WO2022032403A1

WO2022032403A1 - Method for making an interlocking joint (shear key) between prefabricated elements to build a concrete wind turbine tower or similar

Info

Publication number: WO2022032403A1
Application number: PCT/CL2020/050091
Authority: WO
Inventors: Mark WOERING
Original assignee: Mecal Intellectual Property And Standards B.V.
Priority date: 2020-08-13
Filing date: 2020-08-13
Publication date: 2022-02-17

Abstract

Disclosed is a method that provides interlocking joints by means of a bed that separates prefabricated concrete, causing a slight crack to form with the shape of a predefined interlocking joint. When a wall is in tension and the slight crack opens a few millimetres, the interlocking joint will provide shear transfer without negative effects of tensile stress in the wall.

Description

QUALIFICATION

“Method to carry out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or similar”

DESCRIPTIVE MEMORY

The present invention patent application is directed to a method for carrying out a locking joint (Shear Key) between the prefabricated elements for the construction of a wind tower (e.g. advanced tower system (ATS)). Specifically, it addresses a method that provides interlocking joints by means of a grout that separates from precast concrete, causing a smooth crack to form in the shape of a predefined interlocking joint. When the wall is in tension and the smooth crack opens a few millimeters, this is where the locking joint will provide shear transfer with no negative tensile stress effects on the wall.

PREVIOUS ART

Locking joints or shear keys are widely used to join a prefabricated concrete element with the foundation and walls where the element will be installed. In construction these interlocking joints are also known as claw or toothed joints. These latch joints are used to resist horizontal and vertical forces on the structure caused by

two loading effects such as earth and water pressures, earthquakes and wind.

In response to the need to develop large wind towers, precast concrete towers are being promoted to overcome the high cost and limitations of traditional steel as a means of tower construction. The precast segment construction method requires the presence of segment joints to transfer loads between neighboring segments, stressing the importance of ensuring structural safety and serviceability. In this way, research has been carried out dedicated to the behavior of joints by segments. The shear behavior of the joints in segmented precast samples with shear keys has been studied considering different types of joints and levels of lateral force to develop high-strength precast concrete wind towers. This is how there are analyzes to examine the load-displacement relationship according to the type of shear keys and, in case of failure, the modes that the locking joints adopt according to the crack pattern in case of failure.

In recent years, the loads on the towers have increased due to stronger turbines and larger rotors. Increasing rotor diameters has two effects:

• higher torsional loads on towers in rupture procedures;

3 • Decreased allowable tower diameter at a low level in the tower, because a large rotor blade reaches lower and deflects further into the tower. In a recent conceptual design for ATS towers and similar segmented concrete towers, the extreme combinations of simultaneous bending, shearing, and torsion could not be resolved with conventional horizontal joints. Especially the high torque at an opening joint (cracked joint) was problematic. The alternative solution with shear loads perpendicular to the tower walls in the compression zone created extremely high bending moments in these walls. The literature (Betonkalender "Concrete structures for wind turbines" 2013) points out the use of shear keys in segmented bridge decks in these cases. Locking joints could transfer shear and twisting forces across a horizontal joint, even when it is pulling apart a bit. That would result in a transfer of shear and torque through the entire joint, not just the compression portion. However, due to tolerances in large precast sections, ATS towers among other types of segmented concrete towers use ganged joints. These joints are in the form of standard toothed locking joints. If the joint were to crack in a load box with vertical stress on the wall, it would logically crack as illustrated in Figure 5.

Studies on joints grouped in the same way (ref .: Pennsylvania Institute of Transportation Report, FHWA-PA-2010-014-PSU 014) show

4 the appearance of straight cracks, even if the joints are made only for shear transfer. Straight cracks no longer transfer shear and torque when they open larger than the grain size of the concrete aggregate. Although horizontal joints are in the form of shear keys, they do not function as such. All shear and torsion transfer is concentrated in the compression portion of the tower wall. Although horizontal joints are in the form of lock joints, they do not function as such. All shear and torsion transfer is concentrated in the compression portion of the tower wall.

There are different types of solutions to carry out the interlocking joint in precast concrete towers. For example, publication WO2019026056 A1 describes the shear key joint configurations of the facing vertical joint faces, the mortar or cast-in-place concrete accessories that act by means of structural connectors for the transmission of structural stresses during the useful life of the structure.

Locking joint configurations are tongue and groove configurations, cam and socket configurations, or others commonly used in structural members.

Figure 1 (Prior Art) shows how the transverse joint faces 13 can include a locking joint configuration that increases the shear and bending stress transmission capacity between the annular sections.

