Seismosoft | Earthquake Engineering Solutions

Dear,

After retrofitting an RC structure I was able to get all the checks for Shear Force Demands/Capacities lower than one for the Collapse Prevention limits of NTC18. However, when I check the PGA_ratio I noticed that the ratio is much lower than one, it is circa 0.5. What can be the reason for that? Any way to fix this?

Thanks a lot in advance,
Enes

Dear E.Veliu,

I wasn't able to reproduce the error you mentioned. Could you please send me your file at z.gronti@seismosoft.com to check it?

Dear E.Veliu,

As i explained you in the email i sent you, this is a known behaviour that might arise in rare cases.
This is caused because one short beam of your structure has a performance ratio a little bit over 1 in pushover analysis step before the Collapse Prevention limit state, then a local shear force reduction happens due to stress redistribution, so the performance ratio turns to be lower than 1 in the next steps and in the Collapse Prevention limit state.
The PGA ratios are computed for the time step of the first check failure, which in this rare case is before reaching the selected limit state.
You may overcome this by just a slight modification of the short beam's section parameters.