Research On Time-variant Reliability Of Existing RC Beam Bridge Under Fuzziness And Randomness

The structural performance of existing reinforced concrete (RC) bridges gradually deteriorates during active time due to material aging, adverse environment, inappropriate management and service. The structural reliability decreases and regular service is affected. The reliability of existing RC bridge is time-variant. The research on influencing factors of future or former structural resistance and reliability is largely restricted by experimental means and space time. So the limitation of some conclusions can not be avoided, and the uncertainty including fuzziness, randomness, and faultiness of knowledge can appear. The faultiness of knowledge is a weak uncertainty, and can be considered into fuzziness and randomness when it coexists with them.In order to rationally evaluate reliability of existing RC bridge during the whole active life, the problems on the time-variant reliability under fuzziness and randomness for mainly existing RC beam bridge are deeply investigated. This research project is supported by National Natural Science Fund of China under the Project No. 50478032"Research on Time-variant Reliability of Existing RC Bridge"and National West Communication Construction Fund of China under the Project No. 200631800019"Research on Residual Life of Concrete Bridge". The main research works include as follows:(1) The material durability degradation models under fuzziness and randomness are established. The reinforcement corrosion in RC bridge is considered to be induced by chloride ion. The fuzziness and randomness are simultaneously considered. The fuzzy probabilistic characteristic of the corrosion initiation time is studied. The Monte Carlo interval numerical simulation is introduced, and the degradation probabilistic models of time-variant main reinforcement area under two corrosion states are established. Meantime, the degradation probabilistic models under general and pitting corrosion are compared. The effect of pitting corrosion on small-diameter reinforcement is obvious, and the degradation probabilistic model of time-variant stirrup area is established. Based on the experimental investigation on mechanical property of corroded reinforcement in different members, the relationships between the quality corrosion rate and yield strength, the area corrosion rate and yield strength are obtained, and the degradation probabilistic model of reinforcement strength is established. Based on some existing time-variant models of concrete strength, the fuzziness is introduced, and the degradation probabilistic model of concrete strength is established.(2) The resistance degradation probabilistic model under fuzziness and randomness for flexural member is established. The effect of the bond strength degradation on resistance is incorporated. To consider material durability degradation, the fuzzy time-variant functions of the mean value and standard deviation for the unrepaired member resistance are derived based on the fuzzy stochastic process and error transfer theory. The fuzzy random time-variant probabilistic model of flexure member is established by an example RC beam bridge, and the analytical method for the mean value and standard deviation of resistance under the fuzziness changing with time is presented.(3) Based on the laboratory experimental investigation on members from two RC bridges, an estimation method on resistance is presented. Some influencing factors reducing member resistance are analyzed. The fuzzy membership functions on the nondestructive examination results of these factors are established, and the qualitative description is quantified. The fuzzing mathematics and analytic hierarchy process (AHP) are used to systematize these interrelated and interactional uncertain influencing factors. The synthetical reduction coefficient reflecting these influencing factors is computed accordingly. After that the finite element result without damage is combined with synthetical reduction coefficient to estimate the carrying capacity. The theoretical results are agreed with experimental values. This method can provide scientific basis for evaluation of existing RC bridge resistance.(4) The traffic load effect model for the existing highway bridge is established based on the equilibrium renewal process. The existing vehicle statistic data in China are used. The extreme values of the spacing intervals for different continuous arrivals and the vehicle weight are controlled by the truncated probabilistic distribution. The probability density functions of total weight and spacing intervals for n continuous arrivals are computed by the convolution formula. The probability density function of the length of convoy is derived based on the equilibrium renewal process. After that the bridge influence line transitive function is further combined to establish the traffic load effect model for existing highway bridge. This model can consider the varying traffic condition, and apply to reliability evaluation of existing bridges.(5) The design specific density of bridge member is considered as the constant value in exiting statistical data. The statistical parameters of the dead load of existing bridge are difficult to describe truly by the certain value due to some uncertain influencing factors. To consider these problems, the mean value and standard deviation of existing bridge dead load are described as the bounded closed fuzzy numbers, and the probabilistic model for dead load is expressed as the fuzzy probabilistic distribution. The variability of existing bridge dead load distribution parameters can be reflected by variety of threshold valueαin the selected fuzzy membership function.(6) The analytical method on the time-variant reliability under fuzziness and randomness for existing RC bridge is presented. To consider the fuzzy random time-variant characteristic of resistance and live load, fuzziness and randomness of dead load, fuzziness of failure criterion, the fuzzy limit state equation of load carrying capacity is established. The JC method is improved to solve the fuzzy time-variant reliability index, and the computing procedure is developed by Matlab language. The variety in reliability index of an example existing RC beam bridge with time and threshold valueаis analyzed. The variety law of reliability index under the fuzziness changing with service time is discussed. The conventional existing RC bridge time-variant reliability analysis considering randomness is developed to include simultaneously fuzziness and randomness.