Welsh Bridges: 18. Britannia Bridge

Thomas Telford built two significant suspension bridges on the north Wales coastline: the Menai Suspension Bridge (1819-1826), and Conwy Suspension Bridge (1822-1826). These formed part of a significant and much-needed improvement to the nation's highways. However, they were completed just four years before George Stephenson's Liverpool and Manchester Railway would kick start a very different transport revolution.

Roughly two decades after Telford did so for roads, it was George's son Robert Stephenson's turn to bring the railways to north Wales and Anglesey. He built two revolutionary bridges to span the exact same stretches of water as Telford: the Conwy Railway Bridge (1846-1849), and the Britannia Bridge (1846-1850). And just as had been the case for Telford, Stephenson could not do it alone.

The bridge across the Menai Strait was the most challenging element in the Chester and Holyhead Railway, and decisions on how to span the Strait remained unresolved while designs progressed for other parts of the line. Some thought was given as to whether the Menai Suspension Bridge could be modified to carry trains, but the loads required for a railway far exceeded those imposed by the horsepower that initially crossed Telford's bridge.

As in Telford's time, consideration turned to building a new arch bridge, but the Admiralty insisted on the provision of full clearance for high-masted ships across the full width of the Menai. Having settled on an alignment that made use of Britannia Rock in the middle of the channel, Stephenson proposed a flat span structure, with girders supported from above by suspension chains. The bridge towers were designed and then constructed tall enough to support such chains, although in the end they were never installed.

It seems that Stephenson conceived initially of a suspension bridge, and then sought a way in which it could be made sufficiently stiff to carry railway loads. He turned to William Fairbairn to investigate the feasibility of tubular stiffening girders, through which the railway tracks could run. Fairbairn rapidly came to the conclusion that the suspension chains would be too flexible, and should be dispensed with, but the less confident Stephenson kept provision for the chains until the bridge was complete.

Fairbairn undertook many experiments on tubular cross-sections, and in turn involved the mathematician Eaton Hodgkinson to analyse the experimental results. Stephenson's preferred girder design was for an elliptical cross-section, but Fairbairn soon determined that a rectangular section was more efficient. It rapidly became clear that buckling of the top flange of the girder was the key issue, a problem that was resolved by adopting a cellular upper flange to the girder, initially comprising two hollow circular tubes joined together, and later evolving into multiple cells side-by-side. 

Fairbairn constructed a 75ft span model tubular girder to resolve the final details of the rectangular tube design. The side walls required internal stiffening, and in the final design both the top and bottom flanges were made cellular. Although Fairbairn's experiments had been on single spans, the bridge was built as a continuous girder, giving it additional strength and stiffness.

Some of the other key participants in the project included Stephenson's assistant Edwin Clark, and Fairbairn's assistant Mr Blair, who was largely responsible for producing all the bridge's design drawings. After Fairbairn and Stephenson fell out in a dispute over recognition as being the true designer of the bridge, it was Clark who wrote the account setting out Stephenson's side of the story. Fairbairn published his own, and it seems generally to be regarded as the more honest version.

Credit is also due to architect Francis Thompson, who designed the masonry elements in a vaguely Egyptian style, as well as several other works along the railway. Thompson later worked again with Stephenson on Victoria Bridge, Montreal, another tubular bridge, as part of the Grand Trunk Railway in Canada.

Four sculptural lions were installed, one at each corner of Britannia, Bridge,sculpted by John Thomas, who also worked on the Palace of Westminster.

Hodgkinson had also fallen out with Fairbairn, essentially over the latter's willingness to extrapolate the results of his experimental work in the absence of a justifying mathematical theory. Around this time, Fairbairn began building many girder bridges with tubular (box) girders, but suitable theory was only just becoming available to practicing engineers. The sheer scale of the Britannia structure went well beyond what had been attempted previously - just as Telford's Menai Bridge had done a quarter of a century before.

