Risk & Reliability

Completed Projects

Durability-based Service Life Design of RC Structural Elementsc

Durability-based Service Life Design of RC Structural Elementsc

Quantification of environmental aggressiveness towards reinforced concrete structural elements

  • Proposed environmental aggressiveness factor (EAF)
    • Quantifies the environmental aggressiveness
    • Uses the concept of additive fuzzy system
  • Takes into account:
    • ambiguities in selection of exposure condition
    • effect of temperature
Durability-based Service Life Design of RC Structural Elementsc

Proposed method for determination of environmental aggressiveness factor for characterizing the aggressiveness of the environment

Markov chain modelling of crackwidths in RC flexural members subjected to fatigue loading

  • Nonhomogeneous Markov chain model for evolution of maximum crackwidth with applied load cycles
    • Useful for computing reliability of system, against the limit state of maximum crackwidth under fatigue loading
  • Proposed equation for characteristic maximum crackwidth (w*)
Durability-based Service Life Design of RC Structural Elementsc
Durability-based Service Life Design of RC Structural Elementsc

Unconditional probabilities of different states of beam at different load cycles (x – experimentally observed state)

Virtual aging concept for maintenance scheduling of corrosion affected RC structural elements

  • Integrates the concepts of:
    • virtual aging
    • failure rate
    • time-variant reliability
  • Helps in selecting the optimal time and degree of repair at the design stage
Durability-based Service Life Design of RC Structural Elementsc

Time variant reliability analysis as a tool for maintenance scheduling

Durability-based service life estimation of reinforced concrete structural elements

  • Methodology for durability-based service life estimation of reinforced concrete flexural elements
    • Degradation mechanism – chloride-induced corrosion of reinforcement
    • takes into consideration the fuzzy and random uncertainties
Durability-based Service Life Design of RC Structural Elementsc

Proposed methodology for service life design

Recommendations to BIS

Based on the studies carried out at CSIR-SERC, recommendations, which improve upon the existing durability- and serviceability-related provisions for the design of reinforced concrete structural elements in IS 456, are proposed. These recommendations will be useful while standardising of the Indian codes to meet international safety requirements. 

  • Durability-based service life design
    • Service lives for different types of structures
    • Quantification of environmental aggressiveness
    • Detailed exposure classification
    • Critical chloride content value
    • Minimum cover for reinforced concrete slabs
    • Reliability-based design of concrete cover thickness
    • Reliability analysis for the selection of type of surface coating
  • Serviceability limit state

            Characteristic crackwidths for reinforced concrete flexural members under static and fatigue loading

Condition Assessment and Remaining Life Estimation of Reinforced Concrete Structural Elements

Condition Assessment and Remaining Life Estimation of Reinforced Concrete Structural Elements

Condition assessment of reinforced concrete bridge girders based on limited inspection data

  • Uses the principal inspection data
    • Damage/distressed state of bridge girders – estimated using Markov Chain
    • Help in the possible ranking of bridges
  • Helps in the allocation of resources for repair/retrofitting

Corrosion state estimation of reinforced concrete bridge girders using Polya urn model

  • Proposed for the first time
  • Limited data from of field investigations required
  • Addresses the issue of generalized condition assessment when the inspection data from randomly selected girders in a bridge stock is available

Bayesian technique for condition assessment of corrosion affected reinforced concrete bridge girders

  • Useful for realistic service life assessment based on data from field inspection
  • Likelihood function – formulated using engineering judgment

Probabilities of corrosion initiation at the end of 11 years for the  Gimsøystraumen bridge girder

Human judgmental process in corrosion damage assessment of reinforced concrete structural elements

  • Accounts for the uncertainties associated with human mental process in making judgment
  • Multi-level Brunswikian lens model for corrosion damage assessment
  • Risk-based remaining life assessment – Markov chain model
Risk and Reliability

Probabilistic modelling of surface strains in reinforced concrete flexural elements

  • Alpha-stable distribution used for first time for describing the statistical variations in surface strains
    • justified by viewing the cracking process as an emergent structure (in thermodynamical sense)
  • Suitability demonstrated using experimental results
Risk and Reliability

Comparison of CDFs of the surface strains in extreme compression fibre

Stochastic modeling of evolution of strains in reinforced concrete flexural members

  • Proposed Bi-level homogeneous Gaussian MC model
  • Guidelines for:
    • selection of gauge length
    • optimal number of strain gauges
Risk and Reliability

Comparison of mean strains at the level of reinforcement

On-line detection of corrosion initiation in RC structural elements

  • Bayesian and maximum likelihood approaches
  • Formulations for: i) window size, ii) threshold value for decision function
Risk and Reliability

