Peculiarities of calculation and design of slabs on elastic cushion reinforced with non-metallic composite reinforcement

. Fiber-glass composite reinforcement becomes increasingly popular in different spheres of industry and public economy. Unique technology of the reinforcement production allows receiving the high-quality construction material which complies with modern requirements of liability, quality and safety. Pavlivska Square in Kharkiv may serve as an example of efficient application of non-metallic composite reinforcement for the reinforcement of slabs on elastic cushion during the construction of which the composite grids SКS-100/100 manufactured by Ekipage Technological Group were used as the reinforcement units. Pavement slab reinforcement scheme (including the working draft) was elaborated by the specialists of the Building Constructions Department of O.M. Beketov National University of Urban Economy. The arrangement of the pavement slab of Pavlivska Square was conducted within the short period of time. Due to this, for the purpose of mounting the two-layer reinforcing cage of the slab, the workers of Ekipage Technological Group elaborated a new mounting method which allows the essential reduction of the performance time.


Introduction
Today the fiber-glass and basalt-plastic composite reinforcement becomes increasingly popular in different spheres of industry and public economy. Unique technology of the reinforcement production allows receiving the high-quality construction material which complies with modern liability, quality and safety requirements. Noteworthy, the composite reinforcement is undemanding as to the application environment [5,7,8,12]. Thus, reinforcement may be used at different temperatures, from -700С up to +1000С. However, the demand for this material is conditioned, first of all, by the fact that the fiberglass reinforcement is resistant against corrosion and has longer service life [8][9][10]12]. The practicability if replacement the metal reinforcement by composite is constituted by a number of advantages, mainly: tear resistance is two times higher than the strength properties of the steel reinforcement А400С; stainless material; the reinforcement is acidresistant, works well in the sea water; the reinforcement does not bend (higher elasticity); is non-conductive, is dielectric; is not heat-transmitting; is radio-transparent; is magnetically inert (the change of the strength properties of the composite reinforcement under the impact of electro-magnetic fields is excluded); does not lose its strength properties under the influence of very low temperatures; is 5 times lighter than the metal reinforcement, and at the replacement equal in strength is 9 times lighter; any construction length; economic efficiency (reduction of transportation costs) [11]. The comparative characteristics of the metal and fiber-glass reinforcement are shown in Table 1. Based on the data received after many years of studies, a set of regulatory documents was elaborated regulating the application of non-metallic composite reinforcement and items there of for the construction purposes in different countries [2,3].

Project solution
Pavlivska Square in Kharkiv may serve as the example of efficient application of nonmetallic composite reinforcement of slabs on elastic cushion ( Fig. 1) during the construction of which the composite grids SКS-100/100 manufactured by Ekipage Technological Group were used as the reinforcement units [5][6][7]. The square is located in the central part of Kharkiv. The location is unfavorable, primarily, due to a high location and essential fluctuations of the ground water level (GWL). During the floods GWL may reach the land surface. Besides, the soils occurring on such territories, as a rule, have a poor load bearing capacity; they are non-uniform, poorly consolidated, and saturated with water. The sands are quick. The quaternary deposits represented by modern filling layer take part in the geological construction. The filling layer is represented by the humous clay loam and sand with the construction waste, broken brick and break stone. It is 0.6 -2.1 m strong; occurring everywhere. The ground waters of the underground reservoir have the following properties with regard to the material: concretes -slightly aggressive for all makes of concrete; reinforced concrete -medium-aggressive during the periodic immersion; metal constructions -highly aggressive. The factors above constitute the reason for the composite reinforcement application at this object.

Static calculations of slabs
The slab calculation shall be performed in compliance with [1,11]. Slab loading according is 25 tons on axis (loading NK-100). In case of infinitely great slab bearing the localized loading Р. Load deflection reaches the maximum value where D is the flexural rigidity, calculated as Есm -slab concrete stress-strain modulus; k -coefficient of the soil reaction, depends upon the type of the subsoil, according to [1] k = 2760 t/m 3 ;  -slab thickness. Subsoil reaction in the place of the greatest slab deflection Bending moment values may be easily calculated using the formulas [1]: where bt is a medium width of the extended area;  ctm f medium concrete tension capacity determined for the corresonding strength category, according to DBN В.2.6-98, but not less than 0.0013 bt d.  The shank spacing of the main longitudinal non-metallic composite reinforcement does not exceed 3h and is smaller than 400 mm (h -slab length). In the localized load or maximum torque areas, the shank spacing of the main reinforcement does not exceed 2h and is less than 250 mm.
The determination of slab bearing capacity at the suggested variant of reinforcement is conducted with the help of calculation software elaborated (based on the library DSTU_156.dll) by the specialists of the Building Constructions Department of O.M. Beketov National University of Urban Economy [4]. The calculation results are shown in graphic form ( fig. 3-5).    Bearing capacity of the slab section turned out to be enough to bear the operational load.

