 feet, a not unimportant fact to which we shall presently have occasion to allude.

(35.) Secondly, as regards the piers. There was nothing to show that there had been any movement or settlement in any of the foundations; but the joints of the masonry of the hexagonal piers had in almost every case been severely shaken, and in two instances the two upper courses of stone on the west side had been wrenched off and tilted up on end. It was, however, to the columns that the greatest injury had been done. All these, from piers 29 to 40, had been entirely carried away, with the exception of the two lowest tiers on 29, and the lowest on 30. In almost every instance the bolts, which held the columns to their base pieces, as well as those, which attached the several piers to one another, were broken, and the tiers lay some on the piers, but most of them in the bottom of the river to the eastward of the piers. In a great many instances the whole or portions of the flanges had been broken off, sometimes carrying with them part of the shaft. What however was chiefly to be remarked, was that the cast-iron lugs had almost all broken, whilst the wrought-iron struts and ties for the most part remained uninjured. This was especially noticeable on the piers left standing at the two extremities, namely Piers 28 and 41; where the lugs on the sides, facing the fallen girders, were almost all broken, and the ties, which had held the two 15-inch columns together, were hanging loosely from their ends.

(36.) Thirdly, as regards the train. This consisted of the engine and tender, a third-class carriage, then a first-class, then two third-class, then a second-class, and lastly the guard’s van. Of these the engine, the tender, and the four first carriages were found in the fifth or last span of the first section of the high girders, whilst the second-class carriage and the guard’s van were in the fourth, but close to its junction with the fifth span. The engine and tender were on their sides, as well as the last carriage and the guard’s van; but the four intermediate carriages were standing upright on their wheels, having, it is supposed, been floated after the accident by the air enclosed by the roofs.

(58.) It was said, however, that there are marks on the girder which show that the train struck the leeward girder before the bridge began to fall. It seems that Mr. Thomas Napier Armit, who has been employed under Sir Thomas Bouch’s instructions to raise the fallen girders, having discovered certain marks or scorings on one of the lattice bars of the leeward girder, Mr. Charles Meik, Sir Thomas Bouch’s assistant, was sent down to Dundee to examine and make a sketch of them; and this sketch was brought in by him during the progress of the inquiry. Subsequently other lattice bars with similar marks and scorings upon them having been discovered, Sir Thomas Bouch constructed a plan, which he has forwarded to us in a letter dated the 27th May ultimo, after the conclusion of the examinations, and which he says confirms his theory “that at least the guard’s van and the second-class carriage next it had been in “contact with the east girder, before the bridge fell.” The plan shows a number of marks or scorings on the inside of eight consecutive lattice bars, which we are told formed part of the leeward girder immediately in the rear of where the train was found. The marks or scorings are parallel, and cover about a foot of each lattice bar, the lowest being about 11 feet and the highest about 12 feet above the line of the rails. We were told, however, by Mr. Dugald Drummond, the locomotive superinten¬dent of the company, that the top of the second-class carriage, by which these marks are supposed to have been made, would be, as nearly as possible, 10 feet above the rails, so that it is somewhat difficult to understand, how it could, when the bridge was upright, by being tilted against the girder, as is suggested have made these marks or scorings at a height of from 11 to 12 feet above the rails. Moreover, to make these marks upon eight consecutive lattice bars, the carriage must have passed over three bays or openings, each more than 25 feet wide; and if the carriage was at the time leaning with any force against the girder, we are at a loss to understand why, seeing that it was only 22 feet long, it did not fall through one of these openings; and if it was not leaning against the girder with any force, it is equally difficult to understand how it could have contributed to overthrow the bridge.

(59.) But supposing that the second-class carriage and guard’s van did tilt, as is suggested against the leeward girder, is there any reason to suppose that it could have done it any harm? We were told by Mr. Dugald Drummond that the second-class carriage was a very light carriage, very lightly constructed, and that it was in fact the only light carriage “in construction, and of itself, that there was in the train.” To suppose then that the top of such a carriage could have done so much injury to the bridge, as to have caused more than 1,000 yards of it to fall, seems in the highest degree improbable; we are rather disposed to concur with some of the witnesses, who thought that it would have “gone off like match-wood,” without doing the slightest injury to the girder.

(60.) And after all, what is the character of these marks or scorings, which we are told give evidence of a shock of such terrible force? Mr. Armit was asked by Mr. Bidder to describe them, and his answer was “They are black, and in passing your finger over them you can feel that there is more than the paint¬ that even the iron bears a graze; there are hard grazes, the heads of the rivets are very hardly rubbed; in passing your finger over you can feel a distinct hollow; and over the heads of the rivets there has been a very hard graze indeed.” Mr. Meik’s evidence was to the same effect; on being asked by Colonel Yolland, “Are these scorings that you speak of indents in the iron?“ he answered, “Not exactly indents; the paint is all scratched off. There are some scratches in the iron too, but they are not deep.”— A thirty-second part of an inch, or a sixty-fourth part of an inch? —“I did not measure them, but they are very slight.” It is certainly inconceivable that a blow, which was hardly more than sufficient to take the paint off, and which Mr. Meik, a civil engineer and a very competent witness, was not prepared to say had scratched the iron to the depth of one sixty-fourth of an inch, and which he described as “very slight,” should have produced such results. It seems to us that these marks or scorings could hardly have been made, before the bridge had begun to fall; and that even if they had been, they were not sufficient to have caused the fall of the bridge. It seems more probable that they were made by the train, after the bridge had begun to fall over, when the train would necessarily be thrown upon the leeward girder, and not having yet lost all its forward motion, it would not unnaturally make such marks as we see.

(61.) It was, indeed, suggested that there were other marks lower down, which might have been made by the frame of the carriage, which is much stronger than the upper part of it; and our attention was called to a photograph of the second-class carriage, which showed the after buffer on the west side to have been much injured; and it was suggested that this might have been done by the guard’s van, when the second-class carriage was brought up by the fore part of the frame striking the lattice bar. But if so, the fore part of the frame, where it is supposed to have come against the lattice bar, should have shown marks of the collision, but it seems from the photographs to be quite uninjured. There is therefore no reason to think that the frame of the carriage ever came in contact with the girder, at all events before the bridge began to fall.

(62.) There is also the fact that, when the engine was found after the casualty, the throttle valve was full open, the reversing lever “standing in the sixth notch from “full forward gear, or in the third notch from centre.” Now, if any part of the train had left the line or been tilted over against the leeward girder, as is suggested, before the bridge began to fall, there can be little doubt that the engine-driver would have seen it, and have at once reversed the engine full speed, so as to bring the train to rest as soon as possible; and the fact that he had not done so, strongly confirms us in the opinion that the train must have been in position on the rails, when the bridge first began to give way.

Evidende relating to: Strength of wind

On 5th January, Captain Scott was sworn in and examined by Mr Trayner

Did you individually notice the barometer that day? - I did.

What was observable about the barometer? - I observed a rapid fall from noon.

Until when? - Until 7 o'clock.

Did it reach its lowest then? - It reached its lowest at 7 o'clock.

So what the pressure was greatest then? - I presume so.

