Patent Description:
The invention further relates to a method of assembling such an assembly of a first and a second member that each comprise at least one through hole.

The present invention is particularly suitable for offshore applications, e.g. for connecting a wind turbine to a monopile, a wind turbine to a transition piece, a transition piece to a monopile, between members of a monopile or wind turbine, as well as to connections having a much smaller diameter than monopiles, e.g. between members of a jacket.

According to prior art applications in offshore, the members of such assemblies are provided with flanges which are connected using bolts of significant size. Currently M72 bolts are used for connecting a wind turbine tower to a monopile or transition piece. In a first step, these bolts are electrically tightened with <NUM>. In a second step, the preload is increased with hydraulic tools to <NUM>. The bolts itself are heavy and the tools for tightening the bolts are also heavy and hard to handle.

It appears that the actual preload on the bolts after some settling time is hard to predict and control, and may vary significantly. Although it is not exactly clear which factors influence the torque-tension relationship of the bolts, it may be concluded that installing the bolts using a "constant torque" method does not achieve satisfying results. Similar issues occur with tensioning systems for bolting. The preload on the bolts must be regularly checked and adjusted, periodically requiring significant maintenance work.

Furthermore, the bolts are arranged all around the circumference of the flanges, leaving only a very limited gap between adjacent bolts. A connection using flanges with bolts is insufficiently scalable to meet the ever increasing demands resulting from even larger wind turbines and greater depths at sea where they are installed.

International patent application <CIT> of the same inventor proposes an assembly that is improved relative to a connection using flanges connected by bolts. This improved prior art assembly comprises:.

The actuator is radially displaceable with respect to the longitudinal axis of the section that comprises the actuator. This allows the actuator itself to be employed as part of a clamp. During radial displacement of the actuator, an inclined surface of the actuator engages a specially machined surface of the first section and gradually increases the clamping force that connects the first and the second section. Although the assembly of <CIT> already provides a significant improvement relative to the above-described prior art connections using flanges connected by bolts, radial displacement of the actuator required a significant force due to the clamping action. Moreover, sections with a specially designed contact surface were required.

The inventor proposed even further improvements relative to the assembly of <CIT> in the non pre-published international patent application <CIT> that claims priority of the earlier Dutch national patent application <CIT>. The improved assembly described in<CIT> comprised:.

As a result of the pre-tensioned connection between the first member and the second member any load fluctuations going through the connector are reduced significantly resulting in very low fatigue damage levels compared to a non pre-tensioned connection.

Relative to the assembly of <CIT>, a human worker could insert a connector as described in PCT/IB2019/<NUM> into the channel to an end position in a first step, followed by a further step of consecutively expanding said connector radially relative to said channel, to thereby connect the first and second member relative to each other. In this way, the connector could be accurately and easily placed in the channel by a user with very limited hassle or force. Only when the connector is placed in its desired end position, it is expanded in the channel to connect the first and second member relative to each other. Use of a connector according to the invention also makes specially machined contact surfaces with an inclination corresponding to an inclination of the radially displaceable actuator redundant.

Relative to the older prior art of bolted flanges, large scale (e.g. M72) bolts are redundant. Also, the body could be less bulky than a flange comprising through holes to accommodate a bolt. As a result, the assembly according to the invention, required less material, was therefore more compact and lighter, and also more elegant. Whereas thick parts need to be forged, smaller parts may also be rolled, possibly allowing the members to be formed with alternative and more attractive manufacturing methods. The assembly described in PCT/IB2019/<NUM> was also scalable, providing the opportunity to arrange multiple connectors in axial direction of the members.

A further advantage of the assembly described in PCT/IB2019/<NUM> relative to bolted flanges, was the absence of these flanges that would provide a significant mass outside the path where forces travel during driving the assembly into a ground using a hammer. The mass of conventional flanges may result in bending of the neck of the flanges. These bending stresses currently result in significantly reduced life time of the welds of these flanges when installed with a conventional impact hammer.

An even further advantage of the proposed assembly relative to bolted flanges was that it could be applied for connecting members under the waterline. On the one hand, longitudinal members of a limited length could be used, allowing smaller ships to transport them to a desired location for an offshore construction.

The successively tightening the bolts of a bolted flange - which are typically tightened in multiple steps, as mentioned above - is very time consuming and labor-intensive.

