HEC-2 Bridge Modeling
HEC-2 Bridge Modeling
(OP)
I have a question on the modeling of parallel bridges in HEC-2. This is a standard boulevard set of two lane bridges. Each 200-foot, 3-span bridge is 35 feet across, seperated by 30 feet. The low chords are above the 100-year by 2 feet. However the floodplain is about 1500 feet wide.
What is the appropiate method of modeling?
The options I've come up with involve:
1) modeling the bridges as one 70 foot bridge using normal bridge, but this doesn't give a true representation of the
ineffective flow area at the true faces.
2) modeling the bridges as two decks with normal bridge, but does upset the program with that little of expansion
space
3) modeling with special bridge as one long bridge, but
the wsel doesn't hit the low chord
Any suggestions would be helpful.
What is the appropiate method of modeling?
The options I've come up with involve:
1) modeling the bridges as one 70 foot bridge using normal bridge, but this doesn't give a true representation of the
ineffective flow area at the true faces.
2) modeling the bridges as two decks with normal bridge, but does upset the program with that little of expansion
space
3) modeling with special bridge as one long bridge, but
the wsel doesn't hit the low chord
Any suggestions would be helpful.





RE: HEC-2 Bridge Modeling
You also need to use the ineffective area option to limit flow to the bridge openings until the bridges are overtopped. In your case, it sounds like they will not be overtopped at the 100-year event, so your initial estimates of ineffective elevations should not be critical, so long as they are above the 100 year. The ineffective area constraints are specified on X3 cards, one just outside the downstream bridge and the other just upstream of the upstream bridge.
You might consider using HEC-RAS, which has replaced HEC-2. RAS is a much easier program to work with and most agencies, including FEMA specify RAS over HEC-2.
RE: HEC-2 Bridge Modeling
RE: HEC-2 Bridge Modeling
If you have to model in HEC-2....I'd model it as one bridge, and use X3 card to describe the ineffective flow.