Yorkshire Bridges: 33. Western Bank Bridge, Sheffield

Ah, it was good to get out and see an actual bridge again.

I'm not quite sure how I missed this beauty on my previous visits to Sheffield, but never mind.

It was built in 1969 to a design by Ove Arup and Partners and architect Yuzo Mikami. I say "it", but actually there are two bridges here, as shown in the cross-section below.

The bridges carry the steeply sloping A57 Western Bank highway above a pedestrian concourse area in the University of Sheffield campus. They are two-span structures, supported on single bearings below their tetrapodal centre pier, and a pair of bearings at each end.

The bridges were built in a period when the University campus was expanding, and the growth in road traffic had led to the highway being upgraded to a dual carriageway. Up to 10,000 pedestrians were reported to be crossing the road every day before the bridges were introduced.

The reinforced concrete slab decks vary in depth, being 1.2m deep over the central support and 0.84m at the abutments. It's a subtle feature that is not immediately obvious visually due to the large footway cantilevers on the edges of the deck.

Both decks are slightly curved in plan, but as can be seen in the photos, the main bridge deck slabs are straight, with the edge cantilevers varying in width to provide the curve.

From above, there is very little of interest to see. The interest is in the space created underneath the bridge. From below, this is a concrete roof held up on finger supports and providing some shelter from the weather. Glass blocks allow light through the central strip, and recently new lighting has been installed to make this a more attractive space at night.

It's a classic of modernist design, with some similarities to both Kingsgate Footbridge (1963) and Drochaid a' Chaolais Chumhaing (1984). The attraction is in its balance between the monolithic and the skeletal; it's clearly one "thing", like a sculpture, rather than one thing sitting upon another thing, like a conventional two-span road bridge.

The tetrapod supports have an interesting blend of straight and curved geometry: the outer edges form an inverted pyramid, while the inner surfaces of each arm are profiled with the curves of two intersecting hyperbolas. I'm not 100% convinced about the way the arms meet the deck slab and wonder whether a different detail would have been preferable e.g. having the arms project slightly from the side faces of the slab to give more of a "cradling" effect.

The sloping faces in front of the abutments were a conscious design choice, not so much to provide seating as to avoid the "tunnel" effect common to subways with vertical walls. The aim is to integrate the bridge with the adjacent landscaping. I guess the central tetrapods represent a similar visual impulse.

The block seating around the supports is not original. I wonder to what extent it was added to stop drunken students from bashing their heads into the angled support struts?

The concrete appears to have weathered well, and I'm left wondering why such a well-designed bridge isn't a little better known.

The article about the bridge in Arup Journal is well worth reading, including some excellent photographs, design drawings, explanations of the structural analysis, and an unexpected anecdote about students in mini-skirts.

The bridge was rewaterproofed, repaired and had new bearings installed in 2016.

Further information:

• Google maps
• The design and construction of Sheffield University Concourse (Ranawake, Gordon and Tune, Arup Journal, 1969)
• An Encyclopaedia of British Bridges (McFetrich, 2019)

Yorkshire Bridges: 17. Link Bridge, Eyre Lane, Sheffield

I'll finish off this set of posts regarding bridges in Sheffield with a little thing, a link bridge which spans across Eyre Lane.

This links two sections of Sheffield Hallam University, the Arundel Building and Charles Street Building.

I don't know who the structural engineer was, but the architect is Bond Bryan Associates, collaborating with Corin Mellor of David Mellor Design, who are much better known as a designer of cutlery than of bridges. The Mellors once had a workshop on the site.

The bridge combines three materials: glass for the side elevations, weathering steel for the roof and floor, and stainless steel for the decorative ribs.

There's not a great deal more to say: it's short, and it's sweet.

Further information:

• Google maps
• Public Sector Build Journal

Yorkshire Bridges: 16. Pond's Forge Footbridge, Sheffield

Okay. I think we all need to draw a deep breath before looking at this utterly baffling bridge.

This little curiosity is just next door to the Park Square Bridge. It forms one of two approach ramps to a footbridge over the Park Square roundabout, with the other ramp and main structure being much less interesting steel box girder spans. This ramp provides a main access route into the Pond's Forge International Sports Centre.

