Overstrength Factors

Q: How do I include the overstrength factor(s), Ωo in the ASCE 7 load combinations?

1)Open the ''Load Cases & Combinations'' dialog box. Under the ''Base'' tab, select the ''Edit Parameters of Edition'' option. The default values are set to 2.0 (Image 1)#image@033442#Case A: To apply the same factor in the X and Y directions, use the generic (no direction) overstrength factor, Ωo.Case B: To apply different factors in each direction, use the overstrength factor X and Y, Ωo,x and Ωo,y. The generic factor, Ωo in the first row is not used.2) Under the ''Load Cases'' tab, create a seismic load case with Qe as the ''Action Category''. Next, select the ''Additional Settings'' tab and pick the direction (Image 2)#image@033443#'''Note:''' When neither or both directions are activated under the '''same''' load case, the generic overstrength factor, Ωo is used. Create a '''separate''' load case to apply the individual factors, Ωo,x and Ωo,y. 3) Under the ''Design Situations'' tab, select the applicable overstrength Design Situation Type. Both LRFD and ASD methods are available (Image 3)#image@033444#4) In the ''Load Combinations'' tab, verify that the correct factor(s) has been applied. Factors are also shown in the ''Result Combinations'' tab, if applicable. Click OK to exit (Image 4)#image@033445#5) The final step is to assign the applicable limit state type to the overstrength design situation. For members '''without''' assigned seismic configuration, select the "Strength limit state" (LRFD or ASD) as the ''Limit State Type''. For members '''with''' assigned seismic configuration, use “Earthquake limit state – overstrength” (LRFD or ASD) [available in the future release] (Image 5)#image@033446#

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FAQ 005294 | How do I include the overstrength factor(s), Ω-o in the ASCE 7 load combinations?

FAQ Explanatory Video

01
Edit Parameters of Edition

02
Create Seismic Load Case

03
Overstrength Design Situations

04
Verify the Overstrength Factor

05
Overstrength Limit State Type

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10/07/2022

005294

Cisca Tjoa

General

RFEM 6

Steel Design for RFEM 6

Steel Structures

Buildings

Structural Analysis

Dynamic and Seismic Analysis

ANSI/AISC 360

ASCE 7

How do I include the overstrength factor(s), Ω_o in the ASCE 7 load combinations?

Answer

1) Open the Load Cases & Combinations dialog box. Under the Base tab, select the Edit Parameters of Edition option. The default values are set to 2.0 (Image 1)

Edit Parameters of Edition

Case A: To apply the same factor in the X and Y directions, use the generic (no direction) overstrength factor, Ω_o.

Case B: To apply different factors in each direction, use the overstrength factor X and Y, Ω_o,x and Ω_o,y. The generic factor, Ω_o in the first row is not used.

2) Under the Load Cases tab, create a seismic load case with Qe as the Action Category. Next, select the Additional Settings tab and pick the direction (Image 2)

Create Seismic Load Case

Note: When neither or both directions are activated under the same load case, the generic overstrength factor, Ωo is used. Create a separate load case to apply the individual factors, Ω_o,x and Ω_o,y.

3) Under the Design Situations tab, select the applicable overstrength Design Situation Type. Both LRFD and ASD methods are available (Image 3)

Overstrength Design Situations

4) In the Load Combinations tab, verify that the correct factor(s) has been applied. Factors are also shown in the Result Combinations tab, if applicable. Click OK to exit (Image 4)

Verify the Overstrength Factor

5) The final step is to assign the applicable limit state type to the overstrength design situation. For members without assigned seismic configuration, select the "Strength limit state" (LRFD or ASD) as the Limit State Type. For members with assigned seismic configuration, use “Earthquake limit state – overstrength” (LRFD or ASD) [available in the future release] (Image 5)