Residential Bridge (12' span) - Impact Loading?

[adeku]

I am designing a very short bridge for a residence. The road leading up to it is also narrow so traffic speeds should not exceed 15 mph. The span of the bridge is 12' and width is also 12', just wide enough for one car. Girders are steel but everything else is wood. There is a requirement in ASCE 7-05 that specifies a 6000# impact point load at 1'-6" above the road level. I have not looked through the latest AASHTO code but I presume the loads are even more conservative there. Is it reasonable to design the guard rail for this 6000# point load because it seems too high.

 

[bridgebuster]

6k isn't really much; AASHTO standard specs calls for 10k over 5 feet.

Is this a single residence with a few passengers cars and an occasional delivery truck? If so, you don't anything substantial, just something that conforms to AASHTO TL-1 or 2 criteria. Look at your state DOT guidelines and see what they have in terms of guide rail.

Take a look at the attached file as well.

 

[adeku]

Thanks bb! I'm in California and AASHTO is what we design to, so I'll see what they have in terms of guiderail loading.

 

[Teguci]

6 kips service load is appropriate. Although the load occurs at 18" the barrier should be at least 24" high (for the vehicle).

 

[RockEngineer]

Even for single residence bridge you still need to look at loadings for fire trucks and possibly concrete trucks if there will ever be more construction.

 

[MiketheEngineer]

Check with the fire marshal - he will want to be able to get across also....