This thesis deals with solutions for an economic dimensioning of bridge superstructures and bearings with regard to thermal actions. For the design of bridges, the load model by the ÖNORM EN and ÖNORM B 1991: Actions on structures, Part 1-5: General actions - Thermal actions seems to have an uneconomically high reliability level. The optimization of the load model for thermal actions in compliance with the operative failure probability appears to be an appropriate measure to increase the cost efficiency of bridge construction parts.
After explaining the probabilistic backgrounds of the determination of actions on structures according to the Eurocode 0, the causes of thermal dilatations and constraining forces for bridges will be explored. Based on monitoring data of several bridges in Austria, the consequences of thermal actions depending on building material, section dimensions and bearing will be analyzed. In this regard, the thermal inertia of concrete constructions results in a high resistance against short-term variations of external air temperature. Because of the reduction of thermal stress on the structure, the correlation between air temperature and uniform bridge temperature component by Eurocode 1 will be investigated and modified in accordance with probabilistically evaluated measurement data of the Austrian Central Institute for Meteorology and Geodynamics.
For further optimization of the load model for thermal actions, the seasonal variations of air temperature will be analyzed. The statistical evaluation of temperature date for chosen towns shows that the scattering of seasonal fluctuations in Austria are lower than expected according to ÖNORM B 1990-2. Therefore, it is recommended to change the partial safety factor Q,T from 1,35 to 1,25 for the design of bearings and transitions.
In addition to that, the probabilistically determined 98 % quantiles of external air temperature prove that the return period of the characteristic value of Tmax and Tmin pursuant to ÖNORM B 1991 Part 1-5 is much longer than 50 years. Therefore, the National Application Document could be adapted to enable an economic dimensioning of bridges. To integrate properties of atmosphere and terrain such as running waters into the load model for thermal actions on structures, further bridges have to be monitored.