The project innovated in many ways. The extensive reliance on wrought iron was pioneering, and the span was exceptional for a flat-span bridge. The range of experimental work relied upon was impressive, as was the idea for the cellular construction. Even the erection of the bridge required major innovation, with the girders lifted into place by jacking upwards with massive hydraulic jacks. The slots for the jacking process remain visible on the towers, and part of one jack can still be seen near the bridge on its south-west side.

Two million rivets were reported to be used, with workers having to squirm through the box cells to install many of them. This, more than anything else, determined the size of the cells used.

On 24 May 1847, while construction of the Britannia Bridge progressed, one of Stephenson's other railway bridges collapsed, killing five people. The bridge over the River Dee near Chester was constructed of three cast iron girder sections connected with wrought-iron link bars. It was a popular design at that moment of time, with at least thirty-four built prior to the Dee failure. Fairbairn had proposed in 1846 that Stephenson should use a wrought-iron tubular girder bridge across the Dee, but had been turned down.

This incident exposed Stephenson's lack of expertise as a structural engineer, and Fairbairn's views prevailed both at Britannia and more widely - he was involved in over 100 more tubular girder bridges (albeit predominantly with the girders sitting beside the tracks, rather than containing the tracks) within a 5 year period.

While the tubular girder was successful in the short-term for short and medium span bridges, it was not the optimal solution for larger structures, and the Britannia Bridge design would prove a dead-end. Before long, various forms of lattice-girder and truss bridges took over, although early lattice-girder railway bridges experienced their own problems. For more detail I can wholeheartedly recommend John Rapley's and Richard Byrom's books (see list of references below), both of which are excellent.

Britannia Bridge was bold, if not entirely beautiful, but I think there is a great deal to admire in its simplicity of line. It lasted 120 years until, on 23rd May 1970, a fire broke out, irreparably damaging the bridge's two tubular girders.

The replacement bridge seen today was built between 1971 and 1974, with two main truss arch spans over the Menai Strait. Both Telford and Stephenson had considered arch bridges, and finally the navigational restrictions that had forced both into bolder and more innovative designs were no longer an issue.

The form of the present-day bridge, designed by Husband and Co. (merged into Mott, Hay and Anderson in 1989, now Mott MacDonald), owes a great deal to the challenges of safely dismantling the damaged tubular girders, as well as to the need to reinstate a railway line as quickly as possible. 10,500 tons of metalwork had to be removed, forming a load well in excess of the railway traffic that the replacement structure would carry, and the arches were therefore designed and sized primarily to act as support to the demolition operation. Once the tubes were safely and temporarily supported, railway services were reopened through one of the damaged tubes in January 1972. The tubes themselves were cut into short sections, and then hauled off the end of the bridge using small locomotives.

The bases of the towers were extended with small concrete skewbacks to carry stainless steel pins, which carry the entire load of the new bridge. The steelwork for the new arches was assembled by Cleveland Bridge four miles from the bridge, at Port Dinorwic, and floated into place on barges.

The spans were cantilevered outwards from the central tower, with adjustable tie bars passing through the tower to provide temporary support. Lifting gantries moved along the upper chord of the arch truss to lift each new truss unit into place, as can be seen in the construction photograph below (taken from a souvenir booklet about the bridge).

During construction, the arches each briefly formed a three-pinned arch before pre-load was jacked into the upper member to transform the whole system into a two-pinned arch.

Because the arches had capacity well in excess of railway loading, this created the opportunity to add a second deck to carry highway loading, and openings in the towers were enlarged to facilitate this. The railway bridge was finished in 1974 (albeit with only one deck carrying services, as railway traffic was much diminished), and the road deck eventually completed by Fairclough Civil Engineering and Fairfield Mabey in 1980.

The steelwork for the new railway bridge weighed less than half of Stephenson and Fairbairn's original wrought iron bridge, only 4,961 tons, although the road bridge (which is nearly twice as long as the rail bridge) incorporates another 4,338 tons of steel.

