| Concrete box girder outstanding advantages,widely used,but often the beam cracking phenomenon.After research found cracks in the concrete box beam caused by the load only a minority,accounting for more than 80% of the total number of non-structural cracks cracks.Among the many causes of non-structural cracking of concrete box girder,the beam subjected to heat changes caused by heat stress constraints is a major factor.Since there is no readily available commercial software can be a concrete internal water loss to simulate the process,so the structure dehydration shrinkage is calculated using the empirical formula still remain in the estimation stage,and can only be calculated from the amount of shrinkage of the overall structure,shrinkage stress can not be calculated in a specific distribution structure.According to previous findings under isothermal environment and humidity inside the concrete field satisfies Fick’s second law,but the actual engineering of the bridge structure are at ambient temperatures changing,high and low temperature have a significant impact on water loss in concrete internal moisture field must take into account the coupling effect of temperature field simulation.Therefore,it is necessary to heat inside the concrete box girder coupled field study from uneven structural changes of temperature and humidity starting to heat stress concrete box girder is calculated so as to realize quantitative analysis of box beam causes of non-structural cracks,there is great practical value and scientific significance.In this paper,concrete box girder structure surface shrinkage cracks formed as the main reason for the study,based on previous studies on the establishment of a one-dimensional concrete internal linear,nonlinear mathematical model humidity field,to carry out the temperature distribution inside the concrete structures on the concrete drying process Impact Analysis.The results show that the effect of temperature on the diffusion coefficient of concrete moisture is intense,inside the concrete when the temperature exceeds 20 ℃ after the wet concrete will make the diffusion coefficient increases exponentially,so the temperature rise will increase the moisture inside the concrete to pass out.Summed up the water loss in concrete mechanism by adding moisture diffusion coefficient on temperature influence function of the way the establishment of a heat build-field coupling mathematical model.Carefully derived explicit,implicit two difference schemes for the heat inside the concrete moisture field and coupling field equations of the calculation process,calculated thinking.And based on the theory of finite difference in the MATLAB application development platform written humidity field and coupling field calculation program,by contrast with the classical experimental and commercial finite element analysis results verify the computational power of self programming.Meanwhile,in the construction of bridges,concrete box girder structure to carry out the internal humidity,temperature measured experimental data.Test the environmental temperature and humidity effects,different coagulation of fresh concrete wet,thermal variations.The results with the measured data using the analysis method of the basic agreement,further evidence of heat coupled equations one dimension can be simplified description of thin-walled structures such as concrete box girder temperature distribution on concrete drying process.With predecessors resulting theory,to achieve the transformation of stress concrete temperature,humidity,and with the written computer program analyzes the changing environment in temperature and humidity,the development of web box girder concrete surface shrinkage stresses.Data show that,after considering temperature stress from the inner surface of the wet concrete depth of 1cm wide will be before 15 days after the pouring of concrete is beyond the tensile strength of the respective coagulation state,very prone to shrinkage cracking surface. |
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