مقاله انگلیسی رایگان در مورد ارزیابی لرزه ای پایه های پل بتنی – تیلور و فرانسیس 2018

Seismic assessment of existing bridge structures is a key issue especially in regions where most of bridges have been realized without proper rules for earthquake resistant structures, generally designed for gravity loads only or according to obsolete seismic codes. Furthermore, hollow section piers are a very popular structural solution for reinforced concrete (RC) bridge structures due to their economical convenience and higher efficiency with respect to solid sections. Nowadays, the most updated seismic codes require to concentrate energy dissipation in ductile flexural hinges at the base of the bridge piers [Priestley et al., 1996], and avoid brittle shear failure of piers. Vice-versa, existing hollow piers are generally characterized by poor structural details, limited confined concrete core, crucial to seismic energy dissipation, and a deeper degradation of shear resisting mechanisms [Kim et al., 2012]. Their premature collapse is often due to a very limited shear capacity [De Risi et al., 2017]. Moreover, seismic response of hollow RC piers generally exhibits high shear deformability contribution to the global top displacement [Delgado et al., 2009]. The starting point for this study is a comprehensive literature review about the investigated structural typology, as reported in section 1.1.

1.1 Literature review

1.1.1 Experimental works from literature

Despite their widespread use, experimental works in literature have paid proper attention to the seismic response of hollow circular piers only quite recently. In fact, some experimental campaigns on RC members with hollow-core circular cross section and double reinforcement layer (inner and outer) have been found in literature since late ‘80s. A first experimental study, on six specimens, by [Whittaker et al., 1987] was focused on seismic response of scaled RC hollow circular members characterized by two layers of longitudinal reinforcement and well-detailed transverse reinforcement, proving that this kind of members were able to exhibit a ductile behaviour similarly to well-detailed solid members. Five cyclic tests on bridge piers with large diameter were later performed by [Yeh et al., 2001] and [Cheng et al., 2003], focusing on the effect of the transverse reinforcement amount and layout on the cyclic performance. Results showed that the lack of the internal transverse reinforcement between the two steel layers might produce failure in tension of some longitudinal steel bars at the bottom of the column after concrete crushing, buckling during compression cycles, and flexure-shear failure if external transverse reinforcement is not sufficient. Other researchers focused on hollow circular sections with a single longitudinal (and transverse) reinforcement layer, widely used more recently since time and cost needed to place double reinforcement was not counterbalanced by significantly improved performance [Hoshikuma and Priestley, 2000]. The principal goal of these experimental studies was the analysis of the effect on flexural behaviour of the absence of the inner reinforcing layer. First studies [Zahn et al., 1990] showed that the failure was announced by early vertical splitting and crushing of the concrete on the inside face. Despite the lack of confinement on the inner face, in case of low amounts of longitudinal reinforcement, low levels of axial load and reasonably thick wall, a sufficient ductile behaviour was observed, also for this structural solution. These results were then extended and confirmed by [Hoshikuma and Priestley, 2000] – for hollow circular columns with thin walls and realistic axial load levels and reinforcement ratios – and by [Lee et al., 2015].