Although it is often noted that the ordinary observer prefers an arch bridge over any alternative, the modern bridge is, to my eyes, less loveable than the original. Partly this is because of the sheer quantity of truss bracing, and partly that the visual relationship between road and rail decks is uncomfortable. I think this is partly due to the sheer depth of the edge beams at railway level.

On the plus side, the history of the bridge is there to be seen. The excess tower height originally intended to carry suspension chains contributes to the support of the road deck and punctuates the span in a pleasing way (compare Sydney Harbour Bridge). The form of the arches betrays their origin as falsework for a demolition process. The preserved cross-section of  tubular girder (accessible via a path leading to the south-west corner of the bridge) is well worth visiting. The masonry still looks excellent today, and the bridge's best-kept secret, the "cathedral" vaults at each end, are still intact albeit normally inaccessible.

Further information:

• Google maps
• Wikipedia
• Structurae (1850)
• Structurae (1972)
• British Listed Buildings
• Coflein
• Engineering Timelines (1850)
• Engineering Timelines (1974)
• Grace's Guide
• Menai Heritage
• William Fairbairn: The Experimental Engineer (Byrom, 2017)
• A Walking Guide to the Menai Strait Bridges (Daimond and Kovach, 2015)
• Conway and Britannia Tubular Bridges: Stephenson's Team (Barr, ICE Engineering History and Heritage, 2010)
• Building Bridges and Boundaries: The Lattice and the Tube, 1820–1860 (Dreicer, Technology and Culture, 2010)
• The Britannia and other Tubular Bridges (Rapley, 2003)
• The Britannia And Conwy Tubular Bridges Of Robert Stephenson (Chilton, IASS Symposium, 2000)
• Britannia Bridge: from concept to construction (Ryall, ICE Civil Engineering, 1999)
• Design Paradigms: Case histories of error and judgement in engineering (Petroski, 1994)
• Britannia Bridge: The Generation and Diffusion of Technological Knowledge (Rosenberg and Vincenti, 1978)
• The Britannia Bridge (Husband and Co.? souvenir booklet, 1978?)
• Reconstruction of the Britannia Bridge (Husband and Husband, ICE Proceedings, 1975)
• Joint Report on a Fire in the Britannia Tubular Bridge, Menai Straits on Saturday May 23rd 1970 (Caernarvonshire and Anglesey Fire Brigades, 1970)
• Tubular and other Iron Girder Bridges Particularly Describing the Britannia and Conway Tubular Bridges (Drysdale Dempsey, 1850)
• The Britannia and Conway Tubular Bridges Vol. 2 (Clark, 1850)
• The Britannia and Conway Tubular Bridges Vol. 1 (Clark, 1850)
• General Description of the Britannia and Conway Tubular Bridges (Clark, 1849)
• An account of the construction of the Britannia and Conway tubular bridges (Fairbairn, 1849)

Derbyshire Bridges: 5. Headstone Viaduct

This will be my final "Derbyshire Bridge" for now, and this one is a well-known historic classic, Headstone Viaduct, also often known as Monsal Dale Viaduct. It is the star of a famous London Midland and Scottish Railway poster used to attract tourism to the Peak District, depicting a deservedly spectacular location (albeit with some artistic license!)

The viaduct was completed in 1863 as part of the Midland Railway company's Manchester, Buxton, Matlock and Midland Junction Railway. This railway has a long and complex history, which (if so inclined) you are better off reading at Wikipedia than I am repeating in any detail here. Suffice to say that the route connected Derbyshire to Manchester through the hilly terrain of the Peak District, and substantial civil engineering works were required.

It seems a wonder now that there were ever funds available to build a railway through such difficult terrain, necessitating not only major viaducts but a number of substantial tunnels. Perhaps it is worth imagining what the nature of the highways of the time must have been, for this to have been an attractive alternative.

