Seismic Capacity Design of RC frames and environment-induced degradation of materials: Any concern?

摘要

The Capacity Design approach emerged in the second half of the last century and is currently adopted by all the modern codes of practice for construction in seismic areas. It is based on the fundamental concept that the structure under consideration should not exhibit brittle failure modes, as brittle members or mechanisms are designed to be stronger than the maximum expected stresses they possibly get from the adjacent ductile members or mechanisms. This condition is generally imposed at the design stage without considering any degradation in material properties possibly due to the environmental agents. Although structural codes for RC structures usually provide practitioners with sound criteria intended at limiting the development of detrimental degradation phenomena, they have been never assessed against the possible loss in over-strength of brittle failure modes due to environment-induced degradation phenomena possibly occurring during the service life of the structure. This study aims to answer the question stated in the title and, in the authors' knowledge, is one of the first attempts to embrace two traditionally distant research fields, such as Earthquake Engineering and Material Science. Thus, the paper investigates the time evolution of the possible failure modes in beams due to the premature degradation of steel stirrups and longitudinal reinforcement during the service life of RC structures. Both material properties and environmental conditions are taken into account to assess durability and structural safety in seismically designed RC beams and the possible consequences of material degradation on their expected failure modes under seismic actions.