Seismic sequence effects on three-dimensional reinforced concrete buildings Maria Hatzivassiliou a , George D. Hatzigeorgiou b,n a Freelance consulting engineer, Thessaloniki, Greece b School of Science and Technology, Hellenic Open University, Patras, Greece article info Article history: Received 21 January 2015 Accepted 7 February 2015 Keywords: Three-dimensional seismic analysis Reinforced concrete buildings Multiple earthquakes abstract Repeated earthquakes strongly affect the inelastic response of structures and cause in many cases more adverse effects in comparison with the corresponding single ground motions, such as the accumulation of structural and non-structural damage as well as the increment of deformation demands. Numerous research studies have been recently published in the pertinent literature to investigate this phenomenon but most of them are limited either to single-degree-of-freedom (SDOF) systems or to two-dimensional multi-degree-of freedom (2-D MDOF) systems such as multi-storey planar framed structures. With special regard to reinforced concrete (RC) buildings, this study investigates for the first time the inelastic response of three-dimensional (3-D) structures subjected to repeated earthquakes. More specifically, two three-storey and two five-storey RC buildings, which are regular and irregular along their height, are examined under five real strong multiple earthquakes where their two horizontal components as well as the vertical one are taken into account. The investigation focuses on the examination of the maximum displacements, maximum residual displacements, maximum interstorey drift ratio, maximum residual interstorey drift ratio, damage indices and ductility demands. Finally, the building structures under consideration are analyzed for different siting configurations to investigate the effect of earthquake direction incident. It is concluded that the multiplicity of earthquakes should be taken into account for the reliable seismic design of reinforced concrete structures. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Seismic sequences take place frequently at many regions world- wide. As a consequence, the accumulated strains at active seismic faults are not released outright at the first rupture, but sequential ruptures take place leading to repeated earthquakes. In many cases, there is a significant damage accumulation as a result of multiplicity of earthquakes and frequently, due to lack of time between succes- sive seismic events, any rehabilitation process seems to be unfeasible. There are numerous examples of buildings worldwide where the structural damage has been accumulated due to multiple earth- quakes. For example, one can mention the recent Christchurch (NZ) seismic sequence where the Canterbury Television and the Pyne Gould Corp. buildings were damaged due to the first strong earth- quake (4 Sept. 2010) and then collapsed during the second successive strong ground motion (22 Feb. 2011). Although the recognized observable fact for multiple earthquakes, the modern seismic design codes have not considered adequately this phenomenon and they typically focus on the single and rare ‘design earthquake’. Numerous research studies can be mentioned here examining the effects of repeated earthquake phenomena on single-degree-of- freedom (SDOF) systems. One can mention the works of Amadio et al. [1] and Luco et al. [2] where the effects of repeated earthquakes on nonlinear SDOF systems were examined and quantified. Further- more, Hatzigeorgiou and Beskos [3] proposed appropriate inelastic displacement ratios for the case of seismic sequences. Additionally, Hatzigeorgiou [4–6] studied the ductility demands and behavior factors for nonlinear SDOF systems subjected to multiple near-fault and far-field earthquakes. Moustafa and Takewaki [7] and Takewaki et al. [8] examined simple stochastic models representing repeated seismic sequences. In addition, various research studies investigated the effects of multiple earthquakes on multi-degree of freedom (MDOF) systems. One can mention here the works of Fragiacomo et al. [9], Li and Ellingwood [10], Hatzigeorgiou and Liolios [11] and Ruiz-Garcia and Negrete-Manriquez [12], which have examined steel framed structures and Loulelis et al. [13], Faisal et al. [14], Efraimia- dou et al. [15], Di Sarno [16] and Abdelnaby and Elnashai [17] which have focused on multi-storey reinforced concrete frames. It is worth noticing that all these studies, i.e., Refs [9–17], have been limited to two-dimensional/planar structures while according to the best of the authors' knowledge, there is not research work that has examined the effects of repeated earthquakes on three-dimensional reinforced Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/soildyn Soil Dynamics and Earthquake Engineering http://dx.doi.org/10.1016/j.soildyn.2015.02.005 0267-7261/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ30 2610 367769 E-mail address: hatzigeorgiou@eap.gr (G.D. Hatzigeorgiou). Soil Dynamics and Earthquake Engineering 72 (2015) 77–88