Civil Engineering Association

MULTIPLE EARTHQUAKE EFFECTS ON DEGRADING REINFORCED CONCRETE STRUCTURES

Multiple earthquakes occur at many regions around the world where complex fault
systems exist. These fault systems usually do not relieve all accumulated strains at once
when the first rupture takes place. Therefore high stresses form at different locations
causing sequential ruptures until the fault system is completely stabilized. The sequential
ruptures along the fault segment(s) lead to multiple earthquakes which are often hard to
distinguish them as fore-, main- and after-shocks, or a sequence of earthquakes from
proximate fault segments.
Field investigations reported failure of structural systems under repeated earthquakes,
especially where structural retrofitting was not provided due to the short time frames
between the successive shaking. In most failure cases the reported damage is mainly due
to dramatic loss of stiffness and strength of structural elements as a result of material
deterioration under repeated earthquake loadings. Deterioration effects are obvious in
structures that experienced main-shock aftershock earthquake sequence and were able to
withstand the main-shock however they collapsed in the smaller aftershock.
Limited research has addressed the seismic behavior of structures subjected to multiple
earthquakes. Repeated shaking induces accumulated damage to structures that affects
their level of stiffness and strength and hence their response. Given the complexity of
depicting the degrading behavior of structures using the current numerical tools, previous
researchers used simplified approaches to compensate for the absence of important
numerical model features of stiffness and strength degradation, alongside pinching of
load-displacement loops. Moreover ground motion sequences used in previous studies
were randomized and hence the characteristics of ground motions effects on the response