Thomas William Kennard

Designer of the

The Crumlin Viaduct


Prior to the industrial revolution, the little-known hamlet of Crumlin, nine miles north-west of Newport, existed only as a few houses clustered around a stone bridge.

Despite the series of coal levels which gradually opened up along the Ebbw and Kendon Valleys and the arrival of the Monmouthshire canal in 1829, Crumlin remained on the whole unaffected by industry. By contrast, the construction of the Viaduct had an enormous impact on the area: between 1860 and 1900 workmen’s homes, places of worship, a company school, shops, a hotel and a ‘mutual improvement society’ with library and reading room were established in its wake by contractor Thomas Kennard. This new area, known as ‘Crumlin Village,’ serves as a reminder of the importance of the new bridge to the community; Viaduct Terrace, Upper Viaduct Terrace, Kennard Terrace, the Viaduct Hotel and Viaduct Cottage were all constructed here.

The word viaduct derivies from the Latin via (way) and ductus (to lead). A viaduct is a type of long bridge either built as a series of tall towers linked by bridge spans or made by placing a continuous track upon supporting arches. It is designed to carry railways over rivers or valleys and is similar in design to an aqueduct; which was intended to carry water.

Crumlin viaduct was hailed as ‘one of the most significant examples of technological achievement during the industrial revolution’ and ‘one of the most technologically important bridges ever to have been built.’ During 109 years of service, it remained the least expensive bridge for its size ever constructed, the highest railway viaduct in the British Isles and third highest in the world, outdone only by the Aqueduct of Spoleto in Italy and the Portage Timber Viaduct in the United States. Although it should more accurately be known as ‘the Crumlin Viaducts,’ as it actually consisted of two bridges separated by the shoulder of a hill, it was officially recorded as being 497.4 metres (1,658 feet) in length, thus making it the longest iron truss bridge in the world.

"At first sight of the structure, the beholder is impressed with wonder and admiration at its airy lightness, combined with elegance and solidity, and at finding such a specimen of architectural beauty springing up in a wild and rugged mountain pass. To ensure safety in crossing the viaduct, lines of guard rails are raised above the traffic rails."

[Extract from ‘A description of Caerphilly Castle, Castell Coch, Crumlin Viaduct and Viaduct at Hengoed Junction]


Bridge Designer and Contractor: Thomas Kennard

Between July and August 1852, the NAH’s Board of Directors invited tenders for a bridge to cross the valley. Designs were submitted to the board during meetings in the London Tavern at Bishopsgate. By October, two proposals had been marked for consideration: Doyne’s design for what he termed a ‘lattice structure’ and Thomas William Kennard’s ‘Warren bridge.’ Charles Liddell, the chief engineer for the NAH, preferred Kennard’s design which was formally accepted on October 20th. The following December, a contract with a finish date of 1 October 1854 was signed.

The Kennard Family

The Kennard family were descended from John Kennard, a Lombard Street banker. John’s second son was Robert William Kennard (1800 – 1870), MP for Newport and the Isle of Wight and the man behind the building of the major ironworks at Blaenavon and Falkirk. Robert made a fortune during the railway boom of the 1830’s, becoming a top railway financier, director of one of the largest groups promoting French railroads and director of several railway companies. Upon his election as an associate member of the Civil Engineers he was seconded by the influential figures of Stephenson and Cubbitt.

Robert’s eldest son was Thomas Kennard (1825 – 1893), designer and contractor of the Crumlin Viaduct and founder of Crumlin village and the Crumlin Viaduct works. Although Kennard’s first involvement with the Warren Triangular Girder was an unsuccessful tender for the construction of a series of bridges in India, he was responsible for modifications that led to huge advancements in architectural engineering. Thomas settled in Crumlin whilst the building of the viaduct was in progress, but left the area in 1858 to prospect for gold in the United States.

Thomas’ brother was Henry Martyn Kennard (1833 – 1911). Henry directed the company from 1858 until he was bought out by the co-manager and major shareholder, Henry Nathan Maynard in 1872. H M Kennard became High Sheriff in 1863, and was elected as a member of the South Wales Institute of Engineers in 1864. He took out a number of patents whilst he was director of the works.


