Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The competitiveness of composite bridges depends on several circumstances such as site
conditions, local costs of material and staff and the engineers’ and contractors’ experience.
One major advantage compared to concrete bridges is that the steel girders can carry the
weight of the formwork and the wet concrete which means that the need for temporary
structures is reduced. The consequent savings in construction time generally make the
composite bridges economical compared to concrete bridges.
Traditionally, the concrete deck is cast on site, which means that the work with the
formwork, reinforcement as well as the casting takes place outdoors. This work can be
problematic and expensive during wintertime in countries having a cold climate and time
consuming due to the additional time needed for the concrete hardening. Furthermore there
are a lot of bridges in different parts of the world that need to be replaced due to e.g. aging,
increased volume of traffic or traffic load. Therefore, new construction methods are required
to shorten the time disruption. New bridge systems need to be developed that will allow
components to be prefabricated offsite and moved into place for quick assembly.
The further step to improve the competitiveness of composite bridges, in the right direction
towards an industrialized construction, is thus to prefabricate not only the steel girders, but
also the concrete deck. The main advantages obtained by adopting this concept are a shorter
construction time leading to lower road-user costs associated with a lower traffic disruption,
and a higher and homogeneus concrete quality leading to a longer durability.
In this thesis an innovative solution for precast composite bridges adopting dry joints
between the concrete deck elements is investigated. This new concept is presented in a brief
literature review describing the state of the art around how different countries have built
their composite bridges with precast deck elements.
Hence a three-dimensional finite element model accounting for geometric and material
nonlinearity that simulates this special bridge system for a simply supported case is put
forward. Effort is put in order to create a model economical from a computational point of
view providing at the same time an easy to use tool for detailed structural analysis. Its
validity, reliability and degree of accuracy is tested against experimental data available in the
A parametric study is then carried out through a series of FE models with the aim to
investigate the structural performance of the system from initial loading towards the final
collapse. All aspects are studied in relation to the better known cast in place type, which
allows to better highlight the performance of the prefabricated one. Different aspects are
analyzed with focus both on the serviceability limit state and the ultimate limit state. In
particular deflections, stresses in the steel beam, concrete decks as well as in the shear stud
connectors are investigated. An assessment of the ultimate capacity is also given. The main
parameters under consideration in this parametric study are the span length and the initial
gap clearance at the joints.
Finally, conclusions concerning both the FE modelling and the analyses carried out are
presented and directions for further research are suggested. Regarding the aspects analysed
it is evident the influence of the gap clearance at the joints on the structural response mainly
for short spans. In particular the greater effects regard the increasing in deflection and the
shear stud connector behaviour.