Safe Load Tabled - Loading on Precast Concrete

[DavAD]

Hi, (long read ahead - thanks for taking time to read)

I have obtained the Safe Load Tables from a local supplier for Precast Concrete Planks (Sample Attached)
with notes (attached).

I am new to using precast elements, and would like to ask the following, if possible;

1. What is your opinion on precast concrete planks used as transfer slabs i.e. used to roof over an open basement with 5/6 apartment floors above.
Do the concrete planks (with 100mm topping and steel mesh), transfer the Line loads from above efficiently (compared to in-situ concrete)
Basically I am opting for other solutions given that the span at basement level is circa 6m, so reinforced in-situ concrete would result in higher expenses due to
it being high in thickness (400/500mm)

2. When considering line loads falling on a particular slab (1 element of 1.2m width) do you consider the slab acting as one due to topping. Or do you consider each plank individually carrying loads falling direct on it? I will be doing a topping of 100mm with A252 mesh to ensure spread of load on planks.

3. When having a line load of say 300kn/m(unfactored as per notes provided) along the span (parallel), given that the safe load tables are in Kg/m^2, how would you go about changing from kn/m to Kg/m^2 (divide by width of plank?)

and when having say 300kn/m (unfactored) along the span (parallel) and an additional say 250kn/m (unfactored) against span (Perpendicular) , would you find the
moment of the combined loads and revert to a line load Kn/m, and use that as your load?

4. Lastly, the tables gives Shear in Tonnes/panel. Is it safe to say that if we have a shear force of 150KN (from combined loads) - the applied shear is 14 Tonnes?

THANKYOU, your replies are very much appreciated.
(once again apologies for multiple questions)

 

[RPMG]

Just as a starting point, it is typically assumed that there is not load transfer through precast wall/floor panel joints, and the topping is designed to provide a rigid diaphragm.

 

[BAretired]

3. When having a line load of say 300kn/m(unfactored as per notes provided) along the span (parallel), given that the safe load tables are in Kg/m^2, how would you go about changing from kn/m to Kg/m^2 (divide by width of plank?)

and when having say 300kn/m (unfactored) along the span (parallel) and an additional say 250kn/m (unfactored) against span (Perpendicular) , would you find the
moment of the combined loads and revert to a line load Kn/m, and use that as your load?

At first glance, I would not carry such heavy loads on precast planks spanning 6m. 300 kN/m is equivalent to 20,600 plf. I would prefer a deep beam, perhaps one or two storeys high to carry such loads.

BA

 

[KootK]

What is your opinion on precast concrete planks used as transfer slabs i.e. used to roof over an open basement with 5/6 apartment floors above.

I assume that the construction above the precast is light frame, wood or cold formed construction. I design six to ten of these things, as the precast engineer, annually. I've done a tone of these up to four stories transferred, no six stories yet, and a couple of five stories where the precast deck was starting to get maxed out. In my opinion, the trick to making it go on a six story is to use 12" plank everywhere. The usual setup with this stuff is 12" plank over the drive isles and 8" plank between the drive isles where the spans are shorter. It's the 8" plank that's a killer as it struggles with heavy post and line loads and you wind up grouting it solid or, worse, wet casting it solid.

Do the concrete planks (with 100mm topping and steel mesh), transfer the Line loads from above efficiently (compared to in-situ concrete)

I don't know about "efficiently" but the system does seem to work. This is a system that's been successfully employed for at least 30 years in the Midwest US.

Basically I am opting for other solutions given that the span at basement level is circa 6m, so reinforced in-situ concrete would result in higher expenses due to
it being high in thickness (400/500mm)

The 6m span won't be a problem for precast in my opinion. Typical drive isle spans are often in the range of 25' to 28'. For those setups, the deck thickness is typically 15" (12" plank + 3" topping). Depth of the supporting precast beams can be a problem at 24" to 28" + topping but, usually, those can be kept out of the drive isles.

When considering line loads falling on a particular slab (1 element of 1.2m width) do you consider the slab acting as one due to topping.

The topping is usually considered to act compositely with the planks and that can be used to great advantage.

Or do you consider each plank individually carrying loads falling direct on it?

For longer span planks, high intensity loads are able to be shared among several plank units. This document will tell you how that's done in the the US: Link

When having a line load of say 300kn/m(unfactored as per notes provided) along the span (parallel), given that the safe load tables are in Kg/m^2, how would you go about changing from kn/m to Kg/m^2 (divide by width of plank?)

You could use the load distribution rules from the document that I linked to above to work out an approximate kN/m value. In my opinion, you'd be best served by getting some preliminary help from a precaster. Hollow core subjected to localized loads can do a fair bit more than uniform load tables would suggest in the hands a clever precast designer. You may be selling your project short by limiting yourself to those tables.

Do you have an exta zero in that 300 kN/m number? I typically see loads in the range of 1500 plf to 2800 plf for these kinds of buildings.

and when having say 300kn/m (unfactored) along the span (parallel) and an additional say 250kn/m (unfactored) against span (Perpendicular) , would you find the
moment of the combined loads and revert to a line load Kn/m, and use that as your load?

Yes. Usually these kinds of buildings will be dominated by either corridor wall loads or demising wall load though. Sometimes you'll get a bit of both at building knuckles etc.

4. Lastly, the tables gives Shear in Tonnes/panel. Is it safe to say that if we have a shear force of 150KN (from combined loads) - the applied shear is 14 Tonnes?

15.3 Tonnes but, yeah, you've got the idea.