huangyhg

nchrp report 350
i am designing an extended curb that will anchor a test level 3 traffic rail per the nchrp 350 spec and need an impact force. i know how to calculate impact forces, but the report only designates weight, initial speed, and impact angle. i need change in velocity (lateral) for the calculation. the report does give limiting occupant speed and decel (g's) and i am thiking of using those. any thoughts or sugguestions?
check the aashto specs for guardrails...it gives you what you're looking for.
gerald,
aashto requires a design (unfactored) impact load of 400 kips for structures adjacent to a roadway that are not protected by an independent barrier.
or you could assume a final velocity of zero and use f*deltat = m*deltav (impulse relation from high school physics). the smaller the deltat, the higher the f.
jeff

thanks for the input. i havent found the reference in my google searches on aashto guard rail specs. 400 kips for a tl3 design seems very high. the tl3 is a 2000kg pick-up traveling 100 km/hr with a 25 degree impact angle. for a complete stop, yes the loads are very high, but for a glancing blow, veloctiy change is much smaller, but what is it? the 12 m/sec occupant limitation yields 106 kips, which seems more reasonable.
gerald01,
if i recall correctly, the 400 kips was for a tractor-trailer impact or a train impact.
but when the contract doesn't specify the requirements (as a recent letting project did), i bid it high to cover my butt. didn't win the job, but i'm not eating the cost of missing it from the design-build item.
jeff

ok, that makes sense, this will be a secondary road with lower speed limits. i just found a detail on the txdot bridge standards web site that i believe is useable rail anchorage curb for box culverts that i believe i can use without undue concern:

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