ES2582252B1 - CONNECTION SYSTEM OF MIXED CONCRETE AND WOOD STRUCTURES - Google Patents

Abstract

Connection system of mixed concrete and wood structures # The present invention relates to a connection system of mixed concrete-wood structures comprising at least one connector comprising: a head (1) anchoring tungsten to the concrete comprising: a tightening head (2) and at least one washer (3); and a body (4) comprising, in turn: a neck without thread (5), a threaded area (6), and a self-drilling tip (7), where: # the diameter of the washer ({ot} {sub, h}) is 4-8 times the diameter of the neck, the thickness of the washer is 0.5-0.6 times the diameter of the neck, the diameter of the neck is between 4-16 mm, the diameter of the thread is smaller or equal to 16 mm, the angle ({al}) of placement of the screw with respect to the contact plane is less than 90º, the length of the thread is 13 times the diameter of the crest of the thread and the length of the neck L {sub, c}: # {IMAGE-01} # Being: # {ot} {sub, max} the maximum aggregate size # rec the concrete coating # h the concrete thickness.

Description

DESCRIPTION

CONNECTION SYSTEM OF MIXED CONCRETE AND WOOD STRUCTURES

Field of the Invention

The present invention is generally framed in the general field of metal fasteners for wood and in particular refers to a system for connecting mixed structures of concrete and wood and their use for the rehabilitation of structures in which they intervene wooden beams that support a concrete slab.

STATE OF THE PREVIOUS TECHNIQUE

Below are some patents that constitute connections in mixed concrete and wood structures and others that also include systems for their placement. 10

Patent application EP2058448 refers to a metallic tubular connector for the transmission of stress between wood and concrete.

EP 0432484A2 describes a screw-shaped connector that protrudes above the wood.

The utility model ES 1031656U refers to a metal connector using a bent round L-shaped corrugated 15, which is inserted into the wood.

In patent application EP0717149, an asymmetric Z-shaped metal connector is raised, which is slightly inserted into an opening in the wood and screwed in 4 points.

In the industrial forging process, it is worth mentioning patent application 20 WO96 / 25566, which describes a connection based on metal sheets with nails on both sides of its surface, placing the wooden beams nailed to both sides thereof, and protruding the sheet from the top, also with nails, to connect it to the concrete.

Patent FR 2751355 describes a metal connector consisting of three parts, a screw, a transition piece inserted in the wood and a stiffened L in order to serve as a restraint to the shear force in reinforced concrete.

US 5809722 discloses a connector formed by a small metal structure formed by two small C-shaped supports connected to each other by the upper part of the side walls by two plates. The supports are screwed to the wooden beams and 30 by some holes in the plates are inserted steel bars that arranged

they adequately help effectively transmit flush between the walls and the concrete slab.

In EP 0939175 A3, a modular connector in the form of a metal sheet with V-shaped upper legs is presented, which is connected by grooves made of wood. The modules join with steel tubes that also have 5 vertical grooves.

In FR 2775489, a linear metallic connector is proposed to the piece of wood to be connected, although not necessarily in concrete, but to a flooring.

In patent application EP 1314828, a hexagonal head screw-shaped connector is raised, screwed vertically on the wood to be connected. 10

In the patent application EP 2 058 448 A2 a connector in the form of a hollow cylindrical tube embedded in the wood is described.

Patent ES 2326446 describes connectors that consist of U-shaped metal parts screwed to the wood on their upper face by two screws and finally, a vertical piece is inserted into a groove in the wood. fifteen

 In the utility model ES 1075025U, a bolt with a fixing bracket with hooks that are nailed to the wood and at the same time is fixed to the wood with two screws is described.

The patent ES 2557244, the connection is a folded metal sheet formed by a first vertical flat section with holes to connect to the concrete, another also vertical 20 which is a serrated plate to connect to the wood, and a third horizontal section to connect a the other together forming a section in Z.

The ES2511992 patent describes connectors that consist of U-shaped metal parts whose interior houses crossed plates that collect the concrete inside, screwed to the wood by two screws and finally, with a lower vertical piece 25 that is inserted into a grooving in the wood, previously practiced, transmitting the flush between concrete and wood.

