Research on the Internal Thermal Boundary Conditions of Concrete Closed Girder Cross-Sections under Historically Extreme Temperature Conditions

Abstract

The accuracy of the finite element model (FEM) for concrete closed girder cross-sections is significantly influenced by thermal boundary conditions. The internal thermal boundary conditions can be simulated by inputting the convection heat transfer coefficient and the temperatures inside the cavities or by establishing air elements in the FEM. In order to analyze the influence of different simulation methods for the internal thermal boundary conditions on temperature distributions for concrete closed girder cross-sections, the temperature distributions on the cross-sections of a box girder, small box girders, and adjacent box girders were monitored, and the corresponding FEMs were implemented. By comparing the temperature data obtained from the field test and FEMs, the numerical hourly temperature curves calculated by using the measured temperatures inside the cavities provide the closest agreement with the measured results; however, the measurements of the temperatures on site are cost- and time-prohibitive. When there is a lack of measured temperatures inside the cavities, the numerical hourly temperature curves calculated by establishing air elements in the FEM provide the closest agreement. The influences of different simulation methods for the internal thermal boundary conditions on the highest hourly average effective temperatures and the trends of the vertical temperature gradients for concrete closed girder cross-sections were small. The FEM with air elements can be adopted to analyze the temperature distributions on concrete closed girder cross-sections under historically extreme temperature conditions. It can be predicted that the longitudinal thermal movement of concrete closed girders would be underestimated by considering variations in the one-year measured average effective temperature of the cross-sections or the Chinese-code-specified design effective temperature for the highway bridge structures, which are thus unconservative for engineering applications. The Chinese-code-specified design vertical temperature gradients are conservative for the bridge deck surface and unconservative for the bottom flange.

Analytical and experimental analysis of concrete temperature and energy considering open-air environmental variations

“…An efficient vertical discrete model was established for the efficient numerical calculation of concrete temperatures by Fan et al 20 , and the predicted temperatures matched well with the measured values. Shi et al 21 and Lin et al 22 , 23 used both methods to reveal the influence of temperature distribution on various concrete structures. Usually, it is more convenient to evaluate the temperature distribution by numerical simulation than by long-term field measurement since numerical simulation is repeatable and applicable in the design phase.…”

Investigation and Analysis of the Influence of Environmental Factors on the Temperature Distribution of Thin-Walled Concrete

“…Numerical simulations of thermal loads are more convenient to implement in the design stage, but compared to reality, the simulation results are often biased due to their simplification of boundary conditions. For example, solar radiation was omitted in Yan Li's numerical research on the temperature cracking propagation of mass concrete [13], the internal thermal boundary conditions of concrete closed girders were equivalently simulated by air elements in Chen B's research [14], the fluctuation of air temperature was eliminated in Zhou Yunchuan's simulation analysis on mass concrete temperature fields [15], and the sky temperature was assumed to be the same as air temperature in Chenyu Zhang's temperature simulations on steel-concrete composite girders [16]. These simplifications of boundary conditions are applicable in specific cases, but their accuracy should be evaluated.…”

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“…However, the temperature date adopted in this study is the random day in one year, the adaption of data may have certain randomness, which cannot fully reflect the general law of temperature load effect. Lin et al (2020) conducted research on the temperature distributions of different types of box girder. Measured temperature, ambient temperature method, mean temperature method and air element method are applied to analysis the internal thermal boundary condition of box girder cross section.…”