K. Balaji Rao

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.

Neural network-based methodology for inter-arrival times of earthquakes

In this paper, an artificial neural network (ANN)–based methodology is proposed to determine the probability of inter-arrival time (IAT) of main shock of six broad seismic regions of India. Initially, classical methodology using exponential distribution is applied to IAT of earthquake events computed from earthquake catalog data. From the goodness-of-fit test results, it has been found that exponential distribution is not adequate. In this paper, a more efficient ANN-based methodology is proposed, and two ANN models are developed to determine the probability of IAT of earthquake events for a specified region, specified magnitude range or magnitude greater than the specified value. The performance of ANN models developed is validated with number of examples and found to predict the probability with minimal error compared to exponential distribution model. The methodology developed can be applied to any other region with the database of the respective regions.

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).

Handling Uncertainties in Knowledge Modeling and Acquisition for the Development of a Knowledge‐Based System

Knowledge acquisition is perhaps the most important phase in the development of knowledge-based systems (KBSs). Problems associated with knowledge acquisition include creating an explicit model of handling uncertainty for solving models in a complex domain. This article illustrates how knowledge modeling facilitates the acquisition of knowledge that is vague and uncertain. A hierarchical model is adopted for knowledge acquisition. The domain of the problem, i.e., damage assessment and vulnerability analysis of structures subjected to cyclones, is characterized by the presence of uncertainties in various forms. A KBS based on the hierarchical knowledge model has been developed that has the flexibility to handle the uncertainties using probabilistic and fuzzy set approaches depending on the nature of uncertainty. The hierarchical model for handling complexities and uncertainties in knowledge, the knowledge-acquisition strategy, the inference mechanism, and the representation used are described. Two typical sessions, one for damage assessment and another for vulnerability analysis, are presented to demonstrate the working of the KBS and its efficacy in handling uncertain information.

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.

Experimental investigation of reinforced concrete beams with and without CFRP wrapping

Abstract This paper presents the results of experimental investigations on six reinforced concrete beams, with three different shear span-to-depth ratios, which were tested under two-point loading. The aim of the work was to study the efficacy of Carbon Fibre Reinforced Polymer (CFRP) strips in enhancing shear capacity and/or changing the failure mode from brittle shear failure to ductile flexural failure. The results of the study indicate that while there is a marginal increase in first crack and ultimate loads, it is possible to achieve a change in the failure mode, and the monitored strain gauge data can be used to explain the failure pattern observed.

Partial Factors for Safety Assessment of T-Girder of RC Bridges Subjected to Chloride-Induced Corrosion Against Shear Limit State

The health assessment of bridge is becoming increasingly important in the view of the life extension programs. The main focus of this study is to develop a reliability-based procedure to carry out safety assessment against the shear limit state for a typical T-Girder bridge. Chloride-induced corrosion of reinforcement is considered to be the primary reason for deterioration of shear capacity with time. The girder is modeled by series connection of elements in the shear critical region. The shear capacity is determined by mechanical behavior (brittle or ductile) of each element depending on degree of corrosion in each element. Using the time-variant shear capacity obtained from the stochastic analysis, an attempt has been made to determine the partial factors using first-order reliability method (FORM). These partial factors can be used for safety assessment of similar T-Girder bridges located in marine environment and subjected to similar traffic loading.