K. Ramanjaneyulu

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

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 inspectors 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.

Multi-stage approach for structural damage identification using modal strain energy and evolutionary optimization techniques:

Deterioration and degradation of aging structures is a major concern worldwide. It is often necessary to evaluate the integrity of such structural systems. Early detection and eventual quantification of damage are important for improved safety, to prevent potential catastrophic events, and to extend the service life by repairing/retrofitting the components of the structure. Different methodologies have been proposed in the literature for the identification and localization of damage based on optimization techniques and modal-based approaches. The main drawback in using the optimization approach based on evolutionary algorithms is that it requires the evaluation of the objective function for the total population in each generation. As this is computationally intensive, in this study, a multi-stage approach has been proposed. In this, at first, localization of the damage was achieved so as to reduce the number of parameters of the objective function in the optimization approach. These identified damaged elements were analyzed further for exact identification and quantification of the damage using genetic algorithm (GA)-based optimization approach. To demonstrate the efficiency of the proposed hybrid approach, numerical studies have been carried out on selected structures. The approach of using modal strain energy change ratio to identify damage at first-stage identification is found to be very useful in reducing the objective function parameters in the optimization method. This multi-stage approach is found to be very efficient in the exact identification and quantification of damage in structures. The proposed approach could be used for identifying damage in large-scale structures.

Priority ranking towards condition assessment of existing reinforced concrete bridges

Existing old bridges in most countries were designed for less traffic and are inadequate to carry current-day traffic and satisfy the present codal provisions. Even for newer bridges, deterioration caused by unforeseen service conditions and deferred maintenance is causing great concern to bridge engineers. Hence, there is an urgent need for a systematic methodology for priority ranking of the bridges for both their rehabilitation in the future and for the allocation of funding. In this paper, an Analytic Hierarchy Process (AHP), which is an efficient decision making tool for complicated problems with multiple evaluation criteria and uncertainty, has been proposed for the condition ranking of reinforced concrete (RC) bridges. Fuzzy logic is used to handle the subjective judgement, imprecision and intuition involved in a bridge inspectors evaluation report. This methodology would certainly help engineers and bridge management policy makers to overcome the problems related to prioritization and decisions on funding related to the rehabilitation of bridges. The background information, the formulation and the details of the computer program developed in this study for the condition ranking of bridges are presented in this paper. The methodology and its application are demonstrated through a case study.

COMPUTATIONAL METHODOLOGIES FOR VIBRATION-BASED DAMAGE ASSESSMENT OF STRUCTURES

In the present work, computational methodologies based on artificial neural networks and genetic algorithms (GA) have been developed for identification of structural damage utilizing vibration data. The natural frequencies and mode shapes obtained from the finite element analysis for the first few modes have been considered for this purpose. A multi-stage hybrid methodology combining the modal strain energy criteria with GA has also been proposed, which showed improved damage identification capability as compared to the conventional GA, and proved to be computationally efficient. To demonstrate the efficiency of the proposed hybrid approach, numerical studies have been carried out on the truss structure. The efficacy of mode shape expansion in conjunction with GA is demonstrated for damage identification of reinforced concrete beam based on experimental modal data.

Seismic performance evaluation of exterior beam-column sub-assemblages designed according to different codal recommendations

In the present study, seismic performance of exterior beam-column sub-assemblages is evaluated by considering different stages of Eurocode (EC) and Indian Standard (IS) provisions for design of the reinforced concrete structures. The study has brought out the implications of the differences in the guidelines on seismic performance. It is found that the gravity load designed (GLD) structure is vulnerable to even medium intensity earthquake. Among the seismically designed specimens without ductile detailing, the one which was designed as per IS exhibits better performance compared to that designed according to the EC with 10% more energy dissipation under large drift ratio. Among the seismically designed and ductile detailed specimens, the one designed as per EC provisions for medium ductility could not perform as good as that designed as per ductile provisions from IS (25% less energy dissipation). Stiffness degradation of the specimens is also found to be a crucial parameter and varies considerably among the specimens. Therefore, earthquake design and ductile detailing provisions of different standards and their progressive improvements have considerable influence on seismic performance of reinforced concrete structures.

Evaluation of Longitudinal Force on a Railway Bridge Based on Strain Measurements

Evaluation of longitudinal force is very important for the performance evaluation of older bridges and for the design of new bridges. There is a growing demand to increase freight haulage in railway networks, in particular, on the iron ore routes of various zones of Indian railways. This proposed alteration may subject the bridges to higher tractive effort/braking forces together with higher axle loads. It is thus obvious that there is a need to check the performance of the concerned bridges under this proposed increased loading. Hence, as part of evaluating the bridges for higher axle loads, experimental investigations have been carried out on a typical steel plate girder railway bridge. This paper gives the summary of experimental investigations, test setups, and results obtained for the evaluation of longitudinal force. The longitudinal force evaluated based on the experiments for the increased axle loads is found to be within the design limits specified. The special fixtures developed for direct measurement of the longitudinal force are found to give the reliable results compared to the strain gage measurements on the girder. The results show that only part of the rail force is transmitted to the girder.

Seismic retrofitting of damaged exterior beam–column joints using fibre reinforced plastic composite–steel plate combined technique

A conventional gravity load design philosophy for reinforced concrete (RC) structures has been slowly replaced by seismic design since the 1970s. But, till recently, capacity design and ductile detailing were not strictly implemented in practice in many developing countries which are prone to seismic hazard. In the present study, performance of exterior beam–column joints designed based on ductile and non-ductile philosophy has been studied under cyclic load. It is found that although the incorporation of ductile detailing has considerably improved the seismic behaviour of the structural component, it could not assure the damage propagation in a safe zone. Moreover, in both specimens, the main damage has been concentrated in the joint zone irrespective of ductile detailing. Further, the damaged specimens were adequately repaired and suitably retrofitted using fibre reinforced plastic and steel plate and tested again under the same cyclic load. The retrofitted ‘NonDuctile’ specimen, as proposed in this study, could not only be able to regain its original performance (in terms of strength deterioration, stiffness degradation, energy dissipation), but has also shown improved performance in comparison to the original ones which is ideally desirable as well. Further, the retrofitted ‘Ductile’ specimen has shown a promising aspect of the proposed retrofitting strategy for seismically damaged components.

Health Assessment of a Plate Girder Railway Bridge under Increased Axle Loads

Most bridges are aging and do not have complete design information. Hence, field testing for the evaluation of the structural performance and health of bridges is becoming essential, but even sophisticated modern structural analysis techniques cannot replace field testing, especially in the case of determining the live-load performance of bridges. Furthermore, field data can be used to calibrate and fine-tune an analytical model to match the behavior observed in the field. In this paper, details of full-scale field testing and performance-evaluation studies carried out on a typical steel plate girder railway bridge under increased axle loads are presented. One of the primary objectives of the study is to evaluate the longitudinal force caused by the increased axle loads of freight wagons. The bridge superstructure is extensively instrumented to measure the responses under various static and dynamic tests carried out using the test train formation with increased axle loading. The strategies adopted for evaluating structural response parameters are discussed. In addition, dispersion of the longitudinal force from the rail to the superstructure is evaluated using an innovative fixture together with the appropriate instrumentation scheme. It is found that around 50% of the longitudinal force generated at the rail level is transferred to the bridge substructure of the instrumented span. Using the load spectra adopted in the current study, the remaining fatigue life of the bridge is also evaluated using different damage models and is estimated to be around 150 years. The methodologies developed and implemented for the health assessment of plate girder bridges would pave the way for undertaking timely maintenance.

Performance Evaluation of a Stone Masonry–Arch Railway Bridge under Increased Axle Loads

AbstractMany of the masonry arch bridges in the network of railway bridge stock belong to the civil engineering heritage of the railways. Therefore, their maintenance and management require careful consideration. An effective procedure for performance evaluation should promote solutions that are directed toward preservation and restoration of arch bridges by evaluating their existing structural capacity. In this paper, experimental methodologies adopted for the performance evaluation of a stone masonry–arch railway bridge are presented. One of the primary objectives of the current study was to evaluate the longitudinal force exerted on the bridge due to increased axle loads of freight wagons. An innovative technique using a flat jack was implemented for the evaluation of longitudinal stress due to increased axle load. Three-dimensional numerical modeling and analysis was carried out to identify the critical locations for fixing the flat jacks for evaluation of live-load stresses. A special instrumentation...

Evaluation of Strength Hierarchy of Beam-Column Joints of Existing RC Structures under Seismic Type Loading

To evaluate the strength hierarchy, three different types of exterior beam-column joint, i.e., gravity load designed, non ductile and ductile, following two different codes are considered. Strength of different components of beam-column joint, i.e., column, beam, and joint core, is individually calculated from different failure criteria. Shear strength of the joint is evaluated from softened strut and tie model. Strength hierarchy, ultimate strength, and critical failure modes of the specimens are analytically estimated and found to be well corroborated with the experimental results. The study will help in designing the earthquake resistant RC structures in a more rational way.