My only source of information on this structure comes from an ICE leaflet titled "Sheffield: A Civilised Place". This states that the footbridge was required by the client to be "interesting and imaginative", against which criteria it must be considered a great success. If anyone out there can share more information, please do!

At first glance, it seems like some weird preying-mantis version of a cable-stayed bridge, but I suspect this is not correct. At one end of the bridge there is an elevated tower, with two spindly arms cranked towards the span as if holding it up, but it seems unlikely this element can carry any significant load, in the absence of back-stays. The cables themselves are very slender, and they connect not to the bridge deck, but to the upper ends of parapet posts (again, with nothing to balance any horizontal force in the wires). I think these parts are essentially decorative, or perhaps helping slightly to resist twisting of the walkway.

I wondered whether the bridge might be half-through U-frame structure, with the perforated parapet plates acting as the webs, but note that there is no upper compression member, and that these plates are discontinuous before the upper end of the span: the main part of the bridge has parapet plates and posts inclined inwards, but towards this end of the span there are vertical walls contiguous with the mast pieces.

The parapet posts are almost grotesquely over-sized, and are aided/abetted by horizontal parapet rails which seem quite superfluous. My sense is that that parapet posts, which continue under the deck to form clamp-shaped support frames, are simply a series of transverse frames holding up both deck and balustrades.

Every second parapet post is connected at its upper end via two diagonal wires to the lower end of intermediate posts. These positions are then wired to nodes below the deck. I wondered if this might form some kind of stiffening truss, but there are no longitudinal chords. Perhaps they restrain the parapet posts against longitudinal movement, but the parapet panels are quite capable of doing that. Again, I'm left unable to decide whether they help a little to restrain twisting, or are simply decorative.

At the opposite end of the bridge from the "support" tower is a second tower, supporting what looks like an empty signboard. This is connected by wires to a baffling collection of bits and pieces below the bridge deck, but I think all this is doing nothing more than holding up the tower and its (empty) signboard.

The parapet "clamp" frames sit on a single tubular member running below deck, with a combined relationship something like a spine and rib cage. So far as I can tell, this single tube, dwarfed by the massive but seemingly over-wrought metalwork above it, is a simple beam supporting the main span and resisting both bending and torsional effects. This tube is connected to support frames at either end and hence to ground.

I think I have rarely encountered such a confused, confusing shambles of a structure. It is "interesting" in the way that a car-crash is interesting: it's difficult to look away from the sheer horror. It is "imaginative" in the way that a David Smith sculpture is imaginative: a creative juxtaposition of geometries in three dimensions. But a sculpture's primary function is visual, not structural.

In principle, I'm all in favour of whimsy in bridge design. Bridges, especially on a small scale, do not all have to be po-faced and technologically constrained. I'd quite like to like this bridge.

But I don't.

Further information:

• Google maps

Yorkshire Bridges: 15. Park Square Bridge, Sheffield

Park Square Bridge is one of several bridges built for the introduction of Sheffield's Supertram system, completed in 1994/5. This tram system's three branch lines converge in a delta junction just to the west of Park Square, and this bridge carries the western branch above Park Square roundabout and up onto Commercial Street (hence the bridge's other name, Commercial Street Bridge).

Alongside other major Supertram structures, the bridge was designed by Sheffield City Council's in-house team, Design and Building Services. That seems barely imaginable today, it's hard to think of a UK local authority with the capability to design such a major structure any more.

The bridge spans 75m (with two smaller approach spans making a total length of over 100m), and was built by Balfour Beatty, with steelwork by Watson Steel (now part of Severfield).

The main bridge span is a bowstring arch. Inclined steel arch ribs are braced overhead and tied with steel girders, which form the edge members in a ladder-deck arrangement. The bridge deck is a 250mm thick reinforced concrete slab composite with the ladder-deck crossbeams. The deck carries a non-structural concrete slab, containing the tram rails, drainage channels and stray current protection system. The deck is suspended from the arch by 60mm diameter steel hangers.

Although the three spans are each simply-supported, the structural deck slab is continuous, to avoid leaking joints, and a paper on the bridge design states that there are "concrete hinges" in the slab above the piers.

The superstructure sits on reinforced concrete piers and abutments, with concrete blockwork cladding, and these are supported on piles down to bedrock. The design language is a little post-modern, I think, with an elaboration of detail and a type of mock-classical architecture that seems at odds with the high-tech or modernist sensibility of most bridges of recent decades.

