STRUCTURAL ASSEMBLY AND A METHOD FOR ITS MANUFACTURE

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims priority on United States provisional patent application No. 60/738,572, filed on November 22, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to structural assemblies and method for manufacturing structural assemblies and, more specifically, to the manufacture of structural assemblies made of composite material. These structural assemblies are suited for assembling strong lightweight towers for the tower industry.

2. Background Art Towers serve many purposes for different industries. Amongst other things, towers serve to support broadcasting and telecommunication antennas, cables such as power transmission lines, as well as anemometers and windmills. Towers come in various shapes and sizes, and can be classified in groups that include guyed towers, self-supporting towers, or monopoles .

Locations and types of towers are chosen strategically to optimize multiple objectives that often include minimizing cost. Other objectives include: optimal radio coverage, optimal transmission corridor, or optimal strength of wind. Towers are erected in urban, rural and remote areas, on top of buildings and directly on the ground. Each tower site has its own constraints, such as climate (temperature range, wind, ice formation, salt) , soil or building structure, impact on humans and the environment .

Depending on its use and its environment, a tower is designed to resist a specific loading (wind, ice, dead load) . For example, a telecommunication tower of 200 feet (approx. 65 meters) may be designed to hold sets of cellular antennas, microwave dishes at different heights, withstand ice on the structure, all the while moving minimally while being subjected to strong winds of 150 km/h.

The required rigidity and strength is typically achieved with steel structures. Steel structures, however, are heavy and are susceptible to corrosion. Because of weight issues, such towers require costly foundation work or building reinforcement. The weight factor also affects transportation costs including the need to build access roads in remote areas. Furthermore, maintenance and protection from corrosion is an issue in certain environments, such as a maritime environment.

U.S. Patent 6,264,781, issued to Bott on July 24, 2001, teaches an apparatus and a process for the continuous production of structural beams. The process includes: forming a tubular element from fibers of composite material; followed by a separation of the tubular elements into longitudinally extensive circumferentially separated corner caps, then securing sandwich panels between the adjacent corner caps to form a tubular beam. Subsequently, the tubular beam is shaped and cured to produce the structural beam. The apparatus disclosed is such to achieve the process steps previously mentioned. Thus, the apparatus: winds fibers to form them into a tubular member; cuts the member; spreads the member into various sections; adds an inner skin; applies a core material and an outer skin followed by a consolidation of the various layers, and ends with curing of the beam formed.

SUMMARY OF INVENTION

It is therefore an aim of the present invention to provide a structural assembly that addresses issues associated with the prior art. It is a further aim of the present invention to provide a novel method of manufacturing a structural assembly.

Therefore, in accordance with the present invention, there is provided a structural assembly comprising at least two profile members imparting axial strength to the assembly, each of the profile members extending along a length, and at least one ribbon, the at least one ribbon holding the at least two profile members together along their length, the at least one ribbon imparting lateral strength to the assembly by being braced to the at least two profile members.

Further in accordance with the present invention, there is provided a method of manufacturing a structural assembly comprising providing at least two profile members and at least one ribbon, winding the at least one ribbon about a support structure to form a bracing lattice, positioning the at least two profile members in a predetermined position on the support structure, and bonding the profile members to the bracing lattice to form a structural assembly.

Still further in accordance with the present invention, there is provided a mandrel for producing a structural assembly, the mandrel comprising at least one faceplate having a face oriented outwardly; corner members positioned at opposite ends of the at least one faceplate, the corner members each being adapted to support a profile member; actuator members supporting the at least one faceplate and the corner members between an extended position in which a ribbon is wound about the mandrel so as to form a bracing lattice interrelating the profile members, and a collapsed

position in which the mandrel is separated from the structural assembly resulting from a bonding of the bracing lattice and the profile members; and channels defined in the face of the at least one faceplate to accommodate the ribbon wound on the mandrel .

