Seismic assessment of a long-span arch bridge considering the variation in axial forces induced by earthquakes J.J. Álvarez a,⇑ , A.C. Aparicio b , J.M. Jara a , M. Jara a a Civil Engineering School, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Mexico b Construction Engineering Department, Technical University of Catalonia, Barcelona, Spain article info Article history: Received 28 February 2011 Revised 24 August 2011 Accepted 7 September 2011 Available online 4 November 2011 Keywords: Arch bridges Influence of axial load Spatial variability Non-linear dynamic analysis Seismic behavior abstract Axial forces play a fundamental role in the inelastic behavior of concrete elements. This aspect is espe- cially important in those structures whose load path depends on compression forces, as it is the case of arch bridges. During an earthquake occurrence, axial load values in structural elements continually change and element capacities fluctuate as well. Nonlinear analyses of bridges and other structures are usually conducted by determining element capacities using moment–curvature relationships determined for a specific axial load. The influence of the axial forces variation on the ductility and strength capacity and the expected arch ductility demands of a long span bridge, during an earthquake time history anal- ysis, were assessed by means of an inelastic three dimensional model. The study includes the earthquake spatial variability on the response. The bridge superstructure is an upper-deck concrete arch bridge with a main span of 400 m. The non-linear behavior was considered by means of plastic hinges located at springings of the arch and at both ends of the piers. Ten three-component scaled seismic ground motion records were used as input for the simulation analyses. According to the results, the maximum responses, characterized by significant ductility demands at springings and at both ends of the piers, are closely related to the records with the highest peak ground velocities. Additionally, emphasis is placed on the importance of considering the axial force fluctuations on the seismic assessment of this type of bridge structures. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Innovation in the construction processes and improvements of the material’s technology, have resurrected the use of arch bridges for 200–600 m long spans [1]. Even though, bridges up to 600 m long have been projected [2], according to Virola [3], the current long-span world record belongs to the Wanxian Bridge (425 m long main span, completed in 1997) and the Chaotianmen Bridge (552 m long main span, completed in 2009) built by using concrete and steel, respectively. Arch bridges have a complex seismic behavior. The large axial forces usually acting in the arch due to gravitational loads reduce its capacity for ductile behavior. These loads are continuously changing during an earthquake occurrence making necessary the evaluation of the axial load variation effect on the ductility capacity of the arch and a realistic assessment of the expected arch ductility demands during a seismic event. Although, in recent times, the seismic damages in arch bridges are scarce, some bridges as the Bixby Creek Bridge in the California Coast [4] or the Krk I and II Bridges in Croatia [5] have been studied following the upgrading of a seismic code regulation. The Krk I Bridge, 390 m long concrete arch, built in 1980, was the largest bridge of its kind at the time of its construction. In the last 20 years several studies have been conducted to determine and clarify the seismic response of arch bridges. Recently, Torkamani and Lee [6], Nazmy [7], Usami et al. [8] and Cetinkaya et al. [9] analyzed several aspects of the steel arch bridges seismic behavior. Regarding to concrete arch bridges, it must be mentioned the studies of McCallen et al. [4], Kawashima and Mizoguti [10], Sakai and Kawashima [11], and Nakano and Ohta [12]. In spite of the scarce number of studies related to this topic, a complete state-of-the-art is presented by Álvarez and Aparicio [13]. The studies pointed out the importance of an ade- quate evaluation of gravitational and accidental loads to assess the vulnerability and possible structural damage during the bridge life-cycle. A study aimed at determining the influence of the axial load fluctuation in the capacity and ductility demands on a typical con- crete arch bridge subjected to strong motion records is developed. The study also explored the influence of the spatial variability of the seismic excitations through the wave passage effect. A 3D mod- el of the upper deck bridge subjected to scaled seismic records of the Campano-Lucano (Italy, 1980), Michoacán (México, 1985), 0141-0296/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2011.09.013 ⇑ Corresponding author. E-mail addresses: asereno@umich.mx, jjasereno@gmail.com (J.J. Álvarez). Engineering Structures 34 (2012) 69–80 Contents lists available at SciVerse ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct