An international competition has been announced to design new pedestrian, cyclist and tram bridges in Helsinki, connecting a new residential area to the city centre. The bridges, termed Kruunusillat ("crown bridges") fall within a designated heritage area, and are being partly promoted under the auspices of Helsinki's role as World Design Capital for 2012.
The budget for construction is €86m, and these are not small structures, but crossing major waterways. The longest bridge will be over 1km long, rising to 20m above water level.
Prequalification submissions are requested from teams of bridge engineers, architects and supporting specialists by 3rd August. Full details of the programme, jury and how to apply are available on the competition website. More information can be found at the Official Journal of the European Union.
Between 5 and 10 design teams will be shortlisted, and each one is to be paid €50,000 for their efforts (plus expenses towards producing a scale model, and some limited travel expenses). If the contest moves into a second phase, a further €25,000 becomes payable, and there is the prospect of a design contract for the winner. This is pretty generous, certainly when compared to UK standards, although the competition submission requirements are very detailed, including production of numerous drawings, photo visualisations, reports and animations as well as the scale model.
I expect they will attract some very high-powered entrants, although the nature of the site is that designs will tend towards the elegant rather than the spectacular.
26 May 2011
Landsberg footbridge competition winner
Knippers Helbig have kindly sent me details of their recent competition-winning design for a footbridge in Landsberg, Germany, won jointly with Birk und Heilmeyer Architects. I can't offer any information on the context of the competition, but the bridge spans a small river, and is a very unusual sculpted timber structure.
It builds on some of the ideas in their Margaretengürtel design for Vienna, which I discussed here last March, although with a much simpler geometry. The Vienna bridge was formed of a series of horizontal timber layers, glued together like wind-eroded stone strata. In Landsberg, the timber is turned vertical but the contour-like sculpting is the same, with a varying depth timber spine reflecting the bending moment distribution, and a raised bank of timber above the main pier, where the bridge kinks in plan. This provides enhanced structural stiffness but also establishes a seating and viewing area.
The timber layers will be glue-laminated together, and presumably also stressed together with tie bolts, as was the case both on the Margaretengürtel proposal and on their even more sculptural entry to the I-70 Wildlife Crossing competition (again, covered here previously).
It's an attractive design, and it would be nice to see one of these actually get built!
Click on any image for a full-size version.
25 May 2011
Winner declared in North Sheen footbridge contest
This contest was run by Richmond Conservatives to try and find a better design than an off-the-shelf Network Rail structure. It has been won by a local Richmond resident, Stephen Speak, who beat seven other shortlisted designs. I discussed the contest in a previous post, so follow that link for more details on the bridge, which provides access across a railway at times when the adjacent level crossing is closed. Click on the image below for a full-size version of the winning entry.
The design won't win any awards on visual grounds, but seems to have focussed on the key issues of security, vandalism, and practicality which must be of greatest concern to the body actually paying for the bridge, Network Rail. Assuming the designer is a non-engineer, I think he's done pretty well.
It would be interesting to know what else was entered - this was a contest aimed at engaging local amateurs, rather than professional bridge designers. Reportedly other designs included a curved bridge deck, solar powered lights, and laser-cut metal panels.
The winning design essentially adopts the geometry of the previous solution, probably unavoidable given the highly constrained site, and strips out Network Rail's traditional flat steel plates in favour of something more transparent. Essentially, it's based directly on the treetop walkway at Kew, with a lightweight steel truss structure supporting timber handrails and with mesh infill panels.
This offers a number of advantages over the standard solution, chiefly in removing all the space for vandals to spray graffiti, but also in the improved appearance and surveillance that the more transparent approach facilitates. The major disadvantage is that doesn't comply with Network Rail's parapet standards, which require all pedestrian parapets to be solid panels, without any holes at all, let alone a mesh. It would be nice to think that Network Rail would be willing to depart from their normal practice, but they are notoriously rule-bound and averse to setting precedents in this way.
The design simply dispenses the overhead cage which featured in the original solution, which was probably the most unpleasant thing about it. Privacy for an overlooked garden is provided by a series of louvred slats, allowing light and air through but eliminating direct views, and again this is clearly an advance over the flat plates which served the same purpose on the previous design.