The viaduct has five arches each spanning 50 feet (15.5m), and is roughly 25m tall. It originally carried two railway tracks, emerging from a tunnel in the steep hillside to the east and then passing along the flank of another hill to the west.

The railway was closed in 1968, and the route was converted to the Monsal Trail for cyclists and walkers in 1981. The closest you can come now to reliving the steam train experience would be to hurtle westwards on a bicycle at speed from the tunnel mouth into the open air, taking in the views with a sense of astonishment and relief.

The viaduct design has been credited to William Henry Barlow, perhaps best known for the design of another Midland Railway project, the St Pancras train shed. Headstone Viaduct is far from his most notable bridge: along with John Hawkshaw, he completed Brunel's Clifton Suspension Bridge, and he also designed the replacement for Thomas Bouch's ill-fated Tay Bridge. However, Midland Railway engineer Frederic Campion may have held more direct responsibility.

The construction of the arch barrels is a little peculiar. The facing voussoirs on each arch comprise seven rings of brickwork (an inner two bonded together, and then five outer rings), down to springing level. The piers and spandrel walls are in rubble stonework, and stone is also used for the lower part of the inner face of the arch barrel. The upper parts of the arch barrel are in brick. It seems an odd arrangement.

Brickwork is also extensively employed above two arches on the south elevation, possibly associated with remedial work completed in 1907-8. I doubt that many visitors notice!

The overall impression is robust but not excessively so - the scale and nature of the bridge is entirely appropriate to its setting. It's interesting to wonder what would be built if a similarly beautiful valley were to be crossed by a new railway today.

The Victorian polymath and art critic John Ruskin (something of a 19th century Brian Sewell) certainly didn't appreciate either the railway or the viaduct, writing:

"There was a rocky valley between Buxton and Bakewell, once upon a time, divine as the Vale of Tempe ... You Enterprised a Railroad through the valley - you blasted its rocks away, heaped thousands of tons of shale into its lovely stream. The valley is gone, and the Gods with it; and now, every fool in Buxton can be in Bakewell in half an hour, and every fool in Bakewell at Buxton; which you think a lucrative process of exchange – you Fools everywhere."

As is often the case, age provides architecture not only with grace, but it also elevates the perception of the location as a whole. Without the viaduct, this could just be any other pretty green Pennine dale. The viaduct is the centrepiece, the thing that visitors peering down into the valley from above all point their cameras towards.

It also provides a fine platform from which to view the surrounding greenery. Many visitors descend the path from the nearby Monsal Head car park to admire the viaduct and the tunnel entrance without going any further. An encounter with England's green and pleasant land need not require a lengthy trek.

It is certainly worth taking the time to go a little further and follow the path below the viaduct. From above it is impressive, but dwarfed by the surrounding landscape. From below, the opposite is true, it is a stone giant soaring overhead, framing shorter views and guiding the curious visitor eventually to the banks of the River Wye, ultimately responsible for carving this landscape over unimaginable years past.

It has obviously been a site for a more interactive visitor experience in the past. Signs on the viaduct draw attention to metal bars, suspended from the arches and stretched between the stone piers. These are intended to prevent people from leaping off the viaduct attached to a rope and swinging underneath. Certainly nobody was trying it when I visited.

Part of the railway line was reopened as a "heritage" service in 1992. There are broader ambitions to reopen the whole route as a "proper" railway, with Monsal Trail "reprovisioned", whatever that means. Personally, I think it would be a real shame if it denied people the chance to get up close and personal with the trail, its tunnels and viaducts.

Further information:

• Google maps
• Wikipedia
• British Listed Buildings
• Engineering Timelines
• Forgotten Relics
• National Transport Trust
• Institution of Civil Engineers Monsal Trail leaflet (PDF)
• An Encyclopaedia of British Bridges (McFetrich, 2019)
• British Railway Bridges and Viaducts (Smith, 1994)

Derbyshire Bridges: 4. Railway Viaduct, Edale Road, Hope

This is another 1970s structure built to replace one of the original bridges on the Hope cement works railway line (for context on the railway, see my earlier post).

