Assesment of Damages Caused by Alkali-Silica Reactions - Elgseter Bridge, Trondheim

Abstract

Elgeseter Bridge was completed in 1951, and it is a main part of the infrastructure between the south side of Trondheim to the city centre. Early inspections showed signs of elongation of the bridge, but the cause for the elongation and expansion was not recognized at that point. The Alkali-Silica Reaction (ASR) that causes the expansion was not known at the time of construction. This thesis will present the theory of how the structure is affected. The structure is analysed both statically and theoretically, due to the expanding chemical reaction.

The expansive reaction is due to a reaction between the aggregate and the cement in the concrete mix- It causes stresses to occur in places the structure was not designed for. The thesis will consider mainly the two large vertical cracks, which are explained in the report from field inspections in 2012 by Aas-Jakobsen. Eurocodes and Handbooks from the Norwegian Public Road Administration (SVV) are the basis during calculation of the loads and capacities.

The bridge is 200 metres long, and is supported by eight column rows that are anchored in the foundations under the water surface of the river. Modelling of the bridge is done in the frame modelling software FAP, and the 3D modelling program Abaqus.

Modelling in Abaqus has shown that in order to create stresses in the lower edge of the inner beams, the expansion is occurring in both the bridge deck and outer beams. Calculations show that the spans affected by the large vertical cracks have formed plastic hinges in the weakest cross-section of the span. Further investigations must be performed to fully understand how much this affects the structure.