# RE: Input with regard to section 1633.2.4

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Input with regard to section 1633.2.4
• From: Nicholas Blackburn <NBlackburn(--nospam--at)ipd-oak.com>
• Date: Tue, 18 Jul 2000 08:40:03 -0700
```Elements of a structure that are not intended to be part of the lateral
resisting system need to be designed for the forces arising from potential
building drift.  It is assumed that the diaphragm will carry the non-lateral
system elements with it during an earthquake. This calculated relative
displacement (drift) induces forces into the joints.

The '94 UBC and before used 3/8 Rw (Delta) where Rw was the seismic
"reliability" coefficient related to the lateral resisting system, ie Rw=8
for shearwalls and (delta) is the calculated drift due to the applied
seismic forces. Therefore you would design for a drift of 3*8/8 delta=
3delta

The '97 UBC has changed this deformation compatability value to 0.7R(Delta
s) where (delta s) is the calculated drift and R is the new seismic
"reliability" coefficient. As an alternate you can also use 0.0025h where h
is the story height for the level that you wish to examine.  For a shearwall
building R=5.5 so your minimum drift would be (3.85* delta s).
Alternatively, if your floor to floor height,h, is 10', drift would be
0.0025*10'*12"/'=0.3".

The deformation that you calculate is then applied to the element(s).  The
resulting moments and shears need to be accommodated in your design so that
the joints do not fail during a seismic event.  For columns you also need to
check the Pdelta effects (moments due to incresed eccentricity).  For
Concrete columns and beams this usually means that you place ties at 4"oc
for ductility and verify that the increased eccentricity does not blow your
column out.

Good luck

Nick

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