Constructive provisions LEP platorm

IV. CONSTRUCTION PROVISIONS, DETAILS AND RESOLUTIONS REGARDING SPECIAL AREAS IN THE EXECUTION OF LEP SLABS

IV.1. Special areas:

a) Areas with permanent local loads greater than those conventionally taken into account, determined by non-load-bearing walls located in the direction of the beams; brick or terracotta fireplaces/stoves; other objects with a known fixed location, if the equivalent load due to their weight exceeds by more than 0.5 kN/m2 in the occupied area, the standard value of the technological exploitation load corresponding to the destination of the respective surface.
– Solution: Two LEP beams are installed under non-load-bearing walls or other increased weights.

b) Gaps larger than the span of two adjacent beams, requiring the interruption of one or more beams.
– Solution: The resulting larger gap will be longitudinally bordered with LEP beams, and transversely with stiffening ribs in which the interrupted LEP beams are attached.

c) Areas where the floor extends into the console (balcony, awning) and the LEP beams are in the direction of the console.
– Solution: The reinforcement in the LEP beams is checked against the calculated effort of the console, and if there is a difference, additional reinforcement is added to the upper part.

IV.2. Installation of the supporting scaffolding and LEP floor beams:

(a) The installation of the scaffolding supporting the floor beams is carried out in a convenient version for the builder, namely in wood or metal. (fig. 10).
The scaffolding supporting the beams is arranged according to the execution project drawn up by the authorized designer of the work, but at distances of maximum 1.50 m between them or from the structural walls. The props of these scaffolding are placed on the soles, and their height adjustment is carried out either by a wedge system or with mechanical jack-type devices (depending on the type of scaffolding adopted).

If the project provides, in reinforced concrete frame structures, indirect support of the floor beams by means of concrete steel spatial frames, the beams of the supporting scaffolding will be arranged in such a way that they can ensure the support of the LEP beams in close proximity to the frame beams.
According to SR EN 15037-1:2008, annex D, fig. D2, it results that the maximum distance from the walls (or beams) of the first support is 650 mm.
Particular attention will be paid to the scaffolding bracing in order to ensure its stability in the two directions and in this way to avoid the occurrence of subsequent irregularities during the construction of the floor; also particular attention will be paid to the horizontality and verticality of the main components of the scaffolding and from this point of view a careful check will be carried out by the construction engineer.
The project for supporting the prefabricated beams will be prepared by the designer, taking into account the technological phases of execution and the loads foreseen for this stage (assembly and concreting).

(b) In structures with masonry walls, the belts must be 5 cm higher than the height of the ceramic, concrete or polystyrene block floors, in order to be able to create the belt in the area of the LEP beam supports. For details in various cases, see the drawings in Annexes A, B and C.

(c) In the case of reinforced concrete frame structures, the LEP beams will be supported on the supporting scaffolding in the immediate vicinity of the frame beams, so that it is not necessary to support them (during assembly) on the reinforced concrete beams. Moreover, in structures with reinforced concrete frames, it is advisable that the pouring of concrete into the frame beams be done at the same time as the pouring of concrete into the beams and the overcasting of the floor.

(d) In structures with metal frames, the support of the LEP beams will be made on the upper sole of the frame beams by means of elastic rubber or polyurethane bands (see details in annexes A, B, C – support on metal beams). The design of the metal frame beams and the secondary beams of the floor will be made in such a way that the arrangement of the connectors does not prevent the installation of the LEP beams. The connectors will be arranged at distances modulated by the distances between the LEP beams (50÷57 cm) to ensure the cooperation of the floor with the beams of the metal structure. It is not recommended to arrange the LEP beams and ceramic blocks below the level of the upper sole of the metal beams; the small thickness of the overcasting cannot ensure a proper anchoring of the connectors to ensure the cooperation of the floor with the metal beams.

(e) The first LEP floor beam is placed at the limit of the structural wall or frame beam, parallel to the working direction of the floor. The beam will rest on the structural walls or beams on which the floor is unloaded, for a minimum length of 5 cm.
The length of the LEP reinforced concrete beams is modulated at 20 cm.

(f) It is prohibited to cut the prefabricated reinforced concrete elements, section them by chiseling, or partially or completely perforate them.

(g) The installation of the other floor beams is done in a parallel position with the first beam, at interaxle distances of 50, 51, 54, 57 cm (depending on the ceramic blocks used – TP16, TP22, concrete block and polystyrene blocks), according to the project. Ensuring the correct interaxle distance between the beams is achieved with wooden spacers or special devices, as well as by installing rows of ceramic or concrete blocks at each end of the beams.

