cable trench passing over spillway 1

[aakalim152]

We have to design a reinforced concrete cable trench for our powerhouse and substation. The area where the cable trench is passing has a spillway (which is covered with a slab). I have been asked to design the section of the trench which will pass over the spillway.

Now what would be the best approach to design such a section? Any one involved in design of a similar structure. Your input would be really appreciated.

Regards,

 

[JAE]

You might provide a sketch/concept so we could better understand the issues involved.

 

[aakalim152]

Sorry for not making myself very clear in the opening post.

Here is the sketch of cable trench i am talking about. I hope this makes it clear.

I am confused as to how to design this section of the cable trench which passes over the spillway.

I am thinking of designing it as a bridge since trucks and other vehicles can pass over it. However this cannot be considered as a typical concrete deck bridge since there is no deck, only removable trench covers, and live loads can pass over it in any direction, not just along the deck.

 

[JedClampett]

I have some more questions. When you say it will be used as a bridge, do you mean that vehicles will use it to get across the spillway? Or will vehicles be driving across a covered portion? Plus, are you talking about frequent traffic or just occasional vehicles?
To me, that's a big difference. For the first case (trench acting as a bridge over the spillway), I'd design it as a bridge first. That means you need good buttresses at each end, some kind of transition detail and expansion joints to structurally isolate the trench over the spillway from the rest of it. If vehicles are just driving over a covered portion, then you can just design a slab to span over the trench.
Once you allow vehicles to drive over this spillway, using your trench, it's a whole different ball game. It makes it a much more difficult and involved design. And don't forget, you can't control what's going over it once you allow (make it big enough; pave up to it, etc.) for traffic.

 

[aakalim152]

Thanks for your comment.

The traffic will not be frequent, but some heavy machinery will have to be transported to the powerhouse (the main gate of powerhouse is not far away from this trench) and hence heavy vehicles may pass over it. We are talking about a open area between the switch yard and the powerhouse, with a concrete slab. So the traffic (which is already occasional) will only be passing over a covered portion and not primarily over the trench.