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

• f 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

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

Distributed strain measurement

Field Installation

Here

Field Installation

Test Bed Cambridge

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.

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

3.3m 4m

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

Predicted strain at mid-span due to prestress & self-weight

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

One day after release

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

9 days after release

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

Predicted midspan strain after 9 days

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

30 days after release

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20 24 28 32 36 40 44 48 Length along fibre (m) Strain change (microstrain Initial compressive strain after pretension is released

Predicted strain after 30 days

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

• f 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

Results:

Application: FRP Strains

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Results:

Application: FRP Strains

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

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Application: Flexural Testing

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Results

Application: Flexural Testing

Wireless Sensor Networks

Star Topology Mesh Topology Gateway Nodes

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

Hand Calculations Response-2000 Fibre-model with shear considered in each fibre

“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.