BRIEF DESCRIPTION OF DRAWINGS

Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which:

Fig. 1 shows a perspective view of a guyed tower using structural assemblies constructed in accordance with an embodiment of the present invention;

Fig. 2 shows a cross-section of a structural assembly according to one embodiment of the present invention;

Fig. 3 shows an enlarged cross-section of a profile member of the structural assembly illustrated in Fig. 2 in association with ribbons bracing the assembly; Fig. 4 shows a perspective view of a mandrel used in manufacturing the structural assembly of Fig. 2;

Fig. 5 shows a perspective view of a tower segment constructed with the structural assembly of Fig. 2; Fig. 6 shows an elevation view of ribbon- bracing lattice used in the structural assembly of Fig. 2;

Fig. 7 shows an enlarged perspective view of a ribbon-bracing lattice illustrated in Fig. 6; Fig. 8a shows a perspective view of a joint element of the tower segment of Fig. 5 in accordance with one embodiment, including a full flange plate;

Fig. 8b shows a perspective view of joint element of the tower segment of Fig. 5 according to

another embodiment, including a flange plate defining a central hole;

Fig. 8c shows a perspective view of joint element of the tower segment of Fig. 5 according to yet another embodiment, defining a completely opened central hole and exterior flange plate;

Fig. 9 shows a perspective view of a portion of a mandrel according to another embodiment of the present invention; Fig. 10 shows a cross-sectional view of the mandrel according to Fig. 9; and

Fig. 11 shows a side view of the mandrel according to Figs. 9 and 10.

DESCRIPTION OF PREFERRED EMBODIMENTS Composite materials have been used for many applications where weight and specific properties related to weight are issues. The process consists of pulling a fiber reinforcing material though a resin- impregnation bath and into a shaping die where the resin is subsequently cured to form a composite profile. Pultrusion is a known technology with a continuous process that has been used to make composite profiles of constant cross-section. These profiles can be assembled just like steel profiles would be, to form a tower structure.

Ribbon winding is another known technology that has been used to make support structures such as poles. It is a fabrication process that consists of winding a continuous reinforcing fiber impregnated with resin around a rotating and removable form, the mandrel.

Both pultrusion and ribbon winding allow the skilled practitioner to build structural assemblies with different strengths.

Fig. 1 illustrates a guyed tower 100 having a tower structure 150 which may include one or more tower

segments 250. These segments 250 include structural assemblies made of composite material according to the present invention.

The guyed tower 100 includes a central base 106 supporting the tower 150 centrally. Fig. 1 illustrates three peripheral anchoring bases 104a, b, c used to connect guyed wires 102 to the tower 150.

The tower 150 is built by assembling or connecting various lengths of tower segments 250. The lengths (i.e., height when the tower segments 250 are installed) of the tower segments 250 are in an embodiment 40 feet long (approx. 13 meters) , due primarily to transportation constraints. Forty-foot lengths are preferred because they tend to be the maximum length that can be easily loaded onto a truck. The length of a tower segment 250 may be adjusted as needed upon manufacturing the structural assemblies that will determine the length of a tower segment 250. The length of the structural assembly may be limited by the size of machinery used to produce same and by the nature and location of the site where the tower will be mounted.

A cross-section of an embodiment of the structural assembly 200 is illustrated in Fig. 2. The assembly 200 includes a bracing lattice defining a triangular cross-sectional shape. The structural assembly 200 is generally hollow and is designed, for instance, to meet telecommunication requirements of towers. The assembly 200 in Fig. 2 includes a profile member 202 in each of the corners of the assembly 200. The profile members 202 serve to impart axial strength to the structural assembly 200, and thus to the tower structure 150 of the guyed tower 100.

The structural assembly 200 of Fig. 2 includes two ribbons 220, 240 attached to and holding the profile members 202 together. Ribbon 220 is found in the inside

of the assembly 200, while ribbon 240 is found on the outside of the assembly 200 in this particular embodiment. The ribbons 220 and 240 act as a bracing for the structural assembly 200, thereby interconnecting the profile members 202.

