topic Re: Equivalent Static Force Method results seem a bit off... in Robot Structural Analysis Forum

Equivalent Static Force Method results seem a bit off...

Anonymous — Fri, 27 Oct 2017 20:22:32 GMT

Hi everyone,

I modelled this 2 storey building with loads applied to it and ran a Equivalent Static Force Procedure for the seismic calculations. The data that I've gotten doesn't seem to make much sense when I perform the same calculations using RSA's data. Please refer to the attachments for more info.

According to my hand calculations when using RSA's own data for input, I seem to be getting different results when compared to RSA's result. I use the same values for the shear calculation as shown in "Hand Calcs" document and yet the image file shows the base shear as 63.04kips while my hand calculations show 94.55kips. Is this a bug?

Re: Equivalent Static Force Method results seem a bit off...

Anonymous — Fri, 27 Oct 2017 20:23:23 GMT

Model file attached if needed.

Re: Equivalent Static Force Method results seem a bit off...

marcinrakus — Mon, 30 Oct 2017 12:32:50 GMT

Hi,

There is a limitation of base shear according to 4.1.8.11 (2) (I have a copy of NBC2005, but maybe the limitation remains)

Regards,

Marcin

Re: Equivalent Static Force Method results seem a bit off...

Anonymous — Mon, 30 Oct 2017 12:57:08 GMT

Hi marcinrakus,

Applying the values for the max shear does not get me any where close to the 63.04kip base shear. That highlighted equation gives me 48.49kip when I do it by hand....

Am I missing something..??? And yes, that limitation still applies in the NBCC 2010 Code.

Re: Equivalent Static Force Method results seem a bit off...

marcinrakus — Mon, 30 Oct 2017 14:31:19 GMT

My calculations:

Vmax = 2 / 3 * S(0.2) * Ie * W / Rd / Ro = 2 / 3 * Fa * Sa(0.2) * Ie * W / Rd / Ro = 2.0 / 3.0 * 1.3 * 0.17 * 1.0 * 834.35 / 1.3 / 1.5 = 63.72

Regards,

Marcin

Re: Equivalent Static Force Method results seem a bit off...

DennisVDijk — Mon, 30 Oct 2017 15:59:45 GMT

Hello Omusafer,

I think u shoul not convert case 1 in the load to mass conversion. the mass of your stucture wil be counted twise.

when you cut out case 1 your mass wil be lower.

maybe this site will help (input in kN and meters):

http://www.jabacus.com/engineering/load_2005/seismicload.php

Maybe this would help.

Re: Equivalent Static Force Method results seem a bit off...

Anonymous — Mon, 30 Oct 2017 17:11:17 GMT

Hello Dennis,

Thank you for your input. I checked it without its own self weight and it does add its own dead weight into the analysis. Thank you once again for pointing it out.