Saturday, February 22, 2014

TENSEGRITY BRIDGE?

Take a look at the site:



Kurilpa Bridge
from Wikipedia, the free encyclopedia

Official name              Kurilpa Bridge
Carries                        Pedestrians and cyclists
Crosses                       Brisbane River
Locale                         Brisbane, Queensland, Australia
Engineering design Ove Arup & Partners
Design                        Tensegrity Cable Stay

Note that the bridge is described as a ‘tensegrity/cable-stay’ bridge.



The listing continues:
The Kurilpa Bridge (originally known as the Tank Street Bridge) is a (A$)$63 million pedestrian and bicycle bridge over the Brisbane River in Brisbane, Queensland, Australia.[1][2] The bridge connects Kurilpa Point in South Brisbane to Tank Street in the Brisbane central business district. In 2011, the bridge was judged World Transport Building of the Year at the World Architecture Festival.[3]
Baulderstone Queensland Pty Ltd constructed the bridge[4] and the company’s design team included Cox Rayner Architects and Arup Engineers.
A sod turning ceremony was held at Kurilpa Park, South Brisbane on 12 December 2007. The bridge was opened on 4 October 2009 by Queensland Premier Anna Bligh.



It is interesting to see the bridge described as linking Kurilpa Point to ‘Tank Street in the Brisbane central business district.’ A quick look at any map of the city of Brisbane will tell anyone that it would be more accurate to describe the location of Tank Street as being on the western edge of the CBD. It is not in a central location at the heart of the city as the text seems to want to suggest.



Then there is more in the listing on the structure:

Structure[edit]
Kurilpa Bridge is the world’s largest hybrid tensegrity bridge.[5] Only the horizontal spars conform to tensegrity principles. The Kurilpa Bridge is a multiple-mast, cable-stay structure based on principles of tensegrity producing a synergy between balanced tension and compression components to create a light structure which is incredibly strong.[5]
The bridge is 470m long with a main span of 128m and features two large viewing and relaxation platforms, two rest areas, and a continuous all-weather canopy for the entire length of the bridge.[6][7] A canopy is supported by a secondary tensegrity structure.[5] It is estimated that 550 tons of structural steel including 6.8 km of helical strand cable are incorporated into the bridge.
The bridge structure comprises 18 structural steel bridge decks, 20 structural steel masts and 16 horizontal spars or in layman's terms horizontal masts. 72 precast concrete deck slabs sit on the main bridge deck and are secured to the steel structure and together by in-situ concrete stitch pours. The complex cabling system comprises 80 main galvanised helical strand cables and 252 tensegrity cables that are made from superduplex stainless steel. The piecing together of these elements was the highest risk on the project, where any error in the dimension of one of the elements would have halted the critical path of the project. It is a huge testament to all in involved in the design and in particular the construction of the superstructure that it was achieved to within 13mm of its planned vertical position in its final state at the centre of the bridge.
The bridge is lit with a sophisticated LED lighting system which can be programmed to produce an array of different lighting effects. Depending on lighting configurations, 75%-100% of the power required is provided by solar energy.[5] All electrical work was done by Stowe Australia.



The link to Cox Rayner Architects in this Wikipedia item is in red. When clicked, it opens up a new page with a puzzling message:


Cox Rayner Architects
from Wikipedia, the free encyclopedia
This page has been deleted. The deletion and move log for the page are provided below for reference.
02:31, 19 October 2011 Fastily (talk | contribs) deleted page Cox Rayner Architects (G11: Unambiguous advertising or promotion)

The ‘advertising’ link explains:

Wikipedia:Advertising
From Wikipedia, the free encyclopedia
  (Redirected from Wikipedia:ADS)
Wikipedia:Advertising may refer to:
Wikipedia:Spam, guideline on how to avoid different types of spam in Wikipedia articles
Wikipedia:Funding Wikipedia through advertisements, essay on whether Wikipedia should carry advertising
Wikipedia:Publicising discussions, guide on how to advertise discussions inside Wikipedia
Template:Wikipedia ads, banner-style advertisements for internal Wikipedia projects and practices
Wikipedia:FAQ/Readers#Why do I see commercial ads at Wikipedia?, explanation that malware on the reader's computer or a fork hosted by someone else may display ads



When clicked, the Arup link opens up:
ARUP


In the listing of work carried out in Australia is the Kurilpa Bridge, Brisbane.
When this is clicked, one is returned to the first Kurilpa Bridge entry that describes the design as ‘tensegrity cable- stay.’



On reviewing more of this entry, one discovers the statement:

Kurilpa Bridge is the world’s largest hybrid tensegrity bridge.[5] Only the horizontal spars conform to tensegrity principles.





What? Only in the spars are supported by tensegrity principles? Why boast about this structure as being ‘the world’s largest hybrid tensegrity bridge’? Is it not a hybrid cable-stay/tensegrity bridge? Is this the world’s largest con? Does ‘cable-stay’ look just too staid and uninteresting in any promotion? It appears as though the Cox Rayner Architects link has been removed because it broke the Wikipedia rules. One has to wonder if things are being pushed just too hard here, with the ‘tensegrity’ word being highlighted as the core structural principle when it apparently is not.



The ON BRIDGES blog was published on 06/05/2011: see -http://voussoirs.blogspot.com.au/2011/05/on-bridges.html

This blog opens up with a quote taken directly from Wikipedia. It is interesting to compare the words from this date with those in the current listing. They read:

On 4 October 2009, the Kurilpa Bridge opened across the Brisbane River in Queensland, Australia. The new greenbridge is a multiple-mast, cable-stay structure based on the principles of tensegrity. It is also the largest tensegrity structure in existence.