Some of the connections described in the state of the art deplete the test elements (this is what is called the mode of breakage) by local crushing of the concrete around the base of the connector because they work at shear or bending and in general 30 mobilize little concrete in the concrete-connector contact. This is the case with bolt type connectors. In other cases, they are broken by tearing off a concrete cone, and in

other times, the breakage occurs due to tearing of the wood due to the screw thread or sliding of a toothed plate.

There is therefore a need to provide a system that exhibits greater resistance, which has a high rigidity of the connection avoiding certain breakage modes and more effectively than the systems described in the prior art. 5

Brief Description of the Invention

The present invention solves the problems of the prior art since:

- Provides a connection system between wood and concrete that makes the assembly act as a mixed structure of strength far superior to that obtained by the capacity of unconnected wood beams and concrete slab.

- transmits the stresses between the concrete slab and the wooden structure in the form of flush tensions in such a way that the assembly behaves in solidarity and more effectively than if it were two independent parts.

- prevents global breakage by local crushing of concrete around the base and 15 prevents breakage by tearing, also preventing tearing of the wood.

- increases the flexural resistant characteristics.

- transmits the stresses between the concrete slab and the wooden structure in the form of flush tensions so that the assembly behaves in solidarity and 20 more effectively than if it were two independent parts.

Thus, in a first aspect, the present invention relates to a connection system of composite concrete-wood structures, comprising at least one screw-type connector comprising:

 a head configured to anchor the bolt to the concrete comprising:

 a tightening head,

 at least one washer,

 a body that includes:

 a neck without thread, 30

 a thread zone,

 a self-drilling tip

where:

The diameter of the washer is 4 to 8 times larger than the diameter of the neck,

The thickness of the washer is 0.5 to 0.6 times the diameter of the neck,

the diameter of the neck is between 4-16 mm, 5

the diameter of the thread is less than or equal to 16 mm,

the angle of placement of the screw with respect to the concrete-wood contact plane is less than 90º

the length of the thread, is equal to 13 times the diameter of the crest of the thread,

The length of the neck Lc is: 10

image 1

being

Φh the diameter of the washer

Φmax the maximum aggregate size

rec the concrete coating 15

α the angle of placement of the screw with respect to the contact plane

h concrete thickness

In a more particular aspect, the tightening head has a shape selected from: hexagonal, square, Allen, Torx.

In a more particular aspect, the thickness of the washer is increased by the inclusion in the system of several overlapping washers with one another, of equal or different size.

In another aspect of the present invention, the angle of placement of the screw with respect to the concrete-wood contact plane is less than or equal to 45 °.

In another aspect of the present invention, the screwdriver is placed in the plane of symmetry of the wooden beam. In another aspect of the present invention, the screwdriver is not in the plane of symmetry of the wooden beam and is alternately placed at a certain distance from it.

The angle of positioning of the connections with respect to the contact plane, mobilizes an additional flush transmission by friction between the wood and the concrete which, depending on the coefficient of friction between the wood and the concrete can become of the same or greater order of magnitude than that transmitted by the connection.

 5

Description of the figures

Figure. 1 shows the special head screw that constitutes the connection, in which the option of a hexagonal head has been chosen, A: elevation view, B: plan view, C: threaded section

References and parameters of the background: 10

1: head

2: tightening head

3: washer

4: body

5: unthreaded zone 15

6: threaded area

7: tip

∅cr: Diameter in the crest of the thread; ∅f: Thread bottom diameter; P: Thread pitch; ∅c: Neck diameter; L: length of the screwdriver; Lr: Threaded length, Lc: Neck length; ∅h: Washer diameter; e: thickness in the washer; K = Head depth of 20 tighten S = distance between faces in case of hex head

Figure 2 shows three screws with three different types of head (1): A: plan view and elevation of a hexagonal head screw, B: plan view and elevation of a square head screw, C: view in plan and elevation of a screw with Allen head. 25

Figure 3 shows three bolts with three different types of washers: A: plan and elevation view of a bolt with washer X, B: plan and elevation view of a bolt with washer Y, C: plan view and elevation of a screw with washer Z.

