"Thames Bridges" by David C. Ramzan

I do love a bridge book which takes a specific river as its focus, and Thames Bridges (Amberley Books, 96pp, 2022) is a nice addition to this genre.

As far as the Thames goes, it's a pretty crowded field already, with Crossing London's River (1972), Thames Bridges (1973), Thames Crossings: Bridges, Tunnels and Ferries (1981), Cross River Traffic (2005), Thames Bridges: Then and Now (2006), Thames Bridges: from Dartford to the Source (2007), London's Bridges: Crossing the Royal River (2009), Bridges: XXXIV Crossings of the Thames (2011), Crossing the River (2015), All the Thames Bridges from Source to Dartford (2019), Bridges over the River Thames: From the source to the Sea (2020) .... you get the idea! For collectors of bridge books, is there any need for another one about the bridges of the Thames?

Thames Bridges covers the entirety of the river from its source in Gloucestershire to its estuary, passing under over 200 bridges along the way. The book is extensively illustrated, with photographs on almost every page. For some of the minor bridges, the photograph sufficiently illustrates what they are, and their context. The images are a mixture of old and new, and I especially liked the inclusion of the older photographs - so much of the narrative relates to the history of the land, the river, and its crossings, that these help bring that tale to life.

Outside the heart of London, this is the river of Clark's Marlow Suspension Bridge, Brunel's Maidenhead Railway Bridge, the old and new bridges at Runnymede (Lutyens and Arup), Hampton Court Bridge, and of course the mighty Queen Elizabeth II Bridge. It is undeniably an important river, spanned by many undeniably important bridges.

Thames Bridges rarely wastes too many words on any span, and this is definitely not a book that can be considered an in-depth gazetteer. However, it's concisely written, with enough on each structure to grasp key facts, understand their significance, and relate them to the wider history of the area. There is plenty of history, and the book touches on Mesolithic settlements, Roman construction, as well as more modern attempts to reshape the landscape.

I particularly enjoyed the book's sense of pace, which remains unhurried throughout. I think it is best read in order, starting with relatively humble spans and a river that is little more than a stream, and seeing the images of bridges growing very slowly steadily in scale, with tales of increasingly impressive engineering achievement as the book draws you steadily downstream.

For those with a general interest in the Thames, and its history, I can certainly recommend Thames Bridges. It is an accessible, well-written survey. I think that those with greater knowledge of the Thames and its bridges should also enjoy it: it left me with a little bit of a desire to hunt out some maps of the Thames path, as this book would make an excellent companion to a river tour!

Postscript

For some other examples of books in the bridges-by-river genre, here are some that I have reviewed previously:

• Bridging the Tweed (2020)
• Danube-bridges (2018)
• Bridges of Dublin (2017)
• Bridges of Paris (2017)
• The Glow of Paris (2017)
• River Axe Crossings: from Mouth to Source (2012)

London Bridges: 54. Chiswick Park Footbridge

It has been a while since I've visited and reported on a recently-built bridge (May, since you ask, and before that, August 2018), so this visit to see Chiswick Park footbridge in London felt long overdue.

According to the Ian Visits blog, the bridge itself is also long overdue, with planning applications dating back to 2003. It forms part of a walking route connecting Chiswick business park to Chiswick Park tube station. The bridge finally opened to the public in January this year. It was designed by Expedition Engineering and Useful Studio, with the steelwork constructed by Severfield.

I believe it's only the second network arch bridge to be built in the UK, and the first such pedestrian bridge. The design didn't start life as a network arch structure, and has been through a lengthy evolution to get to what was eventually built.

Originally, proposals were for a truss bridge of some form, as per the 2003 and 2006 planning applications shown here:

The bridge's three spans were largely determined by clearances to road and rail routes below, and in these early designs it was indicated that the truss span over the railway would be fully enclosed to prevent risks from vandalism.

