DK2851479T3

DK2851479T3 - Breakthrough reinforcement system with crossbars which have anchoring heads

Info

Publication number: DK2851479T3
Application number: DK14000488.8T
Authority: DK
Inventors: Aurelio Muttoni; Ruiz Miguel Fernández; Marc Barras
Original assignee: Ancotech Ag
Priority date: 2013-02-12
Filing date: 2014-02-12
Publication date: 2017-09-11
Also published as: CH707571A1; ES2640338T3; EP2851479A2; PT2851479T; EP2851479B1; EP2851479A3

Description

DESCRIPTION

INTRODUCTION

[0001] The bearing areas of slabs in reinforced and/or prestressed concrete are subjected to very significant bending and shear forces. Therefore they are often determining factors for the strength and deformability of the structure [1].

[0002] Failures in bearing areas normally occur by crushing of the concrete [1], i.e., by the formation of a tapered crack causing the bearing area to penetrate into the slab (see Figure 1). To increase the strength and deformability of these areas, various solutions have been applied in the past: 1. Modifying the dimensions of the bearing area and/or the bending reinforcement of the slab. 2. Having a metal head enabling the bearing area of the slab to be enlarged (a solution often adopted for very significant loads). 3. Folding the bending reinforcement rods to allow them to bear the shear force. This solution has been practically abandoned since the 1960s but is still present in some special reinforcement systems, to improve the deformability of concrete slabs. 4. Adding transverse reinforcements (with comparable dimensions and properties to the slab bending reinforcement) specifically shaped to prevent the tapered crack from crushing when opening uncontrollably. 5. Having fibers in the concrete (randomly oriented steel or plastic linear elements with a small size and short length).

[0003] When modifying the slab dimensions is not possible for economic or functional reasons, the use of transverse reinforcements is the most common solution. This solution enables the material to be effectively used with the arrangement of high-strength and high-ductility elements (in steel).

PRIOR ART IN RELATION TO THIS INVENTION

[0004] Compared to reinforcement systems used for reinforcing concrete slabs, several systems are currently used:

Stirrups (ordinary reinforcement rods) shaped so as to facilitate installation of the bending reinforcement (Figure 2a)

Reinforcement cages, with several reinforcing strands anchored by adhesion (Figure 2b)

Straight reinforcement rods with anchoring heads, arranged vertically or inclined (one or more assembly rods can be present on one side to facilitate the installation of elements, Figures 2c, d)

Straight reinforcement rods with anchoring heads on one side and welded onto a rail on the other side (Figure 2e) [0005] Other solutions or combinations of previous solutions are still possible [2], In addition, systems composed of embedded or feed-through studs anchored to the ends by means of mechanical plates or elements are also used, but their use is restricted to the reinforcement of existing slabs (Figure 2f).

[0006] The performance of the various systems strongly depends on the anchoring quality (forged or welded heads, anchored by adhesion) and the construction regulations applied to the system (spacing of transverse reinforcements, quantity of reinforcement available (Figure 3 [2, 3]).

DESCRIPTION OF THE INVENTION

[0007] To increase resistance to shear force and to crushing, it was observed experimentally that inclined rods show better performance than vertical parts (Figure 3). Flowever, excessive inclination of studs can induce anchoring problems in the compressed area of the slab (intrados). This solution also revealed difficulties in installing transverse reinforcements, especially when they are not parallel to the directions of the bending reinforcements.

[0008] EP 1 630 315 A1 discloses a system for reinforcement against crushing of a concrete slab according to the preamble of claim 1.

[0009] The invention provides a system for reinforcement against crushing of a concrete slab according to claim 1. In an embodiment according to the invention, a combination of vertical and curved studs with anchoring heads is proposed, see Figure 4.

[0010] The studs are composed of rods in ordinary steel or high-strength steel with two anchoring heads (one at each end of the rod, Figure 4). Rods can be straight or even curved. For curved parts, the curvature can be obtained by a succession of punctiform folds or else by a constant bending radius, and straight areas can also be contemplated depending on the static behavior of the system and the method of producing parts.

[0011] Curved studs, which perform betterfrom the static viewpoint, are arranged close to the bearing region (where the forces are strongest) while straight parts are arranged in the more peripheral regions.

[0012] The studs extend radially from the edge of the column (Figure 5) and have a variable number depending on the degree of loads. In radii parallel to the bending reinforcements, the combination of curved and straight parts is contemplated. On the other hand, for other radii, upstanding straight parts are contemplated to facilitate the reinforcement installation (see Figure 5).