Figure 4 shows A: scheme of the point load of the system of the present invention, B: scheme of shear stress, C: scheme of flush effort, D: profile view of a

embodiment of the present invention in which the connectors are placed with an inclination α along the plane of symmetry of the beam, E: plan view of an embodiment of the present invention in which the connectors are placed with an inclination α along the plane of symmetry of the beam and with a constant separation between the screws.

Figure 5 shows: A: the distributed load scheme of the system of the present invention, 5 B: shear force scheme, C: flush effort scheme, D: profile view of an embodiment of the present invention in which the connectors are placed with an inclination α along the plane of symmetry of the beam, E: plan view of an embodiment of the present invention in which the connectors are placed with an inclination α along the plane of symmetry of the beam and with a variable separation between the screws. 10

Figure 6 shows a plan view of connectors positioned alternately with respect to the shaft.

Figure 7 shows A: an assembly with recoverable formwork and B: an assembly with the usual technique. In assembly A the formwork is placed supported by slats that are screwed to the wooden beams as supporting elements, propping these beams in the center of 15 light. In assembly B the wooden beams are not used as supporting elements, having to prop up the formwork directly.

Detailed description of the invention

Connections: Special screws (Figure 1): 20

The present invention relates to a connection system of composite concrete-wood structures of the screw type comprising:

- a head (1) configured to anchor the bolt to the concrete, and a body (4) that includes a neck without thread (5) and a thread area (6). The latter is screwed into the wood and fixes the screwdriver so that when loading, a component is produced that produces the bolt breakage predominantly by traction in the latter mode.

The threaded area (6), which has to penetrate into wood, is the essential part, since it must be of sufficient length so that, when pulled, the breakage of the trowel takes place rather than the tearing of the latter from the wood. The type of thread is essential to avoid longer lengths. The thread used is the thread for natural wood 30 DIN: 7998, although it could vary, but always decreasing the diameter of the thread bottom

(that is, in the sense of increasing the depth of the fillet), especially if it is plywood or other material produced from wood.

The head (1) consists of a part to achieve the adequate support surface for the tool, tightening head (2) and a washer (3) of larger dimensions than the head and which may well be forged in the same body, or it could be a washer (3) 5 captive next to the head (1).

The tightening head (2) (which is normally hexagonal, can be square, Allen or any other that allows threading) in such a way that a spanner or a fixed wrench (hexagonal), a special wrench (square) Allen wrench can be used, or other, manually operated or preferably electric. The dimensions of the head will be sufficient to allow the tool to embed the entire threaded part in the wood, as is customary in this technique.

The washer (3) will have a much larger diameter than the body in order to transmit stresses to a sufficiently wide area that avoids the crushing of concrete, which happens in the systems described in the state of the art, and causes an exhaustion 15 premature. Specifically, the diameter of the washer (3) is between 4 and 8 times larger than the diameter of the neck, the size varying depending on the resistant capacities of the metallic material and the concrete.

The thickness of the washer (3) must be sufficient to withstand the shear and bending forces that occur therein at the height of the edge of the support part of the tool. In particular, the thickness of the washer (3) is 0.5 to 0.6 times the diameter of the neck (5) depending on the strengths of the materials mentioned above.

The neck (5) is long compared to the usual screws. Its dimension will depend on the thickness of the slab that you want to collaborate directly under the washer among other aspects. 25

Its length is limited by a maximum that is what allows sufficient concrete overlay to exist over the screwdriver and a minimum that ensures that the concrete can penetrate through the space between the connector positioned at an angle to the wood.

The maximum dimension is a function of the thickness of the slab, the diameter of the washer (3) and the angle of inclination of the bolt (α). The minimum dimension is a function of the maximum size

of the aggregate used in the concrete, of the diameter of the washer (3) of the head (1) and of the angle (α) of tilt of the bolt.

The diameter of the neck (5) of the screw ∅c is less than or equal to that of the thread crest (6) with limits determined by a good transmission of tension to the head (1), specifically, the diameter of the neck ( 5) is between 4-16 mm. The relationship between 5 elastic limits (a / c) is another parameter that marks the dimensions of the parts of the screw and will be between 7 -15.

