values to seismic weight per ASCE 7-16 to comply with combination values of dead load?

[quasiblu]

Hi all,

I see that reductions are set for masses in Section 12.7.2, ASCE 7-16 (Effective seismic weight), that's fine, it's related to the likelyhood to have those loads during earthquakes.
It's the combinations in Sections 2.3.6 that are not fully clear to me. If I am requested to consider, for example, a vertical dead load design value equal to 1.2*dead_load (combination 6) I would say I have to consider the 1.2 amplification also in the dead seismic weight (mass from dead loads) because if I have that dead load, well the earthquake will shake all of it. I see there is no custom to do that around me, nor I find in the code any further explanation.
So, in lack of an explicit statement, I would go with a more physically meaningful interpretation (hence if dead vertical times 1.2, then also dead mass times 1.2 to be used in the seismic analysis).
If, otherwise, it is stated somewhere not to apply the 1.2 amplification to the seismic weight, ok, it's all just a design convention in the end, that's also fine. But it should be stated.

Have a good one.

 

[HTURKAK]

The answer is NO!...


Look to C 12.7.2
..........When a building vibrates during an earthquake, only that
portion of the mass or weight that is physically tied to the
structure needs to be considered as effective. Hence, live loads
(e.g., loose furniture, loose equipment, and human occupants)
need not be included....

combination 6 and 7 are for to maximize or minimize load effects for individual member.

 

[quasiblu]

Well dead loads are normally physically tied to the structure.
That section C 12.7.2 speaks about live loads and, ok, for these it make sense to some extent to consider only a part of the vertical load as seismic mass.

 

[HTURKAK]

Well dead loads are normally physically tied to the structure.
That section C 12.7.2 speaks about live loads and, ok, for these it make sense to some extent to consider only a part of the vertical load as seismic mass.

the seismic analysis produce Eh values and these values may represent bending moment, axial force and interaction effects. Consider beam -column elements (M+N) the axial force some cases favorable and some cases unfavorable. These combinations are for investigating most unfavorable effects from seismic loads.
Combination 6 (1.2D + Ev +Eh + L +0.2S ) When the vertical load is unfavorable for the design effect and
Combination 7 ( 0.9D − Ev + Eh ) when the vertical load is favorable .

 

[quasiblu]

Thanks for your replies.