analysis of beams
analysis of beams
(OP)
After analyzing a concrete roof slab , some of what appear as simply supported beams ( single span beam supported at ends by main beams ) the negative moments were much higher than the mid span moment ) , That happen because all connections between beams were assumed to be rigid , shall I design the beams with the high negative moments or release torsion at the connections
Furthermore , in BS EN design code it is clearly stated that the negative moments can be redistributed up to 30% , is there any thing similar in the ACI
Furthermore , in BS EN design code it is clearly stated that the negative moments can be redistributed up to 30% , is there any thing similar in the ACI






RE: analysis of beams
for fem program like staad,etabs,risa, etc. I would usually assign an end moment release on the sub-beam and modify (decrease) the torsional stiffness of the main beam/girder (if the sub-beam is continuous).
RE: analysis of beams
BA
RE: analysis of beams
RE: analysis of beams
RE: analysis of beams
Frankly, I do not understand how you could have torsion from what you describe.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: analysis of beams
If there is sufficient reinforcing and embedment in the simple beams to develop the negative momentat the girder, and the girder is large enough to develop it (I guess this is where the torsion comes into play here) then, yes, design for the negative moment and torsional forces.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: analysis of beams
RE: analysis of beams
BA
RE: analysis of beams
The problem with assuming the end is fully fixed is that it is never fully fixed - the exterior spandrel beam will rotate to some extent and if the torsional restraint is compromised by cracking, you would approach a simple end anyway.
ACI actually deals with this in the design of perimeter beams for torsion as they allow a reduced torsional design if the interior beams/joists are designed as though they were simple ends. (see 11.6.2.2 in ACI 318-05 or 11.5.2.2 in ACI 318-11).
RE: analysis of beams
RE: analysis of beams
I don't do a lot of concrete, so I may not be the best one to ask, but this seems like a situation where most answers are reasonable as long as you're aware of the consequences and are okay with them. Your structure will likely end up acting to match whichever assumption you designed to.
RE: analysis of beams
You can tell the structure how you want it to behave by the reinforcing you provide. Just hope that it does not have a mind of its own...
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com