24 May 2011
The space of all possible bridge shapes: Part 3
In the last two posts, I introduced Stephen Wolfram's idea that it may be possible to use modern computational algorithms to develop entirely new structural forms for bridge, and discussed how difficult it might be to work out whether any of them are actually better than what we design already.
A more coherent idea of the problem can be seen in the example truss forms that Wolfram generated to illustrate his article.
Would any of these offer any improvement on a more conventional truss design? Perhaps there is a greater robustness, but it is unlikely the benefit-to-cost ratio is anywhere close to what can be achieved by simply using a conventional truss form with stronger individual members.
It's a classic case where a specialist with little or no familiarity with another field (in this case, bridge engineering) thinks they can bring some special insight which others are blind to. It's something seen frequently in evolutionary biology, where criticism of neo-Darwinian theory generally comes from biochemists or (sadly) engineers with an essentially shallow understanding of the topic.
However, I wouldn't dismiss Wolfram entirely. There's little doubt that bridge engineers are highly constrained by habit - their own design experiences, and the traditional forms which have calcified into the standard processes of bridge fabricators. Often, new bridge concepts are dead-ended by the inability of steel and precast suppliers to invest in new equipment and technology. Even where new technology is brought in, as with the robotic welding more commonly seen in Japan than in North America or Europe, it is applied only to a very specific problem (e.g. welding of orthotropically stiffened steel plate), rather than to more radically expanding the range of what can be built economically.
As ever, footbridges offer an area where designers can experiment with smaller economic consequence, and are often encouraged to do so by promoters' ambitions. I'm quite confident there are ideas out there in academia, of which Wolfram's is just one, which are underused (or never used) by designers even in this most adventurous of bridge-building fields.
One field which is just about making it into the "real world" is that of topology optimisation. This has been used to show that the theoretically ideal catenary cable is not a single cable but a multi-stranded Hencky net,
and there are various other examples online relating directly to bridge engineering. One paper documents its application to the design of the Knokke Footbridge (pictured, right), which has been featured here previously. This shows the use of computer processing to progressively optimise steel plate thickness (or determine where it can be omitted), something that could have wider applications not just in optimising existing forms but also in generating new ones.
Was Wolfram right that we will see entirely new bridge forms which surprise us in their novelty and apparent randomness? I doubt it, but I do think there's plenty of scope to take use some of the methods discussed here to take a fresh look at bridge designs now and in the future.
A more coherent idea of the problem can be seen in the example truss forms that Wolfram generated to illustrate his article.
It's a classic case where a specialist with little or no familiarity with another field (in this case, bridge engineering) thinks they can bring some special insight which others are blind to. It's something seen frequently in evolutionary biology, where criticism of neo-Darwinian theory generally comes from biochemists or (sadly) engineers with an essentially shallow understanding of the topic.
However, I wouldn't dismiss Wolfram entirely. There's little doubt that bridge engineers are highly constrained by habit - their own design experiences, and the traditional forms which have calcified into the standard processes of bridge fabricators. Often, new bridge concepts are dead-ended by the inability of steel and precast suppliers to invest in new equipment and technology. Even where new technology is brought in, as with the robotic welding more commonly seen in Japan than in North America or Europe, it is applied only to a very specific problem (e.g. welding of orthotropically stiffened steel plate), rather than to more radically expanding the range of what can be built economically.
As ever, footbridges offer an area where designers can experiment with smaller economic consequence, and are often encouraged to do so by promoters' ambitions. I'm quite confident there are ideas out there in academia, of which Wolfram's is just one, which are underused (or never used) by designers even in this most adventurous of bridge-building fields.
and there are various other examples online relating directly to bridge engineering. One paper documents its application to the design of the Knokke Footbridge (pictured, right), which has been featured here previously. This shows the use of computer processing to progressively optimise steel plate thickness (or determine where it can be omitted), something that could have wider applications not just in optimising existing forms but also in generating new ones.
