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A short class with Sarah and her students. The other ways are under More.
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Today, we're going to learn about 'creep' in concrete. Can anyone explain what they think creep might mean when discussing concrete?
Isn't it when the concrete slowly deforms under load?
Absolutely! Creep is the time-dependent increase in strain that happens in concrete when a load is applied. It's quite important for understanding how concrete behaves over time. Remember the acronym 'TIPS' for the factors influencing creep: Temperature, Initial load, Past loading history, and Stress level.
So, if the temperature is high, does that mean creep happens faster?
Yes, precisely! High temperatures can accelerate creep. It's important to design structures considering these factors.
What about humidity? Does that affect it too?
Great question! Lower humidity increases creep as well. Now, let's summarize: Creep is a slow, continuous change in concrete when it's under constant load, affected by temperature, humidity, and other factors.
Let's discuss how creep actually occurs in concrete. Does anyone know the mechanisms behind it?
I think it has to do with microcracks or something in the concrete?
Correct! Creep is caused by viscous flow and microcrack development. Now, can anyone tell me the four stages of creep?
There's Instantaneous strain and then Primary creep?
Yes! You’ve got two of the stages! They are: 1. Instantaneous Strain, 2. Primary Creep, 3. Secondary Creep, and 4. Tertiary Creep. Now, who can describe what happens in secondary creep?
Is that when the strain increases at a slower rate?
Exactly right! It represents a steady strain development. Remember, understanding these stages is crucial for predicting how a structure might behave over time.
Now, let’s explore the effects of creep on concrete structures. What can happen if we don’t account for creep in our designs?
Maybe the structure can become misaligned or fail?
Exactly! Loss of prestress in prestressed concrete and increased deflection in beams and slabs are just a couple of consequences. Can anyone think of a real-world example where this might be critical?
I can see how a bridge could have issues if creep isn't accounted for right!
Absolutely! Creep can lead to dangerous situations if ignored. Always remember to consider the long-term effects in your designs!
The time-dependent increase in strain under sustained load.
Small cracks that contribute to the deformation of concrete over time.
Internal movement within concrete that leads to creep.
The phases of creep including instantaneous, primary, secondary, and tertiary.
Creep in concrete will not sleep, under load, it will peep.
Imagine a bridge that, over years, slowly drags down on its supports—this is creep in action, showing how time changes strength.
Remember the stages of creep with 'I P S T' - Instantaneous, Primary, Secondary, Tertiary.
TIPS: Temperature, Initial load, Past history, Stress level impacts creep.
Term
Creep
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Term
Instantaneous Strain
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Term
Tertiary Creep
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The time-dependent increase in strain under a sustained load in concrete.
Formation of small cracks in concrete that lead to time-dependent deformation like creep.
The gradual deformation of concrete under load due to internal friction.
The immediate deformation that occurs when a load is first applied.
A rapid strain increase occurring immediately after loading.
A steady and slower strain development after the rapid increase.
A rare stage of accelerated strain that may lead to failure.
Creep is the time-dependent increase in strain under a constant load in hardened concrete.
Creep is defined as the gradual change in shape and size of concrete under sustained load, a phenomenon that can significantly affect the durability and serviceability of concrete structures. Understanding its mechanisms and factors is crucial for effective design and construction.
Creep is a critical concept in the study of hardened concrete, defined as the time-dependent increase in strain that occurs under sustained load, even when the stress level remains constant. This phenomenon primarily affects concrete in compression and involves several underlying mechanisms.
Creep occurs due to the viscous flow within the concrete matrix and the development of microcracks within the cement paste. It is influenced by a variety of factors, including:
Creep can be divided into four stages:
The amount of creep exhibited by concrete is influenced by multiple factors:
Understanding creep is essential as it can lead to significant long-term consequences such as: