L shape Beam for bleacher

[JStructsteel]

For a bleacher riser, the L shape concrete beam will be 5'-6" wide, and the slab 4" thick. For the leg, its 1'-5" deep, 6" wide. To form, would you want the stem upward (slab in tension) or the leg downward (slab in compression). To me I want the stem upward, so I can spread the tension load over the slab at the bottom.

Any thoughts? Suggestions?

 

[Agent666]

Yeah I believe having the stem going upwards seems to be the standard configuration.

From my view this seems to be the best idea, as looking from the other perspective it would probably be a little hard to get all the tension reinforcement into the thin stem. If slab is in tension then at least you've got a lot more room to place the tension reinforcement within the section.

 

[JStructsteel]

Thanks Agent666, thats how I am proceeding.

 

[KootK]

X3 for leg up. That's always how you see it in the literature. What's more, I'm not sure that it could be formed otherwise while still retaining the exposed surfaces as sexy, formed surfaces unless they're to be cast in a vertical formwork assembly.

 

[KootK]

From PCI manual and indicating that more exotic things are certainly possible from a forming perspective.

 

[KootK]

For industrial scale production, I've heard of fabricators using setups like this. I'm guessing that your thing is a bit more modest.

 

[JLNJ]

My limited experience with stadium risers tells me stem up and that tolerance and fit-up is a struggle. In our case, seat installation and piece alignment wasn't as smooth or easy as expected.

Determining camber in as-delivered precast is always an issue. My feeling is that the non-symmetric shape of stadia contributes to the problem.

 

[RFreund]

I've also seen this as leg up. Quick question though - do they do that in two pours?

EIT

http://www.HowToEngineer.com

 

[jayrod12]

All of them I've seen are stem up. However they've been casted stem down as the formwork is easier to construct that way and pouring is simpler. Fit up is always a bit of a finicky endeavour but as long as you've got a decent installer and a reasonable acceptance for joint tightness, it's manageable