The temperature on a bridge is a complex phenomena caused by several sources and it is quite difficult to forecast. Its effects cannot be ignored and during the last decades various studies have been made in this field. In order to reduce the complexity of these investigations, some simplifications, which do not entail large risks, are admitted making the problem easier to analyse. The main objective of this thesis is to analyse the thermal influence of the air temperature inside a concrete bridge box cross-section. Usually this ‘detail’ is ignored or simplified by the investigators. With the work developed and presented in this thesis it is possible to understand the dimension of the error introduced in the studies every time this simplification is introduced. To fulfil this purpose, two finite element models were developed in order to compare with experimental values. The experimental values were collected using the instrumentation installed on the new Svinesund Bridge in Sweden. In both the models (A and B) several thermal sources were introduced affecting the cross section from the outside such as air temperature, solar radiation and the night radiance. The difference between the two models is that in the first model (A) the air inside the box cross-section is taken into account and in the second model (B) that air is ignored. The quality of the fit of the values obtained using the models A and B with the experimental values from Svinesund allow to take the conclusions of this work. The difference between the models does not indicate that changes in this detail must be included in the future thermal studies