In October 1852, the NAH’s resident engineer, M. W. Carr, furnished Thomas Kennard with the plans and specifications for Crumlin’s groundwork. Kennard was then free to alter the length of his spans to find the strongest, safest and most economical design for the viaduct. As a whole, the structure had to be capable of dealing with the weight and dynamism of a locomotive. The spans had to be strong enough to carry the loads placed upon them, whereas the piers had to support the bridge itself.

In the interest of efficiency and economy, the fewest materials had to be used. Kennard estimated the cost of a number of different designs and calculated that the distance could be divided most economically into 10 spans. If there had been fewer, longer spans they would have had to increase in strength and therefore weight; if there had been more shorter, lighter spans, the cost of building extra supporting piers would have increased.

Kennard’s subtle understanding of the nature and distribution of stresses in a beam lead to an enormous stride forward in bridge design and the development of the revolutionary lightweight structure of the viaduct. The amount of material used in the Crumlin Viaduct is incredibly economical when compared to other bridges of the age. According to Henry Maynard, the weight of the Viaduct amounted to less than 6 cwt per foot run, whereas the maximum compression is 4 tons per square inch and the maximum tension 5.5 tons.

The Britannia Bridge

"[On Crumlin Viaduct and the Britannia Bridge]…Anyone who wishes to see the use of iron in bridges at its best, and in the strongest possible variety, will still find it worthwhile to visit these two great works, built within two years of each other, at opposite ends of Wales." [Jack Simmons (1961)]

Crumlin Viaduct was not the first large-scale example of wrought iron construction. It was preceded by the Britannia Bridge, built between 1846 and 1849. Spanning the Menai Straits for the Chester and Holyhead railway, this Bridge was constructed by engineer Robert Stephenson and architect Francis Thompson. It consisted of two approach spans of 69 metres (230 feet) and two inner spans of 138 metres (460 feet). Trains ran through two continuous rectangular tubes each 453 metres (1511 feet) in length. The bridge also boasted marble faced towers; originally conceived as supports for auxiliary chains which were never installed as the girders were strong enough in themselves. Stephenson’s bridge was the first to use the hollow box girder (rectangular tubes built from wrought iron plates), a design which gave the extra stiffness of the truss and required less precision. However, this was at the cost of more material; one tube of the central span weighed 1600 tons alone whilst the total mass of the bridge was 11,488 tons.

Although Crumlin Viaduct and the Britannia Bridge were of similar dimensions, Stephenson’s bridge was ten times more expensive. Whereas the strength of Stephenson’s structure came from the amount of material used, Kennard’s revolutionary lightweight design took its strength from the first use of both the Warren Triangular Girder and Cross-braced piers.

The Warren Triangular Girder

A truss is designed to use a small amount of material to carry relatively large loads. Through the use of gravity, it transmits the weight of a load vertically into its supports. As these forces are transferred, the truss or beam becomes subject to tension (pull) in its lower half and compression (tension) in its upper half. As these forces could cause it to bend and break, the design of the truss could only be perfected when materials strong in both tension and compression such as iron and steel became widely available.

The Warren Truss or Warren Triangular Girder was invented by James Warren and Willoghby Theobald Monzani. In 1848, Warren patented the design of the Triangular Girder (patent number 12242) and in 1850, the first Warren Truss bridge was constructed at London Bridge Station. The work was carried out on behalf of the South Eastern Railway, whose director, Daniel Warren, was James’ brother. James also invented a number of other uses for iron, including cast metal screws.

Through the use of equilateral triangles, Warren ensured that no individual strut, beam or tie was subject to bending or straining forces, but only to tension and compression. This design was far superior to the Neville Truss, which employed similar principles but instead used isosceles triangles. Warren’s spans could be constructed to reach between 18 and 30 metres (60 and 100 feet) in length.


Kennard and the Warren Truss

Kennard analysed the stress distribution in Warren’s span and was then able to make design improvements to the top and bottom beams of the girder. These improvements meant that the use of iron could be further economised without compromising the strength of Warren’s design. Thomas Kennard’s acclaimed design was patented in 1853 alongside his plans for bridge piers formed from cast iron pipes clustered in a hexagonal shape.

