Ok, here are the Nine Elms / Pimlico Bridge Design Competition Stage 2 designs in full. Click on any image for a full-size version, or visit the project gallery.
Ove Arup & Partners Ltd with AL_A, Gross Max, Equals Consulting and Movement Strategies
There has been a great deal of NIMBY-ish wailing from residents on the north bank of the Thames (and also from their political representatives), concerned that the bridge may wreak havoc upon one of the few public riverside green spaces in London, Pimlico Gardens. These complaints ignore the fact that this is a contest to select a team, not a design, and that no location for the bridge has been confirmed as yet. However, there's little doubt that an alignment between Pimlico Gardens on the north bank, and the new US Embassy on the south bank, is the most sensible.
Arup's design tries really, really, really hard to minimise harm to the gardens, siting the bridge's necessary cycle ramps in the river rather than on land. This makes for great public space, but is something of an imposition on the river, and it's hard to see how Arup deal with the inevitable issue of boat impact. As shown the ramps are structurally sketchy at best, slender loops of something-or-other with no visible means of support.
It's not an unattractive design, but, having visited the site, I don't think it is best served by having a tall structure mid-river, the riversides shouldn't be so visually dominated by a bridge. It's also not a straightforward bridge to build, with multiple angled and criss-crossing hangers, potentially requiring a great deal of temporary supports within the river.
Ove Arup & Partners Ltd with Hopkins Architects and Grant Associates
Arup, again, this time with a suspension bridge solution. This should, in theory, be much more respecting of the river environment, but for reasons that seem obscure, the designers have chosen to stretch the pylons far taller than is actually necessary, taller even than some pretty tall trees in Pimlico Gardens. By also painting them red, there seems to be an unnecessary dash of "look-at-me" all over this.
The ramps are, again, in the river, although the connection to the Gardens is less well detailed, punching through the middle rather than tucked discreetly into the corner as was the case for the previous design. However, this is the only design that recognises that the route is not fixed, showing clearly in the plans how the same bridge can be adapted to any number of alternative locations without affecting the structure's logic.
The circuitous ramps at least have some means of support, with cable stays radiating from the main pylons, but again they are vulnerable to boat impact and visually intrusive.
I'd also question the choice of deck structure, a steel multi-cellular box girder which seems unnecessarily expensive to me for a bridge of this span with suspension cables on both sides of the deck.
Bystrup Architecture Design and Engineering with Robin Snell & Partners, Sven Ole Hansen ApS, Aarsleff and ÅF Lighting
Bystrup's design shares the first two designs' offshore ramps, but does at least trouble itself to consider boat impact protection, with an "eco-pontoon", a planted floating fender, shown as a possible solution.
It's a cable-stayed design with an S-curved deck supported on opposite sides from the two towers, but I think the curvature of the deck is too slight, and this renders the cable and tower arrangements somewhat inert.
As with the second Arup design, a multi-cellular box deck is shown, symmetrical in cross-section, which make no real sense for a structure with cables on one side only at any given point - too much of the section's capacity is used to restrain its own self-weight torsion.
Buro Happold Ltd with Marks Barfield Architects, J&L Gibbons Landscape Architects, Gardiner and Theobald
Structurally, the Buro Happold design is by far the oddest of all these conceptions. It's an asymmetric cable-stay bridge, but the deck seems to be supported from a suspended cable net rather than from the usual array of stay cables. I found this baffling when the designs were first announced at Stage 1, and I find it baffling now. It seems to add a great deal of complexity for very little benefit, and it would be a nightmare to install and to maintain.
Even Happold's own construction diagrams make clear quite how unbuildable it is, with the main part of the deck requiring temporary props to actually hold up the cable net, even at at point when the cable net is doing nothing to hold up the deck. The deck is therefore temporarily supported along its entire length before being whizzed into position on a barge. This is simply not sensible or economic, given the alternatives available if a conventional cable-stay design were chosen.
It's the only design to dare to antagonise the NIMBYs by putting the ramps onshore, and I admire this. Pimlico Gardens is not, at present, a particularly impressive space, nor is it especially well-used, so it seems to be ripe for re-imagining, if, as this design suggests, the trees can be left largely untouched.
According to the competition website, design teams are now due to enter into "competitive dialogue" with the judging panel, and to submit final tenders (including a fee for their services) in early September. A winning team should be declared in October.