Sustained part of the governing load combination in ßdns

[Blackstar123]

Governing Seismic combination for column design is this:

Pu = (1.2 + 0.2Sds)D + 0.5L + Eh

As per ACI 318 Section 6.6.4.4.4.

My question is what we should take as sustained part of the load combination for calculating βdns,
1.2D or (1.2 + 0.2Sds)D.

I usually take it as 1.2D, because as I understand, 0.2 Sds D is only accounting for the vertical seismic force effect and is not really a sustained load. Therefore, βdns should be calculated as 1.2D / Pu.
I’ll appreciate if someone could confirm my reasoning.

Thanks.

 

[HTURKAK]

If you look the notations , the definition of

βdns =ratio used to account for reduction of stiffness of columns due to sustained axial loads


Clause 6.6.4.4.4 where βdns shall be the ratio of maximum factored sustained axial load to maximum factored axial load associated with the same load combination and I in Eq. (6.6.4.4.4c) is calculated according to Table 6.6.3.1.1(b) for columns ..
and walls.

IMO, the code is self explanatory and sustained load should be understood as dead load.

 

[Blackstar123]

Thank you hturkak for your response. Just wanted to confirm. Some of my colleagues were using total factor of dead load as sustained load for this combination.