The original 1929 bridge was a reinforced concrete trestle structure 347ft (106m) long, with eight spans of varying length. A 13ft (4m) wide deck slab spanned onto rail-bearers and crossbeams, which were supported from raised concrete girders on both edges of the deck. These then sat on reinforced concrete columns, braced with horizontal members to create H-frames.

The viaduct actually consisted of two structures, with a double-trestle in its middle and a copper expansion joint separating the two. The end trestles were buried within approach embankments, and will have provided stability against longitudinal loads from the railway. There is an image in Concrete and Constructional Engineering magazine which shows the finished viaduct:

There is also a photograph on designer Geoff Bond's website showing the 1929 structure hidden behind the new bridge, presumably pending demolition.

The present bridge is a 5-span post-tensioned concrete viaduct, carrying the railway over the Edale Road and the adjacent River Noe. I think it looks rather elegant in an artist's impression from 1973.

The main feature that makes it unusual is the way in which the lower flange of the box girder is extended outwards. Normally, such bridges extend only the upper flange (to form the road or railway deck), there is no obvious benefit to complicating things by extending the lower flange. Geoff Bond was a member of the design team at Oscar Faber and Partners, and his website indicates that the rationale was "to resist reverse bending moments and severe locomotive shear stresses".

I'm left slightly puzzled, and would love to have been able to find more information.

Further information:

• Google maps
• Reinforced Concrete Bridges in Derbyshire (Concrete and Constructional Engineering, 1929)

Derbyshire Bridges: 2. Railway Bridge, Castleton Road, Hope - Update

Many thanks to crisb who commented on my previous post about this bridge, drawing my attention to a number of publications from 1928-29 shedding further light on its history.

The bridge was mentioned on several occasions in the journal Ferro-Concrete: The Review of Reinforced Concrete. I believe this may have been promoted by L. G. Mouchel and Partners as a way of publicising the Hennebique system of reinforced concrete, for which they held the UK license.

The 117ft (35.7m) long bridge was described as having one 54ft (16.5m) central span, and two 21ft (6.4m) side-spans, sized to allow for future widening of the road. As well as being used in production of cement, the local limestone was crushed to form the aggregate for the concrete used in the bridges. Tests were undertaken to demonstrate that sufficient strength would be achieved.

The journal included this picture of the bridge under construction:

An article appeared in Concrete and Constructional Engineering magazine in 1929 on "Reinforced concrete bridges in Derbyshire". This noted the client as Messrs. G. and T. Earle Ltd., the owner of the cement works, and stated the design engineer as being Mouchel's firm. Messrs. F. Mitchell and Sons Ltd. were identified as the contractor.

This article confirmed the key dimensions of the bridge, also reporting that the structure comprises a 7.5" (190mm) thick reinforced slab, carried on 24" x 9" (610mm x 229mm) secondary beams at 4'3" (1.3m) centres, these supported from the main edge beams.

According to Ferro-Concrete, the completed bridges were "of most artistic appearance".

Derbyshire Bridges: 2. Railway Bridge, Castleton Road, Hope

It has been a while since I've been able to get out and about visiting bridges, but during the summer I got to see a few bridges in Derbyshire. The first three all carry a private railway line to Breedon Cement Works near Hope.

This area was historically a lead mining area, and it was not until 1929 that quarrying of limestone began on a large scale and a cement works was built.

The cement works operated for several years before the Peak District National Park was created in 1951. Once the National Park came into being, agreement was reached for the vast bulk of the cement produced here to be transported by rail rather than road (amounting to over 1.5 million tonnes of cement annually). The cement works operates its own private railway track connecting onto the main Hope Valley railway line. The tracks pass under and over a number of bridges, some of which are of surprising interest.