In PCT/IB2019/<NUM> the connectors were axially inserted in said channel by manual labor. A workman positioned each connector to the desired end position in said channel, before said connector was consecutively expanded radially relative to said channel, to connect the first and second member relative to each other and define a pre-tensioned connection there between.

The assembly described in PCT/IB2019/<NUM> was already less labor-intensive and time consuming than a connection having bolted flanges, but there remains a continuous need to further reduce manual labor and construction time.

A disadvantage of the assembly described in PCT/IB2019/<NUM> was that said assembly could only be applied in places where there was enough space for a human worker to work. Although such space is readily available inside a monopile, other types of foundations, e.g. between tubular members of jackets, may not offer sufficient space for a worker inside said tubular members. Consequently, the assembly described in PCT/IB2019/<NUM> could only be applied to small tubular members from the outside thereof inward. Moreover, a connection below the water line would require the human workers to be divers, significantly increasing construction time and human risks.

As will be clear from the description above, the assembly described in the non pre-published <CIT> has many advantages that ideally should be maintained as much as possible. On the other hand, there remains an ongoing need for a further increase in efficiency and/or versatility.

The United States patent application <CIT> is directed to an expansion pin system for construction of a wind turbine structural tower, and is considered the closest prior art. Relative to <CIT>, at least the characterizing features of the independent claims are novel. <CIT> discloses, in terminology of the present invention, a first and a second member, wherein the second member has a fork-shaped cross section with a main body and two substantially parallel walls that each comprise at least one through hole, wherein the first member is arranged between the two walls of the second member, having the through hole, and wherein said through hole of the first member and the through holes of the second member are aligned to define a channel. The expansion pin may be interpreted as a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel, to connect the first and second member relative to each other. When the expansion pin system is inserted into the channel it results in an alignment of the through holes of the first and the second member.

The United States patent <CIT> discloses a configuration that shows some similarity to <CIT>. In terminology of the present invention, it discloses a first and a second member, wherein the second member has a fork-shaped cross section with a main body and two substantially parallel walls that each comprise at least one through hole, wherein the first member is arranged between the two walls of the second member, having the through hole, and wherein said through hole of the first member and the through holes of the second member are aligned to define a channel. A clevis bushing may be interpreted as a connector that is axially insertable in said channel to an end position and consecutively expandable radially relative to said channel. This clevis bushing, upon radially expansion thereof, clamps itself in a through hole of one wall of the fork-shaped second member, and furthermore presses the first member in axial direction against the other wall of the fork-shaped second member.

The Dutch patent <CIT> by the same inventor and the European patent application <CIT> are acknowledged as further prior art.

An object of the present invention is to provide an assembly, that is improved relative to the prior art. Said object is achieved with the assembly according to claim <NUM> of the present invention, comprising:.

By using an actuator that is configured to move the connector in an axial direction relative to the channel, there is no need for a human worker to enter inside one of the respective first or second members, when the connectors are arranged from the inside, or to perform a hazardous diving operation when the connectors are arranged from the outside. The actuator, by virtue of replacing a human worker, allows for an increased level of automation and therefore a reduction in construction time. By automated insertion and expanding of the actuator, a controlled and repeatable force may be applied. Moreover, automated actuation also allows multiple connectors to be expanded simultaneously, thereby further reducing construction time and moreover allowing for an even application of a clamping contact that causes the pre-tensioned connection between the first member and the second member.

An even more important advantage is the increase in versatility. After all, the actuator allows the connector or connectors to be arranged in an assembly of first and second members that are too small for a human worker to fit in, especially if the connections are submerged and the human worker requires diving equipment. Such an assembly may be present in jacket construction, wherein tubular members may have diameters as small as <NUM> to <NUM> meter.

According to the invention, the actuator is configured to consecutively:.

According to a further preferred embodiment, the assembly further comprises a stop configured to set the end position of the connector relative to said channel. Said stop may comprise an abutment that is configured to abut against one of the first member and the second member, and may alternatively, or additionally, be defined by a maximum elongation or displacement of the actuator.

According to an even further preferred embodiment, the connector, in the expanded state thereof, pushes against faces of the through holes of the second member that are directed away from the main body thereof to define the pre-tensioned connection between the first member and the second member.

