structural evaluation of existing buildings

huangyhg

structural evaluation of existing buildings
the ibc, chapter 34, requires the use of design criteria applicable at the time of erection for the alteration and repair of existing buildings.  however, the department of defense (ufc 1-200-01) deletes this chapter and replaces it with asce 11 "guidelines for structural condition assessment of existing buildings" which leaves the determination of design loads up to the engineer (paragraph 2.3.3.1).  what are the implications of using current code criteria to evaluate existing structures?
what i have found in the past, is the wind speed has been upped, and, the bracing systems, if originally optimized, get significantly overstressed.
a few thoughts to consider:
1.  similar topics have been discussed in these forums, you might look at some of those discussions.
2.  asce has a seminar called "condition assessment of existing structures" that i found very well done.  they discuss concrete, steel and timber assessment with both destructive and non-distructive testing methods.
3.  while the selection of allowable stresses, whether based on the original codes or today's updated codes is important, i think equally important is the condition assessement of the building as it exists.  was it well maintained?  what is its' loading history?  has it survived major load changes - wind, snow and overload situations?  can you reasonably apply the total allowable stress or should it be reduced by a larger factor of safety due to the reduced capacity of the existing building?  
4.  will a change in use reduce or increase the loads on the structure?