Vertical component of seismic load - NBCC

RE: Vertical component of seismic load - NBCC

Suvadeep Acharjee — Mon, 13 Dec 2021 10:32:36 GMT

Yes your understanding is correct. The program is not capable of generating equivalent static seismic load along vertical direction for NBCC/NRC 2010 codes. For response spectrum loading program expects user to provide time-acceleration (spectrum type = acceleration) or time-displacement (spectrum type = displacement) pairs. In the data you have provided its not clear what the unit of function S(T) is and you need to check whether data is for acceleration spectra or displacement spectra. If it is for acceleration spectra then just enter the time-acceleration pairs inside the response spectrum loading dialog box. Factors for the input spectrum to be applied in X, Y, & Z directions. In picture you attached direction factor is used as 1.0 for vertical Y direction so if you want to consider 66.666% in vertical direction you should change it to 0.66666. If the acceleration data available for response spectrum is in terms of g's (i.e. acceleration due to gravity) then one needs to account for it. In STAAD we have SCALE parameter which is the factor by which the spectral data will be multiplied for factoring g's to length/sec2 units. This SCALE parameter should be input according to current unit system i.e. it may be 9.81 in m/s2 unit system or 32.2 ft/s2 unit system.

RE: Vertical component of seismic load - NBCC

Mahmoud Hassan — Mon, 13 Dec 2021 09:09:38 GMT

Thanks a lot for your reply. I understand that Staad Pro is capable of generating equivalent static seismic loads in vertical direction using other code such as IS 1893 (see attached Staad Pro file). However, it is not capable of doing that using NBCC/NRC 2010, please confirm if my understanding is right ?

Also I a trying now to use Response Spectrum to generate forces in 3 direction. I am confused what information is required at (Period Acceleration section), and Scale ? (see attached photo).

Below is the design spectral acceleration values of S(T) for the site.

Thanks a lot communities.bentley.com/.../4885.Demo_5F00_1.STD

Period (T), s	S(T)
0	1.1400
0.2	1.1400
0.5	0.7260
1	0.4235
2	0.1905
5	0.0459
10	0.0118
15	0.0118

RE: Vertical component of seismic load - NBCC

Suvadeep Acharjee — Mon, 13 Dec 2021 07:09:07 GMT

The load generation facility has been developed to generate equivalent static seismic loads per NBCC/NRC 2010 along horizontal directions only. However in your model Load Case 3 attempts to generate loads along vertical direction hence the error. You can manually generate vertical component of seismic load in Load Case 3 in Y direction as nodal joint loads instead of NRC LOAD to avoid the error. Amongst horizontal directions (i.e. X & Z) check which direction base shear is more (Z direction in this model) then use PRINT LOAD DATA command to print the joint loading data along that direction in output file. Copy the loading data in excel and apply factor 0.66666 and then apply as joint loads in Load Case 3.communities.bentley.com/.../NRC-2010.STD