According to an even further preferred embodiment, in the expanded state of the connector, wherein the connection between the first member and the second member is pre-tensioned, the through hole of the first member is arranged at an offset relative to the through holes in the second member. As mentioned above, said through hole of the first member and the through holes of the second member define a channel, which means that said through holes are positioned in a way that they are "substantially" aligned. However, a presence of an offset may guarantee that there always remains a slight misalignment of the through hole of the first member relative to the through holes of the second member. This is advantageous, because the offset, i.e. the slight misalignment in the channel, guarantees that the connection between the first member and the second member may be optimally pre-tensioned. After all, the connector is configured to expand in the channel, wherein the connector pushes the first member against the main body of the second member. In order to optimally push the first member towards the main body of the second member, it is beneficial if the side of the connector that is directed towards the main body does not come into contact with the inner walls of the through holes in the parallel walls of the second member. In this way, the side of the connector that is directed towards the main body can fully transfer its compressive force to the first member that is pressed towards and against the main body of the second member to obtain the desired pre-tensioning.

According to a preferred embodiment, the connector comprises:.

In the compacted state, play between the connector and the inner wall of the channel allows the connector to be easily inserted into the channel. Afterwards, a high axial clamping force may be provided by the connector, which has the advantage that the assembly is less susceptible for load variations. This is best understood when compared to how a bolted joint carries a direct load. An adequately pretensioned bolt can survive in an application that an untightened, or loose bolt, would fail in a short period of time. The bolt only 'feels' a small portion of the applied load.

The invention is furthermore directed to a method of assembling a first and a second member that are tubular members of a wind turbine support structure and each comprise at least one through hole, wherein the second member has a fork-shaped cross section with a main body arranged between two substantially parallel walls that each comprise at least one through hole, said method comprising the steps of:.

According to the invention, the step of inserting the connector into the channel to the end position comprises the steps of:.

The actuator thus replaces a human worker and allows the connector to be inserted and expanded from a single, first side. This may be from an inside of the tubular member, but may also be from an outside of the tubular member. However, one side suffices, and consequently the channel formed by the through holes of the first and second members needs to be accessible from one side only.

According to a further preferred embodiment, the step of consecutively expanding said connector radially relative to said channel comprises:.

According to an even further preferred embodiment, the method further comprises the step of setting the end position of the connector relative to said channel by a stop.

According to an even further preferred embodiment, the step of moving said connector in the axial direction in said channel by the actuator is performed until the connector reaches its end position as defined by the stop, and the step of consecutively expanding said connector radially relative to said channel is performed upon further actuation of the actuator once the connecter has reached its end position.

Further preferred embodiments are the subject of the dependent claims.

In the following description preferred embodiments of the present invention are further elucidated with reference to the drawing, in which:.

An example of an offshore construction comprising multiple connections C where an assembly according to the invention may be applied is shown in <FIG>. An offshore wind turbine tower <NUM> is supported by a supporting base structure <NUM> which is in <FIG> embodied as a monopile <NUM> with a transition piece <NUM>. The skilled person will understand that similar connections are present for alternative supporting base structures <NUM>, such as in a jacket construction <NUM> as shown in <FIG>.

The connections C may be applied between separate members <NUM> of the monopile <NUM>, between the monopile <NUM> and the transition piece <NUM>, between the transition piece <NUM> and the turbine tower <NUM>, between members <NUM> of the turbine tower <NUM>, and between a rotor blade <NUM> and a hub of a rotor, or even between different parts of a rotor blade <NUM>. The construction proposed by the present invention does not require a human worker to enter a space inside a tubular member anymore, allowing the assembly to be applied for connecting (tubular) members of a relatively limited size, such as in jacket constructions. The connections C may serve to connect a jacket to a foundation, e.g. pre-piled foundation piles, drilled foundation piles or suction buckets. It may also be used to provide a jacket to jacket connection.

During use, a wind turbine <NUM> will be oriented such that the rotor blades <NUM> are optimally driven by the available wind power. The rotor blades <NUM> drive a (not shown) generator in the nacelle <NUM>, wherein the generator generates electricity. The wind turbine <NUM> causes alternating loads on any connection C in the construction, and dependent on the wind direction, specific parts of the connection C have to absorb most of the loads.

