Strategic Project Grant: Protecting Canadas Concrete Bridge & - PowerPoint PPT Presentation

Strategic Project Grant: Protecting Canada’s Concrete Bridge & Related Research Neil Hoult (Queen’s), Evan Bentz (U of T) Xiaoyi Bao (Ottawa), Michael Collins (U of T), Mark Green & Andy Take (Queen’s)

Overview - Projects Fibre Optic Strain Measurement Digital Image-based Strain Measurement A brief tangent on where this might go Thermal Effects Creep Effects Non-linear Finite Element Analysis

Principle of distributed fibre optic measurement Optical fibres reflect light due to naturally occurring phenomena in the fibre itself. Rayleigh scattering occurs when light in an optical fibre interacts with the silica molecules and is reflected back. Rayleigh scattering is also the answer to the question “why is the sky blue?” Brillouin scattering occurs when light in an optical fibre interacts with quasiparticles and is reflected back. In both cases the frequency of the reflected light is a function of the elongation of the optical fibre, which in turn is a function of the strain due to both applied stress and temperature.

Fibre Optic Strain Measurement Technologies Strain Strain Sampling Technology Measurement Resolution Rate Bragg Grating Discrete ~ 1με < 1 sec Brillouin Optical Time- Distributed ~ 100με > 1 min Domain Reflectometry Optical Frequency Distributed ~ 1με? < 1 min Domain Reflectometry

Distributed strain measurement

Field Installation Here

Field Installation Cambridge Test Bed

Field Installation Three span precast prestressed concrete bridge. Optical fibres were installed in 6 beams in the western-most span of the bridge to measure strain change due to creep in the concrete.

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 3.3m 4m -700 -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 Predicted strain at mid-span due to prestress & -600 self-weight -700 -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 One day after release -700 -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 9 days after release -700 -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 Predicted midspan strain after 9 days -700 -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 -700 30 days after release -800 20 24 28 32 36 40 44 48 Length along fibre (m)

0 Initial compressive strain after pretension is released -100 Strain change (microstrain -200 -300 -400 -500 -600 -700 Predicted strain after 30 days -800 20 24 28 32 36 40 44 48 Length along fibre (m)

In this project Aim to get better than 10 microstrain resolution over a 20mm gauge length. Combine temperature and total strain measurements in one fibre. Determine the effects of temperature on strain readings for internally and externally bonded fibres. Install the system on a reinforced concrete bridge and take measurements during load tests and over the long-term.

Digital Image-based Strain Measurement By comparing a series of digital images, the movement of pixels groups (changes in the pictures) can be tracked. Goal: to develop a 2-D low or high speed strain and displacement measurement system. Example Application: FRP Strains The Problem • Strain efficiency of FRP wrapped cylinders Collaborators • Luke Bisby

Application: FRP Strains Results:

Application: FRP Strains Results: 19

Application: Flexural Testing The Problem • What is the relationship between negative water pressures and the tensile strength of clay? Collaborators • Malcolm Bolton, Gopal Madabhushi, and I. Thushyanthan (Cambridge)

Application: Flexural Testing Experimental Setup

Application: Flexural Testing 22

Application: Flexural Testing Results 23

Wireless Sensor Networks Nodes Gateway Mesh Topology Star Topology

Challenge: Data Management

Temperature Effects – Testing Facilities • 3 large rooms • +40C to -40C • Large specimens • Rapid freeze-thaw • Test at low temperature

Effects of temperature Want to explore the affect of temperature on: Reinforced concrete strength - relationship between crack width and shear strength Sensor readings - what are the offsets for both the fibre optic and PiV based systems Stresses - what’s harmless thermal expansion and what are critical stresses

Varying Load Effects – Testing Facilities • 60 hydraulic jacks: • 40 in-plane, which have a capacity of 1000 kilonewtons (kN) • 20 out-of-plane, which have a capacity of 500 kN • Specimens up to 1.6 m square by 0.4 m thick can be accommodated. • Can be used to apply bending, shear and torsional loading to regular and high-strength reinforced concrete elements

Types of 2D MCFT Analyses Response-2000 Fibre-model with shear considered in each fibre Hand Calculations

“New Element”

Example: Prestressed externally eccentrically post-tensioned bridge Aravinthan, Witchukreangkrai and Mutsuyoshi, 2005

“The maintenance of the works is the most important part of the duties of this office, wherefore it is necessary that whoever is placed in charge of them should know which of them are in need of having money spent upon them." Julius Frontinus, Curator Aquarium, AD 97.