Showing papers by "Structural Engineering Research Centre published in 2008"

Condition evaluation of existing reinforced concrete bridges using fuzzy based analytic hierarchy approach

Abstract: There is an urgent need for a systematic methodology for condition assessment of the bridges because the old bridges of most of the countries are inadequate to carry current-day traffic and satisfy the present codal provisions and even in newer bridges, deterioration caused by unforeseen service condition and deferred maintenance is of great concern. In view of this, an attempt has been made in this study to develop a systematic procedure and formulations for condition evaluation of existing bridges using Analytic Hierarchy Process in a fuzzy environment. Analytic Hierarchy Process (AHP) is an efficient decision making tool for complicated problems with multiple evaluation criteria and uncertainty. Fuzzy logic approach has been used to take care of the uncertainties and imprecision in the bridge inspector's observations. In this paper, first, a methodology has been proposed for condition ranking of number of reinforced concrete (RC) bridges. Then, based on the results obtained from prioritization, rating of the most deserved bridge has been carried out using MADM based fuzzy logic. Computer programs have been developed based on the formulations presented in this paper for evaluating condition of existing bridges and the details are presented in the paper. The methodology and its application are demonstrated through a case study. This methodology would certainly help the engineers and policy makers concerned with bridge management to overcome the problem related to prioritization and decision on funding related to rehabilitation of bridges.

Experimental Investigations on the Seismic Response of a Base-Isolated Reinforced Concrete Frame Model

Abstract: The existing knowledge based on the physical characteristics of rubber-based seismic isolators and the validity of assumptions involved in design can be strengthened with shake table tests and field monitoring during earthquakes. Existing structures can be retrofitted with seismic isolators and successful examples are coming up day by day. This paper presents the results of analytical and experimental investigations of a one-third scaled model of a reinforced concrete soft first-storied structure mounted on natural rubber-based isolators and subjected to uniaxial seismic motion. Translational and rocking responses of the scaled model were measured under four different synthetic time histories, covering a wide range of frequencies. Through base isolation, the time period of the horizontal mode is far removed from the peak spectrum but the rocking modes may well be entrapped in the peak region. Hence, a simplified fail-safe system for protection against overturning was also studied.

Determination of bounds on failure probability in the presence of hybrid uncertainties

Abstract: A fundamental component of safety assessment is the appropriate representation and incorporation of uncertainty. A procedure for handling hybrid uncertainties in stochastic mechanics problems is presented. The procedure can be used for determining the bounds on failure probability for cases where failure probability is a monotonic function of the fuzzy variables. The procedure is illustrated through an example problem of safety assessment of a nuclear power plant piping component against stress corrosion cracking, considering the stochastic evolution of stress corrosion cracks with time. It is found that the bounds obtained enclose the values of failure probability obtained from probabilistic analyses.

Simple Formulation for the Flexure of Plates on Nonlinear Foundation

Abstract: Plates resting on an elastic medium are normally analyzed in a simplified way using the linear Winkler foundation approach. Nevertheless, plates resting on layered medium with vast differences in their moduli exhibit nonlinear behavior under pressure. The present technical note deals with a nonlinear finite-element procedure to analyze plates with linear strain displacement relations resting on a nonlinear elastic media. The coupled problem is formulated using the total potential energy (TPE) concept. The nonlinear foundation stiffness matrices have been derived using the Taylor expansion of the TPE at equilibrium and a symbolism of grouping the energy contributions. The nonlinear foundation stiffness matrices derived in the present technical note have been demonstrated to yield results that agree well with published results in the literature. A brief parametric study on the effects of nonlinearity of the foundation is also presented using the proposed foundation stiffness matrices.

Effect Of Trenches On Attenuation Of Ground Vibration During Pile Driving

Abstract: The ground vibration generated from pile driving, could cause dis- turbances to adjacent structures and also disrupt the operation of nearby sensitive equipment. Raleigh waves that propagate in a zone close to the ground surface carries most of the vibration energy affecting near by structures. Trenches open or filled (wave barriers) are often used in engineering practice to reduce the ground vibrations caused by propagating surface (Rayleigh) waves of relatively small wavelengths. The measurement of ground vibrations during prototype pile driving at a site in Chennai was carried out. The analysis was carried using a finite element code, PLAXIS, to study the ground vibration with and without trenches during driving of steel casing with bottom shoe. This paper presents driving were compared with analytical results. This paper present the results of out to study the effect of parameters such as trench dimension, location of trench from the piling and strength of concrete trenches on ground vibration.

A Graphical Method of Damage Detection and Quantification for Structures

Abstract: Damages occur in all structures due to several reasons. Research in the area of damage detection has been of interest to the researchers for several years. Damage detection methods help in early detection and hence early repair and rehabilitation of structures. In this paper, a graphical method has been implemented to detect and quantify the damage. Further, in this work, the method has been generalised to solve the damage detection in all beam structures, independent of variations in geometric or material characteristics of the structural system. The frequencies are non‐dimensioned as frequency ratios and are used in the studies. Detailed studies have been performed to arrive at the generalised method. The abilities of the method have been highlighted using the numerical simulation results.

Algorithm for Detection of Change Point in On-Line Monitoring Data

Abstract: The detection of abrupt changes in observed/estimated physical processes is an issue of concern in many applications. An algorithm for single change point detection in Gaussian white noise processes is presented in this paper. The algorithm progressively includes and analyzes the observed data points, and hence is suitable for detection of change point in on-line monitoring data. Two example problems are presented, wherein Monte Carlo simulation technique is used, to illustrate the proposed algorithm. The performance of the algorithm with respect to changes in shift amplitude, intensity of the signal, and rate of sampling are studied, and the observed trends indicate that the proposed algorithm possesses the desirable properties of change detection algorithms.