Kennard’s design for Crumlin Viaduct consisted of his own modification of the Warren Triangular Girder, supported by piers made to his own specifications. Although engineer Charles Liddell claimed that he alone was responsible for the design of the bridge and the adoption of the Warren Truss, his claims were never seriously considered.

Thomas Kennard’s method for ascertaining the amount of strain upon various parts of the girders:

When equally loaded:

It is assumed that the heaviest weight one span of the bridge will bear (including the floor, railway and heaviest load) = 270 tons

It is assumed that the weight will be evenly distributed between two girders stretching the length of the span

270 ÷ 2 = 135 tons per girder

Each girder is supported by the points of 9 triangular sections formed by diagonal struts and ties. Therefore the number of tons to be supported on each division of the top flange:

Each set of struts and ties have to bear their portion of the passing load (15 tons). On top of this, the struts and ties support each other, transferring the pressure away from the centre point. Therefore, whilst diagonals in the centre are only required to bear the strain of their portion of the passing load; those nearer the edge must endure this plus the compressive and tensile forces passed on from their neighbours.

The total addition of strains passing through the diagonals are therefore concentrated into the two support points at either end. Alongside the final portion of the passing load (smaller because there is only one diagonal rather than two), the strains pass into the piers upon which the span rests.

Pressure at centre support points = 15 tons (15 tons from passing load)

Pressure at next support points = 30 tons (15 tons from passing load and 15 tons transferred from centre)

Pressure at next support points = 45 tons (15 tons from passing load and 30 tons transferred from centre)

Pressure at next support points = 60 tons (15 tons from passing load and 45 tons transferred from centre)

Pressure at outer support points = 67.5 tons (7.5 tons from passing load and 60 tons transferred from centre) This is transferred into the supporting piers.

67.5 x 2 = 135 (total weight of passing load)

When unequally loaded:

When loads are not evenly distributed, for example, when a train in motion begins the journey across a new section of track, only a portion of the span is loaded, causing the direction and the amount of strain placed upon the diagonals to change. Whereas some would have been wholly compressed under an even load, they are subjected to tension by an uneven load:

Testing the girders

Four girders were used to support the floor of each span: there were forty in total throughout the viaduct. The first pair of girders were tested in the presence of Liddell and Gordon of London, railway engineers, and Edwin Clark, famous for his experiments at the Menai Bridge. A single ¼ inch strut was held in exactly the same position it would have occupied as part of the viaduct and tested with a hydraulic machine. The strut failed at 200 tons (20 tons per square inch) indicating that the maximum weight which could be applied was 21.2 tons (of the breaking weight). Further experiments indicated that the tensile strength of the iron was around 29 or 30 tons per square inch.

After the viaduct had been completed, the greatest deflection caused by a heavily loaded train passing over it was said to be N of an inch, with the girders returning to their original form as soon as the train had passed. This was measured by suspending a weight and pointer from a girder on the end of a wire and attaching it to a sliding scale fastened to the ground below.

A freelance engineer named Charles Wild later adapted the Warren Truss to create a 75 metre (250 foot) long span to cross the river Trent at Newark. Wild’s design was adopted by James Cubbitt for use on the Great Northern Railway.


When Kennard was awarded the viaduct contract in Autumn 1853, his first act was to establish a works at the east end of the viaduct site; the Crumlin Viaduct Works. All fitting and fabrication took place in this custom built assembly plant, including machine riveting, which Kennard insisted on using where possible, as it was quicker and stronger: tests had shown that machine riveting was more likely to compress and fill a hole than hand riveting. Wrought iron was supplied by the nearby Blaenavon Wrought Iron Company, whilst casting took place at Kennard’s plant in Falkirk. Cast iron was transported from Falkirk to Newport by sea and then via canal or rail to Crumlin. The Newport to Crumlin branch of the Monmouthshire Canal had been in operation since 1796 and under the ownership of the NAH since June 1845. The tramroad had been extended in 1829 to ease traffic on the canal. This tramroad eventually became the Monmouthshire Railway.

Whilst the Viaduct was under construction, Thomas Kennard relocated to the area. He commissioned the building of a grand home known as Crumlin Hall, positioned so that progress on the viaduct could be observed from the study window.