The assembly according to the invention comprises the first member <NUM> and a second member <NUM>, wherein the second member <NUM> has a fork-shaped cross section <NUM> with a main body <NUM> arranged between two substantially parallel walls <NUM> that each comprise at least one through hole <NUM>, <NUM>, <NUM>. The first member <NUM> is arranged between the two walls <NUM> of the second member <NUM>, having the through hole <NUM>, <NUM>. Said through hole <NUM> of the first member <NUM> and the through holes <NUM>, <NUM> of the second member <NUM> define a channel <NUM>.

The assembly further comprises a connector <NUM> that is axially insertable in said channel <NUM> to an end position (<FIG> and <FIG>) and consecutively expandable radially relative to said channel <NUM> (<FIG>), to connect the first member <NUM> and the second member <NUM> relative to each other. The connector <NUM> comprises a compacted state (shown in <FIG>, <FIG>, <FIG> and <FIG>), wherein the connector <NUM> has a size that is freely insertable into and out of the channel <NUM>, and a connecting state (e.g. shown in <FIG> and <FIG>) wherein the connector <NUM> is expanded in the channel <NUM> to connect the first <NUM> and second member <NUM> relative to each other.

An actuator <NUM> is configured to move said connector <NUM> in an axial direction in said channel <NUM>. The connector <NUM>, in an expanded state thereof (<FIG> and <FIG>), pushes the first member <NUM> against a face <NUM> of the main body <NUM> of the second member <NUM> to define a clamping contact and thereby a pre-tensioned connection between a face <NUM> of the first member <NUM> and the face <NUM> of the main body <NUM> of the second member <NUM>.

The assembly according to the present invention comprises a first member <NUM> and a second member <NUM>, each comprising at least one through hole <NUM>-<NUM>. The through holes <NUM>-<NUM> may be directly arranged in the first member <NUM> and the second member <NUM>, and consequently prior art flanges are redundant. This has several advantages, one of them being a saving of material and less weight outside the line of travel of forces through the assembly.

By using an actuator <NUM> that is configured to move the connector <NUM> in an axial direction relative to the channel <NUM>, there is no need for a human worker to enter inside one of the respective first or second members <NUM>, <NUM>. The actuator <NUM>, by virtue of replacing a human worker, allows for an increased level of automation and therefore a reduction in construction time. By automated insertion and expanding of the actuator <NUM>, a controlled and repeatable force may be applied. Moreover, automated actuation also allows multiple connectors <NUM> to be expanded simultaneously, thereby further reducing construction time and moreover allowing for a uniform application of a clamping contact that causes the pre-tensioned connection between the first member <NUM> and the second member <NUM>.

An even more important advantage is the increase in versatility. After all, the actuator <NUM> allows the connector <NUM> to be arranged in an assembly of first and second members <NUM>, <NUM> that are too small for a human worker to fit in. Such an assembly may be present in jacket construction, wherein tubular members may have diameters as small as <NUM> to <NUM> meter, and may be impossible to access, either because of their limited size, or e.g. for safety reasons or because they are submerged. Especially under water, human workers would have to carry diving equipment, requiring additional space that is not present in tubular members with such small diameters.

A taper angle at the top of first member <NUM> allows for a certain amount of ovality in either member <NUM> or <NUM> to be forced back into a round shape under the force of gravity by pushing first member <NUM> into second member <NUM>. Although not shown, a similar taper shape may be present at the ends of one or both of the walls <NUM> of the fork-shaped cross section <NUM> of the second member <NUM>.

The assembly shown in the Figures further comprises a stop <NUM> configured to set the end position of the connector <NUM> relative to said channel <NUM>. The stop <NUM> may comprise an abutment <NUM> that is configured to abut against one of the first member <NUM> and the second member <NUM>. Alternatively, the stop <NUM> may be defined by a maximum elongation or displacement of the actuator <NUM>.

In <FIG>, a clamping device <NUM> is arranged inside first and second members <NUM>, <NUM> having a tubular shape and a significantly smaller diameter than the monopile shown in <FIG>. In fact, the limited diameter of the tubular first and second members <NUM>, <NUM> shown in <FIG> and <FIG> may be in the order of <NUM>-<NUM> meter, i.e. too small for a human worker to enter and work in. The first and second members <NUM>, <NUM> shown in <FIG>, <FIG> and <FIG> may be part of a jacket construction. In <FIG>, the connectors <NUM> are each positioned in front of an associated channel <NUM>. <FIG> shows that the connectors <NUM> are each moved by the actuator <NUM> inside their associated channels <NUM>, wherein the connectors <NUM> are each positioned in an end position in their associated channels as defined by the stop <NUM>. The stop <NUM> is here embodied as an abutment <NUM> abutting against an inner one of walls <NUM> of the second member <NUM>.

