Cracking of the End Diaphragm of a Post-tensioned Beam Bridge

Abstract

In concrete beam bridges, the end diaphragm at the end of the bridge is a common structural component that connects the main beams and transfers the beam loads to the bridge bearings. In integral bridges the end diaphragm also retains the soil of embankments due to the absence of abutments. Cracking of the front surface on the end diaphragm has been detected in post-tensioned beam bridges in Finland and Sweden. Presumably the post-tensioning of the bridge and the shaping and detailing of the connection of the end diaphragm and main beam have an effect on cracking tendency. The aim of this study is to examine the structural behaviour and the cracking potential of end diaphragms using linear analysis of the post-tensioned bridge and to find measures to prevent the cracking. The observations collected through field surveys are compared to results of linear FE analysis to clarify the cause of the cracking. The verification of model is performed by comparison of patterns of cracking observed in field surveys and the distribution of maximum tensile stresses in the FE model. With model variations, the effectiveness of measures for the prevention of cracking are observed.

Cracking of the End Diaphragm of a Post-tensioned Beam Bridge

“…For example, the cracking is detected on eight out of a total of 24 post-tensioned bridges in the E18 Koskenkylä-Kotka project. This type of behaviour is also discovered at the end diaphragms of bridges in other projects: Tampereen Rantatunneli, Kehä III VT4-VT7 and Kehä III Lentoasemantie [2].…”

“…The size of the mesh was 100 mm in the area in which the highest tensile stresses are assumed, and 200 mm in other areas in order to keep the calculation time reasonable. The element size was identified by starting with a coarse mesh and refining it, until the calculation time was approximately 30-45 minutes [2].…”

“…It has been detected that cracking after post-tensioning occurs in the front surface on the end diaphragm of beam bridges. This problem has been detected in Finland and Sweden [1,2]. Posttensioned beam bridges are very common bridge structures in Finland.…”