Comparison of actual and predicted times of corrosion initiation

Performance-based remaining life assessment of reinforced concrete bridge girders

  • Performability analysis & Brunswikian theory – applied for the first time
  • Useful for rational decision making regarding repair/replacement
Risk and Reliability

Remaining life assessment of corrosion affected reinforced concrete bridge girders based on data from field inspections

  • Additive fuzzy set along with EAF
  • Uses data from field inspections
Risk and Reliability
Risk and Reliability

Comparison of times for different levels of damage for the Rocky Point viaduct bridge girder

Performance of models for long-term deformations in PSC bridge girder

  • Identification of models for prediction of time-dependent prestress losses and camber
    • based on Comparison of long-term- prestress losses and mid-span camber with field measurements
Risk and Reliability
Risk and Reliability

Comparison of long-term prestress loss with field measurements on a PSC bridge box-girder

Advanced Design Guidelines for Prestressed Concrete Structural Elements

Advanced Design Guidelines for Prestressed Concrete Structural Elements

Stochastic analysis of prestress losses in instrumented prestressed concrete beams

  • Stochastic analysis approach, useful in the assessment of pre-stress losses in existing pre-stressed concrete beams
  • Characteristic prestress loss at any time =  Advanced Design Guidelines for Prestressed Concrete Structural Elements

where Advanced Design Guidelines for Prestressed Concrete Structural Elements is the mean total loss of prestress at time t computed using ACI 209 equation

Advanced Design Guidelines for Prestressed Concrete Structural Elements

Comparison of measured strains with the results of stochastic analysis

Reliability-based Design and Maintenance of Steel Railway Bridges

Reliability-based Design and Maintenance of Steel Railway Bridges

Probabilistic analysis of fatigue life of railway bridge girders

  • Fracture Mechanics approach
    • proposed relation for characteristic fatigue life
    • useful for risk-based inspection planning.
  • S-N curve approach
    • Combines probabilistic S-N curve with fatigue damage accumulation rule
  • Useful for development of optimal reliability-based maintenance strategy
Reliability-based Design and Maintenance of Steel Railway Bridges

Evolution of condition states with time for the bridge girder considered (condition states as defined in USDoT, 1995)

Fuzzy system reliability analysis for reliability-based optimal design railway bridge girder

  • Methodology for design decision making satisfying target system reliability requirements
Reliability-based Design and Maintenance of Steel Railway Bridges

Reliability Analysis of Industrial Structures

Reliability Analysis of Industrial Structures

Reliability analysis of industrial structures subjected to extreme winds

  • Concept of vulnerability index introduced
  • Prediction of possible failure/damage sequence – helps to strengthen the structure/structural components suitably to achieve required levels of safety
  • System reliability – estimated using the concept of hazard rate
    • useful in making decisions regarding type of member to be used
Reliability Analysis of Industrial Structures

Reliability Analysis of Steel Gabled Frame subjected to Extreme Winds

Reliability analysis of steel roof trusses

  • System reliability – Beta-unzipping Method
Reliability Analysis of Industrial Structures

Reliability Analysis of Steel Roof Truss

Risk analysis against overall damage of the industrial structure subjected to cyclonic winds

  • Bayes-Poisson process model
  • Help in estimating the expected structural and non-structural damage
  • Useful for
  • fixing the premiums by the insurance agencies
  • allocation of money by Governmental agencies for damage mitigation
Reliability Analysis of Industrial Structures

Overall Damage Analysis of a Steel Industrial Structure located in Andhra Pradesh Coastal region

Prediction of negative peak wind pressures on roofs of low-rise building

  • Alpha-stable distribution proposed
  • Use justified through its generality and physics of non-Gaussian diffusion process
Reliability Analysis of Industrial Structures

Ratio of observed- to model- 1-second peak wind pressure coefficients corresponding to 1% probability of non-exceedance

Seismic Risk Analysis of Structures and Regions

Seismic Risk Analysis of Structures and Regions

Seismic fragility analysis of structural elements/systems

  • RC bridge piers
  • RC chimneys
  • RC frames
  • Unreinforced brick masonry buildings
Seismic Risk Analysis of Structures and Regions

Seismic fragility analysis of RC bridge pier

Seismic Risk Analysis of Structures and Regions

Seismic fragility curves for a RC chimney

Seismic Risk Analysis of Structures and Regions

Seismic fragility curves for RC frames for the performance level of overall drift

Seismic Risk Analysis of Structures and Regions

Seismic fragility analysis of unreinforced brick masonry buildings

Expected seismic damage to corrosion affected RC framed structures

  • Takes into account effects of corrosion of reinforceemnt
    • reduction in area of steel
    • reduction in yield strength of steel
    • reduction in strain at ultimate strength of steel
    • reduction in compressive strength of cover concrete
  • Uses the modified Park and Ang damage index
  • Useful for determining the relative vulnerabilities of different structural schemes, and help in making decisions regarding repair/retrofit measures to be adopted
Seismic Risk Analysis of Structures and Regions

