26 May 2019

"The Mersey Gateway - A Bridge To Prosperity"

It's not unusual for major bridge projects to mark their completion with a souvenir booklet of some kind. I've recently got hold of three examples where they have gone a bit further and an entire book has been published to celebrate the occasion.

The first of the three is Mersey Gateway – A Bridge to Prosperity (118pp, 2018), published by the project's client and bridge owner Halton Borough Council. The Mersey Gateway connects the towns of Runcorn and Widnes across the River Mersey and Manchester Ship Canal, providing a new route for highway traffic, bypassing the Silver Jubilee Bridge built in 1961.

The new river crossing is a three-tower cable-stayed bridge with an unusual configuration, having a central tower visibly shorter than the two other towers. The new structure has been built to provide improved traffic capacity, reduce reliance on ageing infrastructure, and improve travel times not just locally but for nearby areas, particularly Liverpool and its surroundings.

The book concentrates on the client's view of the scheme. There is very little information on the engineering or architectural design of the bridge, not even an explanation for why the central tower is shorter, to give just one example. However, the book makes up for this with its strong coverage of the bridge's economic and social benefits.

The structure of the book is not chronological, but instead sets out to grab attention from the start. A description of the project's history and development doesn't start until page 77. Instead, the first chapter documents key features of the construction phase: the temporary trestle bridge, foundation cofferdams, the moveable scaffold systems (MSS), deck construction, cable stays, traffic management, and the opening ceremony. It's a well-chosen selection of highlights from the project's construction timeline.

There are short interviews with two people involved in the project: tower crane operator Peter McDonough and visitor centre volunteer Evelyn Edwards. I'd like to have read more of these, as my own experience of major projects is that a huge number of people contribute, and they often have plenty to say.

The second chapter emphasises community and people, including education outreach, local training and apprenticeships, recognition of women in engineering, community volunteers, and also the work of the Mersey Gateway Environmental Trust. This really shows what matters to the project client on a project such as this: it's not just all about quantities of steel or traffic statistics.

The third section, on design, environmental assessment and other aspects of the development phase, is weak by comparison – perhaps it's because I'm a designer by trade, but I feel this was a lost opportunity to tell this part of the story. It reads pretty much as if nobody involved in producing the book had actually spoken to anyone involved in design. The weakness continues into the fourth and final section, which attempts to credit the main project participants but which I think will leave most readers little wiser about what some of those involved actually did.

This reflects the nature of the book as the celebratory record of a very substantial achievement: Halton is a small local authority now responsible for two of the UK's largest bridges – they are right to be proud and to emphasise the benefits of the scheme beyond the bridge as a structure. This also means that the book (like most souvenir publications) has a uniformly optimistic, positive narrative – if anything went wrong along the way, if difficult challenges were overcome, those stories are absent.

The bridge's graphic layout is excellent, and there is a wide range of excellent photographs of the bridge and its construction (taken by David Hunter, and some of them reproduced here). The author or authors are uncredited, but the writing is very clear, and particularly good at explaining engineering and construction issues in lay terms – much better at this than I would normally expect.

It isn't the easiest book to get hold of – I wasn't able to locate anyone selling it online, and I got my copy by contacting Curiosity Bookshop in Runcorn directly – if they still have it in stock, they can take an order over the phone and post the book out (it costs £9.99 plus postage).

Further reading:

19 May 2019

Winner of bridge design competition for Irish National War Memorial Gardens

The Royal Institute of the Architects of Ireland and the Irish Office of Public Works have announced a winner in their design competition for a new bridge at the Irish National War Memorial Gardens. The bridge will span the River Liffey and provide a new entrance to the Gardens for pedestrians crossing from the river's north bank.

In the 1930s, architect Edwin Lutyens designed a three-span arch bridge at the site, pictured below, but it was never built.

The winner receives a €15,000 prize (and the hope that their bridge may be built). Two runners-up receive prizes of €7,500 and €5,000, and two further entries were Commended. In total, the open competition received 61 entries from 9 countries.

Ian Ritchie Architects / Schlaich Bergermann Partner

The winning design is, in the words of the designer, "the most slender and shallow structural arch that is technically possible." It is constructed of stainless steel, with parapets in the form of a screen of reeds, and with footprints on the deck surface intended to commemorate soldiers who never returned from war.

