After a major renovation, we have a deflection of 17 mm on a 4-meter span in the floor structure between the ground floor and the upper floor. This is probably due to a ridge beam being attached to a wall that in turn rests on the floor structure. We have had an engineer involved to ensure it is done correctly, so I am a bit surprised by the deflection. After looking around a bit, I have found, among other things, these tables from Träguiden:
https://www.traguiden.se/konstrukti...sgang/dimensionering-i-bruksgranstillstandet/
It shows that the maximum deflection should be 20 mm OR the length divided by 300. How should one view this? In our case, we have 17 mm (which is less than 20 mm) but also 1:230 (which is more than 1:300).
The floor on the upper floor is level because the carpenters shimmed up the floor structure before the subfloor was laid. It is in the ceiling of the lower floor where the deflection is visible. Should I be worried about the load-bearing capacity? I convince myself it should be okay because in schools and retail spaces, 30 mm or 1:200 is considered acceptable, but convincing oneself is rarely synonymous with the correct answer.
https://www.traguiden.se/konstrukti...sgang/dimensionering-i-bruksgranstillstandet/
It shows that the maximum deflection should be 20 mm OR the length divided by 300. How should one view this? In our case, we have 17 mm (which is less than 20 mm) but also 1:230 (which is more than 1:300).
The floor on the upper floor is level because the carpenters shimmed up the floor structure before the subfloor was laid. It is in the ceiling of the lower floor where the deflection is visible. Should I be worried about the load-bearing capacity? I convince myself it should be okay because in schools and retail spaces, 30 mm or 1:200 is considered acceptable, but convincing oneself is rarely synonymous with the correct answer.
In terms of strength, you don't need to worry.
In wooden constructions, deflection often governs the dimensioning, which is why wooden beams generally become relatively high. There is usually many percent of strength left when you just meet (or don't meet) the deflection requirements.
In wooden constructions, deflection often governs the dimensioning, which is why wooden beams generally become relatively high. There is usually many percent of strength left when you just meet (or don't meet) the deflection requirements.
It has probably been since mid-January.GoForIt said:
The floor does not seem to have bent down correspondingly, so I suspect that the deflection occurred before the carpenters laid the floor on the upper floor. The attachment is done as the designer prescribes, but his model only extends to the wall resting on the joists. It does not describe how the joists should be under this wall. I believe he accounted for the fact that the joists were subjected to more load before we remodeled than they would be afterward. I have not spoken to him further after the construction was completed, but I thought I would start by investigating the situation as much as possible on my own.
I can add that the bjälklaget is over a decade old but that it has been reused for our rebuilding.
The loads must be transferred and distributed all the way down, otherwise issues like the ones you describe may arise.
The carpenters should have raised the alarm already when they began the preparations for the flooring.
The carpenters should have raised the alarm already when they began the preparations for the flooring.
There are a few things that have gone wrong before, so I understand if they didn't take much notice. What do you do at this stage, keep an eye on whether the deflection changes? After how long can the deflection be considered "stabilized"?
Ok, maybe I should start by talking to the contractor anyway. But when it comes to margin - it shouldn't be at the breaking point as it is now, right? I'm mainly thinking about schools having l/200 as the design deflection and storage, etc. having l/150.
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· Etelä Pohjanmaa
· 2 467 posts
How old is the house? If you say that the new floor upstairs is straight, are you sure it's not about an old sag? Old floor plates usually have waves.
The house is 12 years old and there's a thin crack in a drywall joint in the ceiling, indicating some movement has occurred since it was painted, probably 12 years ago. I don't usually look at the ceiling much, but I just discovered this because I was playing around with a newly purchased laser distance measurerF Finndjävel said:
The size of the deflection of a floor structure is affected by 1) the span of the floor, 2) the spacing of the beams, 3) the load on the floor, 4) the cross-sectional dimensions of the beams, and 5) the quality of the beams in terms of strength. Since the span and likely the spacing are given, something has gone wrong regarding the load assumption, the assumption about quality, or the deflection calculation itself. If you want feedback that is more than speculation, you must provide all measurements for the current case.