LFD design of bolted splices

[Dinosaur]

Folks,

As my handle indicates, I work in a "working stress" state and the majority of my experience is in using working stress design methods. Recently I was asked to check some bolted field splice calcs for a steel girder bridge. The designer performed the usual checks on the bolts calculating the force on the critical bolt and checked that against the LFD values for a slip-critical bolt in the AASHTO Standard Specs (e.g. a Type F bolt in AISC nomenclature). However, when he checked the "75%" criteria in accordance with (I think it is) Article 10.18.2 he divided that by the capacity of a bolt bearing against material (e.g. a Type N bolt in AISC nomenclature). I told him he should use the Type F bolt limit for all checks regarding bolted field splices. He showed my an example in an AASHTO commentary that used the Type N values for the "75%" strength limit check and said this was what he was using. Anybody want to weigh in on this? I have always used the Type F limits for bolt performance because the code the splices must be designed as slip critical; therefore, the Type N (or Type X) limits have no meaning in this problem; you have to meet the Type F by my understanding. Thanks. - Dinosaur

 

[koodi]

My steel design experience is virtually nill. And when I am called upon, I use ASD. So my "opinion" here is not based on experience. So,

This is my understanding: 1) under the service loading condition the joint remains slip critical and should be checked accordingly, 2) under factored loads (the strength failure condition) the joint will slip and bear on the bolts. Where both condtitions must be checked.