Hello.
When I search for information about sizing for the spring deck construction, I come across the term utilization rate. What does it mean, for example, in the following sentence:
"C24 45x145 Construction timber, deformation 11 mm (L/227), utilization rate 76%"?
Is 76% good or bad, should I approach 100% or 0%? I can't find a pattern in it.
I guess the deformation is how "wobbly" it gets, or am I wrong?
/Oscar
When I search for information about sizing for the spring deck construction, I come across the term utilization rate. What does it mean, for example, in the following sentence:
"C24 45x145 Construction timber, deformation 11 mm (L/227), utilization rate 76%"?
Is 76% good or bad, should I approach 100% or 0%? I can't find a pattern in it.
I guess the deformation is how "wobbly" it gets, or am I wrong?
/Oscar
Hello. Welcome to the forum.
I am not 100% sure, but almost sure anyway.
Utilization rate is how close you have come to the maximum stress with the chosen dimensions.
So the further you are from 100%, the more safety margin there is, but the more wood is also needed, i.e., larger dimensions and more expensive. You simply want the utilization rate not to be really close to 100%, but not very low either.
The deformation referred to in that example is the maximum deflection (in the middle of the span) at maximum design load.
I am not 100% sure, but almost sure anyway.
Utilization rate is how close you have come to the maximum stress with the chosen dimensions.So the further you are from 100%, the more safety margin there is, but the more wood is also needed, i.e., larger dimensions and more expensive. You simply want the utilization rate not to be really close to 100%, but not very low either.
The deformation referred to in that example is the maximum deflection (in the middle of the span) at maximum design load.
When sizing, both deformation requirements and strength requirements must be met. The utilization rate is the measure of how well the strength requirement is met. A utilization rate below (or equal to) 100% is OK. A high utilization rate (90-100%) means the material is well utilized, well-sized. A 76% utilization rate is normal when the deformation requirement is the determining factor. 0% means extreme over-dimensioning, unused material, economic insanity.
Yes, it is undersized and at risk of breaking, but it doesn't say anything about the deflection.Ochen said:
At short spans, one can have a high utilization rate with low deflection (the strength requirement becomes the dimensioning factor).
The deck will be in two parts, one being 2 meters and the other just under 3 meters. Thus, the span will be just under these measurements. I was thinking of using 45*195 for the wider section and 45*145 for the slightly narrower one. What do you think, is that sufficient?
With a maximum center-to-center spacing of 60 cm between joists, it works fine.
For example, I have a 2.40 span with 45x145 at cc60 in the shed. It's a bit on the edge; you can feel some flex in the joists occasionally. But indoors, you're more sensitive to flex, so for a deck, it might feel 100% OK. A 2-meter span for the deck works splendidly.
45x220 can handle upwards of 4 meters without too much inconvenience, so 45x195 for 3 meters must be OK.
For example, I have a 2.40 span with 45x145 at cc60 in the shed. It's a bit on the edge; you can feel some flex in the joists occasionally. But indoors, you're more sensitive to flex, so for a deck, it might feel 100% OK. A 2-meter span for the deck works splendidly.
45x220 can handle upwards of 4 meters without too much inconvenience, so 45x195 for 3 meters must be OK.