Have you any notes of the readings of the barometer on that day? - I have private notes that I jotted down in my diary; that’s the only thing.

It is also noted down in the ship’s log? - I believe not.

Can you give me the readings of the barometer? - yes, I can give you the readings at noon and the readings at 7.

Give me first the reading at noon? - At noon it is 29 and 6-10ths.

And at 7 o'clock? - Twenty-nine.

It was about half-an-inch more at noon? - Yes, 6-10ths.

That would be a little more than half-an-inch in the course of that period? - Yes, in the course of seven hours.

You have been here for some time, have you not? - For 10 years.

From your knowledge of the coast a falling barometer would indicate, would it not, a rising and coming storm? - Yes, a coming storm.

Was it an unusually strong gale? - Yes.

Will you describe it, how would you describe it? - We describe storms in the navy by numbers, from 1 to 10, 12 would be maximum, 1 to 12.

Twelve represents the maximum strength of the wind pressure or disturbance? - Just so.

On this occasion how would you describe the gale on the Tay by figures? - From 10 to 11 in a squall.

The whole squall made so by a continuous gale, what figures would describe that? - I should call it 10; a whole gale.

In popular language, it was just about as severe a storm as you could have experienced, is that so? - I have experienced more severe storms.

In this country? - I believe so.

If it was represented during the squall by the figures from 10 to 11, and the maximum was 12, there could not be anything much worse than there was on the Tay that night? - It is very difficult to compare one storm with another unless they occur about the same time. I think from my remembrance of the storms upon the Tay previously to the bridge being put up we have had one or two storms quite equal in force in the last two or three years.

Can you tell me from your own observation what the direction of the wind was at noon, when it began to blow? - South-south-west, as near as my memory will help me.

It gradually got to the west? - It shifted, so far as I recollect, about sunset from 4 to 5 o'clock, half round to west.

At the height of the storm somewhere about west? - At the height of the storm west.

Mr Bidder examined Benjamin Baker on 6th May

MR BIDDER: You examined the ruins of the piers? - Yes.

And you have also heard the evidence as to the nature of the defects which are suggested in the bridge? - I have.

In your judgement, as a question of design (apart from the question of workmanship), was the design of that bridge sufficient for resisting the wind strains that could be expected to come upon it? - The design of the bridge was merely, you may call it, a duplicate of previous designs by other engineers, and previous experience had shown the sufficiency of it.

THE COMMISSIONER: That is hardly an answer to the question.

MR BIDDER: May I take it that in your judgement the bridge was sufficient in design for resisting the wind strains that might be expected to come upon it? - If you ask me whether I think the bridge was blown down by the strains that came upon it, I say I think it was amply strong for the wind that it has sustained since it has been erected.

Do you mean this, - that, having regard to the wind on the night of the 28th of December, the design was amply sufficient? - Yes.

Whether it is possible to conceive a wind for which it would not be sufficient is another question? - Of course it would go down in a tornado, or anything of that sort.

In your judgement, having regard to the strength of the wind on the 28th of December last, the design of the bridge was amply sufficient to resist it? - Yes, with a factor of safety of between two and three.

Then, in your judgement, is the cause of the failure of the bridge on that night something in addition to the mere wind pressure? - I think so

You noticed, I think, when you were there what has been referred to by a good many witnesses viz, that the cast iron lugs are mostly broken? - Yes.

Does that give any indication, to your mind as to the nature of the failure? - I think it indicates pretty clearly that the weak point was in the lugs. The lugs failed first, and they would be peculiarly liable to fail by reason of a shock. We know that the slightest shock would break a lug, of course.

You have said that, in your judgement, the base was perfectly safe, having regard to wind pressure alone, having regard to what it had to bear on the night of the 28th of December? - Yes.

You have visited the spot, and have heard all the evidence, what is your judgement as to the wind pressure that the bridge, was a whole (I do not mean any isolated point of it) had to meet? - I do not think the ruling maximum pressure of the wind of that night exceeded 15 lbs per square foot.

THE COMMISSIONER: What are you judging from? - I am judging from the strength of the structures which now exist, but which would have been destroyed had the wind pressure exceeded that amount. There are two signal boxes, one at the end of the bridge and one a few yards farther away; those signal boxes have windows. Amongst other experiences which I have made from time to time, I have tested a great deal of glass up to 1 ½ inches in thickness. I have tested the strength of a window which the sash bars, by placing a ledge round it and pumping water on it till the glass broke. Taking these two things together, I get a very simple rule for the strength of a pane of glass, and applying that information to the windows here, I find that in one case the effective pressure on a pane of glass in the door of a signal box could not have exceeded about 9 lbs per square foot, and in the other about double that.

THE COMMISSIONER: Then there is one other fact also to be taken into consideration: that both these cabins are protected to a considerable extent.

MR BIDDER: That is so, no doubt. They are not exposed to the same extent that the bridge on the centre of the river would be, are they? - No I should say not; but, looking at the effect of the wind on the ballast now remaining on the platform of the bridge, I noticed that there was quite as much disturbance of the ballast near the signal boxes as there was near the centre of the river. It had been blown away, scudded away in both cases.

MR BIDDER: Qualified to this extent: that the bridge itself, at a height of 80 feet across the estuary is necessarily somewhat more exposed than the buildings on the shore at the side? - Yes.

Taking all that into consideration, do I correctly understand that in your judgment there could not have been an average pressure per square foot over the span of the girders greater than 15 lbs? - No, I think not.

MR BIDDER: Of course I suppose you do not deny in giving this evidence that anemometers may record, and truthfully record, in a particular spot higher pressure upon a limited area? - Yes, upon a smaller area there may be a sort of a jet of air, but not over a large area. I should be very glad if any one would give me an example. I have issued a challenge any time during the last 15 years, and I have never got a single example, in this country, of a wind blowing down a structure which would have stood a pressure of 20 lbs per square foot.

You have found, although you have searched for 15 years, no instance of wind doing damage to any structure of reasonable area that would have involved a pressure of 20 lbs, or upwards? - No instance; I have never heard one cited.

MR TRAYNER: What wind pressure do you think was brought to bear upon the bridge upon that night of the 28th of December 1879? - Taking the bridge as a whole, and on the basis of these other structures, of which I have given you the amplest information I can, the inference that I draw is, that the pressure did not exceed 15 lbs per square foot. And I would also call attention to the condition of the ballast of the bridge. It certainly must have been blown away if there had been any such tearing hurricane as they speak of; it would have gone like dust.

You said the pressure was 15 lbs over the bridge, but have you any opinion as to what would be the greatest wind pressure at any point of the bridge? - That I cannot say.

