अभिकलनी संरचनात्म्क यांत्रिकी

Methodologies for impact analysis of concrete structural components

Objectives

  • To develop a generalized concrete damage model for impact analysis of concrete structural components
  • To propose expressions for computation of target penetration depth under impact load

Challenges

  • Impulse load induces wave propagation in targets leading to scabbing and fragmentation
  • Large number of wide ranging parameters involved in concrete damage model

Methodology

  • Simplified analytical model by integrating moment balance equation and Newton’s second law of motion
  • Nonlinear explicit transient dynamic analysis of concrete structural components for impact loading
  • Calibrated the concrete damage model parameters using experimental results

Achievements

  • Developed a generalized concrete damage model for impact analysis
  • Separate expressions for plain and RC targets to compute penetration depth
  • Simplified analytical model capable of predicting target penetration depth, residual velocity and target resistance
Methodologies for impact analysis of concrete structural components

Structural integrity assessment of airborne external antenna and active antenna array unit (AAAU)

Uniqueness

  • Complex structure built with components such as antenna, beams, bottom cover, brackets, connector plate, inner duct, power supply unit, TRMM bay, top cover, rear hood, pylon interface, etc.

Methodology

  • Constraint conditions invoked in the integrated finite element model to interface beam, shell, gap and solid element
  • Free vibration analysis to extract natural frequencies and mode shapes
  • Dynamic response analysis under different loading conditions
Structural integrity assessment of airborne external antenna and active antenna array unit (AAAU)

Structural integrity assessment of a concrete island using seismic soil-structure interaction analysis

Objectives

  • To investigate the structural integrity of a massive concrete island along with built-up structures under seismic loading
  • To conduct soil-structure interaction analysis of the island using finite element method

Unique Features

  • Cluster of built-up structures supported on a common raft of 101.8m x 92.4m x 2.5m
  • Massive structure having a combined mass of 270600 t including the base raft
  • Finite element model of layered soil of extent 420m x 420m in plan and 400m depth
  • Natural frequencies of the structure extracted by free vibration analysis
  • Convolution/deconvolution analysis/technique to derive the base rock level excitation
  • Radiation of stress wave into unbounded foundation medium modelled by transmitting boundaries

Challenges

  • Unconventional and sensitive structure
  • Significant variation in the distribution of stiffness and mass

Analysis

  • Free-field analysis of the layered foundation medium to determine base rock-level excitation corresponding to a given surface-level excitation
  • Free vibration analysis to extract natural frequencies of the superstructure
  • Linear transient dynamic analysis to evaluate time-varying response of the structure and its interfaces
  • Three separate analysis for excitations along two horizontal and vertical directions

Contributions

  • Seismic soil structure interaction analysis of the massive concrete structure using a simple and novel convolution/deconvolution technique
  • Evaluated the seismic integrity of the structure against uplifting and suggested effective improvement measures
Structural integrity assessment of a concrete island using seismic soil-structure interaction analysis
Structural integrity assessment of a concrete island using seismic soil-structure interaction analysis
Structural integrity assessment of a concrete island using seismic soil-structure interaction analysis

Damage tolerant evaluation of wing bottom skin panel of an aircraft

Objective

  • To determine stress intensity factor for the panel during crack propagation
  • To evaluate residual strength (one of the aspects of damage tolerant evaluation) of wing bottom skin panel

Challenges

  • Modelling complexity such as fixtures, bolts, rivet holes, stiffeners, variation in thickness of base plate e
  • Determination of fracture parameter, stress intensity factor for the complex geometry

Methodology

  • Modelled all the parts of wing bottom skin panel including the gap between steel and aluminium near fixtures
  • Mathematical model developed to account for the variation in rivet hole diameter through the thickness of the plate
  • Crack tip singular elements generated to determine the fracture parameter, stress intensity factor (SIF)
  • Evaluated residual strength by using fracture toughness criterion and yield strength criterion

Achievements

  • Crack length vs SIF determined and used for damage tolerant evaluation
  • Evaluated residual strength envelope – useful for repair, retrofitting, schedule for inspection
Damage tolerant evaluation of wing bottom skin panel of an aircraft

Fracture analysis and remaining life prediction of aluminium alloy 2014A stiffened panels under fatigue loading

Objective

  • To determine material properties and crack growth constants of aluminium alloy
  • To conduct fracture analysis and evaluate stress intensity factor of stiffened panel
  • To predict the remaining life of aluminium alloy stiffened panel

Challenges

  • To obtain material properties and crack growth constants for a thin aluminium alloy panel
  • To evaluate stress intensity factor (SIF) for various positions and size of stiffener, size and crack length

Methodology

  • Tension coupon tests and compact tension tests on 2014A to evaluate mechanical properties and crack growth constants.
  • Domain integral technique to compute the Stress intensity factor (SIF) for various cases

Achievements

  • The remaining life of stiffened panel for particular size and position of stiffener can be estimated by knowing the remaining life of corresponding unstiffened panel
Fracture analysis and remaining life prediction of aluminium alloy 2014A stiffened panels under fatigue loading
Fracture analysis and remaining life prediction of aluminium alloy 2014A stiffened panels under fatigue loading

Finite element analysis of retrofitted RC beam with Ultra high strength concrete strip

Objective

  • To conduct nonlinear finite element analysis of damaged RC beam strengthened with ultra high strength concrete strip and to compare the predictions with the corresponding experimental observations

Challenges

  • To obtain material properties of concrete in compression, tension, steel, fracture energy of concrete and ultra high strength concrete (UHSC), stress vs crack width relation for concrete and UHSC
  • Predamage simulation of RC beam & attachment of UHSC strip

Methodology

  • A finite element model was developed accounting for the (i) degree of pre-damage, (ii) fracture behavior of concrete and UHSC through their respective specific fracture energy and stress-crack opening relation and (iii) elasto-plastic behavior of the reinforcing steel.

Achievements

  • An integrated finite element model was developed to predict the failure load and load-deflection behaviour of the retrofitted RC beams
  • The predicted load – deflection found to agree very well with the corresponding experimental observations
Finite element analysis of retrofitted RC beam with Ultra high strength concrete strip