Fixed But Support

RE: Fixed But Support

Sye — Fri, 24 May 2019 19:06:15 GMT

This is an engineer's call. If you are unsure talk to other engineers involved in the project.

RE: Fixed But Support

Iyad Hammad — Fri, 24 May 2019 19:02:06 GMT

the structure is sensitive indeed , where can i get more info about kmx and rotational stiffness to ensure my numbers are reasonable ?

RE: Fixed But Support

Sye — Fri, 24 May 2019 18:50:33 GMT

3 - 5 mm deflection does not seem high unless the structure is really sensitive to deflection. Anyway you may use KMX but ensure that what you are using is realistic.

RE: Fixed But Support

Iyad Hammad — Fri, 24 May 2019 18:49:30 GMT

thanks . ok .

RE: Fixed But Support

Sye — Fri, 24 May 2019 18:45:59 GMT

You should not release FY as otherwise the shears even due to selfweight of the members cannot be transferred to the supporting members.

Use the following

MEMBER RELEASE

12 13 16 17 START MY MZ

12 13 16 17 END MY MZ

RE: Fixed But Support

Iyad Hammad — Fri, 24 May 2019 18:42:55 GMT

Moreover,

I need to keep the supports as fixed , due to the excessive deflection in the cantilever im trying to minimize . The change from fixed with a trial KMX value to a pinned support resulted in an additional deflection in the last portion of the cantilever of about 3-5 mm .

RE: Fixed But Support

Iyad Hammad — Fri, 24 May 2019 18:29:34 GMT

communities.bentley.com/.../5661.Cantilever-2019-_2D00_-Copy_5F00_reviyad.std

I meant when I release the moments and Fy on the bracings i get the following warnings

attached file and warnings screen shot

RE: Fixed But Support

Sye — Fri, 24 May 2019 18:19:05 GMT

If you have an idea of the rotational stiffness offered by the support you may use KMX. If you are using a trial value then you may as well consider using a PINNED support at these locations. Defining partial release is not a problem provided the connections at the end can take up any resulting moments that may be generated. I did not see any warnings without the releases when I run the file in the latest STAAD.Pro CE (22.01.00.39).

You may want to add the LOAD LIST 4 TO 11 command before the design to ensure that design is carried out for the load combinations only. A modified file is attached for your reference communities.bentley.com/.../5661.Cantilever-2019-_2D00_-Copy_5F00_rev.std

RE: Fixed But Support

Iyad Hammad — Fri, 24 May 2019 11:23:02 GMT

Hi Sye,

What I need is to reduce the amount of fixity in the fixed support in order to activate the extension of the beam and the back support.

In case it was totally fixed , the back side of the beam will almost have a utilization factor of 0.00015 , when I added KMX= 300 kn.m-deg it gave a utilization factor of 0.3 .

So my aim is to allow to transfer moment to the back support. is the addition of spring release appropriate ?

attached latest model.

One more thing, for the bracings I added a partial release of moments = 99% due to the warnings I received when marking complete release.

Is the procedure followed correct .

Thanks

communities.bentley.com/.../5661.Cantilever-2019-_2D00_-Copy.std

RE: Fixed But Support

Sye — Thu, 23 May 2019 23:02:04 GMT

For releasing moments at supports, you do NOT need to define KMX, KMY or KMZ. To do that you simply need to check the appropriate boxes on the left under the Release. For example to define a pinned support but which is restrained from rotation about the global vertical axis (Y), you need check the boxes for MX and MZ.

You only need to specify KMX, KMY or KMZ when you want to define rotational springs. The unit is in kN-m/deg because the value you are expected to provide here is the value of moment ( in kN-m units ) that would cause a one degree rotation at the support.