Oskar Larsson

Modelling of Climatic Thermal Actions in Hollow Concrete Box Cross-Sections

Abstract The temperature distribution in concrete structures varies as a result of fluctuations in solar radiation, air temperature, wind speed and long-wave radiation. Variations in temperature may cause longitudinal and transverse movements. If these movements are restrained, stresses and strains can be induced, which may contribute to cracking in the structure. To predict such thermal actions in a hollow concrete section, a finite element (FE) model was developed. Hourly resolution of climatic input data was used in the FE model to capture the daily temperature variations in the structure. The FE model was validated against temperature measurements performed in the hollow concrete arch of the New Svinesund Bridge located at the border between Sweden and Norway. To be able to use the developed model for future studies of other structures, an iterative method to consider the inside cavity air was also developed. The results of the simulations show that the model can capture the daily temperature variations. In addition, the proposed model shows acceptable agreement with the measurements from the bridge, and the calculated linear temperature differences for the bridge show good agreement with the design values in the Eurocode. The model is well suited for predicting temperature distributions and can be used for further studies of bridges, including those with box cross-sections, as well as for other concrete structures.

Climate change effects on design thermal actions for concrete structures

The temperature distribution in a concrete structure varies due to complex interactions with the surrounding climate. Solar radiation, air temperature, wind speed and long-wave radiation all affect the temperature in the material, and may cause movements in the longitudinal and transversal directions. If these movements are restrained, stresses and strains can be induced which may contribute to cracking and other structural problems. A change in the climate may thus have a large impact on the thermal actions and in turn the behaviour of a structure. The representative values in our building codes and regulations are based on calculations using climate data, where the results are analysed using statistical concepts. The climate data used for calculating the design values for thermal actions were obtained during the last half of the 20th century. Due to the projected future climate change, the design values for thermal actions may become outdated in a few years. In this study, the current design loads for thermal actions from different building codes such as Eurocode and AASTHO have been compared with how the design loads may be affected by future climate change. The study shows that the design values for uniform bridge temperature have to be adapted to incorporate effects of climate change. One way is to couple the design value to the service life and an estimation of the temperature change for a certain location, based on climate models. The linear and non-linear estimations may be less affected by climate change due to a smaller effect on the governing climate parameters such as solar radiation and temperature range. The projection is very uncertain however, further studies with more detailed climate models are needed for any conclusions to be drawn regarding these parameters. (Less)

Geometrical influence on transverse thermal stresses in concrete bridge sections

The temperature in a concrete bridge is affected by complex interactions of climatic factors. Varying concrete temperature will give rise to movements in the longitudinal as well as the transverse directions. Inspections of certain box girder bridges have shown cracks in only the thin vertical walls, which may be an indication of a geometrical influence. A sequence of climate input data deemed as an extreme event in a previous study was used to calculate the transverse thermal stresses in concrete box-sections with various geometries. The results show that the most influencing geometrical parameter is the member thickness ratio. If the thicknesses in the horizontal slabs and the vertical walls are different, large tensile stresses will occur in the section. The actual thickness is not as important, nor whether the slabs or walls are the thinner parts. The width and height of the cross-section is not as influential as the thickness ratio. (Less)

Climatic Thermal Stresses in the Vätösund Box-Girder Concrete Bridge

Abstract Severe cracks have been found in several box-girder bridges in Sweden, with the cracks being more frequent on the south side than the north. This indicates that solar radiation has a large impact on the stress field of these bridges, as this is the only factor that is significantly different between the two walls. In this study, the Vätösund Bridge has been studied with a three-dimensional (3D) finite element (FE) model to analyse the thermal stresses that occur following climatic exposure. Meteorological data have been used to simulate the time variation of the temperature field, which is in turn used to simulate the resulting thermal stresses. The results show that the largest tensile stresses appear on the inside of the south wall, with a clear difference compared to the north. Large stresses appear both in the top and in the bottom parts of the south wall. This indicates that the cracks that mainly appeared in the lower parts, at least, partly originate from thermal effects. The boundary conditions at mid-span have a large impact on the location and magnitude of the thermal tensile stresses. The results show that it is possible to predict where thermal stresses appear in a box-girder bridge using 3D FE analysis.

Estimation of Extreme Climatic Thermal Actions in Concrete Structures

The temperature distribution in concrete structures varies due to annual and daily climate variations. Solar radiation, air temperature, wind speed and long-wave radiation affect the temperature in the structure and may cause longitudinal and transversal movements. If these movements are restrained, stresses and strains can be induced which may contribute to cracking. To be able to predict the long-term effects and extreme thermal actions a finite element model has been developed. The model is used with global meteorological data to predict annual maxima of temperature gradients. The results show that the values in the Eurocode concerning the investigated region are underestimated for positive linear gradients. Values with a return period of 5 years are above the design values from Eurocode with a 50 year return period. The type of paving used has a significant effect on the results (Less)