The connector <NUM> comprises at least one expansion block <NUM> and at least one wedge <NUM>, wherein the actuator <NUM> is configured to displace the wedge <NUM> relative to the expansion block <NUM>. The wedge <NUM> has an inclined surface <NUM> facing the at least one expansion block <NUM>.

If the stop <NUM> is arranged on the at least one expansion block <NUM>, it may prevent the expansion block to be inserted fully inside the channel <NUM>. The stop <NUM>,which may be embodied as abutment <NUM>, may thus define an end position of the connector <NUM> relative to said channel <NUM> (<FIG>).

Successive steps of assembling the assembly according to the invention are now further elucidated on the basis of <FIG>. It is repeated that the first and the second member <NUM>, <NUM> each comprise at least one through hole <NUM>, <NUM>, <NUM>, wherein the second member <NUM> has a fork-shaped cross section <NUM> with a main body <NUM> arranged between two substantially parallel walls <NUM> that each comprise at least one through hole <NUM>, <NUM>. The method of assembling starts with the step of arranging the first member <NUM> between the two walls <NUM> of the second member <NUM> (<FIG>). The next step is positioning the through holes <NUM>, <NUM>, <NUM> of the first member <NUM> and the second member <NUM> to define a channel <NUM> (<FIG> also shows that a clamping device <NUM> is inserted inside the second member <NUM> and brought to a position wherein the connectors <NUM> of said clamping device <NUM> substantially align with associated channels <NUM> (<FIG>). The next step comprises the step of inserting a connector <NUM> into the channel <NUM> to an end position (<FIG>), which is performed by moving said connector <NUM> in an axial direction in said channel <NUM> by the actuator <NUM> (<FIG>). Consecutively, said connector <NUM> is expanded radially relative to said channel <NUM>, to thereby connect the first member <NUM> and the second member <NUM> relative to each other, the expanded connector <NUM> pushing the first member <NUM> against a face <NUM> of the main body <NUM> of the second member <NUM> to define a clamping contact and thereby a pre-tensioned connection between a face <NUM> of the first member <NUM> and the face <NUM> of the main body <NUM> of the second member <NUM>.

<FIG> shows the step of setting the end position of the connector <NUM> relative to said channel <NUM> by the stop <NUM>. The stop <NUM>, which is embodied as an abutment <NUM>, abuts against an inner one of the walls <NUM> of the fork-shaped second member <NUM>, thereby preventing the expansion block <NUM> to move further inside said channel <NUM>. The step of moving said connector <NUM> in the axial direction in said channel <NUM> by the actuator <NUM> is performed until the connector <NUM> reaches its end position as defined by the stop (<FIG>). The step of consecutively expanding said connector <NUM> radially relative to said channel <NUM> is performed upon further actuation of the actuator <NUM> once the connecter <NUM> has reached its end position. <FIG> shows how the expansion block <NUM> is stopped by the stop <NUM>, while the wedge <NUM> is pushed further relative to said channel <NUM> by the actuator <NUM>. Due to the inclined surface <NUM> of the wedge <NUM>, the expansion block <NUM> is moved in a radial direction relative to said channel <NUM> until the clamping contact and thereby the pre-tensioned connection between the face <NUM> of the first member <NUM> and the face <NUM> of the main body <NUM> of the second member <NUM> is obtained.

The clamping contact and resulting pre-tensioned connection between the first member <NUM> and the second member <NUM> is now further explained by <FIG>. It is explicitly mentioned that this explanation relates to the orientation shown in <FIG>, but the skilled person will understand the same principle may also be applied in other orientations, such as transverse or upside down relative to <FIG>. In the connecting state shown in <FIG>, the connector <NUM> contacts at its lower side with faces <NUM> formed at the lower side of the respective through holes <NUM>, <NUM> of the second member <NUM>. The upper side of the connector <NUM> contacts a face <NUM> that is arranged at the upper side of the through hole <NUM> in the first member <NUM>. In the expanded state of the connector <NUM>, the connector <NUM> pushes faces <NUM> of the second member <NUM> away from face <NUM> of the first member <NUM>. Consequently, the second member <NUM> is pushed downward relative to the first member <NUM>, and a clamping contact is formed between a face <NUM> defined by the upper side of the first member <NUM>, and a face <NUM> defined by the main body <NUM> of the second member <NUM>. Thus, by expanding the connector <NUM>, a pre-tensioned connection between the first <NUM> and the second member <NUM> can be formed. The faces <NUM>, <NUM>, <NUM> and <NUM> can be best seen in <FIG>. By having sufficient pretension, the load fluctuations going through the connector <NUM> are reduced significantly resulting in very low fatigue levels.

The connector <NUM>, in the expanded state thereof, pushes against faces <NUM> of the through holes <NUM>, <NUM> of the second member <NUM> that are directed away from the main body <NUM> thereof to define the pre-tensioned connection between the first member <NUM> and the second member <NUM>. In the expanded state of the connector <NUM>, wherein the connection between the first member <NUM> and the second member <NUM> is pre-tensioned, the through hole <NUM> of the first member <NUM> is arranged at an offset O or offsets O, relative to the through holes <NUM>, <NUM> in the second member <NUM>.

The assembly may comprise one or more than one further connector <NUM>, wherein the actuator <NUM> is arranged between the connector <NUM> and the one or more than one further connector <NUM>, wherein each of the connector <NUM> and the one or more than one further connector <NUM> is inserted into its own channel <NUM>. The preferred embodiment shown in the Figures comprises a total of twelve connectors <NUM>, of which five are shown in full and two are shown intersected. Multiple channels <NUM> and associated connectors <NUM> are arranged along a circumference of the first <NUM> and the second member <NUM>.

The actuator <NUM> is preferably configured to simultaneously move said connector <NUM> and at least one or more than one further connector <NUM> in an axial direction of their associated channels <NUM>. Automated actuation using actuator <NUM> also allows multiple connectors <NUM> to be expanded simultaneously, thereby further reducing construction time and moreover allowing for a uniform application of a clamping contact that causes the pre-tensioned connection between the first member <NUM> and the second member <NUM>.

The actuator <NUM> may be arranged in a clamping device <NUM>. The actuator <NUM> may comprise one or more than one hydraulic cylinder <NUM>. The shown embodiment comprises twelve hydraulic cylinders <NUM>, i.e. one for each connector <NUM>. A common pressure supply <NUM> may be configured to move said hydraulic cylinders <NUM> simultaneously.

The expansion block <NUM> has a surface <NUM> of which at least a portion is a contact surface with the wedge <NUM> having an orientation corresponding with the inclined surface <NUM> of said wedge <NUM>. When the orientation of the contact surface of the clamping block <NUM> and the inclined surface <NUM> of the wedge <NUM> are substantially equal, a reliable mating interface is obtained. The inclined surface <NUM> of said wedge <NUM> may comprises an inclination with an angle of less than <NUM>° relative to a displacement direction of said wedge <NUM>. By providing an inclination with a relatively flat angle, an axial clamping force Fc results after decomposition thereof in only a very limited radial force component. The relatively small value of the radial force component is typically less than the friction at the contact surface between wedge <NUM> and clamping block <NUM>, resulting in a self-locking contact between the wedge <NUM> and the clamping block <NUM> in the connecting state. As a result, the wedge <NUM> remains in place even if the actuator <NUM> for originally displacing the wedge <NUM> would be loosened or even removed. In this way, a reliable and fail-safe assembly is provided.

In the shown embodiments the first member <NUM> and the second member <NUM> are overlapping tubular members and the through holes <NUM>, <NUM>, <NUM> are radially aligned relative to the tubular members to define the channel <NUM> that is radially extending. Said channel <NUM> may have an elongate cross section extending in a longitudinal direction of at least one of said first member <NUM> and said second member <NUM>. The first member <NUM> and the second member <NUM> may have longitudinal axes that are at least parallel, and that preferably coincide.

A symmetrical force transmission may be obtained if, according to the shown preferred embodiment, the second member <NUM> has a fork-shaped cross section <NUM> with a main body <NUM> and two substantially parallel walls <NUM> that each comprises at least one through hole. In this embodiment, the first member <NUM> is arranged between the two walls <NUM> of the second member <NUM>, having the through holes <NUM>, <NUM>, and said through hole <NUM> of the first member <NUM> and the through holes <NUM>, <NUM> of the second member <NUM> are positioned to define the channel <NUM>. The arrows in <FIG> indicate how a clamping force Fc is symmetrically distributed.

