does this structure called as "tunnel" or bridge ? 1

[yjung]

Hi all,

I have a tunnel-like structure that 300 ft long and 56 ft wide. This will be built under the existing highway. It will have two lane capacity for HOV with 16 ft vertical clearance.

My question is that is this tunnel or not?
what is the design code if this is tunnel?
I am having a hard time to figure out that this structure will require all the tunnel requirement or not?

Your kind attention to this matter will most appreciated.

YC

 

[wiktor]

The major difference in between tunnel and bridge is loading - structure predominantly loaded with self-weight and live load will be called bridge. The tunnel will have most if not the entire load from overburden.

The design criteria are almost the same - in case of tunnel there will be no live load, or it will be very small.
Please note, that the presence of more than 3'of overburden removes impact loading and above 2' the live load is distributed.

The design code should be AASHTO. It's difficult to determine without any details which sections would be applicable. The depth of the overburden and the method of excavation and backfilling (if any) would be crucial.

In general, there is no difference in between shallow tunnel and culvert in the structural design. The major difference is in the ventilation, fire safety and lightening. Forced ventilation is not usually required for the tunnels less than 1000' long.

 

[yjung]

Thanks wiktor,

Appreicate !!
I was looking for anything about tunnel for two days through internet. You were the only one telling me a very useful information.

Could you please tell me more about:

the requirement of the ventilation, fire and lightening.
Where i can find there requirements and how can i know if its box culvert requires any of them or not.

Any code, specification etc.

your attention to this matter will highly appreciated.

 

[wiktor]

Yjung:

For the ventilation requirements check "Standard Handbook for Civil Engineers" - Ventilation Requirements for Highway Tunnels. Up to 1000' length it there should be no problem and natural ventilation will suffice.

Lightening should be designed according to a local codes, with so called transition zones at both ends, to allow for eye's accommodation. Get an electrical engineer specializing in highway lightening to help you with this issue.

The fire safety could be tackled by installation of stand pipes or dry sprinklers along the tunnel - but check with the client and local fire department, they will be able to advice you on the applicable local codes and proffered system.
I would strongly advice this installation. Just try to imagine the accident in the middle of the tunnel, involving several vehicles, some catching fire - and latter the questions what should be designed and installed in the tunnel.

 

[wiktor]

By the way - try to get this publication :
"Tunnel Ventilation, Lighting, and Operation"
by National Research Council Transportation Research Board

 

[yjung]

hi there,

thanks again,

I was getting closer to my answer. Thank you so much,

I have noticed that "ASHRAE Handbook" and "NFPA" also talk about ventilation. I will borrow the book and take look at that(Tunnel Ventilation, Lighting, and Operation.)

Should i follow ASHTAE or NFPA too?

which one is governing code?

 

[wiktor]

Yjung:
As I sated before, for the short tunnels < 1000 feet natural ventilation could be sufficient. The tunnel should be checked for concentration of CO2 in the air. You have to check w/ your local Environmental Agency and DOT, what is allowed by them, and which code to follow.