Extract from Rothery’s (Chairman) report

(64.) In a paper prepared by Dr. Pole and Mr. Stewart, at the instance of Sir Thomas Bouch, which will be found in the Appendix and in which the stability of the bridge and its capacity to resist the pressures, which might be brought upon it, are very fully discussed, we are told that “the ordinary source, from which estimates of the force of the wind have been usually taken, is the well-known table presented by Smeaton to the Royal Society in 1759, which gives a pressure per square foot "of 6 lbs. for high winds, 8 or 9 lbs. for very high winds, and 12 lbs. for a storm or tempest. …”

(67.) Now it appeared to us that, in order to arrive at a correct judgment as to whether the violence of the wind alone could have overthrown this bridge, it would be well to obtain the best information as to the greatest known pressure of the wind, and to see how far it agreed with the opinions which had been expressed by Sir Thomas Bouch, Mr. Baker, Dr. Pole and Mr. Stewart. We accordingly applied to the Astronomer Royal, to Professor Stokes, of Cambridge, and to Mr. R. H. Scott, of the Meteorological Office who kindly attended, and gave us some very valuable and interesting evidence on the subject.

(71.) Professor Stokes was pressed very strongly by Mr. Bidder as to whether such violent gusts as these, which would produce a pressure of 50 lbs. on a plate, would not be only momentary, and whether they would extend over more than a few feet in width; but he answered (Q. 16,248) “a very heavy gust will not be a mere momentary thing, though it will not be of any great duration ordinarily; it will "sometimes go on for two or three minutes blowing very heavily indeed.” And as regards extent Professor Stokes stated that, when we hear of “a heavy gust being confined, to a very narrow track,” he considered that “narrow” meant having a breadth of a few hundred yards, of which he said there were many instances on record. He added that there would probably be a relation between the duration and extent of a gust, and thus one, which had lasted for half a minute, would probably “extend over a considerable space laterally.”

(72.) This very valuable and interesting evidence of Professor Stokes as to the force, the duration, and the extent of a gust of wind was fully confirmed by the Astronomer Royal; who was then asked by Sir Thomas Bouch’s counsel, how he could reconcile that opinion with the opinion given by him in 1873, that the maximum pressure over the area of one of the spans of the Forth Bridge would probably not exceed 10 lbs. per square foot. Mr. Bidder contended that the term “very limited spaces" must mean a point or only a few feet, but the Astronomer Royal stated that that was not at all his meaning, and that it might mean 100 or 200 feet, or even more, and that in his opinion you might have a maximum pressure of 40 or 50 lbs. over an area of 245 feet, the extent of one of the spans of the Tay Bridge, but that it did. not necessarily follow that you would have the same pressure over 1,600 feet, which was the length of one of the spans of the Forth Bridge. He said that the circumstances of the two bridges were quite different, and that that had materially influenced his opinion; that the Forth Bridge, which was a suspension bridge, might be pushed on one side by a high pressure, and would, when the pressure was taken off, return to its original position, without having sustained any injury; but that it would be quite different with such a bridge as the Tay Bridge, standing, as he described it, “on high stilts,” for if once blown on one side and out of position, it could not recover itself, but must come down.

(74.) We think, therefore, after the evidence of these gentlemen, that there can be no reason to doubt that there may be wind pressures of 45 lbs. and even 50 lbs. in this country; and the difference between them and Messrs. Pole, Stewart, and Baker is probably due to the latter having taken the standard pressure instead of the pressure on a plate; a standard pressure of 25 lbs. being, as we have seen, equivalent to a plate pressure of 45 lbs. according to Professor Stokes, and of 50 lbs. according to Sir Henry James.
Extract from Rothery’s (Chairman) report

Storm of 28th December.
(75.) But although in rare and exceptional cases there may be a wind pressure of 40 and even 50 lbs., and for which, therefore, it would be proper to provide, it does not at all follow that the gale of the 28th December last was a storm of that exceptional character. That it was a very violent storm can admit of no doubt, for some of the witnesses speak of it as having been more violent than any that they had ever before experienced on the Tay. On the other hand one gentleman, a Mr. Charles Clark, living on Magdalene Green, near the northern end of the bridge, and who has been in the habit of noting and registering the state of the weather at Dundee for the last 14 years, told us that during that time he remembered about four storms equally violent. But perhaps the most reliable information as to the violence of the wind on the evening in question is to be found in the evidence of the officers of the training ship “Mars,” which was at the time lying at anchor in the Tay about three-quarters of a mile to the east of the bridge; and as the wind at its height was blowing nearly straight down the river, it may reasonably be expected that they would feel the full force of the gale. According to Captain Scott, her commander, it was blowing a whole gale, with what he would call a force of 10 (12 being the maximum), and in the squalls, he said, it was, perhaps, from 10 to 11. He told us, however, that he had experienced more severe storms, even in this country, and one or two “quite equal in force in the last two or three years,” during the time that he had been stationed in the Tay. … Captain Scott’s evidence was confirmed by Edward Batsworth, the Gunnery Instructor, and by Hugh McMahon, the Seaman Instructor, on board the “Mars,” the two men by whom the log was kept.

(76.) Whilst, then, we are quite prepared to admit that it was a very violent storm, there is nothing to show that it was exceptional in its character, or that it had anything like the intensity of a West Indian cyclone or a Chinese typhoon. A storm, which, according to Captain Scott, had been equalled in its intensity by one or two others, which had occurred during the last two or three years, and according to Mr. Clark, by no less than four within his own memory, ought hardly to have overthrown a bridge within 18 months of its having been opened, if only reasonable provision had been taken against it. It becomes therefore important to ascertain what provision was made against wind pressure, or, in other words, what amount of lateral force would have been required to overturn this bridge, assuming it to have been properly constructed.

Extract from Rothery’s (Chairman) report

Force required to overturn the Bridge

(77.) According to Dr. Pole and Mr. Stewart, assuming the bridge to have been pro¬perly constructed in all respects, it would have required, if not held down at its base, a lateral force of 34 1/3 lbs. to the square foot, applied at right angles to its direction, to have overturned it; and with holding-down bolts, from 60 lbs. to 70 lbs. According to Mr. Law a force of a little under 33 lbs. would have been sufficient to overturn it without holding-down bolts; and with holding-down bolts, rather more than 64 lbs. These estimates, it will be seen, do not differ very much, and it may therefore be fairly assumed that, if the bridge had been properly constructed, and in accordance with the plans and specifications, it would have required a force of from 60 lbs. to 70 lbs. applied directly at right angles to have overthrown it.

(78.) We can see now why it was that Sir Thomas Bouch’s Counsel was so anxious to show that the maximum wind pressure over the area of one of these spans must have been so small, and that the term “very limited surfaces” must have meant a point, or at the most only a few feet, and not some hundreds of feet, which may well be called a “very limited surface” compared to the whole width of the storm. For, if the maximum wind pressure over one of these spans was only 10 lbs. to the square foot, and the force required to overthrow the bridge was from 60 lbs. to 70 lbs., we should have had a factor of safety of between 6 and 7, which would be a good margin; and even if the maximum pressure was 20 lbs., there would still be a factor of safety of over 3. On the other hand, if the wind pressure over an entire span could ever be as much as 40 lbs. or 50 lbs., the margin of safety would be ridiculously small, not a half, and the bridge from the first would have been quite unsafe, the usual factor of safety we are told being 4 or 5.

(79.) Assuming, however, the bridge to have been properly constructed, and to have been capable of resisting a wind pressure of 60 lbs. to 70 lbs., it is difficult to see how the wind alone could have overthrown it, even if it had been at its maximum of 40 lbs. or even 50 lbs. to the square foot. It would seem therefore that we must look to something beyond the mere wind pressure to account for its fall.

