Hoping for a little clarification here on toughness requirements. The way I understand it AASHTO makes the assumption that brittle fracture will not occur 70deg F below the tested 15 ft/lb level using a Charpy Impact test. Therefore if a material achieves > or = 15 ft/lbs at 70deg (usng AASHTO tables) it is then acceptable for use in a bridge with design min temp of 0deg. My first question is: Is my assessment of AASHTO's assumption correct? And: Is my understanding AASHTO's determination of material acceptability accurate? And certainly feel free to open the discussion further.
My (poor) understanding of the AASHTO requirements and test temperatures is that there is a 70-degree temperature shift to account for the difference between impact loading and fatigue loading, and so that's why a test performed at 70F is supposed to give you reliable performance in service at 0F.
I have the Barsom & Rolfe book "Fatigue and Fracture Control in Structures" and my class notes from a Lincoln Electric seminar on fracture & fatigue control in structures.
You could try doing a web search for AASHTO, toughness, "temperature shift", but the first few results I got were all papers that had to be purchased.
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