by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : June 2013
Concrete in Australia Vol 39 No 2 29 Why Super Tees are a winner Super Tees beat every competitor on virtually every aspect I have seen, making them desirable and cost effective. e Super Tee is a very efficient structural solution, giving lowest material costs. Precasting off site gives flexible programming and lower labour costs. e Super Tee has a very quick and simple onsite construction method. It is very stable for handling. It provides an immediate safe working platform on erection, and has excellent durability performance and has low maintenance for concrete. It can be detailed for simple inspection and if necessary, bearing replacement. e Super Tee may also be potentially reuseable. Comment on calculations for Super Tees As an experienced designer, I find that many consultants underestimate how difficult it is to design a bridge, and Super Tee bridges for road or rail vehicles really do require substantial knowledge and experience. I will not catalogue the errors and misconceptions I have come across, but all that early training on "city bridges" which I was lucky enough to get is very hard to find for our newer generation of engineers (and even some older ones it seems). is is certainly a downside to the era of design and construct and a problem which will get worse as the experience of people like me dies out, unless the road authorities take some steps to redress it. To design Super Tees you really need to understand torsion and how it relates to shear and the truss analogy. Unfortunately, in that area the Australian Bridge Code AS5100.5 lets us down badly. e most recent Concrete structures standard AS3600 is a bit better but still has some serious drawbacks. Sadly in my experience on Australian Standards committees, the wheels turn slowly and often fail to get us where we want to go. I urge anyone designing Super Tees, or any other concrete box girder bridge, to use the Main Roads WA s Shear and Torsion Rules. ese were developed by Main Roads WA working with some external consultants including myself and have been verified. ey are dove-tailed into the rules in the present AS5100.5 and lead to a straightforward transparent design process, which is clearly based on the truss analogy. To be really efficient in design you should also make sure you have a reliable section analysis program which can apply axial tensile loads at the strength limit, such as RAPT. Aesthetics of Super Tees Bridges, even these lesser bridges, occupy large blocks of our visual environment. ere will always be diehards -- probably at least partly including me -- who could never see a precast beam type bridge in the same light as the simpler minimalist lines of a box girder. Any attempt to make it more aesthetically acceptable would in porcine terms be making a silk purse out of a sow s ear, or in the blunter modern version, putting lipstick on a pig -- at the end of the day it s still a pig. However, if we can put aside the prejudices of people like me who designed "city bridges", and notice that these Super Tees are not a great rack of NAASRA I-girders, with Bondek forms glinting between them, supported on hammerhead piers on a couple of columns where you can still see the spiral form, you can begin to see them in a different light. ey have simple clean lines and reasonably large widely spaced members, especially here in Western Australia where we tend to make quite wide ones. e specifying authorities should and do require some aesthetic guidelines to be followed. In truth, apart from obvious rules like not varying the form along the bridge, the superstructures virtually design themselves aesthetically. It is in the piers, where a pair of bearings must be provided along each beam line, where I believe we need to be most sensitive. Here in principle, I support what Main Roads WA does, but must respectfully disagree with their prescriptively required V-shaped pier. I have suggested that they (and other specifying authorities) provide for piers as a provisional sum, so they allow themselves input with the architect and builder, and control over costs. With a well thought out pier shape these bridges are at worst "unobtrusive" and at best really quite a neat, smart solution. Can Super Tees take over the world? ere are all sorts of reasons why things happen which are not necessarily the most apparently logical. In France, they love grand, bold, aesthetic structures and they certainly have some wonderful bridges. Perhaps there is such a culturally ingrained aesthetic sense that it filters down to this type of bridge and they will carry on much as we once thought we would with our "city bridges". In the UK, I have seen a generation of steel composite bridges spawned by a ridiculous over reaction to one failure attributed to poor grouting of post-tensioning cables and I suspect a very powerful steel lobby. Someone should tell them that Super Tee bridges use pretensioned strands -- would it make a difference -- who knows? I couldn t see the steel producers thinking that it should. But I am a great believer that eventually market forces and common sense will prevail -- and yes -- Super Tees will take over the world, unless someone thinks of an even better idea.