Switch floor structure with steel beam

[Karl_Pedal]

Why not just leave it be? Seems like an incredible amount of work for an aesthetic thing

That is certainly one aspect of it, but what worries me is the potential creep deformation that could pose problems in the long run. The deflection seems to be balanced otherwise and doesn't move even when there is wet snow on the roof and terrace. Am I worrying unnecessarily?

 

[Karl_Pedal]

I still have difficulty orienting myself. An exterior photo plus some general information about the year of construction, construction method, etc., would help. 45x220 c/c 600 span 4.2 m (if they correspond to C 24) results in a deflection of L/300 with a normal distributed load. If there are interior walls, etc., it won't be sufficient, but as bossespecial writes, it's impossible to assess what reinforcement is needed if the additional loads cannot be calculated.

I'll see what I can find. The crux is that the construction was done by a previous owner, and documentation is scarce. It's only the ceiling that we notice a deflection on, but it's possible that the floor joists on the upper floor were shimmed before the floor panels were laid.

The L/300 measurement you mentioned is where my concern stems from. The Wood Guide indicates recommended deflection when sizing against permanent damage as follows:

Residential space: 20 mm or L/300
Office space, school, store, etc.: 30 mm or L/200
Industrial space: 40 mm or L/150

Roof structure with waterproofing of
• corrugated metal at a slope of 1:16 (4°): L/110
• corrugated metal at a slope of 1:10 (6°): L/50

I actually have two questions about this:
1) What type of damage is meant by "Permanent damage"?
2) Presumably, the same construction timber is used in all constructions, so how is there such a range of recommended deflections for the different options?

 

[justusandersson]

By permanent damage, they likely mean lasting deformation. It is difficult to compare different deflections because different normative loads are also considered. Traditionally, the view on deflection has been stricter when it comes to flooring compared to roof structures. A distinction is made between the service limit (deflection) and the ultimate limit (risk of failure). The perspective on these conditions has also changed over time. In addition, a vibration criterion has been added concerning flooring. This is based on studies about how people perceive walking on a bouncy floor. In houses built in the 1930s, a common dimension for floor beams was 3x7 inches. These floors could support large loads but were very bouncy, which we would not accept today.