Technology of slab reinforcement
The arrangement of the pavement slab of Pavlivska Square was conducted within the short period of time. Due to this, for the purpose of mounting the two-layer reinforcing cage of the slab, the workers of Ekipage Technological Group elaborated a new mounting method which allows the essential reduction of the performance time. According to the reinforcement scheme -the sickness of the concrete slab is 200 mm; the distance from the lower grid of the reinforcing cage to the hydraulic seal layer is 50 mm; the thickness of the concrete wall protection layer is 30 mm. The distance of the lower grid of the reinforcing cage from the hydraulic seal layer is provided for by the supporting elements, distributed around the lower grid ( fig.6). The sequence of mounting the supporting elements (SE), h = 50 mm, is performed according to 5-point envelope scheme, with their installation with the spacing of 1 m. The scheme of the SE location is shown in fig.7. SE are installed directly on the fitting shanks of the lower grid chart, which, in their turn, are located in the future lower slab area, which rests on the soil (elastic cushion). In this case, necessary thickness of the protective layer of concrete is ensured due to the SE installation. The peculiarity of formation of the spatial reinforcing cage is the installation of mounting elements inside it. And, in particular, the vertical pillar (VP), L = 96 mm, designed for the installation as a bridging, perpendicular grid plane, to ensure the design spacing between the lower and upper grids of the reinforcing cage. Short Rod (ShR), L = 191 mm, is used for the installation as diagonal bridging between the internal parallel reinforcing shanks of upper and lower grids of the reinforcing cage. Long Rod (LR), L = 196 mm, (marked with the paint) necessary for the installation as diagonal bridging between the external parallel reinforcing shanks. General pattern of the installation of VP, ShR and LR is shown in fig. 8-9. VP are installed on the internal reinforcement shanks of the reinforcing cage, right against the grid nodes, near the SE fixing ( fig.8). ShR are installed on the internal parallel reinforcing shanks of the reinforcing cage grids, in the housing adjacent to the earlier installed SE. ShR are installed between the parallel internal reinforcing shanks ( fig. 8) LR are installed on the external parallel reinforcing shanks of the reinforcing cage grids, in the housing adjacent to the earlier installed SE. ShR are installed between the parallel internal reinforcing shanks ( fig. 8-9). To prevent the shifting of upper grid against the lower, during the mounting operations of reinforcing cage and its filling with the concrete, the pairs of ShR and LR shall be mounted in chessboard order, according to fig. 10. The general order of the reinforcing cage mounting is as follows: the composite grids of the lower reinforcement cage band are installed and interconnected (according to the design documentation); composite grids of the upper reinforcement cage band are installed and interconnected directly on the lower band (according to the design documentation), as a rule, with the half-section flooring; between the upper and lower bands reinforcing the pillars (VP) and brackets (ShR and LR) are installed, besides, in this case the mounting bunks with the supports are used, the construction of which does not damage the below hydraulic seal layer; final operation of mounting the two-layer reinforcing cage is the procedure of lifting the reinforcement cage on the supporting elements (SE) (fig. 11). Final stage of the slab building is filling the reinforcing cage with the concrete according to the design documentation ( fig.12).

Conclusions
General technical and statistical data on the realized project of reinforcing composite cage of the pavement slab in Pavlivska sq., Kharkiv, are as follows: 1. Total area of the concrete slab with the composite two-layer reinforcing cage is 8.7 ths. sq.m.
2. The tear resistance of the two-layer reinforcing cage of the composite reinforcement manufactured by Ekipage Technological Group is 420 kN/m.
4. Total weight of the composite reinforcement used for the reinforcement cage arrangement is 41 tons.
5. Total amount of the binding points for the reinforcing cage construction is 879040 pieces.