Was Wolfram right that we will see entirely new bridge forms which surprise us in their novelty and apparent randomness? I doubt it, but I do think there's plenty of scope to take use some of the methods discussed here to take a fresh look at bridge designs now and in the future.
23 May 2011
The space of all possible bridge shapes: Part 2
In the previous post I discussed Stephen Wolfram's proposition that there exists a space of all possible bridge designs, and that if we could use modern computer techniques to generate this using a set of simple rules, we could find new and unpredictable bridge forms within that space which may improve on traditional ideas.
A key challenge is how to find the better designs, a process which involves testing each option against whichever criteria are required. This can be computationally intensive, but in the age of cloud computing, becomes a little more feasible. Sensible engineers might reasonably object that to analyse a non-trivial array of structural models would defeat even the greatest computing resources currently available, and I would sympathise.
I wonder, however, whether this isn't primarily a flaw of traditional analytical technologies such as the finite-element stiffness matrix method.
Closer to the professional arena, there is Daniel Piker's Kangaroo (pictured left), an add-on for Grasshopper / Rhino which carries out a similar physics-based simulation, and is being explicitly promoted for structural modelling purposes e.g. form-finding of catenary structures.
Nonetheless, I think that non-trivial analysis may still remain computationally too expensive, particularly for structures governed by continuum rather than discrete element behaviour (such as beams and frames), or where non-linear, dynamic or global buckling behaviour determine performance.
Analysis of the individual designs is only half the problem: it's also necessary to test them against pre-defined criteria to decide which are optimal (or, at least, superior to neighbouring designs). Researchers like Wolfram seem to believe that "economy" is readily measurable e.g. by least material. However, real-life economy in bridges is intimately linked to simplicity of construction, and structures which are regular and repetitious are generally cheaper to manufacture and assemble than those which are highly variable. A classic example is the simple rolled steel beam, which contains considerable quantities of material resisting very low stress, yet is almost always cheaper to supply than a latticework or variable section plate girder beam where the stresses have been made more uniform.
For trusses of the sort that Wolfram takes as his example, it is likely that his process will find an optimum 2-dimensional truss with irregular bay sizes or truss angles, reflecting the variation of shear; and with curved top and bottom chords, reflecting the variation of bending moment. But in 3-dimensions, truss members do more than carry shear and bending, they also resist out-of-plane buckling, and regular bays can make the deck design more economic. Curved chord members can similarly increase fabrication costs to a greater degree than the more uniform stress saves material. How then can economy be easily assessed?
If economy is difficult, what of robustness? How can that be readily measured in a manner which is quickly repeatable across a large array of possible designs?
To be continued ...
A key challenge is how to find the better designs, a process which involves testing each option against whichever criteria are required. This can be computationally intensive, but in the age of cloud computing, becomes a little more feasible. Sensible engineers might reasonably object that to analyse a non-trivial array of structural models would defeat even the greatest computing resources currently available, and I would sympathise.
I wonder, however, whether this isn't primarily a flaw of traditional analytical technologies such as the finite-element stiffness matrix method.
I recall a project from some years ago (VISABO) which used Newtonian mechanics in a manner more closely related to Wolfram's cellular automata, exploiting "intelligent" structural elements each of which contained their own rules of physics, global behaviour emerging naturally from their relationships. This has the potential to allow the change of structural response resulting from a change in structural form to be analysed much more quickly: individual members react dynamically when another member is moved, added, or eliminated.
Another, perhaps more accessible example, is the series of Bridge Builder games (pictured above right), which appear to use the same principle (they certainly don't use finite element analysis!)
Closer to the professional arena, there is Daniel Piker's Kangaroo (pictured left), an add-on for Grasshopper / Rhino which carries out a similar physics-based simulation, and is being explicitly promoted for structural modelling purposes e.g. form-finding of catenary structures.Nonetheless, I think that non-trivial analysis may still remain computationally too expensive, particularly for structures governed by continuum rather than discrete element behaviour (such as beams and frames), or where non-linear, dynamic or global buckling behaviour determine performance.