In the 2012 application (top diagram in the image above), the design had become three steel bowstring arches, each of increasing span and height from west to east, with vertical hangers supporting the deck. Tall mesh parapets were indicated above the railway, eliminating the need for full enclosure.

The overall form of the bridge changed very little thereafter. The shape of the arches was the result of a form-finding exercise, to maximise the visual slenderness of the arch. I'm not clear how that will have worked, as the critical bending arrangement for an arch of this sort is usually with only half the span loaded with pedestrians.

That scenario is often more onerous in design than the full span loading which produces the greatest axial load in the arch. In a conventional bowstring arch, the stiffness of either the arch or the deck (or both) is required to resist this half-span bending.

In any event, during design development the bowstring arch was found to perform badly under dynamic pedestrian loading, and was amended to a network arch in the 2015 planning application (middle diagram above).

This is many times stiffer than the previous design, raising the bridge's vulnerable natural frequencies, and eliminating or mitigating the dynamic problems. Bending moments in the arch due to asymmetrical loading arrangements are also greatly reduced.

I believe the previous design incorporated a concrete deck - adoption of the network arch also allowed a lighter all-steel deck to be used, minimising the weight required and making craneage of the spans into place easier.

The final change is indicated in the 2017 planning application (bottom diagram above), and indicates that the design team had failed in their desire to persuade Network Rail that a mesh parapet would be sufficient above their railway line.

The railway authority is never noted for its flexibility when there is a rulebook that can consulted, so the final introduction of a solid (imperforate) parapet screen above the railway tracks is unsurprising. It is at least largely disguised by being hidden behind the facing mesh.

The bridge's spans are 37.0m, 40.7m and 44.4m, totalling 122.1m. The arches and deck are connected integrally to the two intermediate piers, with bearings allowing thermal articulation at each end. All the structural steelwork is weathering steel, with stainless steel parapets and hanger cables. The decking is floored in timber planks.

The articulation is interesting, as conventional wisdom would be that arches of this type should sit on bearings at all points, allowing the tie girder connnecting the ends of each arch span to expand freely. This allows it to take up a full tension balancing the compression in the arch, and allowing the hanger network to interact efficiently with the main steelwork.

In this instance, the V-shaped piers are sufficiently flexible longitudinally that they will offer only limited restraint to the arch thrust, and the network on the central arch will still work although I'd guess with slightly reduced effectiveness.

The most striking aspect of the bridge is the effort that has been expended to make its main elements slender, with cruciform sections for the arch and piers, and a simple stiffened steel plate for the deck. In addition to being slender, all parts are visible for inspection and maintenance, unlikely the closed box sections often seen in footbridges.

What is also very much apparent is an impressive attention to detail. Wherever possible, connections are kept simple, with welding used extensively instead of bolting. The edges of the deck are made clear and sharp in profile, and the hanger and parapet connections are well-detailed and as minimal as possible.



It's the sort of bridge that any designer would be proud of, and especially impressive given that this is predominantly a structure used to get rapidly from A to B, rather than a destination in its own right. it has been shortlisted for an IStructE award, been a finalist in the CE Awards, and won two ICE awards. I'm a little surprised that it hasn't been more widely rewarded, to be honest.

The bridge is not completely without its flaws. Site constraints mean that although at its western end the bridge connects directly with a podium deck level in the business park, at the eastern end the approach is via steps and a lift.

I imagine mobility-impaired users are crossing their fingers in the hope that the lift will be better maintained than is often the case. It is at least attractively detailed in keeping with the rest of the bridge.

Also on the eastern approach I noticed a sign that recommends no cycling, perhaps inevitable given the steps and lift, but also advises users to "Walk With Care" due to gaps in the decking.

The timber decking is visually attractive, but perhaps some users with high heels have found it a problem. In any event, I suspect problems with the decking won't end there.