The structural assembly 200 in this embodiment has three profile members 202 that are pultruded profiles. These pultruded profile members are typically made of a composite material composed of fiberglass and a vinyl-ester resin. Composite materials are generally strong and lightweight and give the structural assemblies in tower segments 250 a substantially lower weight when compared to comparable towers produced in steel. This reduction in weight in turn gives the structural assembly 200 a particular advantage during construction of the tower 100 in isolated areas where access is difficult.

The vinyl -ester resin of the pultruded profile members are in an embodiment formulated with anti-UV additives and additives to facilitate the pultrusion process. Surface treatment may also be performed on the pultruded profiles to allow a better co-curing with the ribbons 220 and 240 that are wound bondingly around the profile members 202, as will be described hereinafter. The skilled practitioner would understand that a composite material is one that includes one or more types of fiber bonded together chemically.

Fig. 3 shows an enlarged cross-section of one of the profile members 202 in association with the ribbons 220 and 240 to form a corner or concavity 210 of the structural assembly 200. The profile member 202 is found in the corner 210 of the assembly 200 and has an interior surface 204 and an exterior surface 206. Although the profile member 202 is illustrated as cooperating with both the inner ribbon 220 and the outer ribbon 240, it is contemplated to provide a single

ribbon 220 or 240 placed on only one side of the protrusion profile member 202. One ribbon 220 may be placed on the interior surface 204 of the profile member 202, or a single ribbon 240 may be placed on the exterior surface 206. Equally multiple ribbons may also be used on the interior or exterior surface of the profile member 202.

It is pointed out that the profile member 202 has edges on both its interior surface 204 and its exterior surface 206, respectively due to a concavity and a convexity. Once the ribbons 220 and/or 240 are bonded to the profile member 202, this configuration will strengthen the structural assembly 200 by forming a nested engagement . Fig. 4 illustrates a mandrel that may be used to produce the structural assembly 200 of the present invention.

The mandrel 300 may be one of many possible types, such as a collapsible mandrel of constant cross- section which facilitates the extraction of the structural assembly 200 after it is hardened. A non- collapsible mandrel can also be used, requiring the use of an extractor to remove the structural assembly 200 therefrom. Alternatively, a set of conical mandrels may be used to minimize the extraction effort.

The mandrel 300 may also have a cross-section that varies, thus producing, for example, a structural assembly 200 that has a cross-section gradually decreasing in size toward one end. The mandrel 300 illustrated in Fig. 4 includes an outer shell, with three faces 302 having a length 304. The triangular cross-section shape is visible on a front face 305 of the mandrel. This cross-sectional shape produces the cross-sectional shape of the structural assembly 200 as illustrated in Fig. 2. The corner 306 at the intersection of the faces 302 are

shaped so as to receive in coplanar relation the profile members 202.

For instance, the mandrel 300 may also have in an embodiment rounded corners 306 at the three angles 307 indicated on the front face 305 of the mandrel 300, as a function of the cross-section of the profile member 202. Each of the corners 306 may be produced by chamfering and polishing the shell to the appropriate smoothness along the meeting line of the three faces 302. The faces 302 or sides of the outer shell may be outwardly rounded along the entire length 304 of the mandrel 300.

A ribbon-winding process is used to wrap the ribbons 220 and 240 around the mandrel 300. This wrapping is achieved by a relative motion of the mandrel 300 with regard to the ribbon applicator (not shown) . In a preferred embodiment the mandrel 300 rotates about the longitudinal axis 310 while the ribbon 220/240 is applied from a spool moving back and forth along the length 304 of the mandrel 300, or set at predetermined locations along the length 304 of the mandrel 300.

