Seismic combinations
Automatic seismic combinations are available in projects calculated according to the IBC code.
Non orthogonal seismic components - e.g. 100% EQX + 30% EQY - may be taken into account using appropriate settings in the seismic action load group.
Make sure, that all relevant seismic load cases are assigned to the same load group.
To take into account non orthogonal seismic components, use a seismic load group with the relationship "Together".
To ignore non orthogonal seismic components, use a seismic load group with the relationship "Exclusive".
Input of Load case combination
There are two types of Seismic combinations - "ASCE-7 (LRFD) - seismic" and "ASCE -7 (ASD) - seismic" available.
Additional properties are displayed for these two combination types in the combination dialog:
Include redundancy factor ρ - ASCE 7-22 Section 12.4.2.1
Use aredundancy factor for horizontal seismic loading. It will be used in seismic combinations according to ASCE 7.
If the checkbox "Include redundancy factor ρ" is ON, the coefficient "ρ" in the combination schema is set as 1.3. If the checkbox is OFF the coefficient "ρ" in the combination schema is set as 1.0.
Add vertical component to combination - ASCE 7-22 Section 12.4.2.2
Take the vertical component of seismicity into account. It will be used in seismic combinations according to ASCE 7.
If the checkbox "Add vertical component to combination" is ON, the coefficient "SDS" in the combination schema is taken from IBC seismic spectrum. If the checkbox is OFF, or such load case is not present, the coefficient "SDS" in the combination schema is set as 0.
Combinations - ASCE 7-22 Section 12.4
The Combo-box can be set to: "Exclude overstrength", "Create only overstrength" and "Include overstrength in all"
Determines which seismic combinations according to ASCE-7 will be generated.
Factor Ω0 - ASCE 7-22 Section 12.4.3.1
Overstrength factor value for horizontal seismic loading. It will be used in seismic combinations according to ASCE 7.
The value of the "Overstrength factor" is applied in the combinations as coefficient "Ω0 with default value 3.0".
Combinations
After adding of load cases to the combination, SCIA Engineer automatically generates combinations accordingly.
In combination schema Qe is represented as a load group type E.
LOAD COMBINATIONS FOR STRENGTH DESIGN (LRFD) - seismic
When a structure is subject to seismic load effects, the following load combinations, given by Section 2.3.6, shall be considered.
If "Combinations" is set to "Exclude overstrength":
"Combinations" is set to "Create only overstrength":
"Combinations" set to "Include overstrength in all" will generate combinations from both sets listed above.
LOAD COMBINATIONS FOR ALLOWABLE STRESS DESIGN (ASD) - seismic
When a structure is subject to seismic load effects, the following load combinations, given by Section 2.4.5, shall be considered.
If "Combinations" is set to "Exclude overstrength":
"Combinations" is set to "Create only overstrength":
"Combinations" set to "Include overstrength in all" will generate combinations from both sets listed above.
An additional info on live load reduction valid for all IBC combinations may be found in Live Load Reduction chapter.