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Imminent and dangerous guide

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It is a risky business.

 

The UBC had a guide titled "Abatement of Dangerous Buildings"

 

Dangerous was when an analysis determined a measurement failed to conform to the code by a factor of 1.5. If there was only 66% or less of required strength, it was dangerous. I agree with this because safety factors range from 1.7 for live and 1.4 for dead.

 

This 66% seemed to apply not only to structural, but also architectural dimensions. If an exit was required to be 3 feet wide but is less than 2 feet is a dangerous condition.

 

This factor probably was only meant for vertical loads. Seismic rules for historical buildings allow structures to stand with far less strength than 66% of the more recent codes. Considering a lateral force of 0.1g for a historical building and the modern code could demand 0.186g then the dangerous thresh-hold for lateral loads might be about 50% strength.

 

The Omega factor, when introduced immediately made some of last code's complying designs appear very very dangerous. But they are not. I suspect these new criteria are not in direct response to an event but a response to designs without detailed analysis.

 

My favorite imminent definition is it is when no other event stands, in time, between now and the event in question. "Other events" could be defined in terms of the life span of the occupant. New occupants create an event and many my work at one location for 30 years or live for 80 years in a residential structure.

 

100 year return period seems a little shaky and is just under what minimum seismic upgrades allow in special cases. Seismic design today is attempting about 500 years. I know that in Sacramento the minimum acceptable flood safety is 100 years and that still seems bad for the public but not dangerous. It seems clear a building is dangerous when the probability of its failure could be the first event to shorten a person?s expected life span.

 

I thought that a building was dangerous, but yet I was willing to walk into it. It seemed that the building was not an eminent danger to my body because my stay was only for two hours, unlike an owner who may be there daily for 50 years or more.

 

David Merrick, SE