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Re: shear flow

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Oops - Andrew is right. For a hydrostatic load, the shear will be quadratic, not linear (as I originally indicated).

Since the shear flow is proportional to the shear in the beam, the shear at the interface will vary in direct proportion with the shear in the beam changes, provided your cross section is constant.

In typical composite steel construction, the shear flow is presumed for practical purposes to be uniform along the entire length of the beam, hence the uniform spacing of shear studs. (There is test data to back up the effective performance, though I don't have the reference handy). I'm not sure whether that simplification would apply to a short, cantilevered member, though.
Jordan


Michael Laplante wrote:

Andrew,

That is exactly the approach I have been using.

The piers act as a simply supported beam. Tied into the foundation at the base and supported by a slab and beam system at the top.  Total height is 9.3m ( 30 ft)  .  The total base shear or support reaction at the base is 1750 kN  (393 kips) and at the top  700 kN ( 157 kips) triangular load (increasing uniform load).   What I am looking for is the theory behind  the value of V.  From all the explanations  that I have seen, V is typically the shear due to the support condition at one end.   V the beam shear change along the height of the member  but does the value used to calculate the shear flow change in the same way as the beam shear.  Is the beam shear related to the value of the shear flow ?  

 

 Just trying to get my head around the issue.

 

Mike

 

De : Andrew Kester, PE [mailto:akester(--nospam--at)cfl.rr.com]
Envoyé : October 21, 2008 10:22 AM
À : seaint(--nospam--at)seaint.org
Cc : dso
uter(--nospam--at)cfl.rr.com
Objet : re: shear flow

 

Mark,

Shear flow formula is valid for any member having a cross section that is symmetric about the y-axis, which I imagine your piers would be.

 

f= (V*Q)/I

 

Q= ybar*A 

 

Q= first moment of the cross-sectional area between the top surface of the beam and the contact surfaces where the shear flow is being calculated.

 

Got this from pgs 284-85,

 

So depending on the loading of the cantilever, shear may be variable (uniform loading) or constant (point load at the end). I think I have that right. So with your piers I don't know if the forces resolve into a point load or if they are triangular load (increasing uniform load)...

 

My question would be is it worth it to vary the repair detail throughout the pier length or will it just be simpler to maintain a typical section for constructability purposes?

 

Regards,

Andrew

 

 

Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Drive, Suite 301
Orlando, FL 32803

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