The bridge span was driven by the highway layout and the presence of a large culvert below ground. However, Supertram planners were also keen to have a "gateway" structure at this prominent position. A cable-stayed alternative was considered but rejected. The choice of a bowstring arch allowed a low construction depth to be employed, minimising the length of approach ramps.

The designers sought to maximise maintainability by avoiding closed structural sections, so the arch rib is a channel section with the open face downwards (similar to another bowstring arch the other side of the Pennines, in Salford).

According to the paper, "careful treatment" was given by the designers to the parapets and to the anti-climb blisters on the arches. The latter are pretty horrible looking, but not enormously so given the scale and clarity of the rest of the bridge.

The arch ribs are pin-ended, which I find really quite odd. Are there other modern bowstring bridges with this detail? The design paper offers no explanation for why this choice was made. It isn't visually incongruous, but I think hinges should generally be avoided in main members of bridges unless there's a very good reason.

Behind the hinges, there are thrust blocks comprising a group of vertical steel stiffening ribs, which transfer the arch thrust into the end node of the tie girders. As you can see in the photograph, they double as a handy waste receptacle.

On the whole, I think this a well-designed bridge, generally with clarity of form and well-proportioned. It is, however, let down by some of the detailing, and not only the impromptu waste-bins, the lumpen parapets or the blisters.

There is a pastel colour scheme used to distinguish between a hierarchy of components, both the hanger assemblies and also the connection of these to the tie girders, which for my taste has been over-elaborated. The use of this number of pale colours is not very successful, as they are simply impossible to distinguish under most lighting conditions. A smaller number of complementary colours would have been enough.

The bridge was the winner of an ICE (Yorkshire) Award in 1994/1995, and Commended in the National Steel Design Awards.

Further information:

• Google maps
• Wikipedia
• Structurae
• LUSAS
• Commercial Street Bridge, Sheffield, UK (Wilson and Jones, First International Conference on Arch Bridges, 1995)

Yorkshire Bridges: 14. Blonk Bridge, Sheffield

The next bridge upstream from Smithfield Bridge is Blonk Bridge, which carries Blonk Street across the River Don.

This is a three-span masonry arch bridge, completed in 1828 by Doncaster-based architects Woodhead and Hurst, the contractor being a Mr Birchett. It cost £250 to build.

The spans are elliptical in shape, or possibly three-centered. The masonry looks well detailed, with the facing voussoirs tying into the main spandrel stone courses, although the geometry is such that the spandrel courses are all of a different height.

The masonry above the stringcourse seems to be of a different type and construction, perhaps associated with bridge alterations undertaken in 1913 (I can't find any details of what was altered online).

The most attractive feature on the bridge is its downstream parapet, which is a decorative cast iron balustrade. It looks pleasant from the outside, and is very nicely painted on the inner face. The casting is "one-sided" which looks decidedly odd from close at hand.

The upstream parapet is in reinforced concrete, and quite out of character with the rest of the structure. There were plans to replace this with a metal parapet back in 2007, but evidently nothing came of it.

The bridge was Listed Grade II in the early 1970s.

Further information:

• Google maps
• British Listed Buildings
• Wikipedia
• Crossin' O'er: About our bridges - past and present (S. Roy Davy, 1984)

Yorkshire Bridges: 13. Smithfield Bridge, Sheffield

Heading upstream along the River Don, from the Cobweb Bridge, you pass under the busy A61 road bridge, and come to a modern footbridge, which appears to be called the Smithfield Bridge after the site of the former Smithfield Market car park.

The new bridge spans 40m, and carries a 2m wide footway, connecting the river banks at high level (above flood defences), and inter-connecting a number of pedestrian routes including the Five Weirs riverside walk. Completed in July 2010, it was designed and built by CTS Bridges, and is a type of bridge they've supplied at several locations across the UK.

Structurally, the bridge is not especially remarkable. It consists of two lightly inclined painted structural steel tubular arches with Vierendeel infill. The parapets are perforated steel plate, which is not very attractive but probably a smart move given the nearby Cobweb Bridge's history of parapet vandalism.

There are two aspects to the bridge that I felt made it worthwhile featuring here.