At least one of the original bridges survives, carrying the railway across Castleton Road. This is a three-span reinforced concrete bridge (perhaps appropriately, given its purpose to help transport cement). Presumably it dates from around 1929 as well. I haven't found any information on who designed it, or built it, or whether an architect was involved along with the engineer. One website suggests this bridge was "something of a showpiece for the works", which I guess might have been true.

There is some traditionalist looking detail on the elevation of the bridge but the arched/haunched main beams are left unadorned. The beam-and-slab deck is a little like what would be called a ladder-deck bridge today, but it is in line with many early reinforced concrete structures patterned after the joist-and-floor layout familiar from iron and timber buildings. The internal arches to the piers are a nice detail that would be omitted in a more modern structure.

There are dents and scrape marks to the underside of the main beams, caused by over-height vehicles. Viewed close up, it looks as though the original reinforced concrete has been overcoated with a thin layer of additional material at some stage.

It's good to see this bridge surviving reasonably well, but it's the bridge in my next post that is the real highlight along this railway, and the reason I visited.

Further information:

• Google maps
• Hope cement works railway

Merseyside Bridges: 12. Sankey Viaduct

Time for a couple more "Merseyside" bridges (using the regional term in a broad sense, before the pedants write in, again).

Completed in 1830, Sankey Viaduct has been described as "the earliest major railway viaduct in the world". Protected by Grade I Listed Building status since 1966, it still carries trains today.

The nine-arch viaduct was built as part of George Stephenson's Liverpool and Manchester Railway, to carry the line over a valley containing both the Sankey Brook and the Sankey Canal. The latter is now defunct, and was infilled at this location in 2002, so the viaduct now spans the Brook and a public footpath.

The viaduct is reported to have been designed by Stephenson's assistant Thomas Longridge Gooch, with William Allcard acting as resident engineer. Both men had worked with Stephenson for several years, and although Gooch is often described as Stephenson's draughtsman, he would in modern terms be called an engineer. Some sources cite Allcard as the main designer.

In 1825, Stephenson had been temporarily displaced as the railway's engineer, and John and George Rennie proposed a seven-arch viaduct 273 yards long. Once reappointed, Stephenson initially put forward a 20-arch brick viaduct, which was rejected by the railway company's directors. Describing his first design, Stephenson wrote to his son, Robert:

I have drawen a plan on the gothick principal there will be 20 arches of 40 feet span it will be quite a novel[ty] in England as there will be a flat arch sprung between the centre of the tops of the gothick and so on it has a fine appearance in the plans.

The Viaduct was only necessary at all because the Sankey Brook Navigation Company refused any obstruction to tall sailboats passing along their canal. Compare this old image of the viaduct with how the valley looks today.

The viaduct is a brick structure with sandstone facing on the two elevations. The piers are generously tapered and robust in appearance. Below ground, they sit on sandstone foundation blocks, which are in turn supported on driven timber piles.

The arches are semi-circular, each spanning 15.2m (50 ft). The keystone is prominent, projecting not just below the elevation, but below the entire width of the arch barrel. The underside of the arch is substantially covered in calcite staining, and in need of at least a clean if not more thorough refurbishment.

New overhead electrification portals were added in 2015; this seems to have been done with some sensitivity, choosing the positions carefully and only with small visible protrusions above the cornice line.

Looking up at the spandrel walls, occasional openings can be seen on one or other side of the central pilaster. I wondered whether these indicated the bridge to be of hollow-spandrel construction, with a series of internal spandrel walls. I found the planning consent application for the overhead electrification online, showing this guess to be correct, see the drawing extract below.

