hapali
Structural
- Jul 20, 2012
- 2
Hi guys,
We have been assigned to do non-linear analysis of an existing structure where the blast loads have increased something like 5 times. I have modelled the steel structure in abaqus as a beam model and assigned it with profiles and sections. In the structure the connections are mostly bolted connections. This gave a challlenge because we first had to calculate the lowest capacity (either shear, axial or moment) at each joint and then used this capacity together with the yield stress of the material to come up with a corresponding cross section area of the joint, we then modelled this as a "dummy element" in all the connections of the structure.
Now my questions is in regards to the material input. I have defined a bi linear material curve with the following properties:
Elastic:
210000 - 0.2
Plastic:
355 - 0
371 - 0.02
The reason I only define 2 % plastic strain is that beacuse in reality the bolted connections cant take that much deformation, and the platic strain is restricted by the maximum elongation of the bolted connections.
What happens after it reaches 371 MPA? I want the the elements that reach 371 MPA to stop taking any more stress. When I have modelled in explicit I used element deleteion but this isnt available in Abaqus standard. I just want to assure that when the connections reach the maximum plastic strain, they fail and dont take any more stress.
Also, my model runs and finishes but I get lots of warning messages, such as the ones below that repeat thoughout the whole analysis:
***WARNING: THE SYSTEM MATRIX HAS 6 NEGATIVE EIGENVALUES.
EXPLANATIONS ARE SUGGESTED AFTER THE FIRST OCCURRENCE OF THIS MESSAGE.
***WARNING: THE STRAIN INCREMENT HAS EXCEEDED FIFTY TIMES THE STRAIN TO CAUSE
FIRST YIELD AT 320 POINTS
***WARNING: THE STRAIN INCREMENT IS SO LARGE THAT THE PROGRAM WILL NOT ATTEMPT
THE PLASTICITY CALCULATION AT 12 POINTS
***WARNING: THE PLASTICITY/CREEP/CONNECTOR FRICTION ALGORITHM DID NOT CONVERGE
AT 52 POINTS
***NOTE: MATERIAL CALCULATIONS FAILED TO CONVERGE OR WERE NOT ATTEMPTED AT ONE
OR MORE POINTS. CONVERGENCE IS JUDGED UNLIKELY.
***WARNING: CONVERGENCE JUDGED UNLIKELY. INCREMENT WILL BE ATTEMPTED AGAIN
WITH A TIME INCREMENT OF 8.44703E-04
I would really appreciate if anyone can help me clarify thes issues. Thanks alot.
We have been assigned to do non-linear analysis of an existing structure where the blast loads have increased something like 5 times. I have modelled the steel structure in abaqus as a beam model and assigned it with profiles and sections. In the structure the connections are mostly bolted connections. This gave a challlenge because we first had to calculate the lowest capacity (either shear, axial or moment) at each joint and then used this capacity together with the yield stress of the material to come up with a corresponding cross section area of the joint, we then modelled this as a "dummy element" in all the connections of the structure.
Now my questions is in regards to the material input. I have defined a bi linear material curve with the following properties:
Elastic:
210000 - 0.2
Plastic:
355 - 0
371 - 0.02
The reason I only define 2 % plastic strain is that beacuse in reality the bolted connections cant take that much deformation, and the platic strain is restricted by the maximum elongation of the bolted connections.
What happens after it reaches 371 MPA? I want the the elements that reach 371 MPA to stop taking any more stress. When I have modelled in explicit I used element deleteion but this isnt available in Abaqus standard. I just want to assure that when the connections reach the maximum plastic strain, they fail and dont take any more stress.
Also, my model runs and finishes but I get lots of warning messages, such as the ones below that repeat thoughout the whole analysis:
***WARNING: THE SYSTEM MATRIX HAS 6 NEGATIVE EIGENVALUES.
EXPLANATIONS ARE SUGGESTED AFTER THE FIRST OCCURRENCE OF THIS MESSAGE.
***WARNING: THE STRAIN INCREMENT HAS EXCEEDED FIFTY TIMES THE STRAIN TO CAUSE
FIRST YIELD AT 320 POINTS
***WARNING: THE STRAIN INCREMENT IS SO LARGE THAT THE PROGRAM WILL NOT ATTEMPT
THE PLASTICITY CALCULATION AT 12 POINTS
***WARNING: THE PLASTICITY/CREEP/CONNECTOR FRICTION ALGORITHM DID NOT CONVERGE
AT 52 POINTS
***NOTE: MATERIAL CALCULATIONS FAILED TO CONVERGE OR WERE NOT ATTEMPTED AT ONE
OR MORE POINTS. CONVERGENCE IS JUDGED UNLIKELY.
***WARNING: CONVERGENCE JUDGED UNLIKELY. INCREMENT WILL BE ATTEMPTED AGAIN
WITH A TIME INCREMENT OF 8.44703E-04
I would really appreciate if anyone can help me clarify thes issues. Thanks alot.
