The
δs factor is an amplifier to account for the P-Δ effects (large P-delta, second order effects caused by relative displacement of the member ends). The
δs factor is calculated for each rigid diaphragm, and differs for each combination.
δs is given as:
| Eq. C4.4.2.3(i) |
where
| ΣN* | = | total vertical load supported by story using AS/NZS load combinations, including gravity column loads |
|
ΔS
| = | the interstory drift (calculated per load combination) and it is based on the drift at the center of diaphragm masses |
| ΣV* | = | the story/diaphragm shear (calculated per load combination) |
| hs | = | the story height |
The δs factors are found in such a way that diaphragm shear forces and story drift values are first resolved along member local system and then the δs factors are calculated according to Eq. (C4.4.2.3(i)).
Note: AS 4100 mandates that if
δs exceeds 1.4 the user should consider applying a second order analysis according to the provisions of Appendix E. It is the engineers responsibility to select P-Delta for the analysis in the event that situation occurs.