Fig. 6 illustrates a bracing lattice having a first pattern 220a obtained by the first wrapping of the ribbon 220 along the mandrel 300 (the mandrel is not illustrated) in a first direction, as well as similar patterns 220b and 220c axially offset from the first patterns 220a. Fig. 6 illustrates that at a regular interval 222, the ribbon 220 wraps around the mandrel

(not shown) at a first axial position (i.e, along the Y axis) . Between these intervals 222, the ribbon 220 is wrapped at a substantially 45 degrees diagonal angle 228 on all three faces 302 of the mandrel 300 by way of the patterns 220a, 220b and 220c. Similarly, Fig. 7 illustrates an enlarged perspective view of ribbon 220 produced where the interval 222 and the angle 228 are shown in greater detail .

Referring back to Figs. 3 and 4, the profile members 202 are positioned on all three of the rounded corners 306 of the mandrel 300 upon which the ribbon 220 has been applied previously. In an embodiment, the profile members 202 and the mandrel 300 are designed such that the profile members 202 have a stable position in contact with the ribbon 220 or 240 upon the mandrel 300. Alternatively, the profile members 202 may be positioned directly on the rounded corners 306 of the mandrel 300 without any ribbon 220 preapplied to the mandrel 300 as a function of the desired configuration of the bracing lattice.

With the profile members 202 now in place (either directly on the mandrel or on the ribbon 220) and fixed, the second ribbon 240 is wound upon the mandrel 300 supporting the profile members 202 using the ribbon-winding process. In an embodiment, the wrapping sequence of the ribbons 220 and 240 is such that the ribbons 220 and 240 overlap each other along the entire length 304 of the structural assembly 200. In such a case, the respective shapes of the mandrel 300 and the profile members 202 are such that the second layer of ribbon 240 is in full contact with the first layer of ribbon 220. However, the ribbons 220 and 240 need not overlap, and may be wound so that the they no longer a substantially co-linear bracing lattice, but make a continuous bracing wall between the profile members 202. Alternatively, the ribbon 240 may not be necessary according to the contemplated use of the structural assembly 200.

The ribbon-wrapping sequence described previously may be a complete wrapping of the mandrel with ribbon-winding orientation varying from close to perpendicular to diagonal . This variant of the wrapping process produces a reinforced monopole tower. Once the profile members 202 and the ribbons 220 and/or 240 are

layered into one another, the assembly is heated or cured (e.g., with UV light) to chemically bond the profile members 202 to the bracing lattice of ribbons 220 and/or 240. The mandrel of Fig. 4 is only illustrative and may take up many rodlike structures having any of a wide variety of cross-sectional shapes. The alternative mandrels whose cross-sections include edges would in these cases also have in an embodiment rounded edges for nesting engagement with the profiles members 202; thus, any profile member produced preferably has a concavity for greater rigidity.

The method may make use of a mandrel of an outside shape with the following characteristics: a convex cross-section which helps to maintain a tension within the interval 222, required by the wrapping technology used; a curvature that matches, after considering the thickness of the inside ribbon if required, the inside curvature of the profile member 202.

The present method may advantageously use the wrapping sequence to minimize residual stress and/or stress resulting from large variation of temperature by ensuring that at the contact between the pultrusion profile member 202 and the ribbon 220, 240 bracing the fibers are preferably in diagonal rather than perpendicular relative to one another. Moreover, the ribbons may be selected so as to be thinner and wider at a point of contact with the profile members 202 or other layers of ribbon.

In an alternative embodiment of the process of the present invention, the mandrel 300 may be replaced with a skeletal structure having the appropriate length and cross-sectional shape, adapted to support the profile members 202 so as to be rotated about an axis, thus also allowing the application of a ribbon winding.

In an embodiment, the ribbons 220 and 240 are made of a composite material composed of fiberglass roving and a vinyl -ester resin. Like for the pultruded profile members 202, the vinyl-ester resin is formulated with additives for UV protection and for facilitating the ribbon-winding process. Other additive can be added to the formulation depending on the needs, e.g., exposure to fire.