Effect of corrosion on the expected seismic damage to a reinforced concrete frame

Modelling of inter-arrival times of earthquakes

  • ANN model for predicting CDF of inter-arrival times of earthquake
    • better alternative to conventional statistical distribution models
Seismic Risk Analysis of Structures and Regions

Comparison of ANN predicted CDF and CDF using exponential distribution for inter-arrival times of earthquakes in Himalayan region

Classification of soil sites of Chennai city

  • Variation of depth of overburden and geotechnical details along two typical sections
    • Seismic refraction and Multi channel Analysis of Surface Wave (MASW) methods used to arrive at the P-wave- and S-wave -velocities of the sites
Seismic Risk Analysis of Structures and Regions

Variation of depth of overburden and geotechnical details along two typical sections for Chennai city

Development of site-specific response spectra

  • Response Spectra for Chennai city for a scenario earthquake
Seismic Risk Analysis of Structures and Regions

Response spectra  (with 5%  damping) for a scenario earthquake of 4.4 moment magnitude and 14 km hypocentral distance

Response Spectra for Chennai city for a risk-consistent earthquake

Seismic Risk Analysis of Structures and Regions

Response spectra  (with 5%  damping) for risk level corresponding to 2475 year return period

Research Contributions in Frontier Areas

Research Contributions in Frontier Areas

Multiscale Modelling of Concrete

  • Probabilistic analysis of modulus of elasticity of concrete through multiscale modelling
    • Useful for identifying the scales at which improvements/ modifications are required to engineer concrete to have required elastic properties
Research Contributions in Frontier Areas

Comparison of experimentally determined elastic modulus with the results of MCS

Probabilistic study of origin of creep of concrete at nanolevel

  • Considers dispersion of packing densities of C-S-H phases
  • Identified the need for using appropriate homogenization schemes
Research Contributions in Frontier Areas

Creep rate of cement paste with different water cement ratios

Adaptive  link mechanism-based model for basic creep of concrete

  • Aging process and mechanical response – described by breakage and replacement of links
Research Contributions in Frontier Areas

Scatter plot showing predicted values of creep compliance versus experimental values

Hybrid Uncertainty Handling

Development of acceleration response spectrum using fuzzy-random models of earthquake ground motions

  • Site-specific acceleration response spectra
  • useful for developing design response spectrums for the different seismic zones in India for different site conditions
Research Contributions in Frontier Areas

Defuzzified acceleration response spectra for different soil profiles in seismic zone IV

Conversion of probabilistic information into fuzzy sets

  • Proposed three approaches for converting probabilistic information into equivalent fuzzy set
    • method of least-square curve fitting
    • conservation of uncertainty (represented by the entropy)
    • Hausdorff distance
Research Contributions in Frontier Areas

Defuzzified acceleration response spectra for different soil profiles in seismic zone IV

Safety assessment of in the presence of hybrid uncertainties

  • New approach for hybrid uncertainty handling – combines vertex method with Monte Carlo simulation
  • Bounds on failure probability can be estimated
Research Contributions in Frontier Areas

Fuzzy sets for probability of failure against stress corrosion cracking for an austenitic steel piping component

Experimental Investigations

Experimental Investigations

Concrete creep testing laboratory

Ten Microtest F-ECH-4c/1200 kN hydraulic systems

  • Rigid 4-legged frame, height adjustable upper crosshead and hinged upper plates
  • Capacity – 1200 kN
  • Integrated hydro-pneumatic loading device
  • Integrated automatic closed loop servo-controlled system
  • Capable of testing 4, 150×300 mm concrete cylinders in series
Experimental Investigations
Experimental Investigations

Investigations on creep and shrinkage of engineered concrete

  • Concrete with 0%, 30% and 40% fly ash with specified 28 day compressive strength
    • -Age at loading: 28 days
    • Strain measurement: embedded vibrating wire strain gauge
Experimental Investigations

Measured strains on OPC and 30% fly ash concrete specimens

Experimental Investigations

Early age strains and internal temperature for concrete with 30% fly ash

Investigations on reinforced concrete beams with CFRP wrapping

  • The wrapping scheme adopted has resulted in change of failure mode from the shear to almost flexural
  • While increase in strength was marginal, significant improvement in stiffness gained by wrapping
Experimental Investigations

Test set-up and locations of electrical resistance strain gauges (30 mm gauge length) on the surface of the wrapped beams