PSI - Issue 64

S. Kolemenoglu et al. / Procedia Structural Integrity 64 (2024) 857–868 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction In modern seismic design codes into which the energy dissipation strategies are incorporated, the buildings are designed to withstand certain levels of damages during earthquakes. The structures, which are assessed as slightly damaged after an earthquake can be used immediately upon completion of simple repair works. However, it is harder to generate effective, reliable and long-lasting solutions for moderately damaged structures due to the lack of sufficient knowledge on seismic behavior of moderately damaged RC members and their performances after repair applications. In literature, there exists a number of studies on the repaired performance of heavily or severely damaged RC members, which are repaired and retrofitted with different materials (Ersoy et al., 1993; Ilki and Kumbasar, 2001, Ilki and Kumbasar, 2002, Ilki et. al., 2003, Ilki et al., 2009; Ozcan et al., 2010; Bedirhanoglu et al., 2010; Sezen, 2012; Parks et al., 2016; He et al., 2013, Bedirhanoglu et al., 2022). Since the investigated damage level in those studies is severe, the scope of the adopted retrofitting strategies is more comprehensive, which may not be necessary for slightly or moderately damaged members. In addition, experimental program for some of relevant studies includes non conforming RC members. Therefore, the investigation of the performance of slight or moderately damaged code conforming RC members, which are repaired with relatively simple strategies without directly aiming to enhance the capacity or ductility of the member would be a valuable contribution to the state-of-the-art. FEMA 306 and 307 (1998), present a concept of plastic hinge modification factors for stiffness “ l K ”, strength “ l Q ” and deformation capacity “ l d ” in order to set modified plastic hinge properties for damaged RC walls. Ludovico et. al. (2013) proposed plastic hinge modification factors for damaged RC columns. JBDPA (2016), determines the behavior of damaged members with respect to the dissipated energy. Shegay et. al. (2022) conducted a full scale 4 story building shake table test to investigate repaired behavior of RC members. They compared the energy dissipation capacities of members before and after repair with varying damage conditions. Sarrafzadeh (2021) prepared a dataset including the experiments of repaired RC bridge columns. ATC 145 (2021) suggested the strategies for post earthquake repair of RC members by presenting plastic hinge modification factors for ductile RC frame members. This document mentioned about the lack of data for columns with axial load ratios, n=N d /(A c .f’ c ), closer to and higher than the balanced case. This paper presents the experimental results for repaired seismic performance of four code-conforming ductile columns subjected to an axial load ratio of n=0.27. The reference column was tested to failure, while the remaining three were firstly damaged and then repaired with mortar and then re-tested. The applied repair mortar was environment friendly with recycled raw materials, the test setup allowed the repair works to be made without removing the axial load and, additionally and quantifiable second order effects could be created during testing to resemble actual seismic loading conditions realistically. 2. Experimental Program The common metrics to determine residual or repaired behavior of RC members are changes in stiffness, ductility, lateral load capacity and energy dissipation capability in relation with the experienced damage (JBPDA 2016, ATC 145). In this study, four identical RC code conforming column specimens were tested for investigating a performance of mentioned repair technique via these behavior metrics. One of the four identical specimens was referred as the reference specimen and tested to failure without any repair. The remaining specimens were first tested to varying damage states from damage level I to III (crushing initiation, local crushing, and spalling of cover concrete, respectively), which is the first stage of testing of repaired specimens. Then, the specimens were repaired with structural mortar and re-tested to failure with the same loading history. The test matrix of the experimental study is given in Table 1. The targeted pre-damage conditions for the first stages of three specimens were determined along with the available post-earthquake damage assessment guidelines (JBDPA, 2016; ATC 145, 2021; TCIP 2024, 2024). It should be noted that, although the damage metrics are similar in these guidelines, damage classification for reinforced concrete members slightly differ from each other. ATC 145 divides the damages into three categories as slight, moderate and heavy. JBPDA (2016) uses five different damage levels, while TCIP (2024) uses four levels. The targeted damage states for the first stage of repaired column tests are presented in Table 2 together with the corresponding damage descriptions of the guidelines and views from the reference column test.