Erecting the Piers

Prior to determining where each pier was to go, Kennard’s men bored a series of trial holes to establish the nature of the ground. The valley floor was found to be composed of sufficiently hard gravel for a distance of 40 feet or more from the surface. Operations began when the canal was dammed up and pumped dry and the surrounding earth excavated to reveal the gravel below. The first pier was placed in the canal basin, determining the position of all others. A few conveniently placed piers were simply bolted onto levelled rock surfaces but typically, the piers were set into foundations consisting of 1 foot of concrete, 4 inch thick Memel planking and a twelve foot thick course of solid masonry composed of blocks 1 foot thick.

After just seven months, the first pier had been raised into place. There was a ceremony to mark the occasion on December 8th, 1853. Lady Isabella Fitzmaurice, wife of the NAH chairman, Sir William Fitzmaurice MP, formally erected it in the presence of several directors, gentry of the neighbourhood and others interested in the work. The pier, one of the tallest in the viaduct, was thereafter known as the ‘Isabella Pier.’

"The ceremony of fixing the first column was performed by Lady Fitzmaurice, on the 8th instant, in the presence of several scientific gentlemen and numerous spectators. Previously to lifting the first girder, it was tested with a weight of 250 tons, and gave great satisfaction to the engineer who inspected it. On the third instant, about half-past three in the afternoon, it reached the position destined for it, from pier to pier on the Pontypool side of the valley. The weight of the girder was twenty-four tons, and it was raised by machinery at the rate of four inches a minute. When the girder was ‘planted’, a loud and hearty cheer burst from the lips of the workmen, who were some of them in the most perilous positions; while one, more courageous than the rest, actually walked across the girder which was about a foot in width and 200 feet from the ground. In the midst of the excitement, Mr HM Kennard, brother of the contractor, ascended a platform and spoke to the men in glowing terms of the dangers to which our troops were exposed in the Crimea, proposing to the men the desirability of contributing something towards the fund, as a sort of commemoration of a memorable day. The proposal was received with deafening acclamations, and a day’s pay was at once cheerfully offered. The work people were afterward regaled by Mr Kennard, who has built a large permanent workshop adjacent to the viaduct.

‘The ceremony of fixing the first column’ – Extract from the London Illustrated News (December, 1853)

"In the presence of the directors and the local gentry, her ladyship (Lady Isabella Fitzmaurice) placed inside a stone, a cup containing the coins of that year, a bottle of wine was broken over the pier, and the permanent bolts were placed in position."

Extract from the ‘Monmouthshire Merlin’ (December 1853)

The cup bore the legend:"Crumlin Viaduct, This column was erected by the Hon. Capt. Fitzmaurice, Chairman, assisted by the Hon. Mrs. Fitzmaurice, Lady Isabella Fitzmaurice, and T. W. Kennard, Esq, December 8, 1853."

The original contract for the construction of the viaduct specified an end date of October 1854. There was however, a three-year delay before the viaduct was finally completed and it may well be that these celebrations were intended to impress shareholders.

The piers of Crumlin Viaduct were slightly flexible due to their height and could deflect several inches without losing their original shape. This was necessary as the expansion and contraction of the girders caused them to bend several inches about their centre (lateral deflection). Every span connected to the next at the top of the piers, effectively making one continuous span. It was particularly important that special bearings were built into the stone abutments, allowing the girders to expand and contract freely. Records of variations in length were kept for some time after the completion of the viaduct, looking particularly at the first seven spans on the eastern side.

Construction of the Girders

After the piers and masonry abutments had been built to the correct height, the hoisting of the girders could begin. Although there were four girders in each span, each girder was built and lifted into place individually. Accurate prefabrication and simple pin connections ensured that it took twenty men only two days to assemble a girder on the ground between the piers. A parallel opening ran up the entire height of every pier, so girders could be lifted up this central groove, moved sideways and lowered easily into place. At each end of the girder, ropes of 8 ½ inches in diameter which were wound through 2 sets of 2-3 wheel pulley blocks; the upper pulley block and roller frame being suspended from a timber crosshead erected at the top of each pier. The total weight lifted by steam winch (including the temporary trussing, rope and tackle) was 25 tons.

As girders were raised at a rate of 10 centimetres (4 inches) per minute, it took an entire day for a gang of twenty men to lift each girder into its highest position: they were usually fixed or set the same night. It would then take the same gang two days to prepare for, build and fix the lifting tackle for the next girder. For their combined efforts, the gang would receive a combined total of £5 per day.

