Good morning,
I have problem with my steel truss bridge design, i've used member specification release MY;MZ and truss. Then this message came after i am running the analysis.
***WARNING - INSTABILITY AT JOINT 490 DIRECTION = MZ
PROBABLE CAUSE SINGULAR-ADDING WEAK SPRING
K-MATRIX DIAG= 3.4113601E+05 L-MATRIX DIAG= 5.8207661E-11 EQN NO 366
***NOTE - VERY WEAK SPRING ADDED FOR STABILITY
Then i change my member specification release to just MZ, but i am not sure this correct to describe my design with actual connection. Although the warning sign not shown anymore.
How do i have to solve this problem with "Very Weak Spring Added for Stability", do i have to change the direction of release specification member into MZ only or any suggestion regarding my design?. I attach my design file, the first is DESIGN-001-MYMZ.std with release MYMZ and the second is DESIGN-002-MZ. Hope you guys can help me to solve my problem. Thanks in advance!
Kind regards,
Muhammad IqbalDESIGN-001-MYMZ.stdDESIGN-002-MZ.std
These instabilities are reported in your model due to member releases. Changing the full moment releases to partial moment releases should fix this issue. I would recommend 99% moment releases as they work well. This means that 99% of the moment is released but a small amount (1%) is retained (a reasonable assumption since no pinned connection in reality is truly moment-free.) Your input would look like that:
MEMBER RELEASE
1 2 5 6 8 9 11 12 14 15 17 18 20 21 23 24 26 27 29 30 START MPY 0.99 MPZ 0.99
1 2 5 6 8 9 11 12 14 15 17 18 20 21 23 24 26 27 29 30 END MPY 0.99 MPZ 0.99
840 TO 848 869 TO 877 START MPY 0.99 MPZ 0.99
840 TO 848 869 TO 877 END MPY 0.99 MPZ 0.99
Answer Verified By: Muhammad Iqbal
Thank you!! yes its solve the problem with the warning sign. Can i have another question regarding the beta angel.
if i'm input the beta angel 90 degree to my H profile, where its gonna change my local direcation of my H profile, thats it will effect the direction of moment release?
like if i'm using 90 degree angel that will rotate the member, so if i want to release the moment Y (according to global direction) instead releasing MY, i should release the MZ. This situation if i only want to release moment at Y direction (according to global direction)
Member releases are applied with respect to member's local axis. You can turn on local axis by click Shift + O in your keyboard. Green color represents local Z, red - local Y and blue - local X.