The first is an observation. The bridge as built is not the bridge that received planning permission, and it would be interesting to learn quite how the original plan was substituted for something much cheaper.

The planning application for the bridge describes and shows a more attractive and generous structure, with a 3m wide rather than 2m wide footway, in the form of a "butterfly arch", described as "both striking in appearance and economical in construction". Evidently, it was not economical enough for somebody involved in the project.

Here is just one of the visualisation images taken from the planning application:

The planning application also shows and describes considerably more attractive parapets, "incorporating stainless steel woven wire infill panels".

The second point of interest is a very odd steel bar which appears to be either suspended from or propping up one end of the bridge. I spent some time on site trying to work out what this was for, without success, but the planning consent documents explain the purpose.

The bridge at this end is slightly lower, and although the bridge deck is above the river flood level, there is a concern that flood-borne debris could strike the bridge. The bridge alignment is skewed across the river, so debris hitting the bridge here could easily become trapped with nowhere to go, impeding river flow or in the worst case pushing the bridge off its supports.

The peculiar bar is therefore a debris fender, designed to channel debris away from the corner and back into the river flow.

It certainly isn't a pretty addition to the bridge, but presumably there was little choice, as the only other option would have been to raise the bridge, with an impact on ground levels, ramps and possibly adjacent buildings.

It would, however, have looked much better.

According to the Yorkshire Post, the bridge was funded by Yorkshire Forward, the Environment Agency, and the European Regional Development Fund, so it seems unlikely that the choice of the cheaper bridge solution can be laid at the door of a penny-pinching developer. Perhaps it owed more to a general tightening of budgets in the wake of the 2008 recession.

Further information:

• Google maps
• Planning consent

Yorkshire Bridges: 12. Cobweb Bridge, Sheffield

Next stop, Sheffield, where I visited several bridges recently.

The Cobweb Bridge was top of my list, I'd wanted to see this bridge for quite some time.

Built in 2003, it forms a key link in the city's Five Weirs Walk. It allows walkers to negotiate two obstacles at the same time: the River Don, and the Wicker Arches railway viaduct (officially the Victoria Viaduct). The Cobweb Bridge spans the river while passing below the Grade II* railway bridge.

The bridge was designed by Sheffield City Council's in-house structures team, and built by Thyssen. It's a lovely idea: a slender platform suspended from the rail viaduct vault by a spider's web of steel cables. Lurking above it at the crown of the arch are giant metal spiders, which house lighting units.

I saw it on a grey and drizzly day, which didn't help, but I found the bridge a little disappointing in reality.

It is S-shaped in plan, with two arced segments at each end connected by a long straight walkway in between. It makes for an interesting series of perspectives, although the main length of the walkway is very tunnel-like.

At one end, the walkway is supported on a set of support legs, designed entirely without visual finesse. At the other end, it spans from the riverside onto an intermediate suspended frame. In places, the geometry of the bridge and its parapets seems slightly mis-aligned.

The support cables are slender steel wires anchored into the stonework of the viaduct via proprietary Cintec anchors. The cables are arranged with a degree of triangulation to eliminate sway, and further stiffness is provided via tie-down cables inclined below the deck. These incorporate turnbuckles, which will have allowed both sets of cables to be stressed against each other. I didn't observe any significant vibration, indicating the design to be effective.

The major problem with the bridge relates to its troubled history, not to its original design. After opening, the bridge suffered repeatedly from vandalism, and deterioration of the original flooring, which appears to have been timber with a red-coloured anti-slip covering.

The parapets as originally designed featured longitudinal steel wires as the infill, and the cleats which supported these are still visible today. You can see how the bridge once looked by following the Wikipedia link below. However, the wires were repeatedly vandalised and stolen, eventually leading to closure of the bridge and a refurbishment programme in 2012. The wires were replaced with a tougher metal mesh, and the timber floor with grey FRP panels.

These appear to be vandal-resistant, but the changes have dramatically downgraded the appearance of the bridge, from something that was once lightweight and open to something more greatly resembling an industrial cage.

It remains a remarkable and interesting structure, and an imaginative way to carry a footpath past obstacles with difficult issues relating to physical geometry, asset ownership and heritage value. I can't think of anything else in the UK with a similar structural form.

It's a tremendous shame to see it in its current state.

Further information:

• Google maps
• Wikipedia
• Structurae
• Cintec