Tunnel Top Slab Flexural Analysis
Tunnel Top Slab Flexural Analysis
(OP)
In the past I have found this forum extremely helpful as I have researched questions but this is the first time that I am posting my own question. The question pertains to an existing tunnel that will now be seeing additional load due to changes on a project(attached is sketch of the tunnel top slab and all the reinforcement). I have ran the analysis and the slab works for shear but the trouble I am having is with the flexure. The factored moment demand on the slab will be 69k-ft but analyzing the top slab as a 9' simply supported span and accounting only for the #8 bottom bars I only get a capacity of 53.5 k-ft (f'c=4,000psi and fy=60,000psi). My questions is whether or not the shear bars can be used to account for additional flexural reinforcement or if there is any other things I am not taking into account that would provide additional flexural support?
Thanks to everyone for helping.
Thanks to everyone for helping.






RE: Tunnel Top Slab Flexural Analysis
2. Consider some restraint from the walls. Slab will not behave entirely as a simple span.
3. Test the concrete compressive strength. Concrete may behave like 5000 psi or so.
4. Roughen the surface and add a 2" topping slab.
Shear bars, because they are not continuous, will not add to your moment capacity.
RE: Tunnel Top Slab Flexural Analysis
I had also thought about your option #4, but that was quickly shot down by the contractor.
RE: Tunnel Top Slab Flexural Analysis
The top bars (#4 @ 12) might be some help if you go to the trouble of calculating the section as a doubly reinforced section. Your 53.5 ft-kips/ft. is based on singly reinforced capacity neglecting the top bars.
The other thing you could do is analyze with some level of fixity from the walls. The walls look much thinner than the top slab so there probably won't be much negative moment at the ends. And you'd have to check whether the walls can even take the negative moment.
RE: Tunnel Top Slab Flexural Analysis
RE: Tunnel Top Slab Flexural Analysis
Thanks again for all your help.
RE: Tunnel Top Slab Flexural Analysis
RE: Tunnel Top Slab Flexural Analysis
RE: Tunnel Top Slab Flexural Analysis
RE: Tunnel Top Slab Flexural Analysis