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RE: Knee Brace Literature

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Bhavin,

I just did a similar experiment in RAM Advanse.  The only difference was
that I changed the aspect ratio of span:height to be 1.5.  I used knee
braces at the 3/4 point up the column (9' on 12' column) and at a 45 deg.
angle.  All 4 models (12',24',36',and 48' high) showed that the drift at the
top of the moment frame (nodal displacement) was consistently 2x that of the
knee braced frame.

I don't think that the aspect ratio is what made our models give very
different results.  What could I have possibly done differently? 

A brief run down of my models
Moment Frame:
- all joints fixed except pinned base
- point loads at each level
- all sizes and materials same as braced frame

Braced Frame:
- columns fixed, beams pinned (not much difference if fixed beams), bases
pinned
- knee braces pinned at each end
- all sizes and materials same as moment frame

Dimensions of frames:
12'h x 18'L

Any ideas why we got different results?

- Jeremy White



-----Original Message-----
From: Bhavin Shah [mailto:bhavin.design(--nospam--at)gmail.com] 
Sent: Friday, February 03, 2006 12:47 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Knee Brace Literature

Dear Stan Scholl,

For comparison of deflection, four simple structures consisting single
bay ( Plane Frame) are modeled (in STAAD). All four structures are
modeled with moment resisting frames and thereafter with knee bracing.
Sizes of members are identical in all the cases. Lateral load was
applied and deflection was checked at the top story for both the
cases. Following shows the brief details of STAAD model and comparison
of the results.

*************************************************
Brief Details of STAAD models
*************************************************

1)      Model 1 :   3m x 3m height
2)      Model 2 :   3m x 6m height
3)      Model 3 :   3m x 9m height
4)      Model 4 :   3m x 12m height

Supports are hinged at the foundation level. Knee bracings are
provided below the beams only. In case of knee braced structure,
moment at the beam-column junctions are released.

*****************************************
Comparison of the results
*****************************************

      % Increase in deflection at top story in case of Moment
resisting frame & Knee braced Structure :

1)      Model 1 :  - 9.6 %
2)      Model 2 :  - 2.6 %
3)      Model 3 :   +12 %
4)      Model 4 :   +15 %


Above values shows that in case of structures having more than two
story, lateral deflection at top story may increase for knee braced
structure as compared to Moment resisting frames. ( Please note that
these values are derived for the specific structures only and may vary
significantly for complex structures. )

Kindly share your experience regarding similar comparison of the
results for more complex structures.

Regards,

Bhavin Shah



On 2/2/06, sscholl2(--nospam--at)juno.com <sscholl2(--nospam--at)juno.com> wrote:
>
>
> my experience (45 yrs.) is that knee braces always reduce deflection
> significantly.
>
> all knee braces I have used are under beams only.
>
> Stan Scholl, P.E.
>
> Laguna Beach, CA

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