Study on Solar Radiation and the Extreme Thermal Effect on Concrete Box Girder Bridges

Thermal effect is an essential factor in the durability and safety of concrete bridges. Therefore, this paper mainly studied the concrete bridge box girder temperature distribution and thermal effect under solar radiation and the thermal load. With a concrete rigid frame bridge as the engineering background, the temperature distribution of the box girder on a clear summer day was observed. Then, according to the solar physics and heat transfer theory, the different surfaces of the box girder cross-section are classified based on the heat transfer conditions, and the variation of solar radiation on different surfaces is investigated. The temperature field of the box girder is simulated by ANSYS. To obtain the extreme thermal condition, the meteorological data of the bridge site from 1990 to 2020 are collected. The data are fitted by generalized extreme value distribution to obtain the extreme temperature and average wind factors in the bridge design lifetime. Combined with the solar radiation, temperature, and wind factors, the extreme thermal condition of the concrete box girder is obtained. Lastly, the thermal effect of the box girder under the extreme condition is analyzed, and the thermal stress is compared with the allowable stress in the design code. The results show that the girder temperature difference is closely related to the solar radiation intensity and heat transfer conditions, and the solar radiation intensity is the more critical factor. The tensile stress caused by the extreme thermal load is more significant than the design strength value in the girder cross-section. The results also provide a method to obtain the extreme thermal condition and evaluate the impact of the thermal effect on concrete box girder bridges.

Load Distribution In Adjacent Precast "Deck Free" Concrete Box-Girder Bridges

Bridges built with adjacent precast, prestressed concrete box-girders are a popular and economical solution for short-span bridges because they can be constructed rapidly. The top flanges of the precast box girders form the bridge deck surface. A shear key is introduced between the adjacent boxes over the depth of the top flange (i.e. 225 mm thick as the thickness of the box's top flange). Canadian Highway Bridge Design Code, CHBDC specifies empirical equations for the moment and shear distribution factors for selected bridge configurations but not for adjacent precast concrete box-girder bridge type. In this study, a parametric study was conducted, using the 3D finite-element modeling, and a set of simplified equations for the moment, shear and deflection distribution factors for the studied bridge configuration was developed.

Load Distribution In Adjacent Precast "Deck Free" Concrete Box-Girder Bridges

Bridges built with adjacent precast, prestressed concrete box-girders are a popular and economical solution for short-span bridges because they can be constructed rapidly. The top flanges of the precast box girders form the bridge deck surface. A shear key is introduced between the adjacent boxes over the depth of the top flange (i.e. 225 mm thick as the thickness of the box's top flange). Canadian Highway Bridge Design Code, CHBDC specifies empirical equations for the moment and shear distribution factors for selected bridge configurations but not for adjacent precast concrete box-girder bridge type. In this study, a parametric study was conducted, using the 3D finite-element modeling, and a set of simplified equations for the moment, shear and deflection distribution factors for the studied bridge configuration was developed.

Modelling noise radiation from concrete box girder bridges as an infinitely long periodic structure excited by a high-speed train

Concrete box girder bridges occupy over 80% of the total mileage of the Chinese high-speed railway. The box girder structure has many natural modes of low frequencies, which can be excited by a train passing at high speed, generating low-frequency bridge noise. This paper is concerned with the prediction of such bridge noise and reports a prediction model. The model, as other existing models of the same nature, also incorporates two parts, one dealing with vehicle-track-viaduct dynamics and the other dealing with sound radiation from the girders, but takes into account more features related to high speed. In this model, vehicle-track-viaduct dynamics is dealt with in the frequency-domain based on the theory of infinitely long periodic structure and the Fourier-series method, predicting vibration frequency spectra for each and every box girder. The predicted vibration frequency spectra of all the box girders are expressed as a sum of propagating waves at different wavenumbers, and sound radiation from each propagating wave is evaluated using the 2.5D acoustic boundary element method. This approach to sound radiation enables contributions from all the box girders to be included at a reasonable computational cost. The paper continues with a comparison in bridge vibration and noise between prediction and measurement for a typical site. And finally, based on the parameters of that site, characteristics of noise radiation from the concrete box girders are studied using the prediction model.