The bridge is still described as ‘is ‘a multiple-mast, cable-stay structure based on principles of tensegrity,’ but it is no longer identified as a ‘greenbridge’; and it is no longer described as ‘the largest tensegrity structure in existence.’ Now it is ‘the world’s largest hybrid tensegrity bridge.’



One wonders why it was ever described as ‘the largest tensegrity structure in existence.’ Surely the designers must have known that there may have been a problem with this description: if not the ‘largest,’ then certainly ‘tensegrity’ should have raised questions? The ON BRIDGES blog suggested that there might be problems in calling the bridge a ‘tensegrity’ bridge as it seemed clear to the ordinary observer that the primary structural elements were the main masts on the concrete pylons that propped up the cables supporting the bridge. The tensegrity elements appeared somewhat incidental to the whole assembly, lacking the purity and clarity that such structures usually display. Was this promotion an exaggerated campaign by those involved, seeking only publicity through the drama of advertising? One wonders what was in the Cox Rayner Architects listing for it to have to be removed from Wikipedia.



What exactly is going on here? There seems to be a reappraisal of the first boastful statement that apparently claimed to be the world’s biggest, best and first: ‘the largest tensegrity structure in existence.’ This bold statement seems to have had problems with the truth, as now the design is ‘the world’s largest hybrid tensegrity bridge,’ whatever this might mean. Can tensegrity principles be ‘hybrid’ and remain tensegrity? This appears uncertain. The more specific correction/admission is that ‘only the horizontal spars conform to tensegrity principles,’ that only a portion of the bridge’s structure uses tensegrity. One assumes that within the main bridge structure that is ‘a multiple mast, cable stay’ bridge, there are additional pieces that are held up using tensegrity principles - the spars. What do these do? What role does tensegrity really have in the whole interplay of stresses?





The text tells that of the pieces in this ‘470m long’ bridge, ‘the  bridge structure comprises 18 structural steel bridge decks, 20 structural steel masts and 16 horizontal spars or in layman's terms horizontal masts. 72 precast concrete deck slabs sit on the main bridge deck and are secured to the steel structure and together by in-situ concrete stitch pours.’ So, out of a total of decks and masts and spars, we have 18 decks; 20 masts; and 16 spars, with only the 16 spars conforming to tensegrity principles. Strangely, somewhat apologetically, the spars are identified for the ‘layman’ as being ‘horizontal masts.’ Why? Are the decks also ‘horizontal mast’ platforms? Is this an attempt to create a greater integrity in the system of words, if not in the structure?





What does this mean? A close look at the structure shows the bridge supported as any mast/cable-stay bridge might be, with some added complexities that expand the same idea of props and cables. What is the tensegrity doing other than being there almost as an added attraction? Why boast of tensegrity when it appears incidental to the whole ‘hybrid’ idea - 18/20 and 16 tensegrity, perhaps extra secondary elements - apparently? Surely tensegrity is better than this: more integral; more rigourous; more explicit; more refined; more committed?



The changes in the Wikipedia listing are interesting, but the bridge still comes up as the main reference in a Google ‘tensegrity bridge’ search. Maybe it should be identified as a ‘cable-stay bridge’ with ‘tensegrity adaptations’ - included just for interest, appeal and difference? Interestingly, and somewhat alarmingly, if one Googles ‘cable-stay bridge’ as the Kurilpa Bridge may be more correctly portrayed, the Kurilpa Bridge does not appear at all - not at all! Why? It is described as something of a mongrel - a hybrid: ‘a multiple-mast, cable-stay structure based on principles of tensegrity,’ but only ‘tensegrity’ grabs the headlines.


Classic cable-stay bridge without 'tensegrity'





Who has minipulated this? Has anyone? Has the early hype fixed matters in minds? The Google listing needs to be corrected to identify the bridge as what it seems to be: not ‘a multiple-mast, cable-stay structure based on principles of tensegrity,’ as this seems to be an awkward idea that mocks the idea of tensegrity; but as ‘a multiple-mast, cable-stay structure with additional elements incorporating the principles of tensegrity.’ This is what the bridge looks like. To leave the bridge with the identity of a ‘tensegrity bridge’ appears to be misleading.






The whole idea of tensegrity is to create a pure and efficient separation of tension and compression. It is ‘hybrid’ only in the sense of this specific interaction. There is an astonishing lightness, a supreme elegance in tensegirty structures. To pretend that these principles can be involved in a hybridisation involving a set of other concepts or principles without any loss or compromise of these principles, seems to suggest an interest in propaganda for publicity purposes alone rahter than an exercise in the pure structural principles and their potential as Mr. Fuller envisaged them. There is indeed a matter of principle involved here that lies beyond advertising hype.






NOTE: 26 JUNE 2015

It was on the trip from Glasgow to Macintosh’s Hill House at Helensburgh that we crossed the Erskine Bridge. This elegant structure built in the period 1967 – 1971 is a multi-span cable-stayed box girder bridge. The surprise is that such a significant structure can have such a minimal presence. Two central blades of cables are all that one sees as one drives along its platform. It stands in stark difference to Brisbane’s Kurilpa Bridge that is a smaller pedestrian structure cluttered with a busy and baffling array of struts and cables: see - https://en.wikipedia.org/wiki/Erskine_Bridge






NOTE: 14 September 2016

For more on architecturally designed bridges, see: Exploding the Myths of Modern Architecture by Malcolm Millais, published by Francis Lincoln Limited, London, 2009: Chapter 11 - BRIDGES BECOME SILLY.


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