5 overlapping. Similarly, figure 2 shows the incorporation of bicones by means of mounting positioners 40 that allow centering the position of the wall pieces 10 when they are superimposed, where the vertical joining faces of two adjacent wall pieces (10) of the same annular section are arranged opposite each other and lack structural screws, structural bolts, local post-tensioning, annular post-tensioning around an annular section, interlocking joint configurations of the opposing vertical joint faces or concrete accessories cast in in situ that act as structural connectors for the transmission of structural stresses during the service life of the structure. The difference that this publication presents with respect to the present invention is that the publication does not provide that the grouped interlocking joints be separated from the adjacent concrete by a release agent or a thin material that is placed in the joint on one side of the joint. locking union. In the publication segmented elements of precast concrete are used. On the contrary, the use of concrete in the publication allows very small tolerances.

Publication US8307593 (B2), as illustrated in Figure 3 (Prior Art), describes an adapter section (270) that can be used to join an upper section (112) to the lower concrete section (214). The adapter section 270 may comprise a prefabricated member in the form of a slab, ring, or cylinder. Adapter section 270 may also have any suitable shape as desired in the specific application. The adapter section (270) is configured to substantially align the loading forces

6 of the tower in such a way that the tensile and shear forces are reduced. The difference that this publication presents with respect to the present invention is given that a method is not used to configure the interlocking joint by filling with a grout between the faces of the interlocking joints.

Publication WO2018193281 defines that the respective geometries of the upper face of the first segment and of the lower face of the second segment define at least one shear key when they cooperate with each other. As can be seen in Figure 4 (Prior Art), the locking joint is defined by a mortise and a tenon, respectively, defined within an element between the upper face of the first segment and the lower face of the second segment. Specifically, the respective geometries of the upper face (UFi-1) of the first segment (Si-1) and of the lower face (LFi) of the second segment (Si) define at least one locking joint (K) by cooperating with some and others. The difference with respect to the invention lies in the fact that the locking union is carried out with a mortise and a tenon and not by means of a locking union that is filled with a grout, achieving that the union adopts the shape of each locking union and thus increase resistance to stress.

Patent registration CL55121 describes a vertical precast concrete stepped tower adapted to support a wind turbine, comprising a foundation base member positioned to support the tower, a first plurality of substantially identical precast concrete cylindrical or annular lower tower segments and lower tower segments

7 cylindrical having the same diameter and supported by the base member and arranged to form a first vertical stack of successive lower tower segments, a first annular or circular transition segment, a second plurality of intermediate annular and cylindrical tower segments of concrete, a third plurality of precast concrete cylindrical and annular upper tower segments substantially identical and with the cylindrical upper tower segments having a diameter smaller than the diameter of the intermediate tower segments, with the upper tower segments being arranged to form a third vertical stack of successive upper tower segments on top of the second precast concrete transition segment, and a series of vertically extending post-tensioning tendons positioned within a chamber defined by the first, second and third pluralities of annular tower segments and connecting all annular tower segments and annular transition segments together. The difference with the present invention lies in the fact that a method for making the locking joint using a grout in the joint itself is described.

In short, the invention differs from the other solutions by the use of a grout that allows large prefabricated elements with reasonable tolerances.

The other solutions mentioned are crushed dry joints, with overlapping elements. That solution works fine, but only allows very small tolerances.

8 BRIEF DESCRIPTION OF THE FIGURES

Figure 1: corresponds to a prior art shear key joint scheme.

Figure 2: corresponds to a prior art shear key joint scheme.

Figure 3: corresponds to a prior art shear key joint scheme.

Figure 4: corresponds to a prior art shear key joint scheme.

Figure 5: Corresponds to a front section view that exemplifies if a joint cracked in a load box with vertical stress on a wall.

Figure 6: Corresponds to a side sectional view exemplifying if a joint were to crack in a load box with vertical stress on a wall

Figure 7: corresponds to a top section view of a horizontal section through the joints.

Figure 8: corresponds to a front section view that illustrates the group of locking elements in which the grout (5) and the non-stick material (4) have been arranged.

Figure 9: corresponds to a side sectional view that illustrates that the grout (5) and the non-stick material (4) have been placed between the locking elements.

Figure 10: Corresponds to a Bredt cut flow diagram. DESCRIPTION OF THE INVENTION

The invention consists of a method for carrying out a Shear Key joint between precast concrete segments for wind turbine construction (for example, but not limited to an advanced tower system (ATS)). Specifically, the method consists of providing interlocking joints that are filled by a grout that is placed on only one side of a precast segment, causing a smooth crack to form in the shape of a predefined interlocking joint. When the wall is in tension and the smooth crack opens, this is where the locking joint will provide shear transfer and allow for significantly higher locking and shear stress.

