Infill panel forces

[FMoreira]

Dear All,

Please consider a 4 storey 2D infilled RC frame, static pushover analysis model.

For a certain level of displacement (instant of analysis) and for the 1st storey, I have estimated the total shear force supported by the infill panels by subtracting the comulative V3 force on the columns of that storey from the total shear force given by the pushover curve for the instant under analysis.
My question: how can I find the same estimate for the upper storeys (2, 3 and 4)? To find comulative V3 force on the columns on the upper storeys poses no difficulty. But I can't find results for the total shear force on the upper storeys.

Additionally, I can't seem to find a good agreement bewteen the above referred estimate for the total shear force supported by the infill panels on the 1st storey and the results given on the "Infill Panel Forces" tab, after converting to the horizontal direction the diagonal forces on the compressed struts. I'm probably doing something wrong. Can you please advise?

Your help is much appreciated, whenever you can. Thank you.
My best regards.
RFM

[seismosoft]

Similarly, to what you did at the ground storey you could subtract the externally aplied loads from the columns shear forces.
Regarding the differences between the external and internal forces, you need to also consider the two stuts under tension (if they have a tensile strength larger than zero), as well as the two shear struts.
Seismosoft Support

[FMoreira]

Dear Seismosoft Support,

Thank you for your swift answer.

Indeed, for the upper storeys, I can subtract the comulative V3 force on the columns of the selected storey and subtract it from the externally applied loads down to that storey. This will work well for static pushover analysis. Might be difficult to implement for dynamic time-history analysis, though.

Anyway, the main goal of my query was to understand well how to obtain the global horizontal shear force on a infill panel from the results given on the "Infill Panel Forces" tab. Here's a numerical example to see if I understood you correctly:

Numerical example (static pushover analysis model, right-to-left loading):
Total storey shear = 345 kN
Comulative V3 force on storey RC columns: 105 kN
Estimated shear force on storey infill panel (only 1 panel exists): 345 - 105 = 240 kN
Infill panel dimensions: Lm = 2,30 m (length); hm = 2,20 m (height); hence, Teta angle = 43,73º
Strut 1 force = -52,80 kN
Strut 2 force = -53,51 kN
Strut 3 force = 0
Strut 4 force = 0
Shear link 1 force = -78,52 kN
Shear link 2 force = 80,57 kN (positive, why??)
So, (52,80 + 53,51) x cos Teta + 78,52 + 80,57 = 235,91 kN, which compares well with the above estimate of 240 kN.
Agreed?

Thank you.

[FMoreira]

One last question (if I may) regarding the capacity of shear links 1 and 2, after analysing their hysteretic curves:

- The capacity of Shear link 1 seems to be governed only by Crisafulli's (1997) Expression 8.17, as the hysteretic curve varies linearlly until it reaches the limit value given by that expression and then remains constant;

- The hysteretic curve of Shear link 2 seems to be governed by Crisafulli's (1997) expressions 8.14 and 8.15. showing linear variation until the limit value given by Expression 8.14 is reached, followed by the drop corresponding the the loss of the initial bond-shear strength, and then varying non-linearly until the limit value given by Expression 8.15 is reached (in correspondence with the capacity of the compressed struts 1 and 2).

I don't understand this separation regarding the governing of the capacity of shear links 1 and 2. Can you help shed some light over this, please?

Thank you.
My best regards,
RFM

[seismosoft]

Indeed your calculations are right. Note the internal offsets of the infill panel element in the calculation of the theta angle. The two shear links have opposite signs, because in the first case the forces are transferred to the infill panel and the second from the infill.
The two shear links have the same curve which is defined in the elements classes module.
Seismosoft Support

[FMoreira]

Thank you for your support. It is highly appreciated.

Best regards,
RFM