Bridge Deck Negative Moment Region Pour

[mattcourage]

Current project is the construction of a five span steel plate girder bridge. It consists of 8 beams on 12' centers, and a staged joint on the 3rd girder...no closure pour. During the deck placement process, after all the positive regions were poured, we consistently had issues tying back into the bulkhead from the previous pour in the positive region. Either we would end up "ramping" down into the bulk head on either side or "ramping" up. It never seemed to tie in smoothly. I was curious if anyone has experienced this and can possibly offer an explanation or advice.

Thanks a lot, any help would be appreciated.

Robert

 

[bridgebuster]

could you clarify a bit: The deck was poured in two stages, I got that. Is the problem between the longitudinal bulkhead or the transverse bulkheads?

 

[mattcourage]

the problem is between the transverse bulkheads...and we haven't poured the deck for the second stage, or set the girders. It seems that everything works during the dry run, but when the it is loaded for some reason we seem to come in to the bulkhead at the end of the pour low, and have to adjust the legs on the machine...most of the time it hasn't been that bad, but there were a few that were concerning.

 

[EQguys]

mattcourage: How were the positive regions poured. Was it poured in sequence 1,2,3,4 and 5 ? Or was it poured 1,4,2,5 and 3 ?

 

[bridgebuster]

Off the top of my head it sounds like a possible camber issue. Is there a pour sequence in the plans?

 

[mattcourage]

There was a pour sequence in the contract plans....all the positives were poured consecutively going stations ahead, followed by the negatives in the same direction.


R. Matthews

 

[MDBridges]

Were the girders analyzed for the pour sequence? It appears the issue may be that the pour sequence was a "typical" or "standard" pour sequence that was not evaluated for how the girders would respond. In other words, the effect of all the positive region pours being placed at the same relative time did not correspond to how the girders were analyzed during the design phase.

 

[OSUCivlEng]

It could also be bad haunch calculations. I had a former boss mess those up one time. The finished product had a very rough ride.

 

[bridgebuster]

Continuous bridge deflections can get tricky and even more so with a longitudinal joint. It depends on how the deflections were calculated vis a vis the placements. Let's say you did 9 placements - 5 Positive moments & 4 negative moments - on 9 separate occasions. Pick any point, the beam deflection is going to vary after each placement - the up and down at the bulkheads. The defections given in the plans may not be reflecting the behavior of the bridge. However, you're on the ball and were able to adjust things on the fly. Let's hope the deck closes along the longitudinal joint.

We had a problem a few years ago on a staged deck placement. The people who designed it didn't take into account staged construction and the deck closure was off by 4".