Limitations of the equivalent lateral force procedure (ASCE7 &EC8) 2

[Ahmed A. Alamin]

Hi, i'm kindda new to ASCE7, i was wondering what are the limitations of ELF procedure, i.e when not to use it. In EC8, it is stated that only in case of vertical irregularity you shouldn't use the simplified lateral force method. Honestly, i'm not fully convinced with this, so i started looking for similar clauses in other standrds. Can anyone help me? Or explain to me why Eurocode 8 allowed this?

 

[r13]

 

[JoshPlumSE]

The ELF method in ASCE-7 is based on the assumption that a single flexural mode controls the seismic response in each direction. Therefore, anything that would make this assumption invalid means that the ELF method is invalid.

Horizontal irregularities described in table 12.3-1: Generally speaking these irregularities mean that torsion becomes a big enough deal that the ELF assumption isn't valid.

Vertical Irregularities of table 12.3-2: These are mass and stiffness irregularities that would suggest more than one flexural mode would not adequately capture the dynamic response.