The timber slats are raised above the bridge deck, the upper surface of which is a flat steel plate. Rainwater drains through the slats, and flows along the deck (which I am told is waterproofed), before spilling straight to the ground at the ends via cut-outs in the deck plate. The whole arrangement is an inspection and maintenance liability - nobody will lift the decking to properly inspect underneath, and it's easy to imagine dirt and detritus leading to trapped water over time.

Despite these oddities, the Chiswick Park Footbridge is a very impressive feat of design and construction and well worth a visit.

Further information:

• Google maps
• Wikipedia
• Structurae
• Steelconstruction.info
• Gennaro Senatore
• Shaped by Walking: Innovative Dynamic Design of Chiswick Park Footbridge (Winslow, Oates and Weir, Footbridge 2014 conference)

"Tower Bridge: 1894 to date. Operations Manual"

Haynes Publishing must be best known for their car and motorcycle maintenance manuals, but they have increasingly branched out into other territories, with recent publications including "The Human DNA Manual" and the "Milky Way Owner's Workshop Manual". In the areas of architecture and infrastructure they have published Manuals for "London Underground", "The Great Pyramid", "Hadrian's Wall" and now "Tower Bridge" (188pp, 2019, ISBN 978-1-78521-649-7).

It is, of course, Tower Bridge's 125th anniversary this year, and this new book by engineer John Smith joins books by Kenneth Powell and Harry Cory Wright published to mark the occasion. A comparison against the Powell book is inevitable, and although there is plenty of overlap between the two, there are some very clear differences.

Powell's book has, on the whole, the better photographs, and is a much easier read for a non-engineer, with much more detail on the context and a strong narrative surrounding those who designed and built the structure. As befits its publication by Haynes, Smith's book has far more detail on the construction work, the bridge components, and its operating technology.

The early sections of the book give a fairly comprehensive account of the somewhat tortuous process by which the bridge was eventually conceived, including the sometimes ingenious and sometimes monstrous alternative designs put forward.

The real dive into detail begins in the third chapter, documenting the eight separate contracts which were let for construction of the bridge, dividing up the works required for the piers and abutments, approach structures, metal superstructure, masonry superstructure, hydraulic machinery, paving and lighting. No client today would take this approach, retaining the entire liability for integrating a complex construction process on their own, but when the bridge was built there would have been no single contractor with the capability to do it all.

It's interesting here to see the extent to which the contract conditions used in the 1890s are very similar to those still in widespread use at the end of the 20th century. Extracts from the very first contract (for the piers and abutments) make this clear: the power of the resident engineer, payment retention, liquidated damages etc. The unrealistic timescales demanded by the client, and unrealistic prices submitted to win the work, also remain familiar today.

The core of the book consists of four chapters which itemise every single element of the bridge, describing them in exquisite detail and explaining just how every piece fits together. At times, the level of detail presented, with dimensions, plate thicknesses, etc, is numbing rather than interesting. For the engineering reader, there are several interesting extracts from drawings included, and the comprehensive nature of the text does mean that there appear to be no significant details left unmentioned.

There are many aspects of the bridge explained here which are essentially absent from the account in Powell's book. One example is the presence of stiffening girders concealed within the balustrades of the southern span, which ensure that water pipes carried across this span were protected against excessive movement. Another is the explanation of the arrangement of the high-level footways, the suspension bridge ties which pass through these, and the additional suspension cable added in 1960 to relieve the footway girders of the weight of those ties. These elements of the bridge are not immediately apparent to the casual visitor, but Smith's text, photographs and drawings make everything clear.

The book contains one excellent cutaway diagram showing how the components of the bridge fit together, and it's a shame there weren't more. My over-riding impression, after reading this book, is quite how complex Tower Bridge really is, and how well it merits this wealth of information. It really is an engineering masterpiece, whatever anyone may think of its architectural merits.