(h) In the case of cellular structures, both in the case of reinforced concrete frame structures and in the case of wall structures, intermediate beams of the floors with an exclusively gravitational role may be provided at a maximum interaxle distance of 2.5m (fig. 11).

(i) Lifting and handling of the LEP beam shall be done only from points located at 1/3 of its length.

(j) The supporting scaffolding shall be provided on the line of the LEP beam supports with work platforms with railings, from which the LEP beams and ceramic or concrete blocks, spacers in the assembly positions shall be handled and fixed. The dimensioning of the number of props and their positioning shall be done according to the specifications in point III.5.

IV.3. Installation of ceramic blocks (concrete, polystyrene) for floors

(a) Before starting the installation of the filling blocks, when unpacking the pallets, their integrity will be checked by the site engineer; no cracked or damaged blocks will be put into use during transport.

(b) The TP16, TP22, concrete or polystyrene ceramic floor blocks are installed side by side, without joints, resting on the LEP beams, creating rows along the beams. This operation is done manually.

In the area where the floor beams rest on a structural wall or beam, the first row of blocks is installed on the inner face of the support; the other blocks are then installed, by joining them (fig. 12).

(c) If the dimensions of a floor opening are not modulated with the dimensions of the ceramic blocks (concrete, polystyrene), the following procedure will be followed:

in the transverse direction of the LEP beams – the distance not covered by the size of a block is distributed equally at the two ends of the beams, resulting in a monolithic area, which will be detailed in the execution project together with the reinforced concrete beam or belt;
in the parallel direction with the LEP beams – the filling body is adjusted to the necessary dimensions.

1÷12- Ceramic blocks (concrete, polystyrene) for the LEP floor

a. Wooden ruler for supporting beams
b. Support posts (props)
c. Prefabricated beams for the LEP floor

Fig. 12 – Installation order of ceramic blocks (concrete, polystyrene) – LEP beams placed in position In the case when the project provides for indirect support of the LEP beams on beams or walls, the distances from the first row of blocks to the supports will be dimensioned so as to achieve the anchoring length when pulling out the LEP beams from the monolithic concrete.

(d) Even though the bending strength of a ceramic block, under laboratory conditions, is about 4 times higher than the weight of a person (4 kN), it is recommended that the movement of workers above the ceramic blocks after installation, either for further installation of the blocks and straightening the connectors on the beams, or for installing the reinforcement and pouring the concrete for the overcasting, be done on wooden box platforms resting perpendicularly on the LEP beams. The tools used will be handled carefully to avoid shocks that may affect the upper sole of the ceramic blocks and the support areas on the LEP beams.

(e) It is not necessary to fill the gaps of the ceramic blocks adjacent to the beams or belts. Concrete losses due to partial filling of the voids are insignificant and the existence of these concrete “wedges” beyond the cross-section limit of the belts or beams only improve the interaction of the floor elements to ensure the effect of a rigid horizontal diaphragm.

(f) In cases where, accidentally, the upper sole of a filling block or the area of support on the beam breaks during installation, it will be replaced in its entirety. Broken filling blocks where the cracks are plugged with various materials (paper, polyethylene, polystyrene, etc.) are not allowed for installation, nor will it be allowed to fill the broken blocks with the monolithic concrete; in order to avoid such situations, the structural designer will provide in the site monitoring program a decisive phase (not necessarily with the participation of ISC inspectors) in which the integrity and correct installation of the beams and ceramic blocks will be verified before the start of the reinforcement of the overcasting.

If, after the reinforcement is completed, one or at most two blocks on a cell of the floor are damaged by breaking the upper sole on max. 10% of the surface, then it can be accepted that these blocks are repaired by stuffing the gap in the upper sole with some light materials – paper, polystyrene scraps – and sealing (grouting) the gap in the upper sole with an adhesive – e.g. CM11. However, if the ceramic block is affected in the area of support on the LEP beams, (cracks or cracks in the shoulder of the support on the beam), the reinforcement will be removed locally and the respective block will be replaced; in the case of reinforcing the overconcrete with welded mesh, the mesh will be cut locally in the block to be replaced and after replacing the block over the cut, a mesh coupon will be mounted on top of the cut mesh, overlapping it by 25 cm in all directions.

