Roadway profile vert & horiz

[tumbleleaves]

I'm looking at a set of plans (standard cast-in-place 4-span 2-lane slab with a metal rail) where the bridge is on a horizontal curve and vertical curve (sag) and I have some questions:
1) What is the cost, it must be more difficult to form?
2) Are there special issues structural, drainage, aesthetics, constructability, or ...?

I am not the designer, eventually I will ask the designer (when it is polite and appropriate). From the posts I've read there are experts posting here and I look forward to and hope you all will share your thoughts even though the question is a bit "general".

 

[DWHA]

It is very typical to see one of these bridges in a vertical curve. The last 3 span slab bridge I designed was in a vertical curve.

I personally have never designed one in a horizontal curve, but I do not believe that the construction would be much more difficult.

Not was I only the design engineer the slab bridge, I was also the R.E. I was really surprised how easy they form those up. Unless the curves are very steep & sharp, I honestly think that there would be very little cost difference.

 

[crossframe]

As noted above, unless the horizontal and vertical curves are severe, there shouldn't be any structural, constructability, or cost issues. Cast-in-place concrete can be pretty forgiving for all types of geometries.

Drainage will depend on the overall length. Always a good idea to get the low point off the bridge.

In most cases, sag vertical curves usually do not look very appealing as they can give the impression that the bridge isn't strong enough. Exceptions are longer structures that "fit" the roadway. In these cases, anything but a sag will look odd. With four spans, the bridge may be long enough that a sag doesn't appear objectionable. The piers/bents will also serve to hide some of the sag within the spans.

 

[Qshake]

I agree with the other two posts, concrete slab bridges are very good candidates for curved geometries, within reason, of course. Moreover, slab bridges are low profile and can accommodate the necessary vertical clearance without raising profile very much say compared to a slab on girder bridge.

If the curves, vertical or horizontal, are minimal no trouble shoud be expected. For more pronounced vertical curvature ther also should not be any problem as it is my experience that contractors can easily shim or haunch the bottom of slab formwork to match the grade. sharper horizontal curves, however, may present more difficulty for the edges of the bridge but even this is not extremely problematic. Again, the edge forms are typically curved to the slab ordinate diagram and when the formwork is done correctly, results in a seemless concrete edge.

In a lot of states the emphasis has been off these types of bridges only due to labor involved in forming them and the long term deterioration due to de-icing salts or chemicals. It's my understanding that slab bridges remain popular in warmer climate areas and regions without strong unions (high labor rates).

Good Luck.



Regards,
Qshake

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

 

[Drumchaser]

No expert....


Horiz. - Dependent on how severe and whether or not the tranition(s) too and from full super are located.

Vertical - Adjustment in PGL may be required once the Girders/beams are set and profiled.

The headache I have encountered is when a skew is present; this creates a little more effort on grading and decking.

C.I.P. deck can mean different things.....do you mean the slab will be totally formed using lumber between the girders/beams, or do the plans provide a few optional forming systems to be utilized on your bridge?


Also....the type of screed you have will dictate some of your costs. For instance with a transverse screed it may be possible to just make one pour vs. a long. screed will requiring multiple pours.