Loading the lesson
Loading the lesson
Search AllRounder.ai
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Learn it your way
A short class with Sarah and her students. The other ways are under More.
Sign up free to listen. Transcripts are free to read.
Good morning, everyone! Today, we will dive into the concept of creep in concrete. Can anyone tell me what they think creep is?
I think it's some kind of change in shape or size over time?
Exactly! Creep is the gradual increase in strain in concrete when it's under constant stress over a long duration. Unlike elastic deformation, which returns when the load is removed, creep is time-dependent. It’s crucial for us in engineering because it affects long-term stability of structures.
So, is it only for concrete?
Great question! While we're focusing on concrete, creep can occur in other materials as well. But the mechanisms vary across materials. Let's explore how factors like moisture and stress levels influence creep.
Now let's discuss how creep actually happens. Can someone mention a mechanism behind it?
I read something about moisture or fluid movement? Does that relate?
Yes! Moisture movement in the gel pores contributes to creep along with viscous flow in the cement paste and microcracking in transition zones. These processes are critical, especially in the different types of creep we've identified: basic creep, drying creep, and autogenous creep.
What’s the difference between drying creep and autogenous creep?
Drying creep occurs when concrete loses moisture under load, which can enhance creep significantly. Autogenous creep, on the other hand, happens even without external moisture and is significant in high-strength concrete. Consider it as 'internal shrinkage.'
Let’s move on to what influences creep. Can anyone name one factor affecting creep?
Is it the amount of water in the concrete mix?
Correct! The water-cement ratio plays a significant role; higher ratios increase creep due to greater porosity. Other factors include stress level, age at loading, and moisture conditions. For instance, loads applied early often lead to more creep.
And temperature matters too, right?
Absolutely! Higher temperatures can accelerate the creep rate. Good observation! Remember these factors as they are key during the design phase of structures.
Finally, let's talk about how we measure creep. Do any of you have ideas on what tools or methods might be used?
Maybe using sensors that measure strain over time?
Exactly! A creep test typically uses a creep frame with a defined load and gauges like dial gauges or LVDTs to measure strain. We can also use a creep coefficient to quantify the relationship of creep strain to elastic strain.
So our measurements can guide us in making better designs?
Yes, that's the goal! Understanding these measurements ensures we design structures that can withstand expected loads over their lifetimes.
The overall deformation of concrete under load, including both elastic and creep strains.
The property of concrete to exhibit both viscous and elastic behavior under stress and strain.
The process affecting creep, where moisture displacement in concrete influences deformation.
Techniques involving special equipment to assess the creep strain in concrete.
Creep is slow, it flows with time, under load it bends, like a mountain's climb.
Once upon a time, there was a tall tree under heavy rain. Even though it stood strong, the constant moisture made it slowly bend over years, representing concrete’s creep under pressure and moisture.
Use the acronym SWAT to remember Factors affecting creep: Stress, Water-cement ratio, Age at loading, Temperature.
CREAT - Creep is Related to: Elastic strain, Age, Temperature.
Term
What is the creep coefficient?
Click to flip
Term
What factors increase the rate of creep?
Click to flip
The gradual increase in strain in concrete subjected to a constant stress over a long period.
Creep occurring when concrete is under load in a sealed environment.
Creep that occurs when concrete loses moisture while under load.
Creep that happens in high-strength concrete due to internal chemical shrinkage without moisture loss.
The ratio of creep strain to elastic strain at loading.
Creep of concrete is a gradual deformation under sustained load that impacts the longevity and performance of concrete structures.
The creep phenomenon describes how concrete experiences gradual deformation when subjected to constant stress over time, which is crucial for civil engineers to consider in structural design. Various factors influence the degree of creep, including the applied stress level, moisture conditions, and type of cement used.
Concrete is a widely used construction material known for its strength and durability; however, it experiences time-dependent deformations known as creep and shrinkage. Creep refers specifically to the gradual increase in strain under sustained load, unlike elastic deformation which is immediate and reverse upon load removal. This section delves into the mechanisms of creep, its types, factors influencing it, and methods of measurement, emphasizing its significance in the design of high-rise structures and critical infrastructures.
Creep is defined as the gradual increase in strain due to a constant applied stress over an extended period.
The mechanism of creep arises mainly from the viscoelastic nature of the cement paste which includes:
Factors influencing creep include:
Creep tests involve using specific setups to measure the deformative response of concrete under controlled conditions. The creep coefficient θ is used to quantify thereacting relationship of creep strain to elastic strain and is critical in assessing material behavior in civil engineering design applications.