I am interested in learning a bit about the background of how the behaviour factors, which are used in Eurocode 8 to calculate the design base shear for a structure, were developed. As I understand it, and please correct me if I am wrong, the factors implcitly comprise several different components:
- first, a reduction in seismic forces to account for system ductility in accordance with the equal displacement principle,
- secondly, a further reduction to account for overstrength of the structural elements,
- and thirdly, some component that accounts for the performance for the structural system.
Can anyone enlighten me as to how the values in the Eurocode were obtained and/or point me towards some appropriate literature. I would also be content with information pertaining to the R valued used in the US as this is somewhat similar.
R value in IS code or in US is basically Response Reduction factor.This is a factor which depends on how the building is responding to earthquake in terms of ductility, reserve of strength and some others.
You may read one interesting article as attached
The behavior fact in EC8 and other seismic codes is aimed to reduce the full elastic demand in a structure in the event of an earthquake. The seismic energy is dissipated through an inelastic response of structure when it is well designed. Therefore, it considers the displacement demand of the structure in the event of seismic activity and compares the displacement capacity. Therefore, ductility, first crack strength, fracture characteristics are important. Most of the seismic codes defined three philosophies for design; minor, moderate, and strong. In moderate and strong earthquakes we allow some cracks in the structure (refer to attached image file). Therefore, the behavior factor is mainly reflecting that design philosophy.
q-factors(EC8) or R-values in US codes or elsewhere, are essentially code -consensus numbers based on the performance during the past earthquakes. A lot of literature about R-values is available in ASCE structural journal . A somewhat recent attempt to 'estimate' R-values can be found in FEMA p695.
You may also find more information in this paper
Article Ductility and overstrength in seismic design of reinforced c...
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