Evidence relating to: Bridge design weakness

Albert Gröthe, resident engineer during the construction of the bridge, was sworn in on 22nd April to be examined by Mr Trayner

MR TRAYNER: Was there any other change in the construction of the bridge adopted in consequence of what you discovered about the bottom? - The length of the spans was altered.

In how many cases, and where? - In the case of that part of the bridge which spans the navigable part of the river.

THE COMMISSIONER: The high girders? - The high girders, and also in some of the adjacent girders, as far as a change was yet possible.

MR TRAYNER: By that time you had built up a certain number of piers upon the south, and you had also been working southward from the north? - Yes.

To what extent were the spans lengthened? - The large spans were intended to be 215 feet long.

Originally? - Yes, and they were altered to 245 feet.

Anything else? - The 130 feet spans were altered to 145 or 146 feet. Those were all the alterations in the lengths of the spans.

MR TRAYNER: You explained that the foundation was altered from its original design, and that consequently upon that the spans were increased; why did the alteration in the design of the foundation lead to an extension of the span? - Because there must be a certain proportion between the money spent on the superstructure and the money spent on piers to produce the cheapest bridge; and it was found that by making the spans as they actually have been made, a cheaper bridge could be produced (without of course sacrificing anything) than if the spans had remained as they were before. A more costly pier was substituted for one which was cheaper before, and therefore making fewer piers and lengthening the spans would re-establish that proportion in which the cost is a minimum.

The new foundation that was substituted was larger and more costly than the preceding one? - Yes.

And the spans, I suppose, were lengthened in order to reduce the number of more costly foundations? - Yes, without sacrificing anything.

Sir Thomas Bouch was sworn in on 30th April. This is the evidence given under questioning by Mr Bidder

There is another matter I must ask you about, and that is as to the turning of the flanges; it has been suggested that it was a disadvantage to have a recess in the flange, and not to have a whole face right across? - I am not quite sure that I understand you.

It was said that your flanges had a recess. I think it is where the bolt came through (like this drawing and diagram). Mr Law took exception to that, because you had not a whole face right across. In your judgement, and according to your opinion, was there any disadvantage in that? - Not a bit.

One other matter I must ask you about. It is also pointed out that you had specified in the specification that the holes through the lugs were to be cylindrical and parallel, and that in point of fact they were cast somewhat conical, enlarging towards the inside in some cases, and that in consequence of that the effect would be that the bolts, instead of bearing upon the whole width of the lugs, would bear upon the outside edge, and when an excessive strain came upon it it would bend, and so the structure would be less efficient. Were you aware that there were any conical holes? - I was not. If I had known I should certainly have had them drilled out square, though that would have somewhat reduced the quantity of metal in the lug, but I should have had that done certainly.

You will so far agree with what has been stated that that was a thing which you would not knowingly have passed, and you think it is disadvantageous? - You could not see the thing by inspection; you could not see the conical shape of the hole.

It would be very difficult to see, even if you were looking at the lug itself before the bolt was in it? - Yes; my own theory is, that the rattling which Mr Noble spoke to was due to the bolt bent in the conical hole. It would be drawn from the straight, and it would take its bearing on the cone.

That gave a certain distance? - Yes, and that would loosen the ties. I think that would occasion the rattling spoken of. I went up the columns with General Hutchinson, and when those big engines were running over at 40 miles an hour we could find no tremor, and hear no shaking of the tie-bars or anything. They were all braced up. I believe it was subsequent to that; it might have been with some of the great storms we had, but I believe subsequent to that the strain of the tie bent the bolt so that it took its bearing on the conical surface. When it was tightened it made it just as strong again. I would rather have had it square, but it tightened it up.

If I follow you, the fact of the hole being conical made it possible when a severe strain came upon the tie for the bolt to be bent till it took its bearing upon the conical hole? - Yes.

That bearing of the bolt gave a certain extension to the tie, and of course the slackness? - Yes.

Till that slackness was taken up again, that tie would not be doing its duty? - No.

Though you said you would not have passed them knowingly, in your judgement, assuming the slackness of the ties was properly taken up after the bolts had bent, did the existence of those conical bolts materially weaken the structure? - No, they did not; not at all.

Extract from Rothery’s (Chairman) report

Defects in the Design

(104.) … the question remains, whether there are not some defects in the design which must sooner or later have brought it down. …We shall therefore proceed to point out what are, in our opinion, the defects in the design, which it will be necessary to avoid if the bridge is to be reconstructed.

(105.) And first it is very greatly to be regretted that Sir Thomas Bouch, when he was designing the bridge, did not take greater pains to ascertain the nature of the foundations, on which the piers were to rest. It is said that he was deceived by the borers, not of course designedly, for they would have no object in so doing. But what right had Sir Thomas Bouch in a matter of so much importance to trust solely to the word of the borers? It is idle to suppose that, if he had looked at the core which was brought up, he would not have been able to ascertain, whether it was the same rock, which is to be found on each side of the river, or that a bed of conglo¬merate could have been mistaken for it. And if he had found that they had come upon a bed of conglomerate, it was his duty to have pierced it with a view of ascer¬taining whether it was capable of supporting the brick piers, on which he designed to place his bridge. Had the solid rock existed, as was too hastily supposed, at a reasonable depth below the bed of the river, so that brick piers could have been built up from the bottom, no doubt the bridge would have been standing at the present day. On the other hand, had it been known that below this thin bed of conglomerate the bottom was only soft sand and mud, either a different design would have been made, or the bridge would have been carried across at some more favourable spot. The mistake, in our opinion, was a very grave one, and for which there is no excuse.

(106.) The next question to be considered is, whether the hexagonal form of the pier, and the way in which the columns were arranged upon it, was calculated to give the requisite amount of stability to the structure. To use General Hutchinson’s words - “no one can say that a broader base would not be a desirable thing.” Now, in what way could this additional base have been given?

(107.) And first, as regards the caissons. They were, as we have seen, 31 feet in diameter. There seems, however, to be no reason why they should not have been constructed in an elliptical form, say 34 feet long by 28 feet broad, which would have given about the same bearing surface for a foundation, would have been more easily sunk in the river from offering a less resistance to the stream, and would have afforded a much longer base east and west, on which to build the piers which were to carry the columns.

(108.) Again, the hexagonal arrangement of the columns with two outer and four inner columns was not advisable. … it certainly seems that it would have been better to have had two outer columns instead of only one on each side. It would have given a wider base, and therefore increased stability to the structure; it would also have had this advantage, that if one of the outer columns had failed, the bridge would not necessarily have fallen, whereas with only one outer column on each side, the failure of any one of them would cause it to fall at once. … Why it was not carried out, has not in our opinion been satisfactorily explained.

(111.) Another great objection to the design was that the girders, which covered the tops of the two triangular groups of columns, were not connected, as they should have been, so as to have formed a continuous girder over the tops of all the columns. This would have given great additional stability to the structure, by binding all the columns together. As it was, the two groups were held together merely by the struts and ties between the columns, which were therefore liable to get out of shape. There was not a witness, we believe, unless it was Mr. Stewart, who did not say that the connection of the two girders at their ends would have given increased stability to the structure.

