ABSTRACT
The structural design under seismic loading has been performed in the last years using force-based methods for considering the effects of elastoplastic behavior. Currently, displacement-based methods are also being used for designing structures under seismic loading. These methods use moment-curvature relationships for determining the ductility capacity of a structural element. This paper intends to analize the seismic performance of bridges using displacement-based methods and evaluate the influence of concrete confinement on the ductility capacity. For this, a two-span bridge is modeled, analyzed and designed, in accordance with AASHTO (2010). A verification of the ductility capacity in accordance with CALTRANS (2006), of the central pier of the bridge is performed for several cases of axial loading, cross sections and concrete confinement, following the provisions for transverse reinforcement of NBR-6118 (2014) and ACI-318 (2011). The ductility capacity results for a typical case are shown in Figure 1. A pushover analysis is done to evaluate the obtained results. Ductility Capacity versus Dimensionless Compressive Force. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig224_1.tif"/>
From the moment-curvature relationships it was noticeable that, for certain values of compression forces (–0.1 ˃ η ˃–0.5), as long as the concrete confinement is increased, the resistance drop is less abrupt. It is possible to assure a good bridge performance, by regulating the compression rate to which the pier is subjected to, for being in its optimal range, avoiding fragile rupture and increasing the possibility of an eventual structure recovery.
After performing nonlinear static pushover analyses, it can be noticed that ductility capacity increased as the transverse reinforcement increases also. It is also noticeable that two-dimensional models provided results that were closer to results obtained with threedimensional models. The two-dimensional model represents satisfactory results regarding bridge’s behavior with respect to ductility capacity. Representing piles by their real length and springs to simulate the soil-structure interaction provides higher ductility values than fixing the piles in the model. It is noticeable than that the determined ductility capacity increases as the foundation representation in structural model is closer to reality.