The book concludes with biographies of the main participants in the bridge's design and construction, and a detailed timeline of alterations and maintenance work in the period from 1894 to date. One of three appendices gives a detailed breakdown of the author's calculations of loads and forces in the bridge's key structural elements.

I couldn't, with any honesty, recommend this book to anyone who is not an engineer, but it is so detailed that it will probably remain a key reference work for Tower Bridge for the indefinite future. It is clear, thorough (sometimes too much so!) and well-illustrated throughout.

Crowdfunding for Cody Dock Rolling Bridge

I thought I'd give a quick mention to this unusual bridge proposal, in case anyone has missed it.

Designed by Thomas Randall-Page, with support from engineer Tim Lucas at Price and Myers, it's a highly unconventional moveable pedestrian bridge, proposed to span Cody Dock at Canning Town in London.

There are three standard types of movable bridge: bascule bridges, which rotate about an axis parallel to the centreline of the river (or other obstacle crossed); swing bridges, which rotate about a vertical axis; and lift bridges, which move vertically without rotating.

There are also examples of retractable bridges which move horizontally, and a handful of bridges which move by transforming their shape, but very few examples of bridges that rotate about a horizontal axis perpendicular to the river centreline. The best known example of the latter is Gateshead Millennium Bridge, which like the Cody Dock design rotates to lift its deck sufficiently clear of the water to permit navigation. There are also a couple of examples in Belgium.

The Gateshead bridge pivots about its base, and so its weight is unbalanced in almost any position, requiring substantial machinery to operate.

The Cody Dock rolling bridge is instead proposed to be operated using a simple hand-crank, requiring its weight to be well-balanced in every position it rotates into. This is achieved by placing its centre of gravity exactly halfway between the floor of the bridge, and its overhead portals. When operated, the bridge rolls sideways like a giant pinion on a specially arranged rack; cog-teeth control the bridge's position.

This could be achieved by enclosing each end of the bridge in a large circular ring, which would roll along a horizontal rack somewhere below the floor level of the bridge. The half of the circular ring which is normally above the bridge deck would need to contain sufficient ballast to exactly balance the weight of the deck.

The Cody Dock proposal uses square portals at the end of the bridge, but rotating about their centre in the same manner as the circular ring. The centre-of-gravity remains horizontal, which means that the support rack has to be shaped to match the path which the rotating square traces in space. I think there will be quite a bit of ballast to pack into the upper part of the portal frames to make this work!

The cost of the bridge is estimated at £197,848, with a detailed budget cited which, perhaps worryingly, includes no contingency or risk allowance. There is currently no public funding for the project, nor any corporate sponsorship, so the project team are resorting to a crowdfunding web page to try and fund the scheme. This is currently sitting at around £62,000 pledged, with only 10 days left until their self-imposed deadline.

It's a very imaginative idea, and I wish them well.

London Bridges series: 53. Holborn Viaduct

I suspect that for many people, Holborn Viaduct in London is known mainly as a street name rather than as a bridge: the street extends for around 425 metres (1400 feet) between Holborn and Newgate Street, but only a relatively short length of bridge is visible where the street passes above Farringdon Street. Elsewhere, most the street is hemmed in by buildings either side.

What can be seen today bears little resemblance to how this site looked in the past. What is now Farringdon Street was once the River Fleet, running north to south through a valley before spilling into the River Thames. The Fleet can be seen on the mid-16th century "copperplate map" of London, which also shows the old Holborn Bridge which then spanned the river.

Fleet Ditch was used as an open sewer, and was eventually covered over, section by section, and converted into a buried sewer. Today it remains there, running below the roadway down to the Thames.

Between 1863 and 1869, the entire valley was improved in a scheme designed by city surveyor William Haywood. The southern end of the scheme included the reconstruction of Blackfriars Bridge, while at Holborn, the old bridge was removed and replaced with what is now Holborn Viaduct. Haywood worked with engineer Rowland Mason Ordish on the viaduct's design.

