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RE: Lateral decision

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I see one problem with your retrofit of the first floor only.  Creating
a very stiff first floor creates a better load path from the ground to
the second floor.  This is where the damage will occur next time.  In
our simplified way of designing these structures we assume the loads are
applied to the upper levels and brought down to the foundation by the
lateral system.  We have to remember that the loads are generated in the
ground and move up.  The fictitious lawyer claiming you changed the
characteristics of the building might not be too far off base.  I think
that you explain to your client that if you retrofit the first floor,
damage may occur at the upper level more than might have in the past.
Have you even seen one of those buildings damaged after an earthquake
where the first floor is badly damaged and the upper floors look fine.
These are the soft first story buildings.  The lateral system of the
upper floors never got tested.  In essence they were "base isolated."
While your building may not be a soft first story, this example
demonstrates how the stiffness and strength of the first floor affects
the floors above.  Good luck with the discussion!

> Sincerely, 
> 
Thomas Castle

> ----------
> From: 	JRTCE[SMTP:jrtce(--nospam--at)mbay.net]
> Sent: 	Tuesday, February 03, 1998 11:23 AM
> To: 	seaoc(--nospam--at)seaoc.org
> Subject: 	Lateral decision
> 
> I am currently writing a proposal for engineering work on a two story,
> early 1900's church. The owners would like to remove and relocate some
> first story walls. No work is proposed for the top story.  Both upper
> and
> lower stories have significant seismic deficiencies from their
> original
> design but have performed well so far. My proposal is for a seismic
> retrofit of the first floor.  I am wondering if I should make it a
> requirement of mine that retrofitting must be done on both the top and
> bottom floors or I dont take the job.
> 
> On one hand, no work is being done up top and I am making the lower
> floor
> far stronger than it ever was so limiting my scope of work to the
> bottom
> floor is acceptable. On the other hand, If there ever was a problem
> with
> the upper floor the owner could say I was negligent in not making them
> correct the upper floor problems. An attorney might also claim that I
> changed the characteristics of the building and that led to an upper
> floor
> failure.  I might also add that to retrofit the lower floor is
> relatively
> easy but to retrofit the upper floor would be very difficult due to
> 20'
> ceilings, alters, etc. and probably outside of the owners means. I
> would be
> interested in your comments.
> 
> Sincerely: Jerry R. Taylor 
> 
> 
>