Numerical Simulation Analysis Of Fire Cracking Of Concrete Beam Bridge

Under the high temperature load of fire,uneven temperature field and hot steam will be generated inside the concrete girder structure.As a result,large temperature stress and steam pressure will be formed,which will lead to cracks.The damage caused to the bridge cannot be ignored.With regard to the bursting and spalling of concrete under high temperature,no accepted research theory has been achieved so far because the factors affecting the bursting of concrete under high temperature are very complicated,involving coupling between multiple physical fields,chemical thermal decomposition at a high temperature,moisture There are many factors such as transportation,steam pressure and concrete damage constitution at high temperature,etc.;As for the method for assessing the bearing capacity of bridges,the method widely used in China is based on the verification method of “Test and Evaluation Regulations for Bearing Capacity of Highway Bridges”,due to its rapid assessment and moderate accuracy.With low cost,it has a good application prospect in China.The main research contents of this article are as follows:1.The relevant materials and literature were consulted,and through comparison and analysis,the numerical values of the thermodynamic performance parameters of the materials applicable to the analysis of the fire field and temperature field of the fire were determined.For the complex mathematical models and influencing factors of the burst spalling,the author carried out a simplified treatment within a reasonable range.2.The use of AUTOCAD-VBA secondary development function to establish a geometric model,the use of ADINA to establish a finite element model,the ISO-834 international standard temperature curve for the fire mode,the temperature of concrete structures at high temperatures,stress,strain,cracks and other key physical indicators Thermal coupling analysis.3.Again using ADINA to conduct high-temperature burst spalling thermal coupling time history analysis,the temperature,stress,strain,cracks and other conditions corresponding to different fire loads at different times were obtained;the influencing factors of high temperature burst spalling were studied,mainly including the number of fire boundary,Fire-rising mode,equivalent thermal expansion coefficient of pore water(pore water pressure),concrete strength grade,external force load of structure field,thermal expansion coefficient of aggregate.4.On the basis of the “procedure” algorithm,considering the impact of fire factors,and correspondingly correcting the deficiency of the formula carrying capacity assessment formula,that is,by introducing the fire damage coefficient K1 to correct two different limit state assessment formulas,and using concrete Carbonation,peeling damage of concrete,and strength of steel bars were used as detection indexes.The values of the fire damage coefficient were determined according to the corresponding technical specifications and analysis methods.5.Based on the engineering background of a concrete box girder bridge with fire,according to the detection results of the bridge after the disaster,material conditions,appearance conditions,etc.,use Midas Civil to establish the finite element grid model of the fire bridge span and conduct RC design verification.For the different limit states,the evaluation of the bearing capacity of post-disaster box girder bridges was carried out using the revised formulas of this paper and the current evaluation formulae of the regulations,and the two assessment results were compared and analyzed.