Source: Grace's Guide

A contemporary drawing (above) shows the full extent of the Holborn Viaduct construction. Most of its length consists of brick arch spans, enclosed on their ends to form chambers, and in addition to the Farringdon Street structure, there are special spans over other roadways and railways. A drawing made in 1941 reveals the structure, exposed by bomb damage to adjacent buildings (below).

Source: drawing by Louisa Puller, via Wikipedia

Work on the new bridge started in 1867 and was completed in two years. The spans over Farringdon Street use paired cast-iron arched members supported on granite piers. The decking was originally constructed from cast-iron troughing topped in mass concrete.

On all four corners of the bridge, a large building was constructed to house a staircase connecting the upper and lower roadways. The one shown in my photograph is a post-war reconstruction, as the two north buildings were damaged by bombs during the Second World War.

The visible bridge is spectacular and ornate, and does make me wonder quite how its construction was funded. It is adorned with ornamental lighting, four statues (representing commerce, agriculture, science and fine art), and the ironwork on the main elevations is finely detailed and highly decorative.

From below, entrances into the masonry vaults can be seen, and perhaps income from letting these spaces and the staircase buildings helped contribute towards the cost of construction.

It can also be seen that the bridge has been extensively altered. By the end of the 1980s, the deck was found to be in poor condition due to water penetration, and calculations suggested the bridge to be seriously under-strength for modern heavy goods vehicle loads. DHV Burrow-Crocker Consulting (since merged into the Waterman group) were appointed to examine, assess and design improvements to the bridge.

The altered arrangement is visible in the photographs and explained in a diagram below taken from a 1993 technical paper. The existing decking was completely removed, and new steel-concrete composite decks inserted in between the cast-iron arch girders. The existing piers were extended upwards in reinforced concrete to encase the ends of the cast iron members, and the new bridge deck was supported via bearings onto the concrete extensions.

It's an exemplary piece of engineering, leaving the historic structure seeming largely unaltered from most point of views, and retaining most of the original fabric. The extensions to the piers are especially well-detailed, and I would not have noted them if I hadn't read the paper.

Further information:

• Google maps
• Wikipedia
• Structurae
• Grace's Guide
• Patrick Baty (history and paint analysis)
• Inspection, assessment and strengthening of the Farringdon Street bridge, Holborn Viaduct (Carruthers and Shiel, in Bridge Management 2, 1993)
• Civil Engineering Heritage: London and the Thames Valley (Smith, 2001)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

"Tower Bridge" by Harry Cory Wright

This lovely new book is part of a series of "pocket photo books", and is published alongside books on the Barbican Centre and Trinity College Library, Dublin. Harry Cory Wright is a photographer better known for his landscape photographs, who applies his sensibility to buildings for these small-but-sweet volumes.

Tower Bridge (Thames and Hudson, 176pp, 2019, amazon.co.uk) measures 17cm x 12cm and features 120 images of this iconic London bridge. There are some similar photographs in Tower Bridge: History - Engineering - Design, which I reviewed recently, displayed there at larger size, but I don't think the pocket format detracts from Wright's images at all.

Unsurprisingly, the pictures have something of a landscape sensibility. Very few show the bridge in its surroundings, but several show the surroundings viewed from within the bridge towers or walkways. Most of the photos show details of various sorts, viewed in a way which emphasises shape, colour and texture.

People are notable by their complete absence, even in images of the control cabin and visitor areas.

This makes an opening interview with Chief Technical Officer Glen Ellis feel like a stray presence from another book, some kind of ghost in the machine (although not in the Cartesian sense). Other than this interview, Wright's book is all machine and no ghost.

There are relatively few photos of the exterior of the bridge, and especially few of the stonework cladding, which is perhaps a shame as many parts of it are exquisitely detailed. However, Tower Bridge makes up for it with everything else that is included.

There are some fascinating images of the interior of the towers, glimpses of steel framework peeking out between stone and staircases. Rivets appear, and then reappear repeatedly.

