Saptarshi Sasmal

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.

Can Carbon Nanotubes Make Wonders in Civil/Structural Engineering?

Nanoscience and nanotechnology provide enormous opportunities to engineers the properties of materials by working in atomic or molecular level. It has not only facilitated to overcome many limitations of conventional materials, but also tremendously improved the mechanical, physical and chemical properties of the materials as well. To develop high performance, multifunctional, ideal (high strength, ductile, crack free, durable) construction material, carbon nanotubes (CNTs) show promising role to modify/enhance the characteristics of the conventional construction materials such as concrete and steel. In the paper, a brief on geometry and mechanical properties, synthesis processes, possibilities and findings of different researchers on CNT reinforced composites is presented. It is also brought out that a crack free durable concrete is possible if certain issues such as uniform distribution of CNT in composite and bond behavior of CNT modified concrete can be addressed. Finally, few pre-proof of concepts are mentioned where CNTs can play the pivotal role to redefine the scope and ability of civil engineering, in general, and structural engineering, in particular.

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.

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.

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...

Remaining fatigue life of steel railway bridges under enhanced axle loads

In this study, various fatigue damage models proposed by researchers have been briefly discussed and found that the models are problem specific and their efficacy needs to be checked for high cyclic fatigue cases such as in railway bridges. Towards this, field studies were conducted to obtain the strain responses from a steel bridge during the passage of scheduled trains and test train formation with enhanced axle loading. Instrumentation was carried out at critical locations to obtain the responses from the girder. Three different scenarios have been considered to avoid the influence of noise. Further, numerical simulation of the bridge subjected to train loading at different speeds was carried out using ANSYS to obtain synthetic data of strain response from the validated finite element model. Analysis was carried out for normal as well as for futuristic speed of the trains. Responses obtained from field measurements as well as from numerical investigations were used to calculate the damage indices. Based on the damage indices, remaining fatigue life of the bridge was evaluated. The present study can be helpful in assessing the health condition of the railway bridges and to check the suitability of further increase in axle load or speed of trains.

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.

Numerical simulation of performance of near-surface mounted FRP-upgraded beam–column sub-assemblages under cyclic loading

This study deals with the performance of the upgrading schemes for the existing gravity load designed (GLD) reinforced concrete (RC) beam–column sub-assemblages using near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars. In this study, exterior beam–column sub-assemblage of a general RC-framed structure has been considered. Numerical investigations of the sub-assemblages have been carried out under cyclic loading using nonlinear finite element analysis. Experimentally validated numerical models have been used for evaluating the performance of various upgrading schemes using NSM bars. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond–slip relations between concrete and steel reinforcement have been incorporated. The study also includes numerical investigation of crack and failure patterns, ultimate load-carrying capacity, strain comparisons and formation of plastic hinges, load–displacement hysteresis, energy dissipation and ductility. Seismic performance in terms of energy dissipation and development of strain in beam bar shows that some of the upgraded schemes are found to be comparable to the seismically designed ductile specimens. The findings of this study would be helpful to the practising and design engineers for developing detailing criteria for newly designed – or strengthening of deficient – reinforced concrete structure.