Further reading:

• Google maps
• Wikipedia
• Structurae
• Engineering Timelines
• British Listed Buildings
• Transport Trust
• Sankey Canal and Restoration Society
• British Railway Bridges and Viaducts (Smith, 1994)
• Civil Engineering Heritage: Northern England (Rennison, 1996)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)
• Aqueducts and Viaducts of Britain (Owens, 2019)

London Bridges: 51. Blackfriars Railway Bridge

I've got a backlog of bridges visited over the last couple of months to write up and cover here, and I'll start with a bridge in London.

Railways first came to London in 1836, but it was 1860 before a railway bridge was built across the River Thames, Grosvenor Bridge. Others rapidly followed, Battersea Bridge (1863), Hungerford Bridge (1864), Blackfriars Bridge (1864) and Cannon Street Bridge (1866). Each bridge sought to bring travellers from south of the river closer to the key destinations of the north bank.

The bridge at Blackfriars was no exception, carrying the London, Chatham and Dover Railway (LCDR) across the river to Ludgate Hill station, and within a year or two of completion, further north along what is now the route of the Thameslink railway. The bridge was a five-span wrought iron lattice truss viaduct, supported on tall cast iron piers, and designed by the LCDR's chief engineer, Joseph Cubitt. This original bridge was dismantled in 1985, leaving only its piers and part of the south abutment behind. The remnant of the abutment still displays the lavish crest of the LCDR.

In 1886, a second bridge was completed immediately to the east, named St Paul's Railway Bridge and connecting to the new St Paul's Railway Station on the north bank. This was a wrought iron arch viaduct, designed by Henry Marc Brunel and John Wolfe-Barry, the latter best known for the Tower Bridge, which commenced construction in the same year St Paul's Bridge was completed.

This bridge continues to carry the railway today, although it has been through considerable change. Originally, there was a railway station at the south end, although this was used by passengers for only two decades before a new station was built at the north side. This station remains in use, and was extended between 2009 and 2012 with longer platforms. A photovoltaic roof was added, making it reportedly the largest photovoltaic installation on a bridge in the world.

To accommodate the extended station, the bridge was widened, strengthened, and largely reconstructed, to a design by Tony Gee and Partners. The arch members remain those from the 1886 structure, but the original deck and spandrel columns were removed and replaced with steel elements, acting as Vierendeel trusses rather than as simple arches.

The bridge was widened to the east with one steel arch supported on the original masonry piers. These had their end elevations rebuilt.

On the west side, one of the three rows of cast iron columns from 1864 was taken down, and the 1886 bridge piers were extended laterally, supported on the original 1864 foundations. The widened piers support three new lines of steel arch ribs.

The work has been artfully done, and although the difference between steel and wrought iron arches is immediately apparent to a professional, I doubt that any casual visitors see this as anything other than a historic railway bridge. The shaping and disposition of the new arches sits happily with the old, even replicating the end hinges on each span.

The treatment of the western extension at foundation level is less visually successful, but clearly far less expensive than building new foundations would have been. The extension stonework doesn't match the detail on the east face, and the horseshoe collar which sits on the old foundation (precast concrete, masonry clad) feels a little awkward to me.

The detailing of the new spandrels is very well done, it matches the historic appearance very well. Overall, the reconstruction is a very impressive piece of engineering, and I think all involved must be very proud of what was achieved. The attention to detail both for permanent and temporary works must have been considerable.

Further information:

• Google maps
• Wikipedia
• Structurae
• Where Thames Smooth Waters Glide
• British Listed Buildings
• New Bridge Over the Thames at Blackfriars (The Engineer, 27 April 1883)
• New Railway Bridge at Blackfriars (The Engineer, 29 August 1884)
• Railway Bridge at Blackfriars (The Engineer, 12 September 1884)
• Civil Engineering Heritage: London and the Thames Valley (Smith, 2001)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)
• Blackfriars Rail Bridge Back in Business (Rail Engineer, 2012)
• Reconstruction of Blackfriars railway bridge, London, UK (Baecke, Proc. ICE Bridge Engineering, 2016)