Reinforced concrete floor (40 m² span) swings slightly

Hello!

This is not a new building, but an old building. I still hope this post is welcome.

Our living room is 40 m² and underneath there is a 40 m² cellar room. It has a reinforced concrete ceiling. What is noticeable is that the floor vibrates when children jump in the middle of the room or when you stomp harder on the floor. The screed is still 40 years old and above it is parquet. Between the screed and the concrete floor, styrofoam was laid 40 years ago when the house was built (it was the same when we removed the screed in the adjacent hallway).

Do I have to worry that the floor will eventually (after all, it lasted 40 years) give way and "sink" a bit or is the vibration normal? 40 m² is quite a large area and back then the concrete was poured with formwork boards. There are also no beams or supports installed in the cellar. The vibration becomes noticeable because the decoration on the glass table wobbles a bit and you can feel that the floor "trembles" a little.

Thank you very much!

There is definitely a steel reinforcement in the ceiling that withstands the vibration. When you jump around on the surface, the ceiling logically vibrates because it rests only on the exterior walls of the building. If that bothers you and you have space in the room below, you could install a steel beam right in the middle of the room!

Attached is a photo showing our former garage. The ceiling thickness was 14 cm. We had to tear it down to create access for heavy machinery to the garden. There was also a long crack in the ceiling, but in hindsight it turns out that the garage would never have collapsed. The jackhammer of the crawler excavator even broke through it. The foundation was 40 cm thick reinforced concrete. Apparently, neither concrete nor steel was spared here and at the house. The house and garage were built at the same time. The garage is only meant as an example of the construction method. The concrete ceilings in the house look similar/the same.

In addition, the two remaining pictures show an excerpt from the structural plan of the house. The thickness of the ground floor slab is 18 cm. Maybe the information is helpful for you!

The garage is perhaps 25 square meters and no people were hopping around on it. Personally, I don’t believe the ceiling will collapse?

I actually can't imagine that either. 18 cm thick reinforced concrete should be sufficient, and the basement room below is more rectangular than square. Besides, the swaying only occurs in the middle of the room. Everything outside of that is solid. It was also inspected and approved by a structural engineer in 1970. During the renovation, we had an oak cabinet weighing nearly 400 kg from my great-grandmother placed exactly in the middle of the room for half a year, and nothing happened. I just had some concerns, especially since we have children, and beneath the living room there is a party basement that we also want to use. The swaying could possibly also be due to the screed. Best regards

I actually can't imagine that either. 18 cm thick reinforced concrete should be sufficient, and the basement room below is more rectangular than square. Besides, it really only vibrates in the middle of the room. Everything outside of that is solid.

It was also checked and approved by a structural engineer in 1970. During the renovation, we had an almost 400 kg heavy oak cabinet from my great-grandmother standing exactly in the middle of the room. For half a year and nothing happened. I only had some concerns, especially because we have children and below the living room there is a party basement, which we also want to use.

The vibrations could possibly also be caused by the screed.

Best regards

Just imagine the energy distribution of the grid/reinforcement in the concrete during vibration! Most of the energy is dissipated in the masonry, and in the middle the steel is under tension and therefore usually carries tons. If anything were to happen due to the vibration, concrete would chip off first, while the reinforcement would remain stable! Perhaps there would be chipping if your family were to massively cause the structure to vibrate on purpose daily together in rhythm for several hours over many years?