[0013] This stud arrangement enables: static performance to be increased in relation to reinforcements with vertical anchoring heads (see Figure 3). This is justified by the presence of inclined curved elements in the area where they are intersected by the shearing crack the installation of vertical studs to be benefited from for areas with bending reinforcements not parallel to the studs or far from the fracture area (see Figure 5) [0014] This system also optimizes the cost of the product with special (curved) parts in regions where loads are heaviest and straight (more economical and easy to install) parts in regions with lighter loads or with increased installation difficulties. Also see Figures 6Ato 6B.

APPLICATIONS

[0015] The object of the invention is to enable reinforcement against crushing of concrete slabs subjected to very high concentrated loads. The objective in terms of resistance is to exceed the objectives of similar products (reinforcement systems against crushing) currently on the market.

[0016] This product can thus be used as a replacement for better-performing (and more expensive) products, such as, for example, metal heads against crushing.

[0017] Another objective of this product is to improve the deformability of slabs, similarly to bent-up rods. This will enable this system to be used as integrity reinforcement (reinforcement to prevent a slab from collapsing after accidental crushing).

BIBLIOGRAPHY

[0018] [1] Muttoni, A. Punching shear strength of reinforced concrete slabs without transverse reinforcement, ACI Structural Journal, Farmington Hills, Mich., Vol. 105, No. 4, 2008, pp. 440-450 [2] Fernåndez Ruiz, M., Muttoni, A. Punching shear strength of reinforced concrete slabs with transverse reinforcement, ACI Structural Journal, Farmington Hills, Mich., Vol. 106, No. 4, 2009, pp. 485-494 [3] Fernandez Ruiz, M., Muttoni, A., Performance and design of punching shear reinforcing Systems, 3rd International fib congress, Washington, USA, 2010, 15 p.

DESCRIPTION OF THE FIGURES

[0019]

A PRIOR ART

Figure 1: Shearing crack developing in a bearing area of a slab without transverse reinforcement.

Figure 2: Examples of existing crushing reinforcement systems: (a) stirrups; (b) stirrup cages; (c) vertical pins; (d) inclined pins; (e) pins welded onto a rail; and (f) bonded reinforcement.

Figure 3: Performance of reinforcement systems against crushing depending on their anchoring and reinforcement types (adapted from [3]).

B INVENTION

Figure 4: Cross-section of a slab reinforced with the proposed invention: several curved pins are arranged close to the column (area of highest loads) while straight pins are arranged in regions with lighter loads.

Figure 5: Plan view of the arrangement of parts and of the bending reinforcement of the slab.

Figure 6A: Anchor with 2 angular offsets in two different directions in an “S” shape.

Figure 6B: Anchor with a succession of punctiform folds and a straight part between the angular offsets or anchors with two or more punctiform folds and a straight part between the angular offsets.

Figure 7A: Anchor with feet that are enlarged by an increase in volume.

Figure 7B: Anchor with at least one head that is not perpendicular to the stud.

Figure 7C: Anchor with an enlarged head for improving the introduction of forces into concrete.

[0020] The systems from Figures 7A to 7C do not comprise curved rods. These systems do not form part of the invention.

Claims

A reinforcement system against breakthrough of a concrete slab comprising rods extending across the slab when the system is installed in the slab, which rods consists of a rod with a cross anchoring head at each end of the rod, the anchoring heads having a larger diameter than the diameter of the rod, which rods, when installed in the plate, have an anchoring head located near the upper surface of the plate and an anchoring head located near the lower surface of the plate, characterized in that the rod in said rods is curved between said anchoring heads.

System according to claim 1, characterized in that the curved rods have at least one straight area.

System according to claim 1 or 2, characterized in that the curved rods have at least one area which is vertical to the concrete slab.

System according to any one of claims 1 to 3, characterized in that the curved rods have at least two folds in the same or different direction.

System according to any one of claims 1 to 4, characterized in that the curved rods together form a vaulted shape.

System according to any one of claims 1 to 5, characterized in that at least one of the anchoring heads is positioned at a not right angle to the corresponding end of the curved rod.

System according to any one of claims 1 to 6, characterized in that at least one of the anchoring heads is positioned at a right angle to the corresponding end of the arc-shaped rod.

System according to any one of claims 1 to 7, characterized in that the arc-shaped rods as the lower anchorage head have a foot which is enlarged relative to the anchorage element.

System according to any one of claims 1 to 8, characterized in that the arc-shaped rods at their lower end have an enlarged zone relative to the rest of the arc-shaped or straight rods.

System according to any one of claims 1 to 9, characterized in that it contains a combination of curved bars and straight bars.

System according to claim 10, characterized in that the bars with arcuate bars are located in the support area while the bars with straight bars are located in more peripheral areas.

System according to any one of claims 1 to 11, characterized in that the curved or straight bars are inclined in the zone of a concrete slab where they are cut by any breakthrough cracks.