Cable pedestrian bridge

[fkd]

Dear Friends,

Yesterday a client asked me about the viability of the construction of a cable stayed bridge crossing a river spanning over 200m with a width of 1.5m and wooden walkway.

Since, here in Brazil, this kind of structure is very uncomum you can guess what a kind of trouble I'm facing, I do have little knowledg (mainly theorical) concerning to this kind of structures and I don't know any local professional able to deal with this. The first issue that arises in my conception is the lateral stability due to wind action plus the little weight of the hole structure, how to deal this?
The other that I think that must be analised with great care is the dynamic behavior, natural frequencies versus induced vibration frequencies due to wind action, people movement and so on.

Any help from you will be very much apreciated, even advices on how to tell an old client that I'm not able to solve his problem....

Thak you in advance

Fred


P.S. I've posted in the WTC thread a question about the tunned mass system in the structure, but seems that this is not the case of that buildings, could please clear this point because maybe I'm wrong since I've received this information when I was doing my MSc studies and I must tell my former teacher that he is wrong, his postdoctoral studies was taken in the MIT in US and that why I've trusted his information.

 

[Rich2001]

Fred,

Here are a couple of links for US companies that manufacture Pedestrian Cable-Stay Bridges

http://www.steadfastbridge.com/

http://www.continentalbridge.com/

On the Continental Bridge site they have their specification/engineering information. Essentially, AASHTO Pedistrian bridge specifications and a worked out example of the design equation.

If you are interested in a truss style

http://www.usbridge.com

along with the other two are good vendors.

 

[fkd]

Rich2001


Thank you very much for the info.


Fred

 

hi fred, what kind of software you are using to model this bridge?
just be careful with the bridge natural frequency, make sure it is higher than 4 Hz in the vertical direction and 1.5 higher in the horizontal direction to avoid having vibration problems. I advise you to talk to your client and tell him what he will face in terms of serviceability problems if the struture is too slender. I'm also from Brazil and I know how things work there, I don't know how the code is there in relation to load combinations...if you have trouble finding information, look at the Canadian Highway Bridge Design Code (S6-00), it has some good information on the design of pedestrian bridges. All I can say is good luck and if I can help more, just let me know. It is indeed a great opportunity for you to design an elegant structure.

 

[ishvaaag]

I can only point a local case. In Zaragoza (then about 600000 ppl) when I was a child there was a suspended bridge of wood floor that was used for years to cross over the Ebro river...by daring people. Its span should be about 120 m and was badly laterally stabilized (probably NO stabilization at all). Even in moderate wind (I think it was closed in strong) one felt unsafe there. It was closed in the mid sixties or so.

I assume that with stabilization in section in 4 quadrants and maybe prestress plus damping the vibration effects maybe more controlled, yet the basic problem will stay there anyway.

Peter Broughton and Paul Ndumbaro seem be experts in cable structures, try to get their informed opinion.