Deck rotation of straight bridges induced by asymmetric characteristics and effect of transverse diaphragms

The 2010 Maule and 2015 Illapel earthquakes recently affected the highway infrastructure in Chile. Deck rotation in straight and skewed bridges, damage to the connection between the superstructure and substructure, and even collapse of bridges were observed in these events. However, deck rotation in straight bridges has been identified as an unusual failure mode. The main objective of this research is to evaluate if potential asymmetries in the bridge characteristics can be a probable reason that explain deck rotation observed in straight bridges. The second objective is to assess the effect of transverse diaphragms on the seismic behavior of these bridges. In order to achieve these objectives, the Chada underpass, which suffered deck rotation, damage to lateral stoppers and prestressed concrete girders during the Maule earthquake, is used as a case study. The asymmetries considered in this study are related to the variation of the strength of the lateral stoppers, the coefficient of friction of the elastomeric bearings, and the gap distance between the lateral stoppers and prestressed concrete girders. The induced asymmetries are evaluated with a three-dimensional model of the bridge developed in Opensees. The seismic response of the bridge is obtained from nonlinear dynamic analyses considering seven seismic records applying both horizontal components simultaneously. From the results of this study, it is concluded that the studied asymmetries induce deck rotations that can explain only part of the observed deck rotation in the studied straight bridge. A maximum relative horizontal displacement of the deck of 58.2 cm was estimated for the case with asymmetric strength of lateral stoppers, which is only 41% of the residual relative displacement measured in Chada bridge after the Maule earthquake. Additionally, it is concluded that the incorporation of transverse diaphragms, which is required by current Chilean bridge design code, improved the seismic behavior of the studied bridge.