PSI - Issue 10

Alk. Apostolopoulos et al. / Procedia Structural Integrity 10 (2018) 49–58 Alk. Apostolopoulos and T. Matikas / Structural Integrity Procedia 00 (2018) 000 – 000

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earthquake of Tang Shan in China confirmed that the failure mode of the building structural steel was LCF as pointed out by Sheng et al. (1997). In the current design practice, a displacement ductility coefficient is used even if it fails to account for the accumulated damage. This happens because it is implicitly assumed that structural damage occurs only due to the maximum response deformation and is independent of the number of non-peak inelastic cycles or strain energy dissipation. However all inelastic cycles must be considered as contributors to damage since they constitute the strain history observed in actual structures and their accumulation may become important depending on the characteristics of the ground motion. During strong earthquakes, yielding structures are subjected to increased number of cycles into the inelastic range and the accumulated damage may significantly affect their overall performance. This type of damage may also evolve from multiple earthquakes, in this case, a series of pre or post shocks combined with the main shock may be treated as a single event of extended duration. There is an assessment of seismic damage which is usually assumed to be similar to metal fatigue under variable amplitude cyclic loading. On the other hand, relatively little attention has been devoted by the research community on the combined effect of corrosion and LCF on steel reinforcement since each one of these factors affects the rebar durability and performance and shortens the life expectancy of structures (Ma et al. (1976); Yoshaki (1983); Shigeru et al. (1995); Clementa et al. (2002); Krawinkler (1987); Kasiraj and Yao (1969)). Many studies in the current literature present significant durability problems in steel rebars resulting in a rapid decrease of their mechanical properties and their dissipative capacity Apostolopoulos et al. (2014). Similar are the results of studies (Meda et al. (2014), El-Bahy et al. (1999), Lehman et al. (2000)), in which a wide range of deformations in ex perimental tests led to buckling of the rebars and then to failure . More recently, Kashani et al. (2013a, b) investigated the impact of corrosion on inelastic buckling and nonlinear cyclic response of reinforcing bars experimentally. Kashani (2014) and Kashani et al. (2013c, 2014) studied the impact of corrosion pattern on inelastic buckling and cyclic response of reinforcing bars using a detailed nonlinear finite element analysis. These results show that the combined effect of corrosion and inelastic buckling has a significant impact on premature fracture of reinforcing bars under cyclic loading. In structures on seismic areas are commonly used high strength steels, harmonized to the general worldwide trend of using steels with nominal yield strengths above 355 MPa. These steels of higher strength can lead to significant savings in structural weight, material costs and CO 2 emissions. High strength steels have been available for many years, and their properties continue to improve as advancements are made in metallurgy. Despite the fact that the use of high strength steels is low in the construction industry, there is undoubtedly a potential for their greater use in the future. Research in this subject could lead to the realization of this possibility sooner. The analysis of the effective LCF (seismic) performance of steel reinforcing bars represents, nowadays, a problem of relevant importance in the widest framework of the investigation of the global ductile behavior of RC structures and remains, till now, partially unsolved by Apostolopoulos et al. (2014). For the purpose of confirming the above mentioned statement it is worth mentioning that European production standards, for reinforcements (EN 10080:2005), do not include LCF tests procedure for the cyclic mechanical behavior of steel bar. However, only Spanish and Portuguese standards prescribe the execution of symmetrical tension/compres sion cycles for the production control of steel reinforcements, while the draft of new European standard for reinforce ments (prEN 10080:2012) gives only some indications for the execution of LCF tests by Caprili et al. (2015). Never theless, the imposed levels of deformation, frequency, number of cycles and free length of specimens in these indica tions for LCF tests are not based on results of scientific research about the real seismic behavior of rebar in RC structures. To this day, many casualties and enormous economic loss were resulted in earthquakes. After that, the scientific community paid closer attention to the seismic capability of building structures. One significant factor which can lead to catastrophic collapse, during an earthquake, is the fracture of the steel bar. As a result, great importance was given to the systematic study of the mechanical upgrade of steel bar. The strength of RC structures greatly depends on the bond between the rebars and the concrete. Many studies have revealed that corrosion existence reduces bonding between the rebars and the concrete, e.g. Apostolopoulos and Matikas (2016). No one can deny the fact that when critical elements of structures (columns, beams etc) are under dual adverse effects of chloride ion corrosive environment and strong earthquakes, the steel reinforcement is under coupling effects of corrosion and low cycle fatigue. Under the above circumstances the performance of RC structures deteriorates rapidly. Therefore, it has important practical significance to carry out research on performance deterioration of corroded RC columns and reinforcing bars under seismic loads.