There's more than a little sense of déjà vu about this bridge design. The same team also won the Stratford-upon-Avon bridge design contest back in 2006, which was also a super-slender stainless steel arch design. That project was cancelled in 2008 due to escalating costs.

Here's the "calligraphic brush stroke" image which is used on the e-architect website for the Stratford bridge:

And here is an image taken from Ian Ritchie Architects' web page for their new Irish design:

I'm sure the resemblance is entirely coincidental.

Second Place
Weston Williamson + Partners / AKT II

The details of this design are unclear, but it it is described as having three girders, with views down through the bridge to the river.

Third Place
Niall Montgomery + Partners / J. B. Barry and Partners / Billings Jackson / Conway McBeth / John Spain Associates / Scott Cawley

This is another steel girder structure, with a granite surface and extensive landscaping works. Standing stones are engraved with illustrations taken from the War Memorial Record Books.

Seán Harrington Architects

I expect there's an engineer involved, although the RIAI don't see fit to credit anyone other than the architects in their competition announcement. This design is an arch-supported stressed ribbon bridge, a graceful modern version of the original Lutyens proposal.

Bystrup Arkitekter & Designere ApS

The final design is stated as being in weathering steel, with a layout which tapers in plan to accentuate the visual perspective when arriving at the Memorial Garden. Of all the designs selected by the competition judges, this one feels the most out of place to me. I also think that forming the curved portal frame shape in weathering steel would be rather difficult.

Bonus entries!
The RIAI haven't released a gallery of any other entries, but here are two more that I've found on the internet. If anyone else would like to email me a copy of their entry, I'll add it here when I get a chance.

Cake Industries / BEaM

This is an attractive and ambitious design, with complex geometry, an interesting combination of materials, and a ramp down to the river bank. I'm only guessing, but I suspect the judges may have thought that it competed for attention rather than paid due deference to the War Memorial Gardens.

Fairfax & Sammons

If the quality and style of illustration won the prize, this would easily be my favourite, a beautifully rendered bridge in traditional style. I think the designer wasn't entirely clear whether they wanted an arch or a suspension bridge, and went for a bit of both.

01 May 2019

Telford Station footbridge

Recently, I was in the town of Telford in Shropshire, and spotted this fairly spectacular new covered footbridge. It connects Telford Central railway station to the town centre, and replaces a previous bridge which was in poor condition. The new bridge opened to the public on 30th November 2018, with the project costing £10.3 million.

There are actually two new bridges, each with a similar design by Jacobs and Nicoll Russell Studios. They were fabricated by SH Structures working for main contractor Balfour Beatty.

The shorter structure spans over two railway tracks, while the longer structure is an impressive 90m long and crosses a dual carriageway road. It's not easy to photograph in a way that makes sense of both structures and their relationship to their surroundings, but you can get all that in this fly-through video:

The main bridge structure is a hybrid steel arch truss. The exploded view below, taken from a design drawing, shows the various structural and non-structural elements:

The form of the bridge is responsible for many of its oddities. The primary structure is an arched truss, entirely hidden within the roof, supported on raking legs at either end.

The central ridge to the roof initially gives the impression that the whole thing consists of two arches inclined against each other, but this is not the case: the raking legs are parallel rather than inclined inwards. It feels like a strange kind of compromise, perhaps benefiting from being largely hidden.

The outer roof covering is tensile PTFE fabric, tensioned against the steel members at each roof edge. The roof soffit is made up of GRP panels fixed to a grid of secondary steelwork, and hidden edge gutters are also constructed in GRP (there are plans and sections on the project website, for those interested in seeing more).

The hanger members are solid structural steel elements, suspending a stiffened steel grid deck (note that the drawings on the website show something different, a steel deck pan filled with concrete).

There are "swallow-tail" details extending the roof covering at each end of each span, which I think would have been better if more flamboyant, or at least if extended to fully cover the space between the two bridges (as things stand, bridge users will have a peculiar experience on a very rainy day).

A consequence of hiding the main truss inside the roof is that the hangers disappear into a featureless ceiling, which feels oddly disconcerting to me.

It's not obvious from the photos, but the roof structure is 7m wide, and hence much larger than the bridge deck, which has a clear width of only 3m (at least according to the design drawings on the project website). There's a certain top-heaviness which results, which is emphasised further by the extreme transparency of the deck and glazed walls. It's a bit like a glass of beer with too much foam left on top.