Analysis of the individual designs is only half the problem: it's also necessary to test them against pre-defined criteria to decide which are optimal (or, at least, superior to neighbouring designs). Researchers like Wolfram seem to believe that "economy" is readily measurable e.g. by least material. However, real-life economy in bridges is intimately linked to simplicity of construction, and structures which are regular and repetitious are generally cheaper to manufacture and assemble than those which are highly variable. A classic example is the simple rolled steel beam, which contains considerable quantities of material resisting very low stress, yet is almost always cheaper to supply than a latticework or variable section plate girder beam where the stresses have been made more uniform.
For trusses of the sort that Wolfram takes as his example, it is likely that his process will find an optimum 2-dimensional truss with irregular bay sizes or truss angles, reflecting the variation of shear; and with curved top and bottom chords, reflecting the variation of bending moment. But in 3-dimensions, truss members do more than carry shear and bending, they also resist out-of-plane buckling, and regular bays can make the deck design more economic. Curved chord members can similarly increase fabrication costs to a greater degree than the more uniform stress saves material. How then can economy be easily assessed?
If economy is difficult, what of robustness? How can that be readily measured in a manner which is quickly repeatable across a large array of possible designs?
To be continued ...
22 May 2011
The space of all possible bridge shapes: Part 1
I guess this is an old one now, dating back to 2007, but I hadn't seen it before.
Shortly after the collapse of the I-35W Mississippi River Bridge in August 2007 (pictured right, courtesy of pmarkham), Stephen Wolfram published a blog post titled "The space of all possible bridge shapes", wondering whether new developments in science could have anything to offer to bridge designers and hence help prevent future disasters. In order to come up with designs which maximise robustness while minimising economy, Wolfram speculates that designers will need to find entirely new structural forms, which may look nothing like those that have emerged from engineering history.
Wolfram is the developer of the popular Mathematica software, and a researcher into computational systems such as cellular automata. The best known of such systems is perhaps John Conway's Game of Life (pictured left, courtesy of kieff at Wikipedia), which demonstrates in a very graphic way how a wide spectrum of behaviour both random and structured can emerge from applying simple rules to the on/off state of image pixels. Genetic algorithms can be used to mutate the results, compare them against various tests, and "evolve" the system over many generations in search of some desired optimum. I have seen some experimental use of genetic algorithm techniques by architects in building design, but in structural engineering it seems to be largely confined to the academics (one of many examples here).
Wolfram's main interest is in the ability of very simple systems to be processed and combined by simple rules to create highly complex outcomes. The range of possible outcomes forms a kind of computational landscape, which can be investigated to determine whether there are useful results other than those that might have initially been predicted. Some of this is explored in Wolfram's book, A New Kind of Science.
Wolfram notes that before the 19th century, there were only a limited number of bridge forms in use (the beam, the arch etc), but with the advent of the railway age, a Cambrian explosion in bridge shapes occurred, all variations on the metal truss. As in the evolution of organisms, a certain feature had to arise before a wide array of new forms could build upon the opportunities it presented (the evolution of evolvability). This image of truss variations is taken from Wolfram's blog post:
Most of the famous truss types (Warren, Pratt, Howe, Fink etc) arose through a process not dissimilar to natural selection: inventors of truss forms were competing in terms of strength, ease of construction, and economy, and simple economics meant that only the fittest survived. It would be interesting to trace the history of the metal truss bridge through some kind of developmental tree, complete with extinctions, hybridisation etc.
As an aside, the generation of truss forms using simple rules was the subject of an interesting paper by Yoshiaki Kubota at IABSE's Venice symposium, which I discussed here before. It forms a subset of the wider systematisation of bridge types, as illustrated in one of Kubota's diagrams below:
Wolfram's proposition is that a wide range of otherwise unpredictable variations in form can be readily generated by combinations of simple rules e.g. add a brace, subtract a brace, subdivide a bay, shorten, lengthen, rotate. It is therefore straightforward to generate a multi-dimensional "design space" containing a myriad of options which a rational designer would never consider. The question is then whether any better designs exist within the space of possible bridge shapes, and Wolfram's experience in other areas makes him believe quite strongly that they would. His other work also suggests they may look like nothing we have seen before, possible quite "random" in appearance.
