Steel Joist

[STRCIVIL]

Currently, 30-ft span roof steel truss joist supporting built-up roof system and other heavy roof-mount equipments. The steel truss joists has been in service for last 30-years, and it's time to replace the equipments now. The design life for the new equipments are 30-years, but I concerned about the life expectancy of the existing steel truss joists. This building is located in corrosive environment close to ocean. The existing truss has coating and no major visible rust. Anybody have opinion on how to determine the life expectancy? What should be the basis? or can I just assume these joist can be in service for another 30-years (total of 60-years in service)?
I would appreciate any comments or available resources.

 

[austim]

strcivil,

As a start point I would suggest that you do some accurate measurements (using a vernier gauge or micrometer) of steel thickness on your trusses, to see if you can identify any significant loss of section. (If you don't know the original design thicknesses, that would not be easy).

Even if the current coating is intact, can you be certain that the joists haven't been cleaned of previous rust and repainted?