instabilities in this warehouse staad model

RE: instabilities in this warehouse staad model

joan mallillin — Sat, 03 Oct 2015 12:28:36 GMT

hi thanks. most of the rafters are failing? will a haunch beam at the ridge and ends make it PASS?

RE: instabilities in this warehouse staad model

DSANJU — Tue, 29 Sep 2015 15:21:48 GMT

communities.bentley.com/.../Framing4K_5F00_0930a_5F00_mod.stdPlease refer to the revised model. In this model, 99% member release is used instead of MEMBER TRUSS specification.

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 13:43:19 GMT

communities.bentley.com/.../2728.Framing4K_5F00_0930a.std

RE: instabilities in this warehouse staad model

Modestas — Tue, 29 Sep 2015 13:32:57 GMT

If top and bottom chords are continuous members, it will take some bending, I believe.

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 13:30:09 GMT

ok. removing truss command for tc and bc. but there should be no bending right?

RE: instabilities in this warehouse staad model

Modestas — Tue, 29 Sep 2015 13:26:40 GMT

I still see that you are using TRUSS specification for top and bottom chords of the trusses. As explained earlier, you may not use TRUSS spec for these members and warnings would disappear then.

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 13:22:54 GMT

model is a 50X60 meter warehouse.

now need to decrease the sizes of the members. the LC also play a significant role too

communities.bentley.com/.../Framing4K_5F00_0930a.std

RE: instabilities in this warehouse staad model

Modestas — Tue, 29 Sep 2015 13:04:14 GMT

Good to hear! Do you need some further assistance with these? If yes, please attach your modified model.

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 12:58:22 GMT

yey! 224 warnings decreased to 4!

RE: instabilities in this warehouse staad model

Modestas — Tue, 29 Sep 2015 12:49:00 GMT

Why did you assign releases in FX, FY and FZ directions to the rafters? These are the translational degrees of freedom. For the rotational DOFs MX, MY and MZ should be released. I think you should be releasing MY and (or) MZ directions for these rafters. MX should not be released as the rafter probably is not able to spin around its longitudinal axis.

I believe that your top and bottom chord members of the trusses would be continuous members so it will be subjected to bending, hence you should not assign TRUSS specification to these members. You can read more on the same topic here: communities.bentley.com/.../339106

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 12:17:00 GMT

yes i fixed that already. and i assigned the crossbracings to member truss instead. still getting instabilities. the rafter section keeps getting bigger and heavier. could it be that i am wrong with the instabilities.

RE: instabilities in this warehouse staad model

joan mallillin — Tue, 29 Sep 2015 12:14:14 GMT

yup did that. instabilities still there.. =(

RE: instabilities in this warehouse staad model

Amitava — Tue, 29 Sep 2015 11:54:16 GMT

In the same line of the suggestion from Modestas, "STAAD TRUSS" means each and every member of the model is a Truss member. Your model is not such ... there are members too those have to carry bending. You can selectively assign the "Member Truss" specification to those members which are intended to carry axial forces only.

RE: instabilities in this warehouse staad model

Modestas — Tue, 29 Sep 2015 10:14:42 GMT

Try to change the first line in the input file from STAAD TRUSS into STAAD SPACE. That should help to avoid instabilities.