Max. span that can be covered with prestressed beam? 1

[JoeH78]

Dear Community Members,

Supposed that I have 180cm of triangular I-shaped prestressed beam should be viable to pass a span of 30mt with that, of course with prestressed strands?

 

[BAretired]

Your question is not clear. Try again.

BA

 

[WARose]

I'm not sure i follow your question either.....but in general (for precast beams) you normally think about max spans at around 120 to 140 feet. Although (in recent years) I've seen some precast guys go up to 175 feet.

But in any case, before you think about designing something like that.....you need to talk to a lot of people because the logistics of shipping and handling such things can be a nightmare. I'd start with your precast fabricator....if one isn't on board yet, I'd stick with something regular.

 

[KootK]

That's only a span to depth ratio of seventeen which should be well within the range of a prestressed element.

 

[BAretired]

What is a triangular I-shape?

BA

 

[KootK]

I'm guessing that it's what would normally be some permutation of what would be coined "bulb tee" in my neck of the woods.

 

[BAretired]

Yeah KootK, looks like a good guess. A little beyond my experience. I'm surprised they can span so far without a wider top flange.

BA

 

[r13]

Effect of prestress and camber minimize the compressive stress on top flange. The wider bottom flange is to accommodate the prestress tendons.

 

[rapt]

BAretired,

The top flange becomes much wider once the composite deck is attached.

 

[BAretired]

rapt,

Yes indeed, rapt. I would think though, that just handling a shape with that profile over such long spans would be a bit dicey; but handling stresses are likely considered during design.

BA

 

[Lomarandil]

Well, it is dicey at those lengths. Specific analysis (see articles by Mast as a starting point) is required for transporting and picking a long girder to prevent cracking the top flange before the bridge is even built. But it can be done. (Some precasters will consider that during their design, others put the risk on the buyer. Good to check)

Like WARrose indicates, the maximum span is mostly a function of regional logistics and the shipping route. Where I used to practice in the states, 140' spans were common, and we were starting to see a few jobs pushing up to 180-200'.

----
just call me Lo.

 

[HTURKAK]

The topic of this thread ( Max. span that can be covered with prestressed beam? ). In past, ( several years ago ) our company designed and constructed full continuity bridge which the span was greater than the length of prestressed beams.

The snap is from FIB Bulletin 29 Precast concrete bridges. Which shows the concept.

 

[Klitor]

This just poped-up on Bentley feed:

https://precast.org/2020/07/reconstructing-illinois-mile-long-bridge/