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pinned connections in trusses

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发表于 2009-9-15 12:34:52 | 显示全部楼层 |阅读模式
pinned connections in trusses
its been a while since i've had to do structural detailing and from my dim memory of truss design in college i seem to remember that if the centrelines of all the members at a joint intersect then the joint has no moment capacity - i.e is a pinned joint. is this right?
the orientation of the intersecting   
i think a truss analysis assumes pinned connections.
truss analysis assumes that the members carry axial load only, that each strut is a simple two force member.  this theoretical state is only achieved if the members join with a single pin (well greased?) and (if you're getting picky) on the neutral axis of each of the members.  
in reality the connection is a multiple pin arrangement (therefore capable of reacting moment) and offset from the neutral axis (of at least some   
if you are using a computer program to analyze a truss, you woud have to make sure that you release the end moments at the right plce to create the pin connection. for example, your top chord may be continuous but have many diagonal members attaching to it. in this case, you should release the end moments for each diagonal   
it is typical in structural engineering to neglect the rotational capacity of the web members in design.  in certain cases, long span, or welded connections, at some times to include the moment effects of the web members.  while theoretically to include web member rotational restraint typical practice neglects the moment capacity of the connection in design even if it has multiple bolts in the connections.  almost all, i would say 90% or more, of civil structural trusses utilize multiple bolted connections and truss action is assumed in analysis.  this has been successfully practiced long before any of us were engineers.  if you have eccentricity at the connections (centerlines not lining up at the panel points) then you need to include this effect in your analysis.  if you choose to analyze the truss utilizing rotational resistance of the web   
if your   
dag i need to read my post before i send them!  above should say, (sentence 3) "analysis including web   
if a "typical" truss were analyzed on a computer as a frame it's my guess that the bending stresses would be not be significant, assuming of course that centerlines and work points intersect.  when member sizes become relatively large then secondary stresses would need to be considered, but i don't re  
kxa,
it all depends on the way the truss is configured and how it is loaded. you could have significant negative moment over the joints for your continuous members.if every single member is pinned at the joints, then the bending moment depends on the load each
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