(113.) But the greatest defect of all was in the cast-iron lugs, to which the ties and struts were attached, and in providing not only that they should be cast with the columns, but with the holes ready made. It is to this, and to the casting of the holes in the flanges of the 18-inch columns, and to not seeing that these holes were made properly cylindrical, and that the bolts fitted them accurately, that the weakness of the piers and the fall of the structure is mainly due. We have dwelt at length on these points, whilst discussing the question of construction, but they belong also to this part of the subject, for it was part of the design that they should be so cast.

Evidence relating to: Manufacture or construction weaknesses

Albert Grothe, resident engineer during the construction of the Tay Bridge, was sworn in to give evidence on 22nd April, and was initially examined by Mr Trayner

Did you do anything personally in the way of testing any of the columns that were cast for the high girders, either to ascertain their strength or the accuracy of the casting? - I never ascertained the strength of the columns. I ascertained, whenever I had an opportunity, the accuracy of the casting.

THE COMMISSIONER: You mean occasionally? - Without making it a special point to go through every one of them.

MR TRAYNER: Will you just tell me what course you took to ascertain the accuracy of the castings? ¬¬- Looking at them - inspecting them; in fact, looking at them carefully.

You mean an external survey of them? - Yes, an external examination.

Did you see any column indicating the existence of a coal-shut? - Yes.

How often? - Very seldom; not often.

Did you pass these columns? - No.

They were broken up, were they? - Every column which I found the least defective, or which was reported to me as defective, was broken up.

Did you see any columns that had blow holes in them? - Yes.

Did you pass any such columns? - No, never.

Can you tell me this; were there any columns that passed your observation that had holes in them filled up with anything like cement or putty? - Yes.

What did you do with those? - Broke them up.

With your knowledge no column went to the bridge that was not, so far as you could tell from external survey, perfect? - Yes, and very positive instructions were given to prevent anything of that kind.

MR TRAYNER: Did you give those instructions to the foreman, or did you direct them to be given through your assistants? - I often gave them, if the assistant was present I would tell him to do so, but if he were not present I would speak to the foreman. I recollect on one occasion particularly having found a column in which a small hole had been filled up with a foreign substance, being in company with Mr Gilkes, and the foreman was called and got a severe scolding for not having prevented this. The column was broken up, and the man received most positive instructions there and then to break up himself, without further authority, any columns which in his opinion, were not perfect, and to report to the manage of the foundry or to myself any which he thought were good enough, though they had some slight defect. He brought some under my notice in that manner, which I invariably ordered to be broken up.

MR TRAYNER: I will put the question in this way: supposing there are two holes that are to contain a bolt an inch and one-eighth on each side of the lug, and there is a plate to be slipped in between these two with an equal hole through which the bolt has to go, my question is, whether you know of any instances in which the holes in the lugs did not correspond with each other so as to admit of the bolt going straight through? - No, I do not know of any instance of that kind.

Where the one hole to some extent overlapped the other? - No, I do not know of a single instance.

If such a thing did occur, would you have approved of a chisel or other instrument being used to enlarge the hole, that was not coincident, beyond the original size? - I would not; but it would depend very much upon the size of the defect what remedy I would apply. If it were only a question of insignificant riming I should have no objection.

Were you aware of any case in which the holes in the channel iron and the lug did not correspond? - I was not aware of any such case till I visited the ruins of the bridge last week.

When you were at the ruins of the bridge did you discover that such a thing existed? - I did.

In many cases, or in few? - I did not see many cases, I only saw a few cases.

MR TRAYNER: Did you discover, on your examination whether any of the holes had been enlarged beyond their original size? - Yes, there were holes which had been enlarged from their original size.

Could you form an opinion, from the appearance of the work, how the holes had been enlarged? - The holes seemed to have been enlarged with a cold chisel.

Was that a thing which you would have approved of if you had known of it? - Most decidedly not. If I had known of it, I would never have approved of it.

On 3rd May, Sir Thomas Bouch was examined by the inquiry commissioner, Mr Barlow

You told us also that the bolt holes ought to have had the sides, as you say, perfectly square or parallel? - They ought to have been.

And if you had known they were not, you would have had them rimed or drilled? - I certainly would. Probably if I had known it earlier, before much of the bridge was built, I should have had them squared; I might have had them rimed out, but I would have calculated the strength of the lug before I began to take the metal out.

When you had them cast, you could have had the holes cast rather smaller, and you could have had them rimed out? - Yes.

That would have been better? - That would have been better. It is not in the specification. The specification says that the holes in the flanges are to be drilled, and it certainly is an omission in the specification so far as the holes in the lugs are concerned. I think it was a fair inference that the holes should have been drilled.

Surely it was intended that the holes to contain the bolts should not be conical? - Yes.

It says: “All bolts to be made of Low Moor iron, or such other make as shall be specially sanctioned by the engineer, and to be neatly finished, head and nut, and not projecting more than ½ an inch through the nuts; to be carefully forged and screwed, and made to fill the bolt holes”? - Yes.

So I suppose there is no doubt whatever, if that had been carried out, you would have had these bolt holes with the sides perfectly level and perfectly parallel? - Most decidedly.

It was a defect not to have them so? - It was.

Extract from Rothery’s (Chairman) report

Defects in the Construction

(80.) In the course of the examinations at Dundee, charges of a very grave and compromising character were made as to the quality of the iron, and the workmanship at the Wormit Foundry, which it was necessary to inquire into, seeing that it was at the Wormit Foundry that all the columns for the high girders were cast. And although all these charges were not fully established, enough has in our opinion been proved to show that there were defects introduced into the structure, which should never have been there, and which certainly did very seriously affect its stability. We will proceed to inquire what they were, and whether they are not sufficient to account for the accident.

(79.) And first as regards the iron, which was said to have been of inferior quality, and from which we are told it would not be possible to obtain good castings. It seems that the iron was for the most part Cleveland iron, sent specially from Middlesbrough by Messrs. Hopkins, Gilkes, & Co., the contractors. Like all Cleveland iron, it was more sluggish than Scotch, and required to be raised to a higher temperature to make it flow freely, without which it would be impossible to get good castings, particularly in the lugs and protuberances on the columns. The result was that was not popular with the Scotch workmen, who were accustomed to work with a more ductile metal, and they complained that a sufficient quantity of Scotch scrap was not mixed with it. Even Mr. Beattie, the engineer, who had for some time the control of the foundry works at Wormit for the contractors, seems to have thought that the introduction of some more Scotch scrap would have been desirable, and suggested that this should be done, but his suggestion was not acted upon. The result was that the iron, although shown by Mr. Kirkaldy’s tests to be fairly good in quality, gave, owing to its sluggish character and to its not being sufficiently heated, in many cases very defective castings. Thus, there were not unfrequently found in the columns, what are called “cold shuts,” caused by the metal becoming chilled, before it had got round the mould; so that, when the two upper edges came together they would not unite, but left a longitudinal fracture in the side of the column.

