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Interactive Audio Lesson
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Understanding Creep Measurement Setup
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Today we're going to learn about how creep is measured in concrete. First, can anyone tell me what tools we might need for this process?
Do we need a creep frame and some gauges?
Exactly! A creep frame with a dead load helps us apply constant stress to the concrete sample. We also use dial gauges or LVDTs to record strain. Any other thoughts on the companion specimens?
Are the companion specimens loaded or unloaded?
Great question, they are un-loaded. This helps isolate the effects of shrinkage from total deformation. Let's remember this setup as CD - Creep Deformation, Companion Specimen; it highlights our measuring approach!
Understanding the Creep Coefficient
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Why do we need the Creep Coefficient? Can someone explain what it represents?
Isn’t it the ratio of creep strain to elastic strain?
That's correct! It’s written as φ = Creep Strain / Elastic Strain at Loading. This coefficient is crucial for quantifying how much deformation is due to creep relative to the immediate elastic response.
What are some typical values for normal and high-strength concrete?
For normal concrete, it ranges from φ = 1.5 to 2.5, while high-strength concrete is from φ = 0.8 to 1.5. Remember this as 'Normal Needs More' versus 'High Needs Less'!
Introduction & Overview
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Quick Overview
Standard
The measurement of creep involves a structured approach using specialized equipment to quantify strain over time under constant stress. The Creep Coefficient helps to quantify creep effects relative to elastic strain.
Detailed
Measurement of Creep
Creep in concrete is measured using a specialized setup that typically includes a creep frame subjected to a dead load. Essential equipment like dial gauges or linear variable differential transformers (LVDTs) record the resulting strain. Companion specimens, which are un-loaded, are often used to separate shrinkage effects from total deformation in experimental measurements.
The Creep Coefficient (φ) is a critical parameter defined as the ratio of creep strain to the elastic strain at loading:
\[ φ = \frac{Creep\ Strain}{Elastic\ Strain\ at\ Loading} \]
Typical values for creep coefficients are approximately:
- Normal concrete: φ = 1.5 to 2.5
- High-strength concrete: φ = 0.8 to 1.5
Understanding how to accurately measure creep is imperative in engineering applications, particularly to ensure the stability and longevity of concrete structures under sustained loads.
Audio Book
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Creep Test Setup
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- A creep test is conducted using:
- A creep frame with dead load.
- Dial gauges or LVDTs to record strain.
- Companion specimens without load to isolate shrinkage from total deformation.
Detailed Explanation
To measure creep in concrete, a dedicated setup is needed. This includes a creep frame which holds a weight that applies stress to the concrete specimen. The strain, or deformation, that occurs over time is monitored using instruments such as dial gauges or Linear Variable Differential Transformers (LVDTs). These tools help in recording the exact amount of deformation. Additionally, companion specimens that are not subjected to any load are tested to separate the effects of shrinkage from those of creep, ensuring more accurate results.
Examples & Analogies
Think of a sponge that swells when wet. If you apply a heavy object on it, it deforms over time, much like concrete under stress. However, to understand how much of its change is due to being squished (creep) versus just losing water (shrinkage), you can compare it with another sponge that doesn't have any weight on it. This setup in concrete testing helps achieve that clarity.
Creep Coefficient
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- The Creep Coefficient is a commonly used parameter:
- Creep Strain
- ϕ = Elastic Strain at loading
- Typical values:
- Normal concrete: φ = 1.5 to 2.5
- High-strength concrete: φ = 0.8 to 1.5.
Detailed Explanation
The Creep Coefficient (φ) is a critical parameter that quantifies creep. It is defined as the ratio of creep strain to the elastic strain that occurred when the load was first applied. For typical concrete, this coefficient ranges from 1.5 to 2.5, indicating how much deformation occurs in response to stress over time compared to the initial elastic deformation. In contrast, high-strength concrete, which is denser and often less susceptible to creep, shows a lower creep coefficient, ranging from 0.8 to 1.5.
Examples & Analogies
Imagine stretching a rubber band. The immediate stretch can be compared to elastic strain, while the gradual extension over time, as it remains under tension, represents creep. If you were to measure how much longer the rubber band stretches after being held for a while versus how much it stretched instantly, you would get a coefficient akin to the creep coefficient in concrete testing. This helps engineers understand how structures might deform over the long term.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Creep Measurement: Involves specialized tools like creep frames, gauges, and companion specimens to determine deformation due to sustained load.
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Creep Coefficient: A significant ratio that measures creep strain in relation to elastic strain, helping engineers assess the long-term stability of concrete.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Example of experimental setup for measuring creep using a standard creep frame and LVDTs for accuracy.
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A case where improper measurement of creep led to structural failure in a high-rise building.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Creep takes time, on strain it will climb, measured with gauges, let’s check it on time.
📖 Fascinating Stories
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Imagine a builder who constantly checks the building’s structure over time. Every time he adds weight, he measures the strain with his tools, making sure everything holds solid without cracking - that’s the essence of creeps.
🧠 Other Memory Gems
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For Measuring Creep, remember 'C.G.C.': Creep Gauge Companions!
🎯 Super Acronyms
C.R.E.E.P. - Creep Ratios Existently Effect Performance!
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Creep
Definition:
Gradual increase in strain in concrete under constant stress over time.
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Term: Creep Coefficient (φ)
Definition:
A ratio used to measure the extent of creep deformation relative to elastic deformation.
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Term: Dialect Gauge
Definition:
A tool used to measure displacements in materials, often indicating strain in creep tests.
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Term: LVDT (Linear Variable Differential Transformer)
Definition:
A device used to measure small displacements and strains.
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Term: Companion Specimens
Definition:
Unloaded concrete samples used in testing to separate the effects of shrinkage from total deformation.