Greetings, dear professionals and amateur self-builders!
Installation of floor slabs is not a very difficult task, "vira", "lane", two hours of time and the floor is completed. 99.9% of builders cope with this work, but if you touch the monolithic sections between these very slabs, then, as practice shows, not all craftsmen concretize them correctly.
Indeed, if we have an ordinary rectangular room without stairs and a second light, then we cover the entire area, by mounting the slabs sequentially taking care of their width in advance so that they cover the entire floor with a minimum lumen.
And if we cannot arrange the slabs in multiples of their sizes without gaps, then we can easily provide small monolithic sections from 5 to 30 cm between the slabs. One such area is enough for the slabs along the edges to come flush to the walls.
For builders, there is even a document "Recommendations for anchoring floor slabs", where it is written in black and white that with a gap of up to 50 mm this section concreted without reinforcement, the gap is from 50 to 100 mm - one flat frame with rods at the top and bottom is placed, with a gap of 100-300 mm - two flat frames:
The diameter of the reinforcement depends on the span length and varies from 6 to 12 mm.
And if you made a mistake when ordering with the size of the slab, a section of more than 300 mm may appear, in this case you can do it like this:
But, not everyone knows that such a solution cannot be used with gaps of more than 1 meter.
What to do when a staircase or some kind of technological opening appears in the ceiling, occupying more than a meter in width, and most often it is 2 meters or more? For example, this is:
There are several solutions and about each in order ...
The worst solution, as inexperienced builders do, is to install an anchor in the floor slabs:
Craftsmen drill holes and drive reinforcement rods into them. But, the anchors can also have a different shape - the rods are bent and put on the floor slabs from above, so that the frame rests on the slabs on the sides, as is the case with meter sections.
The error lies in the fact that the load from the reinforced concrete element will not fall on the entire floor slab, but only on that section of the slab, which is limited by the anchoring depth. We drove the reinforcement rod 30 cm, which means that two edges of the slab will work, and even worse, when they hammer in 15-20 cm, then the monolith is held on one edge of the slab. Imagine that a ton of concrete is hanging on the ribs of two slabs, while in most cases only one reinforcement bar is structurally located in each rib!
Below in the photo is the same case. We see that the monolithic section on the sides will generally hang in the air, and its end is planned to be supported on the channel, which is held only at the edges of the two slabs.
This cannot be done with spans that are more than a meter wide. A screed, partitions, furniture will go from above, and we will definitely overload the slabs, and besides, the load from the monolithic section to the slabs is partially applied (it does not affect the entire slab, but only the edges). As soon as we support a concrete staircase on our monolith, the likelihood that we will get a chip edge of the slab increases significantly.
Now, how to do it right ...
It is impossible to save money here, and for the entire length of the span, two beams must be installed, between which our monolithic section is located. These are either two channels, or two I-beams, or two reinforced concrete beams, erected on site.
In this case, we need to have a span 20-60 cm wider than the design dimension. 20 cm in the case of using a channel / I-beam, 40-60 cm in the case of concreting RC beams.
Therefore, if we have a staircase in the floor, then automatically we add the width of two beams to the span and push the slabs apart by the resulting value during their installation.
That's right:
If these are reinforced concrete beams, then everything is concreted in one pass, only longitudinal reinforcement works in the beams, and in our monolithic section, the working reinforcement is transverse reinforcement. We can even save a little here, and if the height of the two side beams is equal to the height of the floor slabs - 220 mm, then the monolithic section can easily be made twice as thin, that is, 100-110 mm!
And that's all, and I really hope that this information will be useful to you!
Thanks!