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Re: modeling of 3d-frame with shearwall

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This is my second attempt to get a response from members on a subject of
some importance:

To Siamak's query regarding modelling of a 3D frame/shearwall building
Jerome had suggested the following procedure:

>     You must prepare at least three or four nodes to identify the plate 
>     element. Then assign the material properties and thickness. You also 
>     have to identify it if its a membrane or a plate element. For walls, 
>     it should be plate or solid. I usually assign plate.
>     
>     Say you have a 26' long x 12' wide and 20' high (one storey is 3m) 
>     building and the West face is a shear wall.
>     
>     <-- 12'--->    <-----------26' ----------->      <---12'-->
>     14        13    13/14        15/16       17/18  18        17
>     +---------+    +++++++++++++++++++++++++++      +---------+
>     +         +    +            +            +      +         +
>     +         +    +            +            +      +         +
>     +    B    +    +            +            +      +         +
>     +8        +7   +7/8         +9/10        +11/12 +12       +11
>     ----------+    +------------+------------+      +---------+
>     +         +    +            +            +      +         +
>     +    A    +    +            +            +      +         +
>     +         +    +            +            +      +         +
>     +2        +1   +1/2         +3/4         +5/6   +6        +5
>
>
>        West Face           North & South Face           East Face
>        (SWall)
>
>       At the west face, the A (PLATE ELEM 1 ) Plate would be made of node 2 1  
>       7 8; the B (PLATE ELEM 2) plate by 8 7 13 14. You can assign the
>       thickness of, say 10" and E=3260 KSI
>
>        So the input would look like :
>
>        SHELL
>        NM=1
>        1 E = 3300
>        1  JQ = 2 1 7 8 TH = 10
>        2  JQ = 8 7 13 14 TH =10
>
>        You ca then attach your beams/girders and assign your columns.
>

I had raised my doubts about the procedure with the following questions:

>	1. Is it all right to divide a shear wall into plate
>          elements which are one storey high and one bay wide
>	   or should a more refined mesh be used ?
>
>	2. Is it all right to connect beam elements (13-15) and
>	   (7-13) to the plate element (7-8-13-14) ?

Jerome responded with the following answers :

>     A more refined mesh would be better. The resulting stresses are 
>     reckoned from the c.g. of the element. So, if you have more elements, 
>     you will be able to get near "exact" values for every area of wall. 
>     That would mean , however, more time for data preparation and run-time 
>     for the analysis. But I can probably sacrifice that.
>     
>     You can attach the beam elements to the plate and model the 
>     connections as you deem necessary. There is a feature in the program 
>     that allows you to release any of the DOF's you want.
>     
>     So far, I have not tried modeling a shear wall embedded with columns 
>     yet. But what you can probably do, to idealize it, is to assign it as 
>     a solid or plate element with a different thickness.


I agree with Jerome's answers and would like to add that when one attempts
to attach a beam or a column element to a shearwall using plate elements,
it will be wrong to use (storey-high x bay-wide) elements simply from the
consideration of an acceptable aspect ratio. Things are even more
complicated if non-planar shearwalls are present.

This leads to the following questions :

1. What is an acceptable level of mesh refinement?

2. If the mesh size is going to be unmanageable, is it advisable to use
   plate elements at all?


Rudra Nevatia
Central Computing Facility