The tip (7) of the screwdriver is self-drilling so that it penetrates the wood without the need for prior guidance. In the case of diameters greater than 8-10 mm., Depending on the quality and dimensions of the wood, a pre-drill may be necessary. 10 This may be necessary in structures that require large diameter connectors, such as bridges.

Execution of the connection system (Figures 4 and 5):

The screws were placed forming an angle (α) of placement of the screw with respect to the contact plane, less than 90 ° in this way its work to flexotraction is possible. 15 The smaller the angle, the connector will work more clearly in tension but less friction will be made between the wood and the concrete in the contact plane that will help to a lesser extent the transmission of the flush effort, and consequently, will make the connector support higher load.

A preferred placement is when the connector is all in the plane of symmetry of the 20 wooden beam and forms 45 ° with the contact plane. It could also not be in the plane of symmetry of the beam and be placed alternately at a certain distance from the beam (figure 6).

The connector was threaded to the wood by means of the appropriate instruments to the head (1) that was chosen with the help of a guide that ensures its placement with the chosen angle (α), in this case in particular (α) = 45º. 25

This simplicity of assembly of the connection system of the invention is one of its advantages, since no special tools are required for its placement.

The orientation of the tilt of the screwdriver was changed according to the loads supported in order to ensure that the channeling of flush makes it always work flexurally. 30

In the case of beams or slabs designed for point loads, the point of application of the load is the point that marks the change of orientation of the tilt of the screws, whose separation will be generally constant (Figure 4)

In the case of beams designed for distributed loads, the center of gravity of the distributed load will mark the change in orientation of the inclination, whose separation will generally be variable (Figure 5)

This separation between the screws will be a function of the loads to which the mixed structure is subjected, its materials, areas and inertia of the section of each one, the inclination and the stiffness that the connection provides, among other characteristics.

The connection system is mounted with the help of a shoring system according to the usual mixed construction technique that supports the slab during its setting, or a recoverable formwork is fixed to the wooden beams (figure 7).

In a particular embodiment, the system of the present invention was constituted by steel connectors with an angle (α) of 45 °, in which the beams were made of natural or laminated wood, and with a sufficient edge to embed the entire thread (6), the tightening head (2) was hexagonal and the screws were of elastic limit of the order of 10 times higher than the concrete.

The diameter of the crest of the thread (6), ∅cr was the parameter that was chosen first because it was essential, next to the depth of thread (6), to ensure that there is no removal of the wood. Once this was chosen, the rest of the dimensions were determined by all the parameters mentioned in the previous paragraphs.

We choose a ridge diameter ridge ∅cr = 8 mm:

The maximum diameter of the thread bottom (6) ∅f, the thread pitch (6) and the fillet opening angle are given by the thread type (6).

In this case, the thread (6) was a wood screw according to DIN 7998. According to this standard: 25

- For ∅cr <12mm; 11,42857crfC

- For ∅cr≥12mm; 11,3333crfC

As mentioned, this ∅f must be taken as a maximum. In this case, ∅f = 5.6 mm was taken

The opening angle of the fillet is, in any case, 60º ± 6º

The thread pitch P depends on ∅cr according to DIN 7998 and for ∅cr = 8mm, P = 3.6 mm.

The diameter of the neck of the screw ∅c is less than or equal to that of the screw ridge with limits determined by a good transmission of tensions to the head, which depend on the coefficient C1. 5

; being 2crcC121112CC

In our case, the limits are 1 <C2 <1.2143. We take C2 = 1,075 and recommend this value in other diameters for a good transmission, and it turns out ∅c = 7.5

The length of the threading zone (6) Lr for wood of approximate medium density 450-460kg / m3 (C27 or C-30) will generally depend on the type of thread (∅cr, ∅f, P and 10 opening angle) , and of the type of wood and steel. Start-up tests carried out with natural conifer wood and DIN 7998 thread for wood advise that for ∅cr = 8 mm, be Lr ≥ 107 mm. Lr = 110 mm is taken.

For other diameters it is recommended Lr ≥ 13 · ∅cr

The self-drilling tip (7) had a conical shape, however any other shape approximate to it would be valid.

