Voided Prestressed beams

[Canderson]

I'm looking for suggestions on how to support (internally, if possible) some utilities (phone, cable, electric) across a proposed 50' span constructed of prestressed voided slab beams. I think I can run the conduits inside the voids, but am looking for details in the end areas. Anybody have anything they can share (e-mail or FAX details?)

 

[Roadbridge]

Can you not bend some rebar into the shape of the voided beam and use them as chairs. Then place them at appropriate centres along the beam?

 

[TTK]

Is this a private, municipal or state owned bridge? Many owner/agencies will not allow utilities to run in the voids and I don't beleive PCI recommends it either.

The usual solution is to use a channel beam (preferably under a sidewalk), or use a spread beam solution to accomodate the utilities.

 

[Qshake]

They don't always cast the voids to the end of the beams anyway. SOme of those voided beams have a bulkhead at the ends for anchorage zone reinforcement.

either way, you don't want to run a utility in the void since you'll have to tear up the beam to remove it or repair it. Most conduit is made to run under a overhang or on the side of the deck when necessary. Otherwise many DOTs use the barrier curb for conduit runs.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[DRC1]

I agree with the last 2 posts I have never seen utilities run in the voids. Utiliies are either:

1.) Hung off the side on brackets (typ gas or water)
2.) Suspended inside a chanel beam (any utility - cables in ducts)
3. Inside conduit incorperated into a castinplace sidewalk poured on top of the precast. (typ telephone & cable)

 

[Roadbridge]

Several years back I was working on a bridge that made provision for the future use of service ducts through our reinforced cast insitu post tensioned deck. Don’t if they were ever used afterwards but their there.

 

[Zambo]

A 50' span is very short and the utilities are electric and telephone. It would be interesting to know the size of the electric cables, it seems to me that this may be a LV supply that really could be run inside conduits in the bridge deck.

Zambo

 

[Qshake]

Zambo,

You ambition is admirable. However, for a prestressed voided deck beam the actual primary load carry member is the "bridge deck" as you mention.

No owner in his right mind would allow a conduit to pass inside a primary concrete member and no utility worth their weight will want a conduit in a place where access is not easily attained.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Zambo]

Qshake, thanks for your advice. I re-read the original post and I misunderstood the precast units he is using. I thought he was describing prestressed voided slabs which would not be the primary load carrying members of a 50 foot bridge carrying traffic. However I now read that they are also beams - so I have to confess I have never seen these precast units. For cables of many kinds it is common to put them inside ducts where access is not easily obtained. If the cable needs to be changed it is just replaced between draw pits, for this 50 foot is not an excessive length. Regardless of this your point is taken and I agree that the cables should not be placed inside the primary load carrying beams.

Zambo

 

[71corvette]

What type of rail system are you using? Perhaps placing a conduit through the concrete barrier or curb would be an acceptable solution...