In this way, the method comprises having grouped locking joints with a predefined shape. The method also comprises preventing the bonding of the grout to a section of precast concrete (of the two that are joined and that between them forms a shear key), by means of a release agent or a thin layer of material. unbonded, so as to prevent adhesion between prefabricated segments of the tower and to predefine the shape that the actual crack will take when subjected to stress, that is, the shape of a default shear key joint.

The method comprises making the joint between the precast concrete tower segments and the grout non-stick by performing any of the following steps:

• oil or paint one of the locking joint surfaces;

10 • place a thin layer of plastic material on one of the surfaces of the locking joint;

• provide any other material that adheres to the precast concrete surface, such as non-stick resins, and does not deform much when loaded in shear

The result is a series or set of shear keys in unreinforced concrete and grout.

The method is suitable for a total of extreme combinations of bending, shear and torsion, where its application is given in a system consisting of:

• Prefabricated tower walls;

• Post-tensioning of the tower;

• Vertical reinforcing bars across horizontal joints;

• Locking joints (shear keys).

This total system must transfer shear and torque through the entire cross section of the joint formed by the locking joints.

Therefore, a Bredt shear flow occurs through the joints, as in the rest of the tower. It is seen from Figure 8 that this Bredt shear flow diagram has lever arms the size of the full cross-section. It offers much more torsional strength than a horizontally cracked joint with a smooth crack. In case of a smooth horizontal crack the lever arms reduce the compression section to the size of the wall thickness.

eleven DESCRIPTION OF THE PREFERRED MODE

The method of the invention consists of forming a series or a set of locking joints (Shear Keys) (1) along the entire wall segment (5) of each section that forms a prefabricated concrete tower with an external face ( 7) and internal face (8). Each locking joint (1) is filled by a grout (2) that is placed in each locking joint (1) on the face (11). In this way, when the tower is subjected to stress, a smooth crack (3) is formed in the shape of a predefined locking joint (1). This allows the smooth crack (3) to open a few millimeters, this is where the locking joint will provide greater shear and torque transfer. The horizontal joints are reinforced by vertical bars (10) to provide the tensile forces for bending movements along with shear flow through the joint.

Prior to the stage of filling the interlocking joint (1) with grout, it is incorporated on the opposite face (12) to the face (11) that is filled with the grout (2) of the prefabricated segments of each section of the tower , a non-stick material (4) that forms a thin layer that allows each prefabricated segment to be kept separate and not joined. So when the grout (2) is incorporated, it only adheres to one of the faces of the prefabricated segments. In this preferred embodiment, the non-stick material used is oil. In this way, the grout (2) adheres only to one of the faces of the prefabricated segments. The choice of a specific material for the thin layer, or for the release agent between the grout and the concrete defines the possibility of friction in the concrete.

12 diagonal faces of the locking joints. This allows the connection designer possibilities to adjust the behavior of the connection.

On the external face (7) of each prefabricated segment, in the area where the locking joint is located, a seal (9) is incorporated that prevents both the exit of grout (2) when it is incorporated and the entry of external elements.

13

Claims

CLAIMS Method for carrying out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or similar, which allows greater shear and torsion efforts when the tower is subjected to high loads external, CHARACTERIZED because it comprises arranging a set of interlocking joints, in each interlocking joint it is filled with a grout, achieving that, when the tower is subjected to stress, a smooth crack is formed in the shape of a predefined interlocking joint; in that to avoid the union of said grout to a section of prefabricated concrete and consequently with one of the surfaces that make up the interlocking joint (of the two that are joined and that between them the set of interlocking joints or shear key is formed ), there is a thin material or release agent on the opposite side to where it is filled with said grout, so as to form a set of shear keys in non-reinforced concrete and grout. Method for carrying out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or the like according to claim 1, CHARACTERIZED in that said thin material is oil or paint. Method to carry out a locking joint (Shear Key) between prefabricated elements for the construction of a turbine tower concrete wind turbine or similar according to claim 1, CHARACTERIZED in that said thin material is plastic material. Method for carrying out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or the like according to claim 1, CHARACTERIZED in that said thin material is a non-stick resin. Method for carrying out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or similar according to claim 1, CHARACTERIZED because each prefabricated segment has a vertical bar and connection elements between segments. Method for carrying out a locking joint (Shear Key) between prefabricated elements for the construction of a concrete wind turbine tower or similar according to claim 1, CHARACTERIZED because on the external face of each prefabricated segment, in the area where the locking union is located, a seal is incorporated that prevents the exit of grout when it is incorporated and the entry of external elements.