Owing also to the flask or core of the mould having been allowed to shift, the columns were frequently cast of very unequal thicknesses. It is true that many of the columns, in which these defects existed, were broken up; some, however, were passed, and were introduced into the structure; to what extent it is impossible to say, the greater part of the columns of the high girders being still at the bottom of the river. There is, however, conclusive evidence that some of the fallen columns were very defective, having scabs and unsound places in them; and specimens were produced showing the metal on one side of the column to have been occasionally only 5/8 ths of an inch thick, while on the opposite side it was as much as l 3/8 ths thick. Indeed Sir Thomas Bouch admitted that there were some of the columns, which he would not have allowed to pass, had he known of them.

(82.) But it was in the lugs more especially that the principal defects existed. They were, as we have said, cast with the columns; owing, however, to the sluggishness of the metal, it did not readily flow into the pockets or hollows left to form the lugs. The consequence was that many of the lugs came out in an imperfect state, and in some cases an attempt was made to “burn on,” as it is called, a fresh lug by making a mould for the purpose, and pouring in a sufficient quantity of molten iron. It is obvious, however, that perfect cohesion between the parts could hardly be obtained in this manner, for, as the metal cooled, it would necessarily shrink, leaving a space between the lug and the flange, or between the lug and the shaft, and there was strong evidence that this was so. We were assured, however, that none of the columns, on which lugs had been so burnt, were introduced into the structure; and that they had only been used to raise the girders into position, and had then been removed.

(83.) But it was in casting the “holes,” through which the bolts, which held the ends of the struts and tie bars, passed, that the greatest mistake was made. These holes were cast in the lugs, and were already made, when they issued from the mould. We were told, however that it is almost impossible to prevent the workmen from casting the holes conical, as the cores can then be more readily removed; and accordingly we find that the holes in the lugs were for the most part, if not entirely, cast conical. The result was that the bolts, instead of having a plain surface to rest upon, as they would have had, if the holes had been drilled or made cylindrical by riming, or drilling, bore only on one edge, and when a strain came upon them, they would of course give, until they got a bearing upon the sides of the holes. That this was a defect, and a very serious defect, was admitted by Sir Thomas Bouch himself .

(84.) It should also be observed that the holes from being cast would be necessarily irregular in shape and position, and as it would be quite impossible to cast them quite true to size they were made 1¼ inches, while the bolts which went through them were only 1 1/8 inches in diameter. The effect of these three things, namely, the giving of the bolts so as to get a bearing on the sides of the holes, the irregularity of the holes in shape and position, and the holes being larger than the bolts, was to give a certain amount of play to the ends of the ties and struts, which held the columns in position. Moreover the conical form of the hole converted the hold on the lug into a wrenching strain on one side of it; so that it was found, under Mr. Kirkaldy’s tests, that, when the force was applied in the same direction as when in position on the column, and by a steady pull, and without any shock, the lug was able to bear only one third of the pressure, which it should have done according to the amount of its sectional area.

(85.) Another serious defect in the construction of the bridge was in the formation of the flange holes of the outer or 18-inch columns. It seems that the holes in the flanges of the inner or 15-inch columns were drilled by a machine, and they would consequently be true to position and cylindrical in form. When, however, they came to make the 18-inch columns, the machine, which had been employed for drilling the holes in the 15-inch columns, would not serve for the 18—inch columns, and it was not thought necessary to make a machine expressly for the purpose. The consequence was, that the flange holes of the 18-inch columns had to be cast, with the same results as in the case of the holes through the lugs, namely, that they were conical in shape, irregular in size and position, and gave play to the bolts passing through them, which thus ceased to be steadying pins to the columns, and bore upon only one edge of the bolts. According, too, to Mr. Beattie, under whose superintendence these columns were cast, the holes were cast l ½ inches in diameter, whilst the bolts were 1 1/8 inches (Q. 10,048). This was the more serious, seeing that each of the 18-inch columns had to bear not only double the superincumbent weight, that any of the 15-inch columns had, but also the greater part of the wind pressure.

Extract from Rothery’s (Chairman) report

Supervision at the Wormit Foundry

(87.) And here it may be well to inquire what kind of supervision was exercised over the works at the Wormit Foundry, where these columns were cast, for it is diffi¬cult to understand, how the numerous defects, to which we have called attention, should have been allowed to pass, if there had been proper and competent persons to superintend the work.

(88.) And first as regards the contractors. The person, who had the chief control of the works, on behalf of the contractors from first to last, was Mr. Gröthe. Under him were two chief assistant engineers, namely, Mr. Frank Beattie, who went to the works at the latter end of 1873, and remained there until about 12 months before the bridge was opened; and Mr. W. G. Camphuis, who went in August 1873, and remained until October 1878, some months after the bridge had been opened.

(89.) Mr. Gröthe had of course the general superintendence of the works, but according to his own account having no special knowledge of ironwork, the Wormit Foundry was put under the management of Mr. Beattie, who, we are told, had had experience in ironwork; but Mr. Beattie had other duties to perform, and could not therefore be much at the foundry; nor does he appear to have tested the columns by hydraulic pressure or in any other way, which would have insured the detection of any unequal castings, and any defects in the columns; he trusted to what he could discover by looking at them externally, and tapping them with a hammer. When however he left, the inspection of the foundry was entrusted to Mr. Camphuis, who it is admitted had no practical or special knowledge of ironwork, and his duties in connexion with the foundry were consequently “more of an adminis¬trative than of a technical kind ;" to use Mr. Gröthe's own words, “His” (that is, Mr. Camphuis’) “duties were to see to the stores, and to anything that was wanted, and to exercise as much judgment as he could in going over the castings, but he was not a practical foundry man.” The result of course was, as Mr. Gröthe admitted, that the chief responsibility for the columns being turned out in a properly sound condition, at all events after Mr. Beattie left, rested with Fergus Ferguson, the foreman moulder. That this was a condition of things, which ought not to have existed, can admit of no doubt whatever. It is true that Fergus Ferguson and the rest of the workmen were paid, not by the piece, but by day work; at the same time he would naturally be disposed to pass columns, which a more independent person would not have deemed sufficiently good, for the fewer columns he broke up, the greater testimony would it be to his skill as a workman. Mr. Gröthe told us that he discovered a column, which had been passed to go into the bridge, and which he ordered to be broken up, owing to defects which he found in it. This was whilst Fergus Ferguson was the foreman moulder, so that in that instance Fergus Ferguson must either have knowingly passed bad work, or have passed it without examining it. Practically, therefore, there was no supervision of the works on behalf of the contractors, at all events after Mr. Beattie left, and the answers which Mr. Camphuis gave to the questions which were put to him on the subject, showed how unfit he was to have the superinten¬dence of the works, and how incapable he was to have detected any defects which might have existed.

(90.) What then was the superintendence exercised by Sir Thomas Bouch and his assistants over the foundry works at Wormit? So far as we can see, none what¬ever. … Sir Thomas Bouch seems to have left it to Messrs. Hopkins, Gilkes, & Co.; they left it to Mr. Gröthe, and he left it to Fergus Ferguson. With such supervision, or rather we should say with the absence of all supervision, we can hardly wonder that the columns were not cast so perfectly as they should have been, and that the fatal defects in the lugs and bolt-holes should not have been pointed out.

