xyz111
Understanding Deflection ChecksHi,
Please see attached model of a portal frame where I am trying to
carry out a deflection check on lehand post. while using CAN 1
command, Staad reads the nodal deflection at top of the column
(694.2mm) and divides by 10mm (8000mm (post height) / 800 (DEFF
parameter)) to get a UR. Now fthe same post, using CAN 0 parameter
it gives me a UR of 11.4. I am not sure how Staad calculates
that!?
For CAN 0 case, I have split member in to various segments and
the UR (max) now is 11.4 (corresponding to a deflection of
110.4mm!) for member 5, with relative displacements for node 6
being (523.72 -491.74 ~32mm). I still can not obtain 110.4
deflection even while subtracting N6 or Ndeflections from that at
top of the post.
Please suggest!!
Structure1.std
Answer Suggested+
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Shany
2 Replies (Most Recent Reply)
In Staad, the deflection check is carried by:
Ratio = DFF / dff
where dff = Length of the member / actual displacement
and Dff = user defined ( 800 in this case )
The actual deflection of the members are calculated from the
line connecting the DJ1 and DJ2 node. (please see Deflection pic
attached) . For these particular members, you have defined node 1as
DJ1 and node 1 as DJ2.
The actual deflection is the local deflection of the entire beam
between node 1 and 1. This means you need to create a physical beam
between node 1 and node 2, and find the local deflection of this
beam .
Now the actual deflection is calculated as : x2 + y 2 + z 2
where x , y and z are the local deflection of the beam .
So, the actual deflection is : 02 + 113.5792 + 02 = 113.579
Dff = 8000/113/578 = 70.435 ( length of entire beam is 8m)
Hence ratio = DFF/dff = 800/70.435 = 11.4
Page 2 of 3Understanding Deflection Checks - Structural Analysis
and Design - Forum - Structural A...
6/30/2015http://communities.bentley.com/products/structural/structural_analysis___design/f/5932/t/...