The diameter ∅h of the washer (3) that ensures, with a safety coefficient γ∅h, that there is no crushing of the concrete will be

                                                      (1.1) 20

image2

For a γ∅h = 1 the diameter must be ∅h≥33 mm, however we take γ∅h = 1.7 due to the existence of local tensions, and with a = 5600 and h = 300 results ∅h≥ 42 mm

The length of the neck Lc will depend, among other aspects, on the thickness, h, of the slab that is desired to collaborate directly under the washer and the angle (α) formed by the 25 bolts.

It will be limited, as has been said, for a maximum, which is what allows sufficient concrete coating to exist above the screwdriver, and a minimum, which guarantees that the concrete can penetrate through the space between the connector placed in

Angle with respect to the wood .. If we place the screws with an angle ∝, the concrete slab has a thickness h, the coating is rec and the maximum aggregate size is ∅max:

                                                                                                                  5

image3

As we have chosen ∝ = 45º it turns out:

image4

 10

With a maximum aggregate size ∅max = 25 mm, slab thickness h = 12cm, rec coating = 4cm and ∅h = 42mm, it results 49 mm≤ Lc ≤ 92mm. Take for example Lc = 65 mm.

The diameter at the crest and the type of thread (6) defines the dimensions of the head (1). Since the heads (1) are conventional, we calculate their dimensions according to the series that corresponds to the type of head for the DIN 7998 thread. 15

For hexagonal head screws: DIN 751 standard corresponds, for other heads the dimensions of the series will be applied according to their corresponding regulations or the manufacturer's recommendations.

In this case, for hexagonal head results according to DN 751 for ∅cr = 8 mm:

S = 13 mm 20

K = 5.5 mm

S being the separation between opposite faces of the hexagon that forms the tightening head (2), and K the edge of the hexagonal block.

As for the thickness e of the washer (3), the condition is that it is able to withstand the shear stresses and bending moments that are generated in the circular section next to the head due to the pressure of the concrete as a reaction on it when pulling The background.

We consider that the concrete is 60% of its breaking stress, since we have already forced it to be far from the breaking stress when sizing the diameter of the washer (3). So the condition is:

image5

For ∅c = 7.5mm, with a = 5600 and h = 300 results t≥4.13 mm. We take e = 5 mm thickness of washer (3) 5

Once the diameter at the crest of the thread has been chosen, the preferred dimensions of the parts of the thread are defined by the above formulas. For other relationships σa / σh there is only to apply the corresponding formulas.

10

Claims (5)

1. Connection system of concrete-wood composite structures, comprising at least one screw-type connector comprising:  a head (1) configured to anchor the bolt to the concrete comprising:  a tightening head (2), 5  at least one washer (3),  a body (4) that includes:  a neck without thread (5),  a thread zone (6),  a self-drilling tip (7) 10 characterized by: The diameter of the washer is 4 to 8 times larger than the diameter of the neck, The thickness of the washer is 0.5 to 0.6 times the diameter of the neck, the diameter of the neck is between 4-16 mm, the diameter of the thread is less than or equal to 16 mm, 15 the angle of placement of the screw with respect to the concrete-wood contact plane is less than 90º the length of the thread, is equal to 13 times the diameter of the crest of the thread, The length of the neck Lc is:  twenty being Φh the diameter of the washer Φmax the maximum aggregate size rec the concrete coating α the angle of placement of the screw with respect to the contact plane 25 h concrete thickness 2. Connection system of composite concrete-wood structures according to claim 1, wherein the clamping head (2) has a shape selected from: hexagonal, square, Allen, Torx. 3. Connection system of composite concrete-wood structures according to any of the preceding claims, wherein the thickness of the washer is increased by the inclusion in the system of several washers superimposed on each other. 4. Connection system of composite concrete-wood structures according to any one of the preceding claims, wherein the angle, α of placement of the screw with respect to the concrete-wood contact plane is less than or equal to 45 °. 5. Connection system of composite concrete-wood structures according to any one of the preceding claims, wherein the bolt is placed in the plane of symmetry of the beam.