Topping on existing slab
Topping on existing slab
(OP)
Hi good day everyone,
I have an existing suspended slab that needs to be topped up by concrete (attached sketch 1). It is a vehicular ramp with L.L = 15 kN/m2. I have considered 2 options.
(1) Consider the lightweight concrete topping as additional dead load and strengthen the existing slab below.
(2) Design a completely new slab (sketch 2).
But I still want explore and study one more option which is to design the concrete topping as structure & take some loadings. Is it possible?
OR
Roughen the existing slab surface so that existing slab & topping will become one slab with total depth 1150mm. Can it be?
How do guys normally do?
I will be thankful if I can have your advice or reference or example.
I have an existing suspended slab that needs to be topped up by concrete (attached sketch 1). It is a vehicular ramp with L.L = 15 kN/m2. I have considered 2 options.
(1) Consider the lightweight concrete topping as additional dead load and strengthen the existing slab below.
(2) Design a completely new slab (sketch 2).
But I still want explore and study one more option which is to design the concrete topping as structure & take some loadings. Is it possible?
OR
Roughen the existing slab surface so that existing slab & topping will become one slab with total depth 1150mm. Can it be?
How do guys normally do?
I will be thankful if I can have your advice or reference or example.






RE: Topping on existing slab
Thaidavid
RE: Topping on existing slab
IMHO, Thaidavid's concept is well thought out and has potential to be suitable solution, but adds dead load to the foundation, also.
That leaves Sketch 2, demolition and replacement with a similar size structural slab, as the leading candidate. Based on info available to us, that is what I recommend.
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RE: Topping on existing slab
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RE: Topping on existing slab
Foundation is adequate according to project structural consultant.
And I am working for PT specialist.
FYI, this project got a history and is a bit complicated. During construction we can not demolish the existing ramp one way PT slab which is connecting to the existing warehouse. We can't disturb the existing operation. So if I choose option 2, we have to construct half of the new proposed PT slab as conventional RC slab with empty PT duct inside in the meantime the vehicles will use the other half of the existing ramp with proper traffic control. After that demolish that half of the existing ramp. Vehicles will start using half of the proposed new ramp and then construct the remaining half of the new ramp. So option 2 is not as simple as option 1. Sorry if my explanation is not clear enough.
Also the topping is originally around 400mm thick. Option 1 is what we proposed and how we got this project. So my boss want to stick to option 1 (even though I prefer option 2). But later due to architect revised proposed ramp level become 800mm.
At this moment what I am trying to study is how can I utilize the capacity(L.L=15 kN/m2) of the existing ramp.
RE: Topping on existing slab
Could you use void form or rigid insulation locally to effectively turn the new slab into a waffle slab or pan joist system that would be much lighter than 800 mm of solid slab? You'd need to give careful consideration to corrosion protection.
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.
RE: Topping on existing slab
Thanks
So without the roughening and dowels drilled into the existing slab, would the topping slab be like slab on grade?
RE: Topping on existing slab
With the weight of an 800 mm topping in play, you're bound to get considerable composite behaviour even without the dowels. I'd just want the dowels to make me confident that reliable composite action were available.
Slab on grade? I suppose there would be some commonality. In this case, your slab on grade is extremely stiff, highly restrained, and supported by a substrate of variable stiffness in plan.
An 800 topping will require a lot of temperature and shrinkage reinforcing. With that installed, the strength and stiffness of the topping may dwarf that of the existing slab.
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.
RE: Topping on existing slab
RE: Topping on existing slab
Thanks it was great to have your replies.
I would like to bring up this thread again just to share my proposal to client which is under construction now. You may not recall :). Please see the attached step by step construction sequence.
For the topping on the existing slab, we have decided to use Politerm Blu 300kg/m3 with a top layer of 100mm conventional concrete with reinforcement mesh.
http://files.engineering.com/getfile.aspx?folder=8...