Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re : Knee Braced Frame

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Jeremy White :

Please check moments at the junction of beam & column in case of knee
braced structures. If moments are present at the junction than kindly
release the moments and check the results again.

Regards,

Bhavin Shah

On 2/7/06, Jeremy White <jwhite(--nospam--at)holbertapple.com> wrote:
>
>
> Bhavin,
>
>
>
> I 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
>
>
>
> ******* ****** ******* ******** ******* ******* ******* ***
>
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
>
> *
>
> *   This email was sent to you via Structural Engineers
>
> *   Association of Southern California (SEAOSC) server. To
>
> *   subscribe (no fee) or UnSubscribe, please go to:
>
> *
>
> *   http://www.seaint.org/sealist1.asp
>
> *
>
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
>
> *   send to the list is public domain and may be re-posted
>
> *   without your permission. Make sure you visit our web
>
> *   site at: http://www.seaint.org
>
> ******* ****** ****** ****** ******* ****** ****** ********
>
>

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********