Post-earthquake recoverability of existing RC bridge piers retrofitted with FRP composites Mohamed F.M. Fahmy a, * , Zhishen Wu a,1 , Gang Wu b a Dept. of Urban & Civil Eng., Ibaraki University, Japan b International Institute for Urban Systems Engineering, Southeast Univ., Nanjing 210096, China article info Article history: Received 16 April 2009 Received in revised form 3 November 2009 Accepted 18 November 2009 Available online 21 December 2009 Keywords: Seismic Bridges RC columns Recoverability Secondary stiffness Residual deformation Fiber-reinforced polymers Design abstract The novel concept of this paper is to investigate the required recoverability of existing important rein- forced concrete (RC) bridges retrofitted with fiber-reinforced polymers (FRP) to restore their original functions after a moderate or strong earthquake. Hence, this paper presents an up-to-date literature search on the inelastic performance of 109 FRP-retrofitted columns with lap-splice deficiency, flexural deficiency, or shear deficiency. The study is conducted in the following steps: using post-yield stiffness as a seismic index, the effectiveness of FRP jackets in enhancing the inelastic stage performance of non-ductile reinforced concrete columns is scrutinized for the available database; the performance of col- umns which successfully achieved post-yield stiffness is categorized in accordance with the required recoverability after an earthquake; and according to the definition of a controllable recoverable structure, the appropriate composite jacket thickness is calculated. In the view of a proposed mechanical model of an FRP–RC damage-controllable structure, 61 columns of the available database exhibited idealized lat- eral performance with stable post-yield stiffness, or secondary stiffness. Lateral drift at the end of the recoverable state is defined from the hysteretic responses of 39 columns and is visualized as a ratio of column lateral drift by the end of the post-yield stiffness with explicit consideration for the effect of both column cross-section shape and deficiency. Finally, suitable FRP design assumptions and concepts certi- fying the reality of post-yield stiffness are given. Furthermore, in the light of Seismic Design Specifica- tions of Highway Bridges in Japan, a FRP strengthening design guideline that considers and evaluates structural recoverability is proposed. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The damages incurred by many concrete bridges under the ef- fect of near-fault ground motions have led to the implementation of several significant improvements to bridge design codes. Recent advances in earthquake engineering favor performance based ap- proaches for the seismic design of new structures and for the assessment and rehabilitation of existing structures located in ac- tive seismic zones. In the seismic design of structures, it is impor- tant to have a clear vision of the desired seismic performance. Important decision making questions like, ‘‘What is the required performance for the structure during and after an earthquake?” are undoubtedly important. Generally, new seismic design philos- ophies for bridges recommend that important bridges subject to a near-land-large-scale interplate earthquake or an inland earth- quake near the structure should be able to sustain the expected maximum lateral force in the inelastic stage with limited damages, to ensure quick recoverability. In Japan, a new code called ‘‘Seismic Design Code for Railway Structures” (in Japanese) has been published recently, which re- flects recent advances in earthquake engineering. It includes some new ideas for seismic design drawn from lessons learned from the devastating Hyogoken-Nanbu Earthquake of January 17, 1995, [23]. In Fig. 1 the seismic performance of structure is categorized into 3 levels that correspond to the required level of repair after an intense earthquake. These performance levels are defined by the degree of structural recovery necessary after an earthquake. This is an established relationship between the levels of earth- quake motion and seismic performance, with two levels of earth- quake motion defined in the code. One is the so-called L1 earthquake motion (level I), which has a recurrence probability of a few times during the service life of the structure. The other is the L2 earthquake motion (level II), which is caused by a near- land-large-scale interplate earthquake or an inland earthquake close to the structure. For L1 earthquakes, the structural seismic performance I (SPI) should be satisfied by all the structures de- signed. For L2 earthquakes, seismic performance II (SPII) should 0950-0618/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2009.11.020 * Corresponding author. Mobile: +81 80 3274 2057; fax: +81 294 38 5268. E-mail addresses: mfmf1976@yahoo.com (M.F.M. Fahmy), zswu@mx. ibaraki.ac.jp (Z. Wu), g.wu@seu.edu.cn (G. Wu). 1 Tel.: +81 294 38 5179; fax: +81 294 38 5268. Construction and Building Materials 24 (2010) 980–998 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat