lateral deflection

Actually, deflection checking is based on the resultant Beam Relative Displacement values, so the use of DFF will correctly evaluate lateral deflections in addition to vertical deflections.  I am jumping into a class right now, but I will post an example after I get out.

Cheers,

Chris

Hi Rohail,

Could you please try again to attach your model?  The way it is coming through, it is very difficult to interpret in a meaningful way.

 In addition, here are a few things you can check:

1. Verify that the parameters are consistent with the units being used.

2. Create separate DJ1 and DJ2 parameters for each unique girder to be evaluated.

3. Note whether the ratio of 9 is being controlled by deflection or stress.

4. Verify that bracing parameters are defined and assigned correctly (K, L, UNT, UNB).

Cheers,

Chris

What version of STAAD.Pro are you currently running?

The procedure for copying and pasting the content of the STAAD.Pro input file is as follows:

1. With the model open in STAAD.Pro, click Edit > Edit Input Command File in the Menu Bar.

2. Select the entire file.  (Either click at the top and drag to the bottom, or click anywhere within the file and then press CTRL + A.)

3. Click Edit > Copy in the STAAD Editor Menu Bar.

4. Move to the open Forum post form, right click, and choose Paste from the pop-up menu.

Regards,

Chris

I was able to manually parse your input file and have spent a good deal of time observing the ratios that are indicated as a result of numerous different model configurations.  Here is a list of my observations:

• Your model contains loading in all three global axis directions, therefore the most appropriate structure type would be SPACE as opposed to PLANE.
• In seismic definitions, the magnitudes of the specified weights are summed algebraically to arrive at the building weight.  Therefore, the seismic weights should always be specified as positive values.
• If your intent is only to check the roof members for deflection, then DFF 180 should not be assigned to columns, brackets, etc.
• The loading that is being applied to this frame is causing excessive deformations.
• The deflection check is not appropriate for this application because of the double-pitch of the roof member. Deflection check works for members that are collinear.
• When performing a deflection check, STAAD.Pro evaluates members at sections along the length of the member.  At each section, it considers deflection in all three global axis directions, and normalizes those deflections to account for the displacement at the DJ1 and DJ2 nodes. 
• When the maximum resultant normalized displacement is identified between DJ1 and DJ2, then dff is calculated as "deflection length"/maximum resultant normalized displacement.
• Finally, the unity ratio is calculated as DFF/dff.

At this point, I would recommend completing the remainder of the model (or providing some out-of-plane bracing to resist the extreme displacements in the global Z direction), and then evaluate your deflections for this gable roof manually by observing nodal displacements along the ridge.  Note, however, that the maximum deflection may actually turn out to be at some distance from the ridge.  This is because the two sloping rafters tend to stiffen the roof at the ridge where they intersect.  Close study of the Beam Relative Displacement Detail table will help you locate the points of maximum displacement and decide if they are significant, or if it is close enough to just read the nodal displacements at the ridge.

I hope this is of some help to you.  Please don't hesitate to let us know if we can help further as your model develops.

Cheers,

Chris

Sir,  your answer is helpful to me. But calculating dff value manually does not match with staad output value. Beam length is 1105 max displacement in this beam is 0.1404 then l/d =7870. But in staad output dff = 1439. Can you answer this??

Can you please upload the .std file here and mention the member#. Also please mention the version number for STAAD.Pro you are using.