Structural Instability & Zero Stiffness: Part 2 - Instability condition and rectification of model
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- เผยแพร่เมื่อ 6 ก.ย. 2024
- Structural Instability and Zero Stiffness conditions are very common in a model, but if these problems are not rectified, that may lead to incorrect analysis and design result or complete failure of the structure.
In this video, I have discussed about instability condition, different types of instability, how to interpret the warning message and finally how to rectify the structure. Following is the concerned warning messages --
***WARNING - INSTABILITY AT JOINT 2 DIRECTION = MX
***NOTE - VERY WEAK SPRING ADDED FOR STABILITY
It is very crucial for structural integrity to understand the problem and accordingly rectify the problems - identification and rectification of instability problems will be covered in this video series.
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Kindly make a video on all design parameters lx,ly, lz..etc as per is code and as well as American code...
Your videos are simply superb 👌 👏 👍 😍 🙌
I have discussed about some of these parameters in this video - th-cam.com/video/LJEPFxBEyow/w-d-xo.html. I will post a detail video on these very soon.
Effective length about y direction is called ly
Effective length about z direction but use local axis
Lx and ly is same in mostly lx use in bending strength find out
Thanks sir.
For the truss example of instability, where you assigned partial moments in truss members to remove instability, not only we released moments in truss members but we also let the members take shear in Z-direction, due to which static check is satisfied and instability is removed. Am i correct on this ? So , whenever we assign partial moment release, we not only allow minor moments to develop but we also allow full shear to develop on the truss members.. I hope i got it correctly.
Fantastic explanation sir.thanks
Hi, I have a confusion about the beam/column displacement and deflection. IF the deflection (lateral displacement) check for a column (considering allowable L/400 for example) is pass using (DJ1,2), however at certain node along the column the node displacement (in Z direction in my case) for the same LC exceeds the allowable limit , then what is the use or purpose of the node displacements?
What I understood from many Bentley communities discussion that DFF is applicable for beam (deflection) and column (displacement).
Not sure about this specific scenario. In general, local deflection values in three global axis are considered during actual deflection value calculation (dff) and then it is compared with allowable deflection limit (DFF) to find out the deflection ratio. There is no separate checks for beam or column, during steel design, all members are treated as a general member. When you specify DJ parameters, deflection length and local deflections are calculated considering that information and those members specified under this.
You can go through this video (th-cam.com/video/hqqMsi1LNp0/w-d-xo.html) for more details about deflection check - though it is for IS800:2007 code, but the concept is same for all other international design code.
@@surojit_ghosh thanks for your reply. Sorry, I believe I was not clear enough, I meant to say the deflection check (dff and DFF) is clear for me in term of implementation in STAAD. But as the code requirements (most of the international codes) the lateral displacement check is required as well, here we have to check the global nodes displacements, my question is if I perform the deflection check for the columns, is this enough or I have to check the NODES displacements as well?
thank you so much for such a great information
Hello Mr. Surojit_ For shear connection in the beams cant we just provide My and Mz and releases and be done to get rid of the instability instead of the partial release?
Another question is that if we give a partial release of the moments in either directions then how are we going to make sure that the provided relaxations in the moment are taken care in the connection design?
Kindly find the time to revert on this
Yes Sandip, releasing the end moments (My and Mz) for shear connection is a common modelling technique. Complete release of My and Mz does not always cause instability. You can start modelling with full My and Mz release for shear connections, and if there is any instability for this release, then change that to partial release. But don't release Mx, that causes several problems.
If you partially release the moments, then you need to ensure that the assigned connection has the capacity to transfer that moment. One solution- we can use the beam/weld group option available in RAM Connection Standalone to cross check the capacity of any connection. There are several other methods also to cross check the capacity of any joint.
Sir please make a video a double basement building challenges
I support
Good presentation
MAY I GET YOUR CONTACT DETAIL IM MODELINGINGN A PARKING SHED IN THAT IM FACING INSTABILY IN MODEL STILL CAN YOU HELP ME ITS JUST A SIMPLE CANTILEVER PARKING SHED
You can post your query and upload your model in Bentley Communities (communities.bentley.com/products/ram-staad/f/ram-staad-forum#pifragment-25818=1) for review.