Hollow core covering slabs are characterized with possibility to be used in the situations with increased spans and/or loading, guaranteeing significant reduction of the time of work execution on the construction site and excluding necessity of application of additional supports as it’s fully self-bearing.
The product is widely used in realization of covering elements in industrial, commercial, civil and residential construction.
Application of hollow core covering slabs has the following advantages:
- it allows covering of significant spans and bearing increased loading;
- owing to its significant strength, the thickness of the covering can be reduced;
- the slab is fully self-bearing and, thus, additional supports are not needed;
- it can be quickly installed, people can walk on the installed surface immediately;
- in the majority of cases, it is enough to seal the longitudinal seams, which minimizes the expenses related to installation;
- the internal surface of the covering is completely smooth: such surface can be left as it is or just painted;
- there can be executed covering, which requires fire resistance for any period of dangerous impact;
- high quality of concrete guarantees high stability of a structure;
- observing rules of application and installation of hollow core covering slabs guarantees high level of safety during works on the construction site.
A structure consists of slabs, with openings, of vebropressed concrete the R’ck strength of which is more than 50N/mm2; physical-mechanical characteristics are controlled at the laboratory of the producing plant.
While significant loading and in seismic zones, it is necessary to consider two options of installation of the covering made of hollow core slabs. In the first case, it is necessary to grout slab side ends with the concrete with the strength, not less, than R’ck 30N/mm2 and install additional enforcement, where it is calculated the necessary number of hackings for accommodation of reinforcement, their length (up to three hacking per end), size and diameter of inner reinforcement of the supports. The additional reinforcement shall be installed while concrete casting, according to the hackings and concrete diaphragm between adjacent slabs. Besides, in compliance with paragraph 7.0.а. of the Eurocode, it is necessary to consider lower additional reinforcement for supports, equal to the hacking, which will be able to accept the tensile load.
In the second case, if while calculation of the first version, bearing capacity of the covering under the load is not sufficient, then there is considered creation of an additional monolith layer made of the concrete with thickness not less than 4 сm. If there are no other instructions, such additional grouting shall be done using the matrix with the strength characteristics not less than R’ck 30N/mm2, material – vibroconcrete, so that it is guaranteed complete sealing of the longitudinal seams and hackings, encapsulation of the reinforcement and gripping with the manufactured concrete surface. The sealant diameter shall not be more than 12 mm.
With the help of hollow core slabs spans can be made according to technical requirements, given in the following schemes: the first version is better for medium spans, not so large cantilevers and not so high loadings, but the second version is better for larger spans, long cantilevers and high loadings as compression from the negative moment on the lower slab side end felt by the executed grouting and not by the slab side end concrete, which are loaded by pre-stress anyway.
For preliminary calculation of the slab sizes, there are attached technical conditions and diagrams for each height of the slab, span length and various types of fire resistance, differing by location of pre-stressed reinforcement with various values of the height of a protecting concrete layer.
The technical conditions are giving geometrical and mechanical characteristics of the slabs, graphs show imposed loading depending on the span and enforcement type. The full line of the graph refers to the case for pinned slabs at the ratio of the span length to the slab thickness L/h≤35 is recommended as the maximum value for interflooring, in other cases described below the given value of the ratio can be assumed higher.
- Flooring with partial restraint or continuous L/h≤42
- Roofing with pinned slabs L/h≤50
- Continuous roofing L/h≤55
Should you need any additional technical information, please, contact the Technical Department of the producing plant.