Evidence relating to: Bridge maintenance

On 27th February, John Evans, who had worked on the painting of the Tay Bridge in the summer of 1879, was sworn in and questioned by Mr Trayner

Did the passing of the trains have any effect on the bridge? - Very much.

What was its effects? - Oscillation, I would term it first, side to side movement

Was there any other movement? - Yes

What? - Vertical movement

With regard to the oscillation or lateral movement, was that severe? - Yes, it was very severe.

What effect did you see the motion thus produced have on anything that was placed on the bridge? - I have seen the spilling of a pail of water a long while before the train approached. You could feel the oscillation half a mile off.

But you have seen a pail of water upset? - No, not upset, only the water oscillating and spilling over the side.

Had it any effect on the paint-pots? - We always secured them with every passing train.

Were both those movements greatest inside or outside of the high girders? - Inside, about the centre.

Alexander Stewart, a joiner from Dundee employed to provide boxing for the water pipe from Dundee to the south bank, was sworn in to give evidence later on 27th February to Mr Trayner

When the two movements got combined was there a severe movement of the particular place at which you were standing? - Yes, it would make an unaccustomed man feel a little strange.

Not steady on his legs you mean? - Yes, that is the feeling; you felt the under part shaking under you.

And you felt it shaking from side to side? - Yes.

COLONEL YOLLAND: At the time when you felt the side motion most you were over a pier, were you not, where the high girders and low girders meet? - Yes.

Did you at that time look along the piers either to the north or the south so as to notice whether you were sensibly deflected to the east or to the west? - Yes, if you looked along the side of the girders.

Did you form any opinion at the time to what extent the deflection took place? - I would say it was considerable but I could not say exactly in inches what it was.

Did you form any opinion at the time? - Yes.

What was it? - I would say from two to three inches.

You formed an opinion, but you cannot say what it is now? - From two to three inches.

Would that two to three inches be the extreme of the motion eastwards to the motion westwards, or was it half that quantity? - Well, I could not say; it was difficult to measure, but the motion was distinct and large.

MR TRAYNER: And visible? - Yes.

On 19th April, Mr Noble, Inspector of the Tay Bridge for the North British Railway Company, was sworn in and questioned by Mr Trayner

Leaving the foundations, let us go up a little bit. Did you discover whether any of the ironwork of the bridge was getting unstable or loose? - In taking those soundings that I have spoken of, I noticed or heard a chattering of the bars.

You heard them moving or shaking? - Yes.

Was it in the lowest tier of bars nearest the stone work that you found the bars chattering? - Generally. As far as my remembrance goes, it was something like the third or fourth tier down. I cannot positively say: Such a thing might have taken place in the second tier from the top to the bottom.

Were those loose bars within the high girders or without the high girders, or both? - They were both.

Did you examine the bars in order to see what was the matter with them, or whether they needed any repairs? - Yes.

Tell me what it was you found to be wrong with the bars on your examination of them? - I do not know whether I can explain it to you. I found that the cotters in coming together had got a little loose - there was not a sufficient width to get a good grip, and they had got a little loose.

What was the use of those cotters? - To tighten up the bracings.

What was the purpose of having the bracings tight? - To make the bridge stable.

But you thought it a sufficiently important thing to induce you at once to repair it? - Where I heard a noise from the jingling of the bars I tried to remedy it.

Sir Thomas Bouch was sworn in on 30th April - in this extract he is answering questions from Mr Bidder.

When the structure was completed, General Hutchinson inspected it on the part of the Board of Trade? - He did; he spent three days on it.

I believe you accompanied him on his inspection? - I did.

And that inspection, I believe, was of an unusually thorough and searching character? - it was the most strict inspection I ever experienced of the many I have had through the Board of Trade’s hands. I never knew so much time and pains spent in a Board of Trade inspection as was spent by General Hutchinson at that time.

You were present at the time. So far as you could see, do you agree with General Hutchinson that the bridge was in every respect complete and efficient, and remarkable rigid? - I felt so. I thought so when I went through the inspection. I went along the piers with General Hutchinson, and I put my arms round the columns when those great engines were going over at full speed, and there was no tremor at all; they were so rigid I was surprised at it.

Mr Noble, as we know from his evidence, continued to be employed upon the bridge with a certain staff? - Yes.

And Mr Noble stated that as regards his examination of the piers of the bridge, I think that he did it simply of his own motion: is that correct? - That is true. The staff was given him of two men, and when they were not sounding and finding out about the scour, which was the principal thing that I was afraid of, they were to be employed upon the piers seeing that the nuts were all right.

That which you were most anxious about, as I understand, and though there was most cause to fear, was the possibility of scour? - Yes, it was; that was the only thing that I was at all alarmed about and anxious to watch and provide against.

Letters sent by Mr Noble to Mr Bouch read out at the Inquiry by Mr Trayner to Mr Bouch

“I am happy to say that the piers are not only secured at the price named, but upon a strict scrutiny made every day there is not the slightest sign of a settlement at any of the piers. My staff of men who work the steamboat are always busy overlooking the bracings, &c, while I am attending to the Newport Branch. At high and low water I never neglect, in fine weather, to keep the sounding lines going between the tides”. It is within your understanding that his staff of men were continually engaged in overhauling the bracings and ties throughout the bridge? - Yes, that was the arrangement I made, that they should devote their spare time to examining them.

On the 1st of November, I think, you had another report, “In my last letter or report, dated September 30th, I told you I have gone over the whole of the sounding once more to see if the September gales had any effect in causing scour around the piers. I am happy to be able to state that the severe gales we have experienced here during the last six weeks at intervals have made no perceptible alteration in the bed of the river, so far as I have been able to accomplish up to present time.”

Then on the 18th of December 1878 he writes this report, … “I deem it to be my duty to inform you that the number of workmen employed under my directions in the examination of foundations can now be reduced to two. Two workmen would only be required to assist me in continuing the soundings and examining the bolts and bracings of the columns during my stay here. In regard to the scour of the bed of river around the piers, I am happy to inform you that no alteration is perceptible since my last soundings, taken in September and October, and the quantity of rubble stones used since is only two cargoes, one since I saw you at your office, and one previous. There will be no more rubble required at the piers unless something occurs very different from what I expect. The superstructure stands the traffic first class; there is not the least defect in the entire length of bridge, nor any sign of settlement at any one of the many piers.”

“I am now anxiously watching the effects of the large quantities of ice (with which the river is covered) on the piers. In looking over my diary for 1874, I find we had blocks of ice 12 inches in thickness, and no damage was caused except a slight graze on the brickwork. Certainly we only had six piers out on the north side between the shore and No 57, and of course a greater space for the ice floes to pass backward and forwards with the current. I shall be as vigilant as I can possibly be over this affair.”

Is that also in accordance with your understanding that you had at this time, December 1878, Noble and his staff continuing to occupy themselves, and to watch and examine the bolts and bracings of the columns of the piers? - It is so.

