Design of concrete structures

As noted in earlier chapters, EC8 aims to ensure life safety in a large earthquake together with damage limitation following a more frequent event. Whilst the code allows these events to be resisted by either dissipative (ductile) or non-dissipative (essentially elastic) behaviour, there is a clear preference for resisting larger events through dissipative behaviour. Hence, much of the code is framed with the aim of ensuring stable, reliable dissipative performance in predefined ‘critical regions’, which limit the inertial loads experienced by other parts of the structure. The design and detailing rules are formulated to reflect the extent of the intended plasticity in these critical regions, with the benefits of reduced inertial loads being obtained through the penalty of more stringent layout, design and detailing requirements.This is particularly the case for reinforced concrete structures where such performance can only be achieved if strength degradation during hysteretic cycling is suppressed by appropriate detailing of these critical zones to ensure that stable plastic behaviour is not undermined by the occurrence of brittle failure modes such as shear or compression in the concrete or buckling of reinforcing steel.With this in mind, three dissipation classes are introduced: • Low (ductility class low (DCL)) in which virtually no hysteretic ductility is intended and the resistance to earthquake loading is achieved through the strength of the structure rather than its ductility. • Medium (DCM) in which quite high levels of plasticity are permitted and corresponding design and detailing requirements are imposed. • High (DCH) where very large inelastic excursions are permitted accompanied by even more onerous and complex design and detailing requirements.