# Re: UBC'97, Orthogonal Effects

• To: seaint(--nospam--at)seaint.org
• Subject: Re: UBC'97, Orthogonal Effects
• From: Jake Watson <jwatson(--nospam--at)inconnect.com>
• Date: Tue, 11 Apr 2000 21:20:16 -0600
```Let me preface by emphasizing I am an E.I.T., but I will take a stab at
it.  I have been doing similar calcs recently.

Question 1:

Try this as your building (If only it were shaped like this....)

_________________  North End
|               |
|               |
|               |
|               |
|               |  <---- Vu
|               |
|               |
|               |
|_______________|  South End

Because the force is due East, the transverse END (not direction
"...at
one end of the structure transverse to an axis....") would be the North
and South ends of the building.  This means that if applying the force
through the center of mass displaces the North end 1" and the South end
1.2", you must amplify the force.  A direct answer; no, you do not have
to calculate deflection of Y to determine torsion for X.

Question 2:
Under dynamic provisions, you must consider orthogonal effects.
You
haven't mentioned if this is dynamic or static procedure.  I'm not so
sure about static, but under dynamic you have two choices.  You can use
square root of the sum of the squares (SRSS) or you may take 100% of
your force in the X direction and 30% of the force in the Y direction.
I don't have a UBC in front of me or I would quote you section numbers.
This is all un ch 16 somewhere.  If you are doing dynamic, I recommend
you go to CSI's web site and read some of their papers.
(http://www.csiberkeley.com/Tech_Info/edwilson.htm)  Secondly, you have
to ask yourself a question, "Can I have a structure twist only along the
X axis?"  Torsion by definition is rotation, not translation.  My
opinion here, no code to back it up - you should consider it torsionally
irregular in both directions.

Question 3: Sorry, not a clue.  But when in doubt, be conservative.
Easier said than done...... :)

One last thought - if you are using concrete shearwalls in a C shape be
aware that ACI318-99 treats perpendicular joined walls differently.  If
I remember right (please check this for yourself) ACI318-99 will let you
use 15% of the clear height for the maximum flange width to draw
forces.  For example, on my box above, if the North wall is 50 feet long
and 10 feet high I can only use 1.5 feet for my flange width.  ACI318-95
gives you different percentages for compression and tension (makes
dynamic analysis next to impossible).

Best of luck to ya.

Jake Watson, E.I.T.
Salt Lake City, UT

```