can a load-bearing beam sink somewhat over the years ?

[AnnaAnka]

Is anyone on the forum knowledgeable about whether a load-bearing beam can sink over the years and what would be normal over time?

Are there any time-related factors if it were to sink in a 50-year-old house, settling, or other factors that could affect it? Are there measurements that indicate what is normal and what differs from normal conditions?

Thanks in advance!

/AnnaAnka

 

[witten]

Hi! Yes, that knowledge is part of the designer's toolbox and can be calculated to determine the expected deflection. Here is some background information on the influencing factors, primarily moisture and long-term load. I assumed it was wood you were asking about.

https://www.traguiden.se/konstrukti...er/3.1.3-lastvaraktighets--och-klimatklasser/

 

[AnnaAnka]

Thank you for the response, and sorry for the late reply.

Are there any established measurements on how much it can/should normally sink? I read the article you sent but could use some sort of list if there is one.

Best regards, AnnaAnka

 

[witten]

When designing something new, it is common to limit the maximum deflection to the floor joists' length / 300 (under floor load). The vibration requirements are often stricter than this deflection requirement.

 

[heimlaga]

Wood has always had both an elastic deformation that returns upon unloading and a plastic deformation called creep, which does not return upon unloading. Therefore, different time classes are used when calculating deformations in wood structures. Creep occurs slowly over decades, so short-term loads cause negligible creep.

Older joists often are not dimensioned with regard to creep, and therefore the deflections can be very large by today's standards, even if the strength is more than sufficient. People accepted the existence of creep instead of trying to prevent it. In old log houses, they often hewed the inter-floor beams from somewhat crooked logs and turned the curve upwards, thinking that the inter-floor might straighten over time. Some took extra measures, thinking it would look better if the joist curved upwards rather than downwards.