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Re: Lateral decision -Reply

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Tim McCormick wrote:
Your tale of retrofitting within economic means is often told. For this
reason, some retrofit standards allow the work to be done in stages. I
believe engineers have an obligation to educate building owners about
both the benefits and limits of seismic retrofit improvements. When
documented, such education should help limit the value of negligence
claims. As for the lawyer, you can point to the acceptance criteria for
retrofitting lateral-force-resisting-systems in UBC Section  3403

" Alterations of existing structural elements, or additions of new
structural elements, which are not required by Section 3401 and are
initiated for the purpose of increasing the lateral-force- resisting strength
or stiffness of an existing structure, need not be designed for forces
conforming to these regulations provided that an engineering analysis is
submitted to show that
1. The capacity of existing structural elements required to resist forces is
not reduced,
2. The lateral loading to required existing structural elements is not
increased beyond their capacity,
3. New structural elements are detailed and connected to the existing
structural elements as required by these regulations,
4. New or relocated nonstructural elements are detailed and connected
to existing or new structural elements as required by these regulations,
and
5. An unsafe condition as defined above is not created."

Hope this helps,

Tim McCormick. P.E.
City of Los Angeles
 

Tim, I'm curious how Building Officials interpret the "unsafe condition as stated above" provision of exception item #5.

I read the definition in 3403.2  "if an addition or alteration will cause the existing building or structure to become structurally unsafe or overloaded....." as possibly addressing the second story requirements. If the lower level of a two story is strengthened, perhaps the added new "stiffness" pushes load further up the building and therefore may cause to second story to become "unsafe". There are examples of such, in Los Angeles I believe, where the "soft" story of a damaged building was "strengthened" only to have pushed the damage upward in the building during a later earthquake.

I realize this is intended to provide some relief to property owners such that economic development is possible, and that this pushing the force up and consequent damage may not in fact be a reality all the time, and that doing something good downstairs is better than doing nothing, but where can we reasonably expect defense of agreement for non action (i.e. doing nothing). Unfortunately, the liability issue makes this a sticky question in my opinion. There undoubtedly are "professionals" who would endorse a certificate of merit based on some arguement as stated above.

I hope you don't take this as any kind of accusation or indictment against the Building code or Building Officials. We write code to help remove risk for the public, and sometimes the meanings are clear and othertimes not. Could you help shed some light on this issue for me (us)?

Barry H. Welliver
wellive(--nospam--at)ibm.net

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