IV.4. Installation of reinforcement in the upper pre-girders (riders), reinforcement of stiffening beams, reinforcement of belts, reinforcement of the over-concrete slab

(a) On the upper part of the LEP beams, Ø8÷Ø16 (PC52) and Ø8÷Ø14 (BST500S) reinforced concrete bars are mounted on the supports (see tables 3÷12), with a concrete cover of 2.5 cm. Spacers (fleas) are used to hold the bars in the required position. The bars are anchored with hooks or hooks in the belts at the ends of the beams.

(b) In structures with structural masonry walls, the reinforcement of the belts on the walls on the contour of the floors is mounted according to the details in the project (for example, the annex with drawn parts presents the details currently encountered in such structures).
The dimensions of the belts and their minimum reinforcement will satisfy the provisions of the CR6 Code, point 7.1.2.2.2, of the P100-1/2006 Code, point 8.5.4.2.2 and Code P100-1/2013 point 8.5.4.3.2:

cross-sectional area ≥ 500 cm2;
width ≥ 25 cm and ≥2/3 of the wall thickness;
height ≥ 20 cm;
minimum percentage of longitudinal reinforcement – 1% for seismic areas with ag≥0.20g and 0.8% for seismic areas with ag≤0.16g;

The minimum diameter of the longitudinal bars is Ø10mm and the minimum diameter of the stirrups is Ø6mm; the minimum distance between stirrups, in the current field, is 15 cm and in the area of the longitudinal bars is 10 cm.
The order of operations could be the following:

the position of the LEP beams is checked and any corrections are made, freeing up the spaces for the passage of the longitudinal bars of the belts (see the drawings);
the belt stirrups are temporarily mounted in position, at the distances mentioned in the project;
the longitudinal bars of the belts are passed through the stirrups and are connected in the corners of the stirrups and, possibly, in the middle of their sides; the longitudinal bars can be inserted, by overlapping at least 60Ø, along the belts and at the ends, when anchored in the perpendicular belts, provided that in the same section no more than 50% of the number of bars are inserted and the distances between two successive insertions are not less than 1.0 m.

(c) In cases where the dimensions of the floor require the arrangement of stiffening beams – when the distances between the supports of the LEP beams are greater than 5.0 m – then the spacing of the stiffening beams must not exceed 2.5 m and their reinforcement will be done simultaneously with that of the perimeter belts and will comply with the same construction provisions as for the belts, with the following additional specifications:

the width of the stiffening beam will usually be equal to the width of the filling blocks – i.e. 20 cm; (if the distances between the walls on which the beams rest are not modulated to 20 cm, in order to avoid adjusting the ceramic blocks by cutting, the width of the stiffening beam can be reduced to 15-20 cm). The longitudinal reinforcement of the stiffening beams will be done with min 4Ø12 PC52;
the height of the stiffening beam will be equal to the height of the floor, but its reinforcement will develop only above the LEP beams;

(d) After installing the reinforcement in the ribs and belts, the over-concrete reinforcement is installed – made of meshes (welded or independent bars) made of Ø6/100 – Ø6/100 PC52 concrete steel, tied with wire and anchored with hooks on the supports (fig. 13).

(e) The nets shall be tied with black wire to each loop of the welded beam of the LEP beams and to the rib and belt casings.

(f) The nets shall be mounted, as a rule, with the lower row of bars perpendicular to the LEP beams and shall be overlapped by at least 25 cm;

IV.5. Execution of overcasting

(a) The concrete overlay will be made with concrete of the class provided in the project but at least class C20/25; the same class of concrete will be poured both in the perimeter belts and beams of the floor and in the ribs and the concrete overlay. The specifications will specify that the concrete be prepared with aggregates with a grain size of up to 16 mm. In frame structures, the concrete overlay will be poured together with that in the beams and frame nodes.

(b) The ceramic (concrete) floor blocks are excessively moistened, after which the concrete is poured simultaneously into all the elements that make up the floor – ribs, stiffening beams, belts, frame beams and the concrete overlay layer (fig.14).

(c) The activity will be planned so that the concreting of the floor is done continuously (without interruptions). The upper face of the concrete is leveled, so as to respect the thickness of the overcasting layer (according to the project). The concrete will be protected with mats that are moistened throughout the hardening of the concrete, 1-2 times a day. (fig. 15).

(d) The duration of curing of the concrete after pouring will be established according to the Code of Practice NE012-2007/2010, depending on the composition of the concrete, the atmospheric conditions during and after pouring and the service and exposure conditions of the structure after pouring.

(e) The scaffolding supporting the floor beams is dismantled only after the concrete has completely hardened, namely after 28 days.

(f) The specifications drawn up by the authorized designer must provide for the working conditions and any restrictions regarding labor protection, depending on the specifics of the respective construction.