Finite element simulation of a pre-stressed concrete girder
bridge: influences of construction stages and ground
settlements on Gruvbron in Kiruna

Abstract: The railway line in Kiruna is planed to be moved before year 2012 due to
expected cracking in the underlying rock. The cracking is initiated by the
mining in the Kirunavaara-mine. The cracking is expected to cause
increasing ground motions that affect the whole infrastructure in Kiruna.
For one of the bridges, The Mine Bridge (Gruvvägsviadukten), settlements
are expected in the future. Initially at its west side and further
eastwards towards the city. An early assessment of the bridge showed that
the bridge has enough load-carrying capacity but that the length of the
reinforcement close to the interior columns probably is a little bit too
short to fully compensate the prestressing force in top of the concrete
girder. A certain worry has been expressed that the ground movements may
cause some existing cracks to propagate upwards to the girders top i.e.
that the cracks goes through the whole girder which may reduce the shear
capacity remarkable.

Luleå University of Technology is asked to perform a more thoroughly study
of the bridge's capacity to resist different scenarios of settlements. This
thesis is a part of the work and deals with non-linear finite element
modelling and analysis of the bridge's capacity to resist the settlements
and to evaluate limits for certain expected scenarios of settlements.

To confirm the correctness of the final model, the displacements from the
model is compared to measured displacement for a known truck load. The
comparison shows that the model is somewhat weaker than in the reality.
This is believed to depend mainly on a generalization of the deck's
geometry and a stiffer construction during the field measurement. However,
the model is still judge to be usable for studying what limits can be used
for allowed settlements and the reason for why some cracks already exists.
It is found that the most serious failure that can be expected is
compression in bottom of the longitudinal girder, in middle of the
considered span. This appears at a 25 mm settlement of the interior column
raw in support no 2.