Fig. 5 illustrates a perspective view of an embodiment of the tower segment 250 which includes the structural assembly 200 illustrated in Fig. 2 and joint element 400b of Fig. 8b, attached at opposing ends of the assembly 200. The structural assembly 200 has three profile members 202 and ribbons 220 and 240 bracing the profile members 202 together.

The method of assembling the structural assemblies 200 to build a tower structure 150 comprises the step of rigidly attaching one type of the joint elements 400a, 400b or 400c, respectively illustrated in Figs. 8a, 8b and 8c, at the extremities of the structural assemblies 200. The tower segments 250 are then assembled by coupling the opposed joint elements at the end of two structural assemblies.

The rigid assembly of the joint elements with the structural assemblies 200 preferably involves the bonding of the assembly 200 to the outer surface 402a, 402b or 402c of the joint elements. The joint elements 400a, 400b or 400c include the similarly numbered features as the mandrel 300, and a cross-sectional shape chosen to match that of the structural assembly 200. The joint elements 400a, 400b or 400c include: inner faces 409a, 409b or 409c; rounded edges 406a, 406b or 406c; and the rounded edges and the faces defining substantially same angle 407a, 407b or 407c. The joint elements 400a, 400b or 400c are designed to fit with the structural assembly 200 framework.

The rigid assemblies of the joint elements pair wise are advantageously bolted assemblies which allow replacement of a structure assembly 200 when needed. The joint elements 400a, 400b and 400c respectively have flange plates 405a, 405b or 405c, which may define a plurality of bolt holes 412a, 412b or 412c, respectively. Two complementary joint elements 400a, 400b or 400c of two rigid assemblies to be attached can be connected with bolts which in an embodiment are made of stainless steel or of other suitable strong and corrosion-resistant material .

The joint elements 400a, 400b or 400c are preferably made of composite materials in a sandwich configuration using reinforcing fibers such as fiberglass and a resin such as vinyl -ester for the skins, and a core element that can provide structural stiffness for the part.

The manufacturing process for the joint elements 400a, 400b or 400c may be an infusion process or a composite closed molding process such as resin transfer molding, light resin transfer molding, compression molding, and autoclave molding.

The shape of the joint element 400a, 400b or 400c is designed to match that of the structural assembly, whereby its cross-section is "L" -shaped. Depending on the application, the "L" -shape of the cross-section may be oriented towards the inside (400a and 400b) or the outside (400c) of the structural assembly. If the "L" -shape is oriented towards the inside, the joint element 400a, 400b or 400c may define a center hole 414b (in the case of the joint element 400b) . For the joint element 400c with an exterior bolting flange 405c, the central hole 414c is not obstructed, which is particularly advantageous for telecommunications towers where wiring is often run within the structural assemblies of a tower 100.

The structural assembly 200, now including the joint elements at one extremity, may be cured by heat in a oven, by light such as ultraviolet light or by other means known to the skilled practitioner. The mandrel 300 is then collapsed and removed, or extracted. Curing with UV light provides the advantage of curing as the ribbon winding progresses.

The thickness and width of the ribbon bracing may be adjusted to minimize the gaps where the ribbon bracing 220 and 240 overlap. These overlaps occur opposite the profile members 202, and thus the widening contributes to a better contact between the pultrusion profile members and the ribbon bracing.

The structural assemblies 200 described and produced by the above-described method may be used for telecommunication towers 100. The said method can also be used to produce structural assemblies 200 for other purposes such as broadcasting antennas, power transmission towers, windmills, anemometric towers, building or stage structures.

The number of profiles allows different configurations that can serve a variety of purposes. For example, a structural assembly with two profiles could serve as a support column; a structural assembly with four profiles could serve as a power-transmission pylon.

According to another aspect, there is provided a structural assembly made of composite material to build towers. This structural assembly 200 has structural properties that are not found in the components (profile members 202 and ribbons 220 and 240) when considered alone. For example, a pole made by ribbon winding is weaker in flexion than in torsion.

