Coupled Safety Assessment of Cable Stay Bridges

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  • Modern Applied Science; Vol. 6, No. 7; 2012 ISSN 1913-1844 E-ISSN 1913-1852

    Published by Canadian Center of Science and Education

    64

    Coupled Safety Assessment of Cable Stay Bridges Alessio Pipinato1

    1 University of Padova, Padova, Italy Correspondence: Alessio Pipinato, Department of Civil and Environmental Engineering, via Marzolo 9, Padova 35131. Tel: 39-042-533-292. E-mail: alessio.pipinato@unipd.it Received: June 1, 2012 Accepted: June 20, 2012 Online Published: June 25, 2012 doi:10.5539/mas.v6n7p64 URL: http://dx.doi.org/10.5539/mas.v6n7p64 Abstract The life of the large stock of concrete bridges that still exist throughout the world must be extended, while at the same time ensuring that safety is not compromised for economic reason. In fact, environmental damage and fatigue life estimation of historical bridges represent a coupled structural issue for managing cost-effective decisions regarding rehabilitation or replacement of existing infrastructure, hence there is a need to estimate how long these structures could remain in service. In this paper, a coupled environmental and fatigue assessment of a representative cable stay bridge, is analyzed and assessed. Based on the analytical study, parametrical results on the lifespan of the bridge have been presented. Keywords: bridge structure, concrete cable stay bridges, historical bridges, assessment 1. Introducation The risk associated to the vulnerability of bridges and infrastructure is a relevant issue to guarantee standard safety and security of citizens in everyday life. ASCE Committee on Fatigue and Fracture Reliability (1982) reported that a relevant amount of bridge failures are related to fatigue and fracture, and this data is confirmed by Byers et al. (1997). The problem of fatigue assessment (Pipinato et al. 2011a; 2012b; 2012a) becomes further complicated if the deteriorated conditions of the existing structures need to be considered: defects of superstructures represent the 20.5% of causes for replacement of steel highway bridges (Nishikawa, 1997) while each year, about 1200 bridges reach the end of their design life (Yazdani & Albrecht, 1990). Most of them must be strengthened, repaired or rebuilt to ensure an acceptable level of safety considering present and future traffic conditions. Cracks originating from flaws could propagate under a time-varying random load process and the structural integrity is expected to degrade with time. When a fatigue crack grows up to a critical size, the structure could fail to be useful for its use (Zhao, 1996). These effects could be more significant when an exceptional event strikes the structure during its service life. In this context, according to authors knowledge a correlation between fatigue effects and environmental actions is not deeply analysed in literature: so this is a crucial argument in bridge engineering, especially to estimate a precise cumulative effect of the total damage and to achieve the remaining life of historical infrastructures. Other existing approaches to the problem of lifetime performance prediction, for example, in the field of concrete structures affected by corrosion are shown in e.g in Biondini and Frangopol (2008; 2009). Moreover, interesting considerations on safety assessment under multi-hazards can be found in Duthinh and Simiu (2010). While the introduction on the matter could be found in Pipinato (2011), and in Pellegrino et al. (2011), a coupled approach, considering fatigue and seismic events is described in Pipinato et al. (2011b). Other studies on this relevant field have been presented in Pipinato et al. (2010) including the analysis and assessment of diverse existing steel bridges; in Pipinato and Modena (2010) a structural analysis of an existing arch metal bridge is reported; moreover, step level procedures have been implemented in order to give some insights on a rational procedure to be adopted in existing bridges (Pipinato, 2010); finally, experimental detail category have been studied and proposed by analizing the full scale testing results of dismantled bridges (Pipinato et al., 2008; 2009). Belonging to the aforementioned experience, in this paper a method for fatigue damage estimation of existing bridges in presence of environmental loading is presented, in particular dealing with cables in cable stay bridges. A companion paper analysis has been presented dealing with the design of new bridges, as illustrated in Pipinato et al. (2012). But this issue is relevant also in existing cable-stayed structures, suffering from the continuous aggression of environmental agents (urban, industrial, marine, etc.): these effects appear through corrosion, whose direct consequences are the strong modifications of the geometrical and mechanical characteristics of the components, and finally of the structure as

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