Analysis On Reliability Of Serviceability Limit States For Reinforced Concrete Flexural Members

In recent years, the structural system constructed with high strength and light materials isdeveloping more and more, but its flexibility is bigger and damping is small, therefore easy toproduce larger deformation or vibration, and that can not meet the requirements of normaluse. The design experience shows that in some cases the cracks and deflection limits oftenhave an important role in the choice of section and the material consumption. At present,there are less study on the reliability of the serviceability limit states and the sensitivity of therandom variable influenced on the reliability. Reliability and sensitivity of the serviceabilitylimit states will be studied in this paper beyond this background.In order to have a more accurate prediction of the reliability of the reinforced concreteflexural members, the specification limits, the working load, the model of calculation, thegeometric size and material property will be treated as random variables in these paper,combined with the methodology of reliability,the paper will give the sensitivity coefficient ofall the random variables by AFOSM firstly, then make a quantitative analysis according to themagnitude of the sensitivity coefficient. According to the results of analysis, the designpersonnel can make appropriate adjustment according to the influence degree of each factor,the economy and practicality in the structure design. The analysis results can also provideforecast and optimization guidance, as to better meet the structure security requirements.According to the national standard “Code for Design of Concrete Structure”, the reliabilityindex for the structural members of reinforced concrete have not beengiven, which are controlled by serviceability limit states. A methodological framework wasproposed, which made use of fuzzy invalidation rule for reliability analysis of reinforcedconcrete members, and then the fuzzy reliability index of cracks and deflection of reinforcedconcrete members were obtained. Because the fuzzy reliability using conventional methods isan average，and there may be a lot of discrete between the average reliability and actualreliability. So it is necessary to discuss the calculation method for the confidence interval offuzzy reliability under the given degree of confidence. Engineering design personnel canmodify the design scheme and provide the theory basis according to the extent of the designrequirements.Also this paper comprehensively considers the safety, serviceability and durability of thereinforced concrete flexural members, introduces the concept of integrated reliability. Thecalculation method of integrated reliability is the same as the one of series system, Whichtreats the destruction of the flexural members as a series system composed by bend destructive, shear failure, big deformation and overrun crack. Finally a numerical exampleproved that this method in this paper can provide reference for engineering design, comparedwith the national standard “Unified Standard for Reliability Design of Building Structures”.