The Randomness Of Greep And Reliability Of Prestressed Concrete Beams

Creep has a significant impact on the structure especially for prestressed structure which is more sensitive on it's effect. Accurate prediction of concrete creep and creep effects play important roles on prediction for it's long-term structural behavior. It is widely accepted that in the structure deviations caused by creep prediction model is much larger than that caused by the simplified method especially for that is more sensitive to the structure of creep. At present there is a big deviation between all the established results of creep models and the actual measurement, the deviation of each model predictions are not the same. Among them, the closest model with actual results is B3 model set by the Bazant professor, the model is based on the BP-KX model as a result of continuous improvement. This paper based on reliability theory takes the creep process as a random process, the factors that influence the creep of concrete as a random variable, calculating creep from the perspective of the probability. Uncertainty of concrete shrinkage and creep is as the following three parts:1) External uncertainty. That is from the parameters related to uncertainties such as age of concrete began to shrink, the thickness and the relative humidity of external environment component, etc.2) Internal uncertainty. That is from uncertainty of the mechanical properties and the process of the micro-shrinkage and creep.3) The uncertainty caused by imperfect calculation mode. With the help of finite element software, we establish finite element mode by using the Monte Carlo method.At last, the paper analyzes the reliability of the test beam on the basis of creep stochastic research. According to the method above-mentioned, the paper builds up finite element model of the test beam to investigate creep effect on the structural, and regards its middle span deflection and capacity as indexes to get influence causing by concrete creep. The calculation results reveal that reliability of test beam is declining caused by concrete creep. Then the paper makes sensitivity analysis of creep random variables and some suggestions are proposed.