huangyhg

long span truss questions
i've searched the archives and have found lots of useful posts, but i have a few add'l questions.
the trusses are ~180' (55 m), simply supported on cast-in-place concrete columns, top chord bearing.
- considering the case of a fire, what temperature difference should we use to size end clearance? i was thinking 350f (180c). i realize that i can design the columns with lighter reinforcement designed to yield prior to the chord buckling, but i'd prefer that the column be symmetrical so there's no chance of a mix-up.
- on the pinned end should the connection be rigid, such as welding to an embed plate, or should it allow some movement?
- we will be performing the erection analysis for suspending the trusses from several sets of panel points. how is lifting strategy usually specified? do you provide a maximum angle/minimum base height for a two legged sling? provide a maximum chord compression force?
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you will have to decide how much of the load to carry on each sling. then decide how many slings can you put on one machine to get the number of machines. i'd call two or three specialty rigging and erecting contractors before anything else is done.
richard a. cornelius, p.e.
for long span trusses, the movement at ends is quite big. because of uncertainty about frictional forces, we generally go for neoprene pad bearings instead of a sliding pad type of detail and it works satisfactorily.
ciao.

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