Podium Construction - Transferring forces to Precast Slab

[RFreund]

I am curious to know what options other engineers have had success with as far as anchoring hold downs to precast concrete planks or any other floor system when designing podium type buildings. I was thinking I'd like to avoid drilling/epoxy in anchor bolts due to the fear of hitting/dealing with slab reinforcement. So are weld plates an option? Problem there is I don't think Simpson makes a weldable hold down, or maybe they do...

Thanks!

EIT

http://www.HowToEngineer.com

 

[TehMightyEngineer]

The precasters probably have that reinforcement maxed out so cutting any bars in a panel is definitely be avoided. A rebar scanner should be able to help you miss the bars. Can you contact the precaster? Hopefully they can provide insight into what they suggest.

How would you connect the weld plate to the precast concrete?

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[KootK]

I've found this to be kind of a nightmare really. Particularly when you consider that the tie downs may well land quite close to the edges of individual planks. Some thoughts:

1) Cast in plates can be installed. Precsters certainly don't love this, but they can do it. With the voids in the plank it's tough to get great capacities.

2) Thru-bolting. This leads to aesthetic and fire protection issues that need to be resolved.

3) Force the use of solid planks where high demand hold downs land. Then use drill and epoxy.

4) None of the details shown below are precast friendly but, in a perfect world, I'd want to do something similar.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[mike20793]

I've only ever done PT podium slabs and it's always a nightmare.

 

[RFreund]

Planks will likely be solid. I'd love to do P.i. / epoxy, but edge distances worry me and drilling into rebar. I like kootk's details but worry about placement accuracy of the rod. I'd like an oversized plate that they could weld the H.D.to (cutout the bottom plate) but I'm not sure that's possible and it involves field welding...hmmm...

EIT

http://www.HowToEngineer.com

 

[TehMightyEngineer]

There's a lot of good threaded anchor embedments (we use dayton superior at my work) and if you coordinate with your precaster I bet you can get the capacity you need.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[sandman21]

Are we talking about using an ATS system? Simpson has a weld cage for them. Link If not Simpson has couplers along with a number of manufacturers, Lenton etc.

 

[RFreund]

So it should be reasonable to expect that the cast in hold down anchor rods would be in the correct location?

EIT

http://www.HowToEngineer.com

 

[KootK]

You've got two tolerance issues:

1) location within the plank. Maybe 1/2".
2) Final location of the plank. Say 1".

So allow for 40 mm +/-? Maybe TME can better define the appropriate tolerances.

I like the weld plate idea if it can be made to work,

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

If you coordinate with the precaster so they can specifically ensure the inserts are properly located before the pour you should be able to have tolerances around a 1/4" for inserts. KootK's estimate sounds about right that the final location of the plank is probably around 1".

The weld plate may be a better way to go if the tolerances can't be accommodated otherwise. We've used embedded weld plates for precast utility buildings with the slab an walls shipped separate. Worked well.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com