In order to elucidate the forces in the assembly, the axial clamping force Fc is interpreted as a value <NUM>%, directed in the axial direction of the assembly, i.e. in the axial direction of the first member <NUM> and the second member <NUM>. The distributed clamping forces Fcd in each wall <NUM> of the fork-shaped cross section <NUM> of the second member <NUM> will have a value Fcd = <NUM>/<NUM> = <NUM>%.

When the actuator <NUM> moves the wedge <NUM> of a single connector <NUM> in an axial direction of the channel <NUM>, i.e. in the radial direction of the assembly of the first member <NUM> and the second member <NUM>, a required actuation force Fa of tens to several hundreds of tons is needed. This force that is in the axial direction of the channel <NUM> will be used to overcome the friction force in interfaces <NUM> and <NUM> and to generate a clamping force Fc. The friction forces are typically between <NUM>-<NUM>% of their load perpendicular to the friction plane (friction coefficient of <NUM> - <NUM>). With an assumed friction coefficient of <NUM>% at both surfaces <NUM> and <NUM>, the horizontal actuating force required to overcome this friction force is <NUM>% of the preload Fcd. Additionally the inclined plane will result in a force amplification of the load Fapp that is applied in the axial direction of the channel. This causes the clamping force Fc. For a single wedge (unlike the system in application. where double wedges are used) this results in a roughly double as high preload (Fc) than was applied in axial direction of the channel. If the axial force applied on wedge <NUM> would be <NUM> tons than the preload Fc (with a typical inclination between wedges <NUM> and <NUM> of <NUM> degrees) would be <NUM> tons. This <NUM> ton horizontal force needs to overcome the friction on the interfaces <NUM> and <NUM> (<NUM>*<NUM>*<NUM>)=<NUM> tons and the remaining force would be used to generate the preload through the inclined plane. In the configuration described above, the force levering ratio is <NUM> (<NUM> Fc versus <NUM> applied Fapp) for a single wedge. This ratio can increase further with smaller wedge angles and lower friction coefficients.

In order to generate the <NUM> ton horizontal load (Fapp) in the direction of the channel <NUM> an equal reaction force needs to be applied on a wall <NUM>. If the connectors <NUM> are applied from the inside of the first and second members <NUM>, <NUM> as shown in <FIG>, <FIG>, <FIG> and <FIG>, the inner wall <NUM> of the fork-shaped cross section <NUM> of the second member <NUM> will be subjected to a large bending load. By applying opposing pairs of connectors <NUM> simultaneously, such reaction forces would cancel each other out.

The channel <NUM> preferably has an elongate cross section extending in a longitudinal direction of at least one of said first <NUM> and said second member <NUM>. Relative to channels having a circular shape, such an elongate cross sectional shape provides a relatively large amount of material between successive channels <NUM> if multiple channels <NUM> and connectors <NUM> are arranged along a circumference of the first <NUM> and the second member <NUM>.

Although shown as an integral part in <FIG> and <FIG>, the fork-shape of the second member <NUM> may comprise an assembly of a (tubular) main body <NUM> and the two substantially parallel walls <NUM> connected thereto. The parallel walls <NUM> itself may each comprise a plurality of plates <NUM> arranged along the circumference of the main body <NUM>. Said plates <NUM> may be attached to the main body <NUM> with a bolted connection <NUM> (<FIG>).

<FIG> shows an embodiment wherein the actuator <NUM> is arranged in a fastening device <NUM> that comprises a support <NUM>. This support <NUM> may be configured to be supported on an inner one of the walls <NUM>. The actuator <NUM> may be rotatably arranged relative to the support <NUM> to allow the actuator to successively engage a specific connector <NUM> or connectors <NUM>. Preferably, the actuator <NUM> is configured to simultaneously move said connector <NUM> and at least one or more than one further connector <NUM> in an axial direction of their associated channels <NUM>. In <FIG>, two connectors <NUM>, that are arranged opposite relative to each other, are actuated simultaneously. In this way, reaction forces may cancel each other out. In this respect it is remarked that a cancelling out of reaction forces may also be obtained with other configurations, such as with a triangular configuration of three hydraulic cylinders <NUM> that are oriented at <NUM>° relative to each other. A square configuration may comprise four hydraulic cylinders <NUM> that are oriented at <NUM> ° relative to each other, etcetera.

