According to current codes for the seismic design of structures, the design base shear is calculated by dividing the base shear obtained through modal synthesis in conjunction with an elastic design spectrum by the strength reduction (behavior) factor.
How do engineers calculate Reduction factors in the seismic code?
Is there any method to determine Reduction factors without using Pushover or Nonlinear Response History Analysis?
The only officially prescribed procedure for a seismic reduction factor determination is in the FEMA P695 (2009). It is valid for the North American codes (different for example from the Eurocodes). This and also the procedures proposed by various authors are all based on nonlinear (static or dynamic) analyses.
Since the factor is dependent on the plastic deformation the system can endure, it is very much associated with ductility and energy absorption capacity. Thus, with pushover or some nonlinear static equivalent, one may only assume such factor based on experience. No alternative at all.
I would like to point out another issue here. The conventional design force assessment you talked of has a strong limitation in another sense. This is because stiffness and strength are related for many structural elements and therefore initial estimates of period often appears irrelevant.
For further information on the above, see papers of Paulay, Priestley, Calvi, Kowalsky and many.
When you say "reduction factor", I presume that you mean response factor. If this is the case, Iztok Sustersic is correct about the FEMA P 695. The FEMA P 695 was developed to aid response factor development for new systems. Response factors have evolved since the days of the old Blue Book in which there were some limited studies and a handful of response factors for particular systems. Other response factors were developed based on previous response factors. The FEMA NEHRP Provisions and Commentary provide a history of the development and a road map for future response factors.
- Badges
- Science topic
- Similar topics
- Engineering
- Mechanical Engineering