History of AASHTO Rail (Impact/collision) load?

[KMA]

AASHTO 2.7.1.3: Is anyone familiar with where the requirement of 10 kip rail (impact) load came from? I am investigating an 8" concrete slab overhang on a bridge as per AASHTO 3.24.5.2. Is this load crash test related(?) not truck related? Is this good for HS20 & HS25 type trucks?

 

[rowe]

I don't have any documentation on the origins of the 10 kip load, however, I have always used the 10 kips horizontal load for cantilever slab design, regardless of the truck loading (HS15, 20, or 25). I also check the vertical wheel load (for the design vehicle) but the moment arm is usually small and doesn't often control. I believe that the 10 kips rail load would be "code compliant" for all design vehicles listed in Section 3 of AASHTO, but you could always be conservative by multiplying the 10 kips by 1.25 (HS25/HS20).

If your interested, check out NCHRP Report 350 "Recommended Procedures for the Safety Performance Evaluation of Highway Features" which includes barrier rails.

Good Luck.

 

[fuchsjr]

NCHRP 350 provides the crash test certification methodology. You can find increased barrier/railing loads in AASHTO LRFD section 13 and 13A. The loads in these section are based on instrumenting barrier/rail that was crashed under NCHRP 350. You'll find out that 10 k is too low. A lot of State DOTs are switching to the higher loads.

Good luck.