There are some great images of well-preserved control gear within the bridge operator's cabin, and of the bridge machinery, both operational parts as well as the preserved but now motionless steam engines. The epic bascule chambers appear, but so also does the inside of the accumulator tower, which is not something I've often seen photos of.

Towards the end, there are some particularly nice photographs of small machinery parts, valves, cogs, regulators and the like, as well as workers' tools and shelves full of spare nuts and bolts.

The reader is left to make of it all what they will. Some brief information is given for each photograph in a section at the end, for the curious to pursue.

What stood out for me is the extent to which Tower Bridge really is one of our greatest surviving examples of Victorian engineering, notable for assembling in one place such a variety of interesting parts. It is extremely well cared for, and if it has been substantially altered then that is generally very well hidden.

Obviously, this is a book which should appeal to anyone interested in architecture and engineering, but also admirers of fine photography. The price and size also make it an affordable gift. I very much enjoyed it.

"Tower Bridge: History - Engineering - Design" by Kenneth Powell

Tower Bridge: History - Engineering - Design (Thames and Hudson, 192pp hardback, amazon.co.uk) has recently been published to mark the occasion of the bridge's 125th anniversary (which falls on 30th June this year).

The bridge is one of the most iconic and memorable in the world, and it certainly merits this excellently researched and beautifully presented volume.

The title is a good guide to the contents, which emphasise the achievement of the engineers involved and avoid the temptation to focus on the bridge as an architectural artefact.

The book starts out not with the bridge but with the River Thames itself, the earlier river crossings, and the role of the Pool of London as a key part of the city's port facilities prior to the construction of new docks at the Isle of Dogs in the early 19th century. Setting the tone for the rest of the book, this section is copiously illustrated with old photographs, plans and paintings.

Until the Dartford Crossing was finished in 1991, Tower Bridge was the last bridge across the Thames before the sea. Prior to its completion in 1894, that honour had been held by London Bridge for over 600 years.

As well as discussing the history of several of the key Thames crossings (both bridges and tunnels), the book features several that were never built, such as George Dance the Younger's 1800 idea to replace London Bridge with two parallel bridges, and Thomas Telford's 1801 proposal for a huge cast iron arch.

This is all interesting, but the story of Tower Bridge really began in the 1870s. London Bridge was increasingly congested and a committee was established by the City Corporation to investigate the possibility of a new bridge or subway. Numerous schemes were developed, some by well known engineers such as Joseph Bazalgette and Rowland Mason Ordish, and Powell's book covers these well, including some great illustrations of what now look like quite absurd ideas.

The twin bascule solution was originally proposed by City Architect Horace Jones in 1878, and is shown in detailed original drawings included in the book. This was a drawbridge design, with ornate towers helping to support an arch from which, in turn, the bascules were slung.

The involvement of engineer John Wolfe Barry in the project from 1884 led to the change to a design essentially similar to what was eventually built, with suspended side spans anchored to two elevated, horizontal tie girders, which eliminated the risk of the original arch being struck by tall ships and also served as walkways.

Powell's book does well to cover the many key individuals who were responsible for the bridge's design and construction. These include John Jackson, the lead contractor; William Arrol, whose firm fabricated the steelwork (most of it hidden behind the tower cladding); and William Armstrong, whose firm supplied the hydraulic operating machinery.

Horace Jones died in 1887, a year after the laying of the bridge's foundation stone, and the task of preparing the architectural detail drawings fell to George Daniel Stevenson, who later established his own architectural practice. Several of Stevenson's beautiful drawings are reproduced in the book, along with a handful of engineering drawings and plans. I'd happily have seen more of these, but the book is judicious in its choices.

After describing the architecture, structural engineering and construction work, the book devotes a full chapter to the machinery and operation of the bridge, with more excellent photographs and diagrams. The engineering aspects are well-explained, and I think the level of detail given is about right for a lay-readership - informative without being too extensive.

