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History of AASHTO Rail (Impact/collision) load?

History of AASHTO Rail (Impact/collision) load?

History of AASHTO Rail (Impact/collision) load?

(OP)
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?

RE: History of AASHTO Rail (Impact/collision) load?

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.

RE: History of AASHTO Rail (Impact/collision) load?

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.

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