The first girder was hoisted into place on December 3rd, 1854. To winch it into place, the steep natural slope at the east edge of the valley was levelled from 1:3 to fill at least half the distance between the first two piers. The remainder was spanned by trussed timber beams to create a level platform upon which the girder was built. Materials had to be pulled up a temporary incline to this platform using a rope, which passed over a pulley at the top and a drum on the engine below.

The first girder to be lifted into position was hoisted without any form of temporary lateral support. However, the next girder to be lifted in this manner buckled; then slipped and fell. One man, who was standing on top of it, was dashed to the ground and died, and a further two were seriously injured. This was the only serious accident during the construction of the viaduct, although there were false rumours in September 1855 that a painter had fallen to his death.

Following the incident, pairs of safety slings were placed at the end of each girder. These slings were made from bars of iron 15 centimetres (6 inches) wide by 1 ¼ cm (½ an inch) thick with 3 centimetre (1 ¼ inch) holes punched 5 centimetres (2 inches) apart. They were moved steadily up the groove in the pier, one on top of the other; providing a surface that a falling girder would come to rest upon should the lifting harness break. Kennard also ensured that all other girders were temporarily strengthened with timber banjo bracing, which followed nearly the same template as the girder itself. Long timbers 15 centimetres (6 inches) thick by 22 ½ centimetres (9 inches) wide were laid parallel at a distance of 1 metre 80 (6 feet) apart. They were connected every 1 ½ metres (5 feet) by pieces of timber. The whole construction was secured horizontally on top of the compression bar of the girder and could be removed in small pieces as the permanent bracing was fixed.

Following the raising of the last girder on December 17th, 1855, Mr Kidd, the foundry manager, led a procession from the viaduct works, through the village and up the Kendon Valley to the viaduct, across which a temporary footway had been laid. Thomas Kennard was the first to cross the narrow planking, followed by his wife, who was loudly cheered upon reaching the opposite side.

"The procession having moved forward upon the viaduct, just as the centre had been reached, a number of cannon on the hillside poured forth thunder peals, which reverberated through the valleys; the workmen joined in rounds of cheering for Mr. and Mrs. Kennard and their friends; and again and again discharges of cannon resounded from height to height.

When the procession reached the Pontypool side of the viaduct (the view from which spot was strikingly picturesque) a Welshman of the neighbourhood ascended a platform and delivered a short and appropriate address in Welsh, congratulating Mr Kennard upon the completion of the majestic viaduct.

The procession did ascend the hill, singing ‘cheer, boys, cheer!’ Shortly after, two barrels of beer were broached by Mr Lewis Richards, in front of the Navigation Hotel… (and) singing, music and dancing concluded the gratifying proceedings."

"Raising of the last girder – Monmouthshire Merlin (September 26th, 1855)"


In July 1857, disagreement began to arise over costs in the Viaduct account that had not been agreed. By February 1859, Kennard was offering to settle with the NAH for £50,000, although they were holding out for £46,000. Charles Liddell’s original estimate for the cost of the work had been £40,000, plus costs for rails and switches; but this appraisal had been raised to £42,000.

The difference between the Kennard’s £62,000 and the NAH’s £46,000 is probably explained by labour costs and possible work on the foundations by external contractors.

The Kennard brothers issued a writ for payment in July 1859 and following a court hearing, NAH accountants paid out a meagre £944.

Breakdown of the actual cost of the Viaduct (After Maynard, 1862):





Material and labour in ten Spans of wrought iron, including Saddles, Bearing pieces, and Cross-bracing




Lifting the Girders to the top of Piers, and all the temporary apparatus used




Material and labour in the Piers, such as derricks, blocks, inclines, wins, etc., from the foundations to the setting of triangles, and including the Masonry Abutments











Sundries, including Handrail testing, Painting, etc.




Accidents and breakages








Cost per foot: £47 7s.

Subject: Re: Thomas William Kennard
Date: Thursday, June 21, 2001 9:41 AM
Please note: it has all been prepared for general users, not specialists so it
tends to simplify in places...

Laura Hilton
Local Studies Officer

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