This post is getting quite long, so I'll continue this tomorrow.
Wolfram's main interest is in the ability of very simple systems to be processed and combined by simple rules to create highly complex outcomes. The range of possible outcomes forms a kind of computational landscape, which can be investigated to determine whether there are useful results other than those that might have initially been predicted. Some of this is explored in Wolfram's book, A New Kind of Science.
Wolfram notes that before the 19th century, there were only a limited number of bridge forms in use (the beam, the arch etc), but with the advent of the railway age, a Cambrian explosion in bridge shapes occurred, all variations on the metal truss. As in the evolution of organisms, a certain feature had to arise before a wide array of new forms could build upon the opportunities it presented (the evolution of evolvability). This image of truss variations is taken from Wolfram's blog post:
Most of the famous truss types (Warren, Pratt, Howe, Fink etc) arose through a process not dissimilar to natural selection: inventors of truss forms were competing in terms of strength, ease of construction, and economy, and simple economics meant that only the fittest survived. It would be interesting to trace the history of the metal truss bridge through some kind of developmental tree, complete with extinctions, hybridisation etc.
As an aside, the generation of truss forms using simple rules was the subject of an interesting paper by Yoshiaki Kubota at IABSE's Venice symposium, which I discussed here before. It forms a subset of the wider systematisation of bridge types, as illustrated in one of Kubota's diagrams below:
This post is getting quite long, so I'll continue this tomorrow.
19 May 2011
Bridges news roundup
UNESCO science committee approves construction of Haliç metro bridge
New bridge won't affect Istanbul's World Heritage Site status
Another bridge crossed in bid to mark US steel links
Will Sheffield get its replica of Brooklyn Bridge?
Burley Bridge Association carries on its century-old fight
They've been trying to get stepping stones replaced with a bridge for 113 years - see http://www.burleybridge.com/ for more.
Tony Meadows' 10-year wait ends as Borough Market viaduct installed
Only 10 years? You should try waiting 113 years, mate.
IQ Winnersh footbridge up for award
Ramboll's tree-lined structure is an unusual design, to say the least.
Fort York bike bridge project in limbo
The original headline to this story read something like "Fort York bike bridge dead", to which somebody presumably responded "it's not dead, it's just resting". Having already called a halt to this iconic bridge scheme, Toronto Council were challenged by one local councillor to reconsider, but have decided to stand their ground. Council officials are still being asked to identify a cheaper alternative. The desire to move it ahead was partly motivated by the fact that the railway it spans will be closed for other work in 2012, and any delay will miss this opportunity, potentially increasing construction costs considerably. Apparently, they were relying on the rail closure to allow the curved deck and arch to be temporarily propped. The structural form was never well suited to building across a railway to begin with, and is unlikely to survive the rethink.
New bridge won't affect Istanbul's World Heritage Site status
Another bridge crossed in bid to mark US steel links
Will Sheffield get its replica of Brooklyn Bridge?
Burley Bridge Association carries on its century-old fight
They've been trying to get stepping stones replaced with a bridge for 113 years - see http://www.burleybridge.com/ for more.
Tony Meadows' 10-year wait ends as Borough Market viaduct installed
Only 10 years? You should try waiting 113 years, mate.
IQ Winnersh footbridge up for award
Ramboll's tree-lined structure is an unusual design, to say the least.
Fort York bike bridge project in limbo
The original headline to this story read something like "Fort York bike bridge dead", to which somebody presumably responded "it's not dead, it's just resting". Having already called a halt to this iconic bridge scheme, Toronto Council were challenged by one local councillor to reconsider, but have decided to stand their ground. Council officials are still being asked to identify a cheaper alternative. The desire to move it ahead was partly motivated by the fact that the railway it spans will be closed for other work in 2012, and any delay will miss this opportunity, potentially increasing construction costs considerably. Apparently, they were relying on the rail closure to allow the curved deck and arch to be temporarily propped. The structural form was never well suited to building across a railway to begin with, and is unlikely to survive the rethink.
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