Vol.:(0123456789) 1 3 Iranian Journal of Science and Technology, Transactions of Civil Engineering https://doi.org/10.1007/s40996-018-00232-0 RESEARCH PAPER Probabilistic Seismic Response Analysis on Continuous Bridges Under Near‑Fault Ground Motions Hai‑Bin Ma 1  · Wei‑Dong Zhuo 1  · Davide Lavorato 2  · Camillo Nuti 1,2  · Gabriele Fiorentino 2  · Yin Gu 1  · Bruno Briseghella 1 Received: 22 March 2018 / Accepted: 29 December 2018 © Shiraz University 2019 Abstract This paper focuses on the pulse-like near-fault ground motion, developing a probabilistic seismic demand model to estimate the seismic response of regular continuous bridges. A three-span bridge with continuous deck is taken as the basic case to establish 25 representative samples by changing the geometrical parameters and modeled with OpenSees software. The ground motions of both near fault and far fault are selected from PEER NGA strong ground motion database. The seismic response of the bridge is evaluated using the drift ratio at the top of the pier. A series of nonlinear dynamic time history analysis is carried out to compare the damage obtained with near-fault and far-fault ground motions for three diferent site conditions. Subsequently, a sensitivity analysis is performed on the design parameters according to the orthogonal experi- mental design methodology. After selecting the Housner intensity as the most suitable intensity measure and drift ratio as the engineering demand parameter, the probabilistic seismic demand model is established for the near-fault earthquake on the site II condition which is classifed by Chinese design code. The results show that the near-fault earthquake can lead to more serious damage with respect to regular bridges and that the probabilistic seismic demand model allows for a quick evaluation of the seismic behavior of regular continuous bridges under pulse-like near-fault earthquake. Keywords Near fault · Continuous bridges · Orthogonal experimental design · Intensify measures · Seismic demand model 1 Introduction Continuous bridges are key elements in the functionality of transportation networks, especially in case of disastrous events such as earthquakes (Yao 2008). However, current bridge design codes are mainly based on ground motions with source-to-site distance greater than 20 km (far fault). As a result, bridges located near ruptured fault and designed in accordance with current codes can experience severe seis- mic damages even in case of medium-grade earthquakes (Chang et al. 2004; Jónsson et al. 2010; Wang and Lee 2009). When compared to far-fault ground motion, near- fault ones are characterized by: short duration, pulse-like ground motion (one or more pulses) and signifcant vertical component (Beniof 1955; Abrahamson 2000; Bray and Rodriguez-Marek 2004; Li and Zhu 2004). Therefore, near- fault earthquakes can result in higher seismic demands on bridge structures which are not considered by current codes. For that reason, the defnition of the proper seismic actions and the evaluation of bridge damage mechanisms in case of near-fault earthquakes should be investigated to improve the seismic design prescriptions. Some authors addressed the issue of the response of bridges to near-fault ground motions. Saadeghvariri and Foutch (1991) indicated that, in gen- eral, the vertical motion would increase the level of response and the amount of damage sustained by a highway bridge. Vertical motions generate fuctuating axial forces in the col- umns, causing instability of the hysteretic loops and increas- ing the ductility demand. Furthermore, vertical motion could generate forces of high magnitude in the abutments and foundations that are not taken into account by the current seismic design guidelines. Bozorgnia et al. (1995), based on the characteristics of response spectra of free-feld vertical ground motion * Wei-Dong Zhuo zhuowd@fzu.edu.cn 1 College of Civil Engineering, Fuzhou University, Fuzhou, China 2 Department of Architecture, Roma Tre University, Rome, Italy