Impulse Response (IR) Applications: Pile integrity testingPile integrity testing Floor slabs, walls and pavementsFloor slabs, walls and pavements Concrete consolidationConcrete consolidation Cylindrical structures (silos, chimney stacks and tanks)Cylindrical structures (silos, chimney stacks and tanks) Concrete bridgesConcrete bridges Cladding on high-rise buildingsCladding on high-rise buildings

Impulse Response Method Impulse Response Method

Impulse Response in use on Concrete Tank

Impulse Response (IR): Fundamentals in Pile Testing Low strain impact on pile head generates axial bar wave (compression stress)Low strain impact on pile head generates axial bar wave (compression stress) Impact force measured by load cellImpact force measured by load cell Response to impact measured by velocity transducer (geophone) in time domainResponse to impact measured by velocity transducer (geophone) in time domain FFT on force and velocity, combined to give transfer function: Mobility (v/F) v. frequencyFFT on force and velocity, combined to give transfer function: Mobility (v/F) v. frequency Theory well establishedTheory well established

Idealized Pile Response Curve

Impulse Response (IR): Basics in Structure Testing Low strain impact on structural element generates compression stress wave (as in Impact-Echo method, but lower frequency band [0-800 Hz] & much greater force input)Low strain impact on structural element generates compression stress wave (as in Impact-Echo method, but lower frequency band [0-800 Hz] & much greater force input) Impact force measured by load cellImpact force measured by load cell Response to impact measured by velocity transducer (geophone) in time domainResponse to impact measured by velocity transducer (geophone) in time domain FFT on force and velocity, combined to give transfer function: Mobility (v/F) v. frequencyFFT on force and velocity, combined to give transfer function: Mobility (v/F) v. frequency

IR Parameters – Structure Testing Dynamic stiffness in MN/mm from mobility slope between 0-50 HzDynamic stiffness in MN/mm from mobility slope between 0-50 Hz Average mobility from Hz (function of element thickness and concrete quality)Average mobility from Hz (function of element thickness and concrete quality) Slope of average mobility (function of concrete consolidation and proximity of structural shape changes)Slope of average mobility (function of concrete consolidation and proximity of structural shape changes) Peak/average mobility ratio (support beneath slabs on grade, voiding)Peak/average mobility ratio (support beneath slabs on grade, voiding)

Stiffness Average Mobility Example of IR Slab Test

IR from Highway Pavement Voiding beneath slab

IR from Cooling Tower Honeycomb Mobility Slope

Test point indicating low thickness and good support (Black) Test point indicating good thickness and good support (Blue) Mobility Plots Impulse Response Test Output

Debonded Bridge Deck Overlay