I do like the commitment to transparency, as covered bridges often give a very enclosed feeling. It lightens the overall impression of the bridge, giving good views for bridge users and I'd think a greater feeling of security as a result.

The bridges include two unusual curved expansion joints, and the larger span incorporates holding down bearings, presumably to resist overturning under high wind loads. Tuned mass dampers have also been installed, reportedly the first use of magnetic / eddy current dampers in the UK.

Further information:

10 April 2019

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:

07 April 2019

Bridge competition debris part 29: Network Rail Footbridge Design Ideas Competition

I posted last July when Network Rail announced this contest, but what with one thing and another, I've neglected to write about the result.

Quick recap: Network Rail were looking for ideas which were "innovative, challenge presumptions and raise expectations for the quality of future designs". The contest ran alongside a more conventional commission for a consultant team to refresh the organisation's station footbridge designs, which led to the appointment in October of Arup and Knight Architects.

The ideas competition was open to pretty much any entrant, offering a £20,000 prize fund but no commitment to use the winning idea or to commission any further work.

The winner was announced in December as Gottlieb Paludan Architects, Denmark, with Strasky, Husty and Partners Ltd, Czech Republic (above). The judges also highly commended a design from Hawkins\Brown with WSP (below).

There were a further 18 entries on the judges' longlist. In total, 121 entries were submitted, so clearly something about this contest struck a chord amongst the creative professions. Given the very low probability of actually getting any significant reward, it's interesting how many well-known names took part, but perhaps also unsurprising that many entries look like they were dashed off in a spare lunch-break.

One thing that strikes me about the entries is the proportion which adopt a modern or futuristic approach. I believe the competition identified the need for station footbridges which would link railway platforms in both a new-build context, and also upgrades to existing stations, some of them heritage settings. Network Rail included examples of historic lattice-truss bridges in the material they supplied to entrants, but very few designers submitted ideas which appear adaptable to different settings. There were quite a few entries with a latticework theme, but hardly any which looked adaptable to many situations.

Another thing that jumps out is that this competition probably created a significant learning opportunity - assuming (from the quality of the design images) that many of the entries will have been prepared by younger professionals, it must have been a marvellous opportunity to test out their design and illustration skills.

Many of the entries are impractical, even amongst those where an engineer is named as well as an architect. However, I think it's clear that a good proportion of entrants did understand that this was a contest about ideas - the more pragmatic looking entries generally didn't make the longlist.

I can strongly recommend spending a few minutes checking out the competition website. I'm only going to include the winning, highly commended and long-listed designs here, but although there's a fair bit of dross, there are also quite a number of thought-provoking concepts, and one or two interesting styles of illustration.

Winner: Gottlieb Paludan Architects / Strasky, Husty and Partners Ltd
The winning design is beautifully presented and highly minimalist in its conception: a staple-shaped deck below a staple-shaped roof, modular and suitable for a variety of spatial arrangements.

Highly Commended: Hawkins\Brown / WSP
Like the winner, this is a modular, adaptable design, but with the structure and architecture secondary to the potential for a bridge as a social and commercial space. It's a smart, enticing idea, perhaps well-suited to some urban locations but over-ambitious for most other sites.

Long list (selected images only: see competition website for more)

Luca Poian Forms, UK with Soluxn Ltd

Weston Williamson + Partners, UK with AKT II Ltd

Atkins Architecture, UK

 PHASE3 Architecture + Design, UK with AKT II Ltd

Miguel Costa, Andy Fisher, Melanie Davison, Priscille Rodriguez & Jan Verhagen

CF.Architects, UK with Cake Industries

Softroom, UK with Eckersley O'Callaghan and Inverse Lighting

[Y/N] Studio, UK

 Xing Design Studio, People's Republic of China

 Pelizziarchitettura, Italy

 Squire and Partners, UK

 Marks Barfield Architects, UK with COWI

 Sweco Architects, Sweden with Sweco Civil and Sweco Structures

 Method Architecture, UK

 Kashdan Brown Architects Ltd, UK

 AWW, UK with Mott MacDonald

 Metropolitan Studio of Architecture, Pakistan

 Fereday Pollard Architects, UK