Long term behaviour of UHPC shear key connections in adjacent box girder bridges under thermal loading

Abstract

This thesis studies the cold weather performance of Ultra High-Performance Concrete (UHPC) shear keys within an adjacent prestressed concrete box girder bridge reinforced with steel dowels across the interface. Field data from the Little Morris River Bridge is reviewed to establish general trends in structure behaviour and a finite element model is created in Abaqus CAE to examine the cold weather behaviour of the shear key and bridge girders.

The finite element model included a developed traction separation model to represent the UHPC to girder concrete bond behaviour. The bond behaviour is established using the results of direct tension test in accordance with ASTM C1404/C1404M-98, slant shear test in accordance with ASTM C882, and Bi-shear test results to represent the response to different modes of loading across the shear key to girder bond. From these tests appropriate values for damage initiation and evolution were defined. Finite element modelling revealed that damage and subsequent debonding initiates at the top of the shear key and progressively de-bonds further down the shear key under colder increments of temperature. It demonstrated that the primary mechanism of shear key damage is debonding in direct tension under increased increments of cold weather.

From parametric testing, decreasing the coldest on record temperature profile by a progressive 5 oC, it was found that debonding initiated at the top of the shear key by -37oC and reached the level of dowels by -42 oC. Further, it was found that the evolution of shear key damage initiation and ultimate debonding is more pronounced at mid span compared to at the support. As the damage to the shear key to beam bond progresses it is demonstrated by the finite element model that the dowels begin to transfer increasing tensile strain and resultant stress within the connection between the girders.