Structural Instability & Zero Stiffness: Part 1 - Zero Stiffness and Degrees of Freedom

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 various reasons of zero stiffness condition, what is degrees of freedom, and how to interpret the warning messages to identify the problem in the model. Following is the concerned warning messages --
*WARNING- ZERO STIFFNESS IN DIRECTION 4 AT JOINT 16 EQN.NO. 16
**WARNING - THERE WERE MORE THAN 12 DOF WITH ZERO STIFFNESS.
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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Seismic Analysis based on ASCE/IBC code - Response Spectrum Method -- • Seismic Analysis based...
STAAD Advanced Concrete Designer -- • Advanced Concrete Desi...
Steel Structure Optimization with STAAD -- • Steel Structure Optimi...
STAAD.Pro CONNECT Edition Update 8 : What's new -- • STAAD.Pro CONNECT Edit...

[@usmanraza7587]

Great Quality and to-the-point content. Adressing all queries that can come in one's mind.

[@arocenajesussusmerano174]

Sir you are the best, that I ever found, in youtube in terms on how you well explained the issues in Instability. The best ever. TBE!..Well done sir..Hope all the best and success in whatever you do...Thank you so much...

[@surojit_ghosh]

Thanks, nice to hear that.

[@shrishanmuganandini4908]

Thank you sir

[@ActualMLC]

Best ever explanation... salute to you

[@AT-wx2bw]

Excellent explanations on how to mitigate errors and warnings.

[@surojit_ghosh]

Nice to hear that. I hope you will enjoy rest of the videos of this series, specially part 3. Keep watching.

[@win-pe7ud]

great sir, thanks.

[@josephlucas4115]

Good presentation

[@doortry3879]

Nice concept sir

[@kamaldhar2100]

Nice informative video..keep uploading the same

[@surojit_ghosh]

Thanks Kamal, I will post part 2 and 3 next week. Keep watching.

[@kamaldhar2100]

@@surojit_ghosh Hello Surojit, thankyou for update. However, if possible could you also upload a video providing detailed explanation about design and connection philosophy as per Sec.12 Seismic design and STADD. I know you have covered some part of it in Part 3 of Implementation video but detailed video will help.. Thankyou in advance

[@juuliusantony4890]

**WARNING- THE AXIAL COMPRESSIVE STRESS EXCEEDS THE EULER STRESS FOR MEMBER
how this can be resolved plz

[@surojit_ghosh]

Which design code you are using, AISC ASD or IS800:1984? Though I am not sure about the exact reason, the likely reason for the warning is following --
If you look at the AISC equation H1-1 (or similar equation mentioned in IS800:1984), you will find the following terms in the denominator : (1-fa/Fez) and (1-fa/Fey)
Currently in STAAD.Pro, if either of these terms is less than or equal to 0.0, that term is set to 0.0001. This causes the corresponding moment term of the AISC equation to be magnified by 10000. Consequently, the ratio becomes enormous. We did this to bring to the user's attention the fact that this member has an axial stress which exceeds the Euler stress. If you use a bigger cross section or a shorter one (a smaller KL/r) for which the Euler buckling terms Fey and Fez are bigger than the axial stress, this problem will not occur.