eqrst_disp
Structural
Good day!
I would like to know your insights on some questions I have with linear dynamic analysis with my current project:
Project description:
1. Structure analyzed using seismic provisions from UBC 1997
1. 2-storey, Irregular Structure (Torsional Irregularity) per UBC 1997
2. 5 km from nearest fault line (Type A source), Sc soil type
3. Soil embankment at left side of the structure (applied on shear walls, 0.35m thk, as lateral earth pressure (EP))
After 20 iterations using Eigen Value analysis (subspace iteration), I got 97%, 94%, 68% 94%, 96% mass participation for Tran X, Tran Y, Rot X, Rot Y and Rot Z (Torsion) respectively,
Questions:
1. I got 0.4251 sec (Method B) as structure period for the mode 1 (Rot Z), shall I use it as User-input for the structure period instead of the limit 1.3*(period from Method A, Ct*h^3/4)?
2. Is there a code requirement/general rule that the first mode shapes (usually with larger % mass participation) after the analysis should have [governing] translation instead of rotations first? For example, mod 1 tran-X, mod 2 Tran-Y, mod 3 Rot-Z? For my case, I got Mod1 RotZ, Mod2 TranX, Mod RotX. Does this mean I have errors with my analysis or is this has something to do with my framing system? Is there a way to check whether the obtained mode shapes are correct?
3. Shall I adjust the seismic load direction factor to the equivalent excitation angle while applying the 100:30 EQ provisions? or shall I use either the seismic load direction factor or the 100:30 provision separately?
Appreciate your responses! Many thanks!
I would like to know your insights on some questions I have with linear dynamic analysis with my current project:
Project description:
1. Structure analyzed using seismic provisions from UBC 1997
1. 2-storey, Irregular Structure (Torsional Irregularity) per UBC 1997
2. 5 km from nearest fault line (Type A source), Sc soil type
3. Soil embankment at left side of the structure (applied on shear walls, 0.35m thk, as lateral earth pressure (EP))
After 20 iterations using Eigen Value analysis (subspace iteration), I got 97%, 94%, 68% 94%, 96% mass participation for Tran X, Tran Y, Rot X, Rot Y and Rot Z (Torsion) respectively,
Questions:
1. I got 0.4251 sec (Method B) as structure period for the mode 1 (Rot Z), shall I use it as User-input for the structure period instead of the limit 1.3*(period from Method A, Ct*h^3/4)?
2. Is there a code requirement/general rule that the first mode shapes (usually with larger % mass participation) after the analysis should have [governing] translation instead of rotations first? For example, mod 1 tran-X, mod 2 Tran-Y, mod 3 Rot-Z? For my case, I got Mod1 RotZ, Mod2 TranX, Mod RotX. Does this mean I have errors with my analysis or is this has something to do with my framing system? Is there a way to check whether the obtained mode shapes are correct?
3. Shall I adjust the seismic load direction factor to the equivalent excitation angle while applying the 100:30 EQ provisions? or shall I use either the seismic load direction factor or the 100:30 provision separately?
Appreciate your responses! Many thanks!
https://files.engineering.com/getfile.aspx?folder=7c0b2b0d-700c-454e-8ecc-4420fcfba309&file=Iso1.PNG
