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Re: Apartment Building Collapse

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I think that the 50-year service life number is an arbitrary factor used in economic considerations.  The service life of a building is only partly an engineering matter.  I suppose the engineer can design for an extended serviceability period, but design rules for doing that are not commonly available, or used.  The service life of a building has a lot of other facets:
The owner/investor wants to get a return on his investment in a given period of time, and may not be concerned about it lasting any longer than that [recent demolitions in Las Vegas of high-investment buildings and replacement with newer higher-investment buildings are probably examples];
Successor owners want returns on their investments as well, and must factor in the costs of repairs and maintenance;
The materials of construction have a limited serviceability period [ordinary reinforced concrete -- about a century plus or minus a few decades, with extended periods provided by good maintenance and timely repairs as rebar corrosion becomes apparent];
Environment has positive and negative effects;
Appropriate maintenance and repair can extend the serviceability period of a building indefinitely -- like the family hatchet that is handed down from generation-to-generation, having had its handle replaced many times, and its blade a few times, too.
L.A. is a young city -- its oldest remaining buildings are probably not much more than about 50 years older than the one that collapsed, but many of the oldest [residential, commercial and churches] are in fine shape, ready for the next hundred years if they continue to receive attentive care.  Buildings that are much older continue to serve well in eastern cities.  Traditional buildings all over the world are much older than any in this country, some of them surviving recent earthquakes while nearby modern buildings suffered irreparable damage.]
I'll pass on the liability question -- except to say that the design engineers on the buildings I work on [almost all older than I am] are gone and no longer liable.
Nels Roselund
Structural Engineer