Pushover Analysis

Question:

Good Afternoon,


I am trying to run the pushover analysis on a bridge, but was having trouble getting it to run properly. I decided to focus my attention on Bent A; the model for the single pier is attached to this email. I was using the model on the Midas forum found at http://globalsupport.midasuser.com/helpdesk/KB/View/13257123-midas-pushover-analysis for reference. In the model for Bent A I added a unit push load of 1 kip, some arbitrary loads to reach the 20 nodal mass limit for the eigenvalue analysis, and applied the hinge values that we calculated. Generally, the state that we work in likes to use a bilinear type skeleton curve and moment rotation; therefore these values were entered manually. We are trying to determine the maximum displacement point at which the structure collapses, which seems to be what is called the second yield point in MIDAS. This failure point should coincide with the values that we entered for P2 and D2 in the hinge properties. Is there a way to set the analysis stopping point to be the rotational value, because the analysis stop functions in the global control do not seem to stop at collapse? Can the pushover be run for the whole bridge or does it have to be analyzed bent by bent?  







Answer:

FYI. I tried to send this to you at ts@midasuser.com on 10/4/18 and ts@midasit.com on 9/24/18. Not sure if you received the emails because I never got confirmation. I tried sending it through this site, but it wasn't working until I realized my adblocker was preventing it.

Hello,

Sorry I couldn't write back to you before.  The response are as below:
1.  Is there a way to set the analysis stopping point to be the rotational value, because the analysis stop functions in the global control do not seem to stop at collapse?
A:  The bilinear curve defined in midas Civil just considers the first and second slope.  It wouldn't be considering failure at the specified P2, at least for the pushover curve.  However, personally in this case, I'd rather suggest to use the trilinear curve.  In a trilinear curve, we can input the same value for second and third yield, thereby effectively restricting the overall force carrying capacity.
The analysis won't be stopping at collapse, but from hinge yield status, we can judge the collapse.  If it is required to reduce capacity to 0 at collapse, then I'd recommend using the moment rotation with proper hinge length.  This option could be activated as shown in the image below.

2.  Can the pushover be run for the whole bridge or does it have to be analyzed bent by bent?  
A:  This can be done fro entire structure simultaneously. 

Kindly note that now the e-mail address for support are not functional.  New tickets need to be posted on the globalsupport portal as done in this case.  Do let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS
Creation date: 10/17/2018 9:09 PM (dklee@midasit.com)      Updated: 10/18/2018 6:39 AM (dklee@midasit.com)
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Skull Creek (Bent A).mcb
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