Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations Danlap on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Integral bridge deck pour sequence explanation

Status
Not open for further replies.

Redacted

Structural
Mar 12, 2016
160
Hi there,

I have been involved with the design of a integral bridge structure that comprises a main steel box girder with a composite deck supporting the carriageway. I am trying to better understand the proposed deck pour sequence.

The pour sequence splits the integral diaphragm pours from the deck pour. Is there a reason this is done separately instead of pouring the integral diaphragm and pier deck at the same time e.g. P1 deck and diaphragm together? See attached image.

I guess another general question would be, why are positive moments commonly poured separately to the negative moments? Is this strictly to reduce shrinkage cracks or are there other reasons? If so what would they be?

 
 https://files.engineering.com/getfile.aspx?folder=2e075b6f-fb1a-4af6-8937-0232af196125&file=bridge_pour_sequence.png
Replies continue below

Recommended for you

There was probably a concern that the change in cross section from the diaphragm to deck would lead to transvers cracks in the deck, if it were done monolithically.

Positive moment areas are typically poured first. If the negative area is placed first there's a chance it could crack when the positive area deflects. A continuous bridge deck can be placed in one continuous operation if the volume isn't too large (< 360 CY) and set retarders are used.
 
Thanks bridgebuster, what you wrote is very helpful. Do know of any sources that would go a bit further into the theory of the cause of transverse cracking in the deck for monolithic pours with the integral diaphragm?

 
RStars- I’ll look through my files; might have something. The diaphragm and the slab will shrink (drying shrinkage) at different rates. In a way, the diaphragm would act as a restraint for the slab.
 
Thanks bridgebuster, very helpful.
 
The attached photos show another good reason to properly sequence bridge deck construction AND demolition. The photos show how the bridge beams lifted up off their abutment bearing seats because the deck was removed in an incorrect sequence. The continuous 3 span bridge had hinged beam splices just inside the middle span. The first span lifted as the middle span (over the highway) dropped due to the weight of an excavator using a slab crab to remove deck sections.


PICT0224_z88r9y.jpg


PICT0230_adcwzj.jpg
 
Looks like a fairly large skew, which compounds the problem of, placing or removing a deck. Where was this PEinc?
 
It is just outside Philadelphia. The bridge had those now-banned pin hanger connections. As the excavator removed deck sections and moved from span 1 to span 2, it passed the hinge point and the deckless beams for the first span pivoted about the pier. The pinned ends of the first and second span beams dropped as the abutment end of the deckless beams rose up off the rocker bearings. That's when they called me.

 
Status
Not open for further replies.

Part and Inventory Search

Sponsor