Bonded Concrete Topping for Suspended Slab
Bonded Concrete Topping for Suspended Slab
(OP)
Hi guys
I have a rc beam design which was a 450wide x 800deep (18"x30") beam spanning 6500 (22'). Now the design load is increased by a topping slab. Because the rc beams is overstressed with the increase in loads, I thought I would bond the topping essentially increasing the depth of the beam by 200mm (8"). I was looking at a product for a bonding agent which gives a bond strength of 2MPa which I have checked for longitudinal shear and is okay.
What are the critical aspects of design when it comes to bonded topping for structural suspended slab applications?
I have a rc beam design which was a 450wide x 800deep (18"x30") beam spanning 6500 (22'). Now the design load is increased by a topping slab. Because the rc beams is overstressed with the increase in loads, I thought I would bond the topping essentially increasing the depth of the beam by 200mm (8"). I was looking at a product for a bonding agent which gives a bond strength of 2MPa which I have checked for longitudinal shear and is okay.
What are the critical aspects of design when it comes to bonded topping for structural suspended slab applications?






RE: Bonded Concrete Topping for Suspended Slab
Dik
RE: Bonded Concrete Topping for Suspended Slab
RE: Bonded Concrete Topping for Suspended Slab
BA
RE: Bonded Concrete Topping for Suspended Slab
RE: Bonded Concrete Topping for Suspended Slab
KeerthiR
RE: Bonded Concrete Topping for Suspended Slab
Dik
Shear was not an issue, the existing design had enough additional capacity.
BA
The slab needs to be raised for a mechanics workshop.
RE: Bonded Concrete Topping for Suspended Slab
Here are a few other things that you have probably already thought of but I will remind you anyway,
1. The existing system must be able to take the wet weight of concrete + construction loads if not possible consider propping. Propping can be problematic due to the existing structure. If the propping solution is selected I wouldn't leave it to the propping guys, as they will not understand the problem. I would also make sure you spec the max construction loads, as the concreter is liable to think he can load your structure to the max while he works.
2. Check the shear strength of the existing slab for construction loads.
3. If the beams are continuous, you will have to consider your approach to the negative bending areas, as these can become interesting.
4. If you are going to use a bonding system ensure you consider the shrinkage behaviour of the slab. Noting that almost all existing crack will reflect into your new slab.
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: Bonded Concrete Topping for Suspended Slab
2.0 MPa shear is approaching the upper end of the recommended design values and requires nominal ligs across the interface as well as roughening and treatment of the surface.
Note that British concrete strength is based on test cubes, multiply by 1.2 to convert to f'c.
I can post the relevant section if required.