Understanding compression

Weights on floor - understanding compression

Is the insulation strong enough? Will it take the weight of my furniture, or even my car? What about my balcony, will I be able to walk on it?

If you’ve asked yourself any or all of these questions, today’s blog is here to explain how we go about identifying the maximum loads our insulation can withstand and simplify what is regarded as a technically challenging topic.

Before we get started, we thought it might be helpful to define a few key words that you’re likely to hear along the way:

  • Relative deformation – a material’s reduction in thickness from its original state
  • Strain – a force that creates relative change in a material’s shape
  • Yield – the point in which a material fails / gives way
  • Compressive strength – the point at which the load causes the insulation to yield, before it reaches 10% relative deformation
  • Compressive stress – when the compressive strength is not reached, the point at which the load stress causes a 10% relative deformation of the insulation

When identifying the compressive capabilities of an insulation material, it undergoes two tests:

  • Short term testing (Compressive Behaviour BS EN 826:2013), and;
  • Long term testing (Compressive Creep BS EN 1606:2013)

Test 1 – the compressive behaviour test

The compressive behaviour test, also known as the ‘short term’ test, involves increasing a load at a constant rate of compression until the material’s compressive strength, or compressive stress at 10% relative deformation, is determined.

You might be wondering why some materials yield before 10% strain and others don’t. Well, different materials have a different levels of elasticity, meaning they can withstand different loads before they yield, hence the test would be continued until 10% strain is achieved if the material has not yielded before this.

The compressive strength or compressive stress figure identified through carrying out this test determines the maximum load that should never be exceeded during the product’s life.

Test 2 – the compressive creep test

Once you’ve identified the compressive stress / compressive strength of the material, you can then carry out the compressive creep test, also known as the ‘long test’, to determine the acceptable load that can be continuously applied to the material over its lifespan. This involves imposing a constant load on a material under specified conditions of temperature and humidity over a specific period of time, repeatedly measuring the material’s deformation.

Generally each test involves applying three differing loads onto three separate samples (unless you are looking to determine the long term effect of applying a specific load, in which case you would apply that load to all three samples). Each load would be a percentage of the figure identified in the compressive behaviour test; 15%, 20% and 25% for example. The three test samples are measured over a specific time period with the continuous deformation measured, these results are then used to estimate the product’s deformation over a 10, 25 or 50 year period. Typically, you would be looking for the material’s deformation to not significantly exceed 2% over the 20 – 50 year period.

Once the data has been collected, a qualified specialist such as a structural engineer can identify if the product is fit for purpose in its intended application, and if continuous loading of the material is within acceptable tolerances over the lifetime of the building.

So, there you have it: the basics of compression.

If you’d like to know more about the products we offer, take a look at the product pages on our website. These provide information on their suggested loading capabilities.

Alternatively, get in touch with a member of our technical department on 01544 387 382. They can further advise you regarding our insulation, as well as provide you with the relevant compressive data to assist your project.

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

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