Increasing existing slab thickness

[am]

Hi

I am required to upgrade a existing foundation slab by casting a new slab over it. Generally short starter bars are installed on the existing concrete in drilled holes (and using epoxy grout) to achieve good bonding.

My question is, how to calculate the tensile force in each starter bar due to flexure. Will it be ok to use analogy of shear connector design for composite beam design? Also, if I use additional epoxy binder between old and new concrete, how much reduction of starter bars and embedment length can I achieve?

Any help will be much appreciated.

Regards

AM

 

[dik]

How thick is the bonded topping? and is it needed for strength purposes?

Sika makes some excellent toppings that are secure and likely would not require any mechanical anchorage; they are somewhat costly.

Alternately, there are some good acrylic or latex bonding agents to secure the topping.

If a mechanical anchorage is required, then I would use tau=A'ybar/Ib to determine the shear at the interface and connect for this value assuming elastic straight line flexural stress. I'd use larger dia bars (less likely to flex if loaded) and splitting hairs, might angle them so that loading will force the topping towards the existing slab.

I'd also put in some WWM to distribute the forces from the pins to the topping.