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RE: Knee Brace Literature

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Knee brace ends should be pinned

 

Matthew Stuart

Structural Department

Manalapan

Extension 1283

 

-----Original Message-----
From: Jeremy White [mailto:jwhite(--nospam--at)holbertapple.com]
Sent: Wednesday, January 18, 2006 12:35 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Knee Brace Literature

 

Bhavin,

 

Thanks for the tips.  Currently I have the building modeled in RAM Structural.  This should give similar results as a space frame model (using special software?), correct?  With regard to item #6, I thought that the knee braced frame would have at most the same drift as the moment frame or maybe smaller if the braced and moment frames used the same beam and column sizes.  This would be because the rigid joint is larger making the effective length of the beam and column shorter.  My RAM model is giving me results that lead me to believe this is happening.  What could be a reason that the deflection would be greater?

 

Thanks,

Jeremy White

 

-----Original Message-----
From: Bhavin Shah [mailto:bhavin.design(--nospam--at)gmail.com]
Sent: Wednesday, January 18, 2006 12:08 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Knee Brace Literature

 

Dear Jeremy White,

 

            To avoid moment connection at the beam-column junction, knee bracing may be provided, if space is available for the same. Some of the basic points regarding knee bracing are listed below which may be helpful to you :

 

1)        Knee bracings should be modeled in the Space Frame Model.  

2)        Moment at the beam-column junction may be released partially or fully. Knee bracings are to be designed accordingly.

3)        Due to vertical loads, knee bracing will be under Compression. However, due to lateral loads, knee bracing may be under compression or tension, depending upon the direction of the lateral load. Hence, knee bracing and its connection with the beam-column are to be designed for Compressive load as well as for tensile loads.

4)        In the beam and column, at the junction of knee bracing, force in the knee bracing may be resolved in two components (horizontal & vertical). These components will cause bending in the beam & column. Hence, beam and column are to be designed for bending at the junction of knee bracing.

5)        As mentioned above, local concentration of force will be there at the junction of knee bracing and beam, column. Hence, local strengthening may be needed at the junction of knee bracing and beam & column.

6)        If  knee bracings are provided to replace the moment connections, overall deflection of the structure may increase under the effect of lateral loads. To decrease the deflection, partially restrained moment connection may be provided along with the knee bracings.

7)        Beam-column junction may be designed as a shear connection or partially restrained moment connection, depending upon the assumptions considered in Space Frame Model.

 

Regards,

 

Bhavin Shah

 

On 1/16/06, Jeremy White <jwhite(--nospam--at)holbertapple.com > wrote:

I'm working on a two-story steel office building and I'm investigating moment frames vs. knee bracing on our wind frames.  We have plenty of ceiling space so we believe knee braces may be a good alternative to moment connections.  I intuitively understand how knee bracing works, but I want to know if there are any nuances that might be overlooked.  I've checked in some of our steel books around the office and can't find anything that discusses knee bracing (just x and k bracing).  Does anyone know of a good resource for info about knee brace design and/or theory?

 

Thanks,

Jeremy White