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re: Residential URM

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The structure does not require an upgrade if it is part of one of the
exemptions of CBC 3403.2. The URM ordinance lead to a dead end upgrade. It
does not allow the use of the upgraded URM materials for additions or
changes. Upgraded URM elements can remain if the 3403.2 exemptions apply.
Such as, the existing strength is not reduced, no additional loads have been
added, and the condition is not hazardous. The URM codes can be considered
the threshold for a hazardous condition.

Existing buildings can remain, as long as their capacity is greater than a
dangerous condition, and many times a complying existing structure is less
than current code. The URM code usually exempts a home from a mandatory URM
reinforcement but does that mean it is not a dangerous condition?

"Dangerous" for structures is defined in the Abatement of Dangerous
Buildings Code as adopted by CBC. It has a rule that any measured stress or
requirement that is less than 66% of compliance of requirements for new
construction is dangerous and must be abated. One exception is San
Francisco, only a building official can deem a building, dangerous. Some
elements of the URM requirements appear to be less than 66% of code for new
buildings, but for lateral forces only.

Each jurisdiction adopts the URM ordinance with possible revisions. As an
example, the home exemption is one of the first paragraphs of the San
Francisco Code (16B, 1602B-Scope). The exemption of a home from the
mandatory URM upgrade, is probably an economical and political decision, not
because the URM is safe due to fact that it is a home.

I have been labeled a hypocrite because I walk into and inspect dangerous
buildings. I perform my committed duty. Daily, I do not live, or work in
dangerous buildings.

As for un-reinforced systems, you may have seen some of my inquiries about
using a Seismic R of 1.0 and what would omega be? The same goes back to your
inquiry of mammoth stone sculptures. All of these are essentially
un-reinforced as is not allowed by code, directly. Just how is the rammed
earth system per code? How are adobe buildings being built?

This is for discussion only and hope to hear further responses to Mr. Wish.

David Merrick, SE

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