The structural assembly resulting from the previously described method can be designed to withstand different loading conditions by adjusting, globally or

locally, the thickness and properties of the different components .

For certain loading conditions, a ribbon 220 bracing on the inside or the outside may be sufficient. However, the structural assembly 200 is advantageously resistant when the ribbon 220 and 240 bracing constrain the displacements of the V-shaped profile members 202 by being physically in contact on both the inside and the outside of the profiles. The shear stress on the contact between profile members and ribbons 220, 240 is thus reduced as the strains are distributed through physical contact.

Depending on structural requirements, other kinds of matrices can be used for the composite material. Polymeric resins are the preferred choice: thermosets such as unsaturated polyester, epoxy, urethane and polyurethane and thermoplastic such as polyether-ether-ketone (PEEK) , polyethylene and polypropylene . Depending on structural requirements, other kinds of fibers can be used for the composite such as carbon, aramid and basalt.

Fig. 9 illustrates another embodiment of the mandrel 500. The mandrel 500 includes an outer shell 501 formed by three faces 502 of faceplates, each extending along length 504. The generally triangular cross-sectional shape 505 of the mandrel 500 is visible at one end.

The mandrel 500 presented in Fig. 9 also includes retractable corners 506, as will be described in greater detail hereinafter, at the edge of each of the faces 502. The corners 506 each support one of the profile members 202 (Fig. 2) when the assembly 200 is produced on the mandrel 500. The faces 502 each have two opposite longitudinal edges that each meet at an opposite one of the corners 506 The faces 502 include

at least one channel 512 defined therein which produces a pattern with respect to the length 504 of the mandrel 500. The channel 512 is sized to accommodate ribbon 220 therein (Fig. 7), so as to allow for the secure and precise placement of the ribbon 220 along the length 504 of the mandrel 500.

The channels 512 are positioned on the mandrel 500 as a function of the desired cured configuration of the tower segment 250 (Fig. 1) or like structure produced with the mandrel 500. In an embodiment, one of the channels 512 runs in a spiral along the length 504 of the mandrel 500 so as to produce the patterns 220a/220b/220c of the ribbon-bracing lattice as illustrated in Fig. 7. Other ones of the channel 512 are optionally provided at a fixed position along the length 504 of the mandrel 500, so as to receive the ribbon that will define the axial bracing at the intervals 222 (i.e., annular members), as visible in Figs . 6 and 7. As the ribbon is wound about the rotating mandrel 500, the channels 512 ensure that the ribbon is positioned on the mandrel 500 in the desired patterns, by accommodating the ribbon. In one embodiment, the rotational speed of the mandrel 500 is synchronized with the velocity of displacement of the ribbon spool .

Because of various factors associated with the production of the ribbon bracing (e.g., non-circular cross-section of the mandrel, thickness of the ribbon- bracing lattice, coordination of speed between spool and mandrel) , without the channels 512 axially restraining the ribbon-bracing, small slippage could be experienced with the ribbon-bracing, producing not completely uniform shape which is preferable to ensure a standardization of mechanical properties for the structural assembly 200 (Fig. 2) formed with the ribbon- bracing lattice.

The channels 512 defined axially in the faces 502 afford the mandrel 500 the advantage of allowing the ribbon to be maintained under greater tension during the winding process, which grater tension would otherwise result in slippage of the ribbon axially along the faces 502 of the mandrel 500.

A close-up of one end of the mandrel 500 is presented in Fig. 10. The mandrel 500 rotates about an axis illustrated as direction 510. The faces 502 are part of faceplates supported by a plurality of actuators 550 placed at intervals along the length of the mandrel 500. Accordingly, the faces 502 are collapsible. Similarly, the corners 506 are supported by actuators 552, and are thus retractable themselves. The actuators 550 are typically cylinders, such as pneumatic, hydraulic or electrical ones, and project radially from a shaft 514.

In Fig. 10, the mandrel 500 is illustrated in a configuration suited to receive the profile members 202 (Fig. 2) as well as the ribbