Flared Wings At Endwall Abutment 3

[sponcyv]

Probably an easy one for you guys, but I have a cantilevered abutment wall for a stream crossing. I was wondering what affects the angles of the flared wings of the abutment. The bridge is on a tangent.

 

[bridgebuster]

If the abutment is at the waters edge, the wingwalls should be flared to improve the hydraulic entrance condition. If possible, the elevation at the end of the wingwall should be higher than design high water or, as a minimum, the ordinary high water.

Wingwalls on the upstream side should be aligned to direct the flow through the bridge opening. For ease of construction, downstream wingwalls can be made mirror images.

 

[sponcyv]

bridgebuster,

I am performing the structural design of the bridge. I assume the orientation of the wingwalls may be a question for the hydraulic engineer on the project? To give you a little more information about this project, the stream crossing is very close to a railroad crossing and thus the road cannot be re-graded to raise the bridge. The bridge is completely underwater at the 100 and 500 year flood events. One abutment is very close to the top of bank of the stream.

Thanks

 

[cvg]

I would advise you to sit down with the hydraulic engineer and hammer out the alignment of the bridge, abutment walls and wing walls as well as heights of all structural elements. Then wait until the hydraulic model is approved before moving on. Given that your bridge flows under pressure during 100-year flood, you will also need to design everything to account for scour and water pressure.

 

[MiketheEngineer]

The wing walls may help any over turning problems you might encounter.

 

[sponcyv]

My main question is the angle of the wing walls. Does anyone know or have any reference to setting this angle based on parameters such as direction of flow, etc.?

 

[msquared48]

cvg:

"Given that your bridge flows under pressure during 100-year flood".

Are you suggesting that he design a floating bridge for the 100 year storm? i.e. ... as in using REAL BIG drift pins?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[sponcyv]

Since you brought up the 100 year storm question....the bridge is to be designed for the 500 year storm. The dead weight of the structure is still large enough to resist the forces from buoyancy and stream flow, so really it isn't considered a floating bridge right?

Has anyone designed a bridge that is located under the design flood stages?

 

[msquared48]

I wasn't serious as this is not a timber bridge. I was justgiving cvg a hard time.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[cvg]

yes, bridges are occasionally designed to be under water for 500-year and sometimes for 100-year. But I usually recommend that the bridge be designed to pass the 100-year with some freeboard to the low chord, 3 - 4 feet if possible. If you are crossing a levee, than 4 feet is required to gain FEMA accreditation.

It doesn't really matter whether it's concrete or timber, the structure should be stable regardless. Nothing preventing you from designing a floating bridge that I can see. Might be a good option.

 

[sponcyv]

cvg,

Do you know where I could find design guides/references/examples for designing a bridge that is located below the design flood events? We are locked in as the grade can not be altered. The state DOT must approve the bridge to be built at this elevation of course.

 

[ACtrafficengr]

Can you increase the span to get a larger waterway opening?

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

 

[Bobber1]

Just from another reason for the wingwalls: They have to retain the soils beyond the edges of the abutment, so the shortest wingwall will be at right angles to the slope they are retaining.

But as noted, hydraulics may predominate and angling the walls would be necessary.

 

[sponcyv]

Yes, I should specify. The wingwalls are really part of the retaining wall abutment that will turn back at angles to serve retaining and hydraulic purposes. If the only concern was retaining earth, typical wingwalls at 90 degree angles could be used.

 

[IDS]

Ignoring hydraulic considerations, the shortest wing wing results if the wall bisects the angle beween the over-road and the under-road, with the fill sloped up/down perpendicular from each road to the face of the wall.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Hemifun]

If there are no other factors to consider, I will usually flare the wings 30 degrees if there is no skew and the stream approaches the bridge at right angles. This gives good hydraulics and seems to work pretty well.

 

[sponcyv]

Hemifun,

Thank you so much for directly answering my main question! I was going at 30 degrees, so nice to have some reinforcement.