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Today's article will touch upon the 3 most popular brands of hollow-core floor slabs found in our market: PC, PTK and PB. We will analyze in detail the design features, reinforcement technologies and the differences between the brands.
PC brand
So, the first slab manufactured using formwork technology without prestressed reinforcement: slab series 1.141-1.60, slab grade PK.
The maximum length is 4.2 m, which is precisely due to the absence of prestressing of the reinforcement. Serial production 60 - slabs with round voids, the working lengths of which are: 4180, 3580, 2980, 2680 and 2380 mm., With the width of 1790, 1490, 1190 and 990 mm. Reinforcement was made with steel rods of class A-III and BP-I.
The technological process for the formwork production of such slabs is as follows:
1. The mold is lubricated with emulsol (preventing concrete from sticking).
2. Reinforcement meshes and frames are installed in accordance with the specifications in accordance with GOST.
3. Punches (void formers) are placed in the molds and additionally covered with reinforcing meshes.
4. The future slab is concreted and vibrated.
5. After the time allotted for hardening, the punches are removed.
6. Grouting of irregularities and drilling of holes for hinges is performed.
7. The stove is placed in the steaming chamber.
Consider a variant of a slab with a width of 1200 mm., - PK 42.12-3T (42 - length in dm., 12 - width in dm., 3Т - load index).
The first working tensile mesh consists of 5 longitudinal reinforcement bars with a diameter of 8 mm, transverse bars - 4 mm each. It is this mesh (red in the figure) that absorbs the entire tensile load.
The upper mesh - comes as a constructive (blue), the diameter of which is only 3 mm. (Class of bars Вр-1).
Frames (green) are located in the support zones of the slab and act as a transverse reinforcement of these zones, between them mounting loops are embedded (highlighted in yellow).
It is forbidden to cut this plate across. When shortening the slab, the frame is removed from one edge, as a result, we get a support node without transverse reinforcement, where there is a very high probability of oblique cracks formation.
PTK brand
The next slab of the II-03-02 series: PTK grade - is manufactured similarly to the PC grade using the molding technology (ie, formwork), but already with prestressed reinforcement.
Consider a PTK plate using the example of a product PTK 59-12.
The working reinforcement is made with reinforcement rods with a diameter of 14 mm. and 16 mm. At the bottom there are only 4 rods, two of which are φ14 - pre-stressed at the edges and two are φ16 mm. - in the center.
The design of the PTC is almost identical to the PC plates, there is a frame in the support zone for the perception of lateral forces, from above structural mesh made of 3 mm bars, but there is no mesh below, and only 4 prestressing bars are located fittings. The working armature is tensioned in one of two ways: electrothermal or mechanical.
Additionally, in this design, a U-shaped frame (in the illustration - a black mesh) is added at the ends of the slab, which perceives local stresses in the support zones.
The mounting loop is already slightly more comfortable and extends beyond the plate to facilitate the attachment of the lifting hook.
This brand is also forbidden to cut across!
Brand PB
Hollow floor slab made according to no formwork from IZH 568-03 series - PB grade
Example in question: PB 60-12-10
The construction of this plate is the simplest and contains a minimum of assembly units. The maximum length of the slab is 9 m, the minimum is 2.4 m.
Reinforcement technology is performed by bundling: five bundles of 4 rods each. Depending on the length of the span to be covered, the number of beams and rods in each of the beams is selected separately.
Reinforcement with a diameter of 5 mm is located in the upper and lower zones. class Вр-2. The lower belt is working, the upper one is constructive.
The question of using rods with a diameter of 5 mm. BP-2 consists in the fact that a rod of a larger diameter has a limited length, the lengths of which are 11.7 m, and the production of products metal roll Вр provides for winding into coils, therefore, the technological process of manufacturing plates using reinforcement of class Вр - easier.
The PB slab has 1 category of crack resistance and its performance characteristics are higher than those of the others considered (PC and PTK).
An important feature of such slabs is that there are no mounting loops and special traverses are used when lifting.
None of the considered floor slabs work as a console, i.e. top reinforcement is constructive, and therefore their use in the "balcony" position (overhang of part of the slab) is strictly prohibited!
Thanks for attention!
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