A chapter towards the end of the book addresses Tower Bridge's life following construction and its status as an icon, although I think there was more that could have been said here (compare, for example, Peter Spearritt's book on Sydney Harbour Bridge). The Tower Bridge clone in Suzhou, China, doesn't even get a mention!

The final chapter discusses a few of the people involved in the bridge during its operational life, such as the various Bridge Masters, and although this is very welcome I think it would have been better to integrate these tales into the body of the book. There are also chapter notes, a bibliography and helpful index.

Overall, this is a genuinely excellent book about a bridge which certainly merits this level of in-depth attention. In addition to the historic images, there are many very high quality photographs of the bridge today, which make the book a joy to look through. It should certainly appeal to bridge enthusiasts, but more widely to readers interested in London, architecture and engineering.

Related posts:

• Tower Bridge (with links to other resources)
• Tower Bridge ... some musings (on the rarity of stiffened suspension "cables")

London bridges series: 52. London Wall Place Highwalks

Look, up in the sky! Is it a bridge? Is it a walkway? Is it a skywalk? No, apparently it's the return of London's pedways.

The original pedway scheme was the idea of London's town planners in the 1950s and 1960s, an attempt to elevate pedestrians above increasingly car-dominated city streets. Several new buildings were required to include provision for pedway access at first-floor level, but few of the pedways  planned were actually built.

They were perhaps most fully realised in the vicinity of the Barbican development, spanning across roads, and connecting the new Barbican cultural centre to the residential blocks which surrounded it.


However, with most foot journeys originating and ending at ground level, pedways were often as much of an inconvenience as a boon, and the idea soon died away. Despite their lack of success, pedways continue to exert a strong fascination for design and architecture critics and bloggers, and I've included various relevant links below providing more information.

With the construction of a massive new office development at London Wall Place, the idea has been revived. This was an original pedway location, so the new development is essentially reinstating what had once been there, albeit with a 21st century sense of style.

The new walkways span one busy road (and others that are less busy), and at least do serve a useful function in connecting into the Barbican's pedways, which do still form a useful connection. However, the walk below the pedways at ground level also an attractive route with extensive public realm enhancements in the St Alphage Garden section.

The walkways were designed by the team also responsible for the office building, Make Architects and WSP. Spacehub contributed to the landscape architecture.

The walkways are accessible from several staircases, and there's a new lift, although that wasn't in operation when I visited. The detailing on the main staircase is particularly nice.

In two places where the walkways span across roads, they are cantilevered from the office buildings, with the aid of stainless steel masts and stay bars. The walkway is suspended in an attractively-shaped weathering steel trough.

I found the mast-and-stay system visually awkward - it gives something of the impression that these are independent structures, although they obviously depend on the buildings for support. There's something about the arrangement that is out of place with the rest of the scheme.

The "centrepiece" of the walkway is another trough structure which snakes across the public space, skirting the ruins of an old church. This structure is a continuous beam cantilevering from each end, and it gives the impression that it's floating in space, thanks to the lack of intermediate supports.

It would have been so easy simply to have a multi-span walkway across this stretch, in the same style as other spans, but it's definitely this curved span that puts the whole scheme at a higher level of quality.

The various spans have spaces for seating, ensuring the walkways feel part of the public realm as a place to stop and breathe rather than just another way of traversing the city as rapidly as possible.

The whole scheme has been very well designed, and is a great addition to this one small corner of central London. I certainly can't see it inspiring yet more elevated pedways - the city streets are already too constrained and difficult an environment, but it's good to see it resurrected here.

Further information:

• Google maps
• Steelconstruction.info
• The Guardian
• Ian Visits blog
• Diamond Geezer blog
• Londonist
• The Pedway: Elevating London
• City of London Pedway scheme (Wikipedia)
• High Lines: Barbican Highwalks