Evidence relating to: Train speed

Mr William Robertson was sworn in on 26th February to give evidence to Mr Trayner

Why did you take so much notice of the speed of the train through the girders only once, and take frequent notice of the speed over the whole bridge? - The ease at which the train travelled at the two ends of the bridge had produced no uncomfortable feeling in my mind as a passenger, and therefore gave me no concern.

Then the reason of your observing the speed within the girders was from the fact that the speed at that point did produce some discomfort and concern? - Yes.

Can you tell me what was the speed at which the train passed over the bridge from shore to shore at the time you observed it? - Four minutes and 20 seconds from signal box to signal box.

The length of the bridge is from box to box what? - Two miles about.

Given that distance and that rate of progression, what was the speed at which the train was running? - It must have been in excess of 25 miles an hour from box to box. Slightly in excess of 25 miles an hour.

Did that speed occasion any discomfort with reference to the girders? - Very much so.

Will you tell me what was the effect produced in the girders by that rate of speed upon you as a passenger? - There was a very perceptible vertical vibration and also a very perceptible lateral vibration upon that part of the bridge with the train running at that rate of speed. When the train was within the girders it was running at a higher speed than average speed.

Kindly tell me what was the highest rate of speed at which the train passed those high girders, you being a passenger? ¬- 50 seconds.

That was at the rate of 42.94 miles per hour? - Yes.

Did that rate of speed happen often? - I have just seen it twice.

Apart from the exceptional cases of the highest speed that you have given us, and the lowest speed you have given us, it seems to be the results of your personal experience that the train usually went across the girders at a rate of nearly 36 miles an hour, 35.78? - Yes; I should say as to the whole of the observations that I have taken, which have been very many, not only as a passenger, but when I have not been travelling, the range of speed would be from 30.67 to 35.78 miles per hour.

Having a ticket which entitled you to travel both ways, why did you give up, in the middle of December, travelling from south to north by railway? - I did not feel comfortable on the bridge.

And it was this discomfort which made you give up this travelling by it in that direction? - It was.

By discomfort do you mean bodily discomfort or mental discomfort? - Mental discomfort.

And that mental discomfort arose from what? - From the high speed at which the train was travelling.

From anxiety as to your safety, occasioned by this high speed? - Yes.

In a word, did you consider it dangerous? - Yes.

Extract from Rothery’s (Chairman) report

(98.) It may be well to say a few words in regard to the speed, at which trains were allowed to cross the bridge. It has been said that in General Hutchinson’s report of the 5th of March there was a recommendation that it would “not be desirable that trains should run over the bridge at a high rate of speed” and he suggested “25 miles an hour as a limit, which should not be exceeded.” This seems to have been interpreted by the servants of the Company to mean that from station to station they were not to go at a greater average speed than 25 miles an hour, and this they seem to have done. Seeing, however, that they had, in approaching the cabin at either end to reduce the speed of the train to some two or three miles an hour in order to take the baton, and had then to mount an incline before reaching the summit, it is obvious that, if they did the distance from cabin to cabin at the rate of 25 miles an hour, they must have been going through the high girders, where it is level and on the summit, at a very much greater speed.

(122.) The Company also are in our opinion not wholly free from blame for having allowed the trains to run through the high girders at a speed greatly in excess of that, which General Hutchinson had suggested as the extreme limit. They must or ought to have known from the advertised time of running the trains that the speed over the summit was more than at the rate of 25 miles an hour, and they should not have allowed it, until they had satisfied themselves, which they seem to have taken no trouble to do, that that speed could be maintained without injury to the structure.


Bill Dow – Theory A Train
“The rear carriages of the train derailed and ran into one of the coverplates. The force of this impact would shatter the cast iron lugs – leaving the bridge in a high wind without its proper structural support.”

The girder closest to Wormit, in the high girder section of the bridge, had bent during the lifetime of the bridge. The girder had been dropped during construction and bent. It was straightened out and reused, but over time it returned to the bent shape. As a result, the rail tracks that ran over it developed a kink. This kink, combined with the high wind, may have been responsible for the derailment.


Tony Martin – Theory B Wind
“The disaster was investigated using modern computer analysis in conjunction with a modern approach to wind loading. The bridge was examine with and without the train to see what effect on the performance of the pier structure. And a pier was analysed under various load conditions with a view to proposing a mechanism for collapse of the navigation piers.

The bridge was simply not strong enough to withstand the strength of the wind that night. Although the presence of the train does affect structure, even without the train the bridge would have fallen that night.


Peter Lewis – Theory C Fatigue
“It was almost certainly the dynamic effects of the bridge itself well before the disaster that brought the bridge down. These led to gradual deterioration of the ironwork supporting the high girders.

On the night of the storm, the bridge piers were no longer capable of supporting the applied load. Within that, fatigue and crack propagation probably played an important role.

Who’s Who

Sir George Airy, Astronomer Royal, and expert witness on wind speed and pressure

Thomas Napier Armit, superintended raising of fallen parts of high girders

Benjamin Baker, distinguished civil engineer and expert witness for Bouch (designer of present Forth Bridge)

Mr Balfour, chief counsel for North British Railway

William H Barlow, commissioner on the Tay Bridge Inquiry and President of the Institute of Civil Engineers

Frank Beattie, Assistant Engineer employed by contractors to Tay bridge

Mr Bidder, chief counsel for Sir Thomas Bouch

Sir Thomas Bouch, railway engineer and consultant to the North British Railway (NBR), designer of the first Tay bridge

Gerrit Camphuis, Assistant Engineer employed by the Tay bridge contractors

John Cochrane, civil engineer and expert witness for Bouch

Dugald Drummond, distinguished designer of locomotives and Locomotive Superintendent for the NBR

John Evans, painter of the Tay bridge during the summer of 1879

Fergus Ferguson, Foreman moulder at Wormit foundry

Albert Grothe, Resident Engineer employed by contractors for Tay Bridge

Major-General CS Hutchinson, RE, inspected and approved Tay bridge for BoT

David Kirkaldy, expert materials investigator who tested the wrought iron for Bouch, and the tie bars and connections for the inquiry

Henry Law, chief investigator for the Board of Trade

Charles Meik, assistant to Sir Thomas Bouch

Henry Abel Noble, Inspector of the Tay bridge employed by NBR and reporting direct to Bouch

Henry Pole FRS, mathematician and expert witness for Sir Thomas Bouch

William Robertson, Harbourmaster in Dundee, ex-Provost of the city and frequent traveller over the Tay bridge

Henry Cadogan Rothery, Commissioner of Wrecks, chairman of the Tay Bridge Inquiry

Captain Scott, Superintendent of the training ship "Mars", moored at Dundee in sight of Tay bridge

Alexander Stewart, joiner who fitted boxing to the water pipes on the Tay bridge

Allan D Stewart, design assistant to Sir Thomas Bouch and co-author (with Henry Pole) of a report ordered by the inquiry team

Professor G G Stokes, academic from Cambridge University, authority on fluid mechanics, wind measurement, expert witness to inquiry

Hercules Strachan, Foreman moulder at Wormit foundry

Mr Trayner, chief counsel for the Board of Trade

Colonel William Yolland, Chief Inspector of Railways




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