In his name is the judge
Hi
I think the best way to assign the nonlinear effect of steel components like beams that to model it with a plastic hinge.
So To build a nonlinear model of a one-story steel structure I use the Modified Ibarra – Krawinkler model to model my beam. In fact, I model a beam with two hing (zero length element) at the start and end and one elastic beam in the middle.
I used material developed by Lignos and Krawinkler named uniaxial material Bilin and here is more information about this material
https://opensees.berkeley.edu/wiki/index.php/Bilin_Material
After all, when I extract the output belonging to the stress-strain of this material under seismic loading like Kobe I get something like this diagram. (kobe0.5g) based on
"Ibarra L.F., and Krawinkler, H. (2005). “Global collapse of frame structures under seismic excitations”, Rep. No. TB 152, The John A. Blume Earthquake Engineering Center, Stanford University, Stanford, CA."
named article and this diagram (ref1) the stress-strain shows the right modeling and performance. consider that my record is near fault and the diagram of reference also belongs to near-fault loading.
If I use the 1g scale for the Kobe record I get this diagram (kobe1g) and here is the diagram of the 2g scale for the Kobe record (kobe2g) So my best shot is this when the record multiply and the ground accel become higher the material reaches the capacity of its deterioration very more quickly(In fact after a short time the strain of material switch between 1e10 an-1e10 and strain is between about -2 and 2) but it's a little non-sens for me in the other hand there is one benchmark( in the reference is named it before this benchmark is for standard loading) diagram for this material stress-strain (logos) and my diagram is different with it.
In the end here are the 1M$ questions
1- why when I give more scale to record the diagram become like that?
2- and why my diagram is different from the benchmark stress-stress of material?
Any help is greatly appreciated.
Take refuge in the right.
Dear Mohammad,
Please note that pre-cap plastic deformation (rotation) capacity is relative, not absolute. It represents the distance between the yield and maximum moments. Although in the two diagrams the absolute maximums are different, the distance between the yield and maximum moments are the same.
Regarding your second question, please make sure you assigned monotonic backbone parameters with some cyclic deterioration. From the rapid in-cycle deterioration (softening) in the diagrams you have sent, I suspect you have assigned the first-cycle (cyclic) backbone parameters.
BR.
A plastic hinge in a steel beam typically occurs at the point of maximum moment in the beam, where the steel has reached its maximum allowable plastic deformation. However, if a plastic hinge does not form at the expected location, it could be due to a number of factors, such as an incorrect design of the beam, improper fabrication or installation of the beam, or a lack of consideration for the effects of environmental factors such as temperature and humidity. Additionally, if a plastic hinge forms prematurely, it could indicate that the beam is overloaded or that the steel has a lower yield strength than expected. To understand the reason why a plastic hinge for steel beam didn't work, it would be necessary to examine the specific details of the beam and the conditions under which it was loaded.
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