Supporting existing precast plank
Supporting existing precast plank
(OP)
I have an existing precast plank roof, and we're adding a taller addition, so it will cause snow drift on the existing plank. If I install a new beam line to break up the existing span into two smaller spans, do I need to saw-cut the precast over the beam so I don't produce any negative moment? (essentially creating two simple spans) Has anyone done this before? Do you have any direction? Do I need to cut all the way through the plank, or can I just saw cut the top of it down to the core?
Thanks!
Thanks!






RE: Supporting existing precast plank
RE: Supporting existing precast plank
With that situation - seems like there'd be a cause for concern as to the shear capacity just off the new beam edge if the crack didn't "happen" right over the beam.
Thoughts?
RE: Supporting existing precast plank
RE: Supporting existing precast plank
I don't know if this complicates matters, but there's about a 4' cantilever on the far end. I've attached a sketch of my situation.
Thanks for your input, everyone!
Another question I have is what is the best way to fasten the top flange to the precast for lateral support for the beam. Sleeve anchors through the top flange of the beam into the bottom of the plank?
RE: Supporting existing precast plank
Mike McCann
MMC Engineering
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RE: Supporting existing precast plank
For my case, let's assume a worst case. Is it worst case to assume only steel in the bottom? If so, is it necessary to saw cut the plank over the new beam?
Are there other considerations I'm not considering?
Thanks!
RE: Supporting existing precast plank
Any other thoughts?
RE: Supporting existing precast plank
It would be prudent to sawcut directly over the beam to ensure that the slabs are adequately supported each side of the sawcut. The sawcut does not need to go through the entire depth of plank. In fact it should not because you want to keep the bottom strands intact. A sawcut depth equal to the thickness of top flange is adequate.
So far as the 4' cantilever is concerned, it was there before and you are not making it any worse, so leave it alone. Hopefully, the original engineer reinforced it adequately on top.
BA
RE: Supporting existing precast plank
As to bracing the beam, I would do it outside the flange. Maybe bolt sections of angle or plate to the planks. That way gives better access for drilling. Some sort of drilled in anchors, maybe into the cores to miss the strands.
RE: Supporting existing precast plank
RE: Supporting existing precast plank