In the alternative and more preferred embodiment shown in <FIG>, the clamping device <NUM> is arranged inside the second member <NUM>. By arranging the clamping device <NUM> inside the second member <NUM>, a correct positioning of the connectors <NUM> relative to the through holes <NUM>, <NUM> of the second member is guaranteed. Consequently, the connectors <NUM> of said clamping device <NUM> are not only in alignment with the through holes <NUM>, <NUM> of the second member, but they are also in alignment with the associated channels <NUM>. In this way, the connectors <NUM> may be easily positioned, also in under water conditions.

Although they show preferred embodiments of the invention, the above described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention. <FIG> shows an offshore wind turbine tower construction and <FIG>, <FIG>, <FIG> show tubular members of a limited diameter as e.g. applied for jackets. The first and the second member may be members of an offshore construction, preferably of an offshore wind turbine construction or a jacket construction. Each of the first <NUM> and the second member <NUM> are preferably tubular members of a monopile or a jacket construction. Alternatively, one of the first <NUM> and the second member <NUM> may be a rotor blade of a wind turbine, wherein the other of the first <NUM> and the second member <NUM> is arranged on a hub, or both the first and second member <NUM>, <NUM> may be parts of a turbine blade <NUM>. It is however explicitly mentioned that the assembly according to the invention is not limited to offshore use, nor to wind turbine applications alone.

Although the Figures show embodiments wherein the clamping device <NUM> is arranged inside the second member <NUM>, the skilled person will understand that an axial insertion of the connector <NUM> into an associated channel <NUM> may also be performed by a clamping device <NUM> that is arranged outside the first and/or second members <NUM>, <NUM>. A clamping device <NUM> arranged outside the first and/or second members <NUM>, <NUM> provides the additional advantage that it may easily be removed afterwards, and possibly re-used for arranging connectors <NUM> of further assemblies.

It is remarked that in the description of the shown embodiments, the lower member is denoted as the first member <NUM>, and that the upper member is denoted as the second member <NUM>. The skilled person will understand that the lower member could be interpreted as a second member <NUM> and the upper member could be interpreted as a first member <NUM> within the scope of the invention.

Claim 1:
Assembly, comprising:
- a first member (<NUM>) and a second member (<NUM>) that are tubular members of a wind turbine support structure (<NUM>), wherein;
- the second member (<NUM>) has a fork-shaped cross section (<NUM>) with a main body (<NUM>) arranged between two substantially parallel walls (<NUM>) that each comprise at least one through hole (<NUM>, <NUM>);
- the first member (<NUM>) is arranged between the two walls (<NUM>) of the second member (<NUM>), having the through hole (<NUM>, <NUM>);
- wherein a through hole (<NUM>) of the first member (<NUM>) and the through holes (<NUM>, <NUM>) of the second member (<NUM>) define a channel (<NUM>);
- a connector (<NUM>) that is axially insertable in said channel (<NUM>) to an end position and consecutively expandable radially relative to said channel (<NUM>), to connect the first member (<NUM>) and the second member (<NUM>) relative to each other;
characterized by
- an actuator (<NUM>) configured to move said connector (<NUM>) in an axial direction in said channel (<NUM>), and further configured to consecutively;
- insert said connector (<NUM>) into said channel (<NUM>) from a first side,
- move said connector (<NUM>) in the axial direction in said channel (<NUM>) to the end position, and
- actuate the connector (<NUM>) from the same first side to expand the connector (<NUM>) radially relative to said channel (<NUM>) and thereby connect the first member (<NUM>) and the second member (<NUM>) relative to each other; and
- wherein the connector (<NUM>), in an expanded state thereof, pushes the first member (<NUM>) in a radial direction relative to said channel (<NUM>) against a face (<NUM>) of the main body (<NUM>) of the second member (<NUM>) to define a clamping contact and thereby a pre-tensioned connection in said radial direction relative to said channel (<NUM>) between a face (<NUM>) of the first member (<NUM>) and the face (<NUM>) of the main body (<NUM>) of the second member (<NUM>).