prefabricated metal frame analysis

huangyhg

prefabricated metal frame analysis
renovation of existing frame that was a prefabricated metal frame with taper column and girder frame supporting thin wall box purlins (severly corroded to be removed).
any suggestions on simple analysis to determine existing frame capacity?
i assume these are tappered portal frames... do you have the original drawings?  how much information are you able to obtain?  depending on how familiar you are with cold-formed steel and buildings using same for bracing, etc, you may want to read "bracing cold-formed steel structures" by thomas sputo & jennifer l. turner.
if these are pre-engineered metal buildings, they generally have little residual strength above the design values and safety/load factors.
you have to be cautious about any additional dead loading... i was involved in one study where the roof deck was corroded so badly that the new deck and insulation proposed generated $.5m repairs... the building ended up abandoned.
most metal building outfits will not review these... even if originally fabricated by them... they sold it, they built it and that's their involvement.
analysis is very time consuming and plate thickness are incremented by 1/16's of an inch... little slop... and stability issues are also critical due to the long clear spans and changes in moment envelope with varying loads...  also have to check original loadings with current loadings.  in manitoba they have gone from a 1/30 year return period for loads to a 1/50 year with a subsequent increase in loading...
dik
don't know of a simple analysis.  we have analyzed a few of these.  we take the shop drawings, if available, and actually imput the members into risa or staad to analyze frame.  if we don't have drawings, we field measure, with calipers, the member sizes.  that gets expensive.  be sure to input the reduced sections due to the corrosion.