emperature load in outdoor steel structure

huangyhg

temperature load in outdoor steel structure
for outdoor industrial structures, the forces to be caused by ambient temperature change is something we’re lack strong guidance and big confidence. some always considered this load case, some never did by saying: the deformation (slid) at bolted connections will accommodate the temperature expansion/contraction. what do you think?
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i have always either taken the thermal loads in calculations or just provided sliding supports at one of the ends to take care of it. but never trusted bolted-connection to take care of thermal expansion automatically. the connections, i think, are too rigid for thermal expansion which is generally larger as compared to fabrication tolerances.
ciao.
i concur wit flamby.  at least in steel work.  consider a steel pipe rack, with bents spaced at 20'.  using a delta t of 60 degrees, one that i think is not unlikely to occur, the change in length of a 20' long strut is .094"  this is larger than half the 1/16" oversize in bolt holes.  also, considering that friction between bolted surfaces may well prevent expansion in a snug tight bolted connection, and almost definitely will prevent the expansion in a pretensioned connection, it is best to design a sliding connection.  don't forget to detail that sliding connection with enough room to expand.  i mean to make the   
for something like an outdoor pipe bridge, i always allow for thermal strains by providing a fixed end at one end of the span, and a sliding end at the other end.  when you're using slotted holes to allow for the movement, you have to make them pretty big.  another thing to consider is that the temperature of the steel can be a lot higher than the ambient air temperature.
the design of sliding bearings is interesting, i have seen some designers have steel sliding on steel with large slots, and others with slide bearings that have teflon plates and mirror finished stainless steel in contact. con-slide is one system i have used.  i have also used masticord elastomeric pads.
thanks for the input. i'm with you for these opinions.
someone argues that the structures designed without this load case have been in operation for many years. i think this is because they followed some besign rules like expansion joint every 100ft, for piperack for example, and single anchor bay. in this case member exapansion/contraction doesn't cause big force. on the other hand, when i consider member temperature i usually model the piles with springs, this sometimes will make a big difference.