M. B. Anoop

A Refined Methodology for Durability-Based Service Life Estimation of Reinforced Concrete Structural Elements Considering Fuzzy and Random Uncertainties

A reliable method for service life estimation of the structural element is a prerequisite for service life design. A new methodology for durability-based service life estimation of reinforced concrete flexural elements with respect to chloride-induced corrosion of reinforcement is proposed. The methodology takes into consideration the fuzzy and random uncertainties associated with the variables involved in service life estimation by using a hybrid method combining the vertex method of fuzzy set theory with Monte Carlo simulation technique. It is also shown how to determine the bounds for characteristic value of failure probability from the resulting fuzzy set for failure probability with minimal computational effort. Using the methodology, the bounds for the characteristic value of failure probability for a reinforced concrete T-beam bridge girder has been determined. The service life of the structural element is determined by comparing the upper bound of characteristic value of failure probability with the target failure probability. The methodology will be useful for durability-based service life design and also for making decisions regarding in-service inspections.

Probabilistic Failure Analysis of Austenitic Nuclear Pipelines against Stress Corrosion Cracking

Abstract Stress corrosion cracking (SCC) is an important degradation mechanism to be considered for failure assessment of nuclear piping components made of austenitic steels. In this paper, an attempt has been made to compute the failure probabilities of a piping component against SCC with time using Monte Carlo simulation (MCS) technique. The initiation and propagation stages of stress corrosion cracks are modelled using the general methodology recommended in PRAISE modified by using the recommendations given by ASM for more rational modelling of stress field around cracks for estimating their growth with time. Degree of sensitization, applied stress, time to initiation of SCC, initial crack length, and initiation crack growth velocity are considered as random variables. An attempt has been made to study the stochastic propagation of stress corrosion cracks with time, using MCS technique. The trend of the distribution of crack depths at the initial stages obtained from simulation are compared and is found to be in satisfactory agreement with the relevant experimental observations reported in the literature. The failure probabilities are computed using two different failure criteria, namely (a) based on net-section stress and detectable leak rate as recommended in PRAISE and (b) based on R6 approach (using R6-option 1 curve as the failure assessment diagram). The procedure presented in the paper is general and the usefulness of the same is demonstrated through an example problem.

Probabilistic Fatigue Life Analysis of Welded Steel Plate Railway Bridge Girders using S-N Curve Approach

In this article, a generalized procedure for estimating probabilistic fatigue life of steel plate railway bridge girders with welded connections, considering plate breathing and a loading spectrum, is presented. The procedure combines the probabilistic S–N curve with Palmgren-Miner’s fatigue damage accumulation rule. One of the features of the study is determination of effect of the modeling error associated with the S–N curve on estimation on the fatigue life of bridge girders. Expressions for probability density functions of number of cycles to failure and accumulated fatigue damage are obtained in the closed form and Monte Carlo simulation, for the cases of without and with modeling error considered in fatigue life estimation, respectively. The use of the proposed procedure is illustrated by considering two railway plate girder bridges designed according to Indian Railway Standards. From the results obtained, it is noted that plate breathing is an important mechanism to be considered while estimating the fatigue life of the railway bridges. The results of the present investigation clearly bring out the importance of carrying out fatigue reliability analysis of different bridge spans, while establishing railway line reliability (as reliability of the weakest span would govern the line reliability).

Stochastic Analysis of Flexural Strength of RC Beams Subjected to Chloride Induced Corrosion

Importance of consideration of chloride induced corrosion in service life design of reinforced concrete (RC) structures situated in marine environment is well known. This paper attempts to provide, within the framework of Monte Carlo Simulation, methodologies for durability based service life design of RC members. A methodology using fragility curves is proposed to assist in the service life design of freely degrading RC flexural beams. For maintained RC beams, a methodology is developed, that incorporates the concepts of virtual aging, failure rate approach and time-variant reliability analysis. By addressing maintenance at the design stage itself, the methodology developed would help in sustainability based service life design. The use of both the methodologies is demonstrated by considering an example of T-beam. From the results of the example problem considered, it has been found that corrosion initiation time would govern the service life. 30% replacement of cement with pulverized fuel ash is considered as a sustainable alternative for construction of durable structures satisfying the service life performance targets with lesser number of repairs.

Condition assessment of structures: some issues related to handling uncertainties

It is known that the condition assessment of reinforced concrete structures subject to corrosion of reinforcement involves handling information coming from different sources beset with different types of uncertainties. This paper summarises some of the R&D investigations carried out at CSIR-SERC in developing the methodologies for condition assessment of reinforced concrete structures subject to chloride-induced corrosion of reinforcement. Two types of uncertainties namely, probabilistic and fuzzy are considered. The paper draws upon the results of already published technical material. Also included are some of the unpublished investigations related to the development of methodologies for condition assessment that are indicative of possible future research extensions.

Alpha-Stable Distribution for Prediction of Negative Peak Wind Pressures on Roofs of Low-Rise Building

In this paper, an attempt is made to study the applicability of alpha-stable distribution for modeling the negative peak wind pressures on low-rise building roofs. The required wind pressure data is obtained from the aerodynamic database of Tokyo Polytechnic University. The generality and flexibility offered by alpha-stable distribution makes it a candidate distribution as a single model for predicting the extreme values of negative peak wind pressure coefficients at different regions on the building roof. The results suggest that for the prediction of extreme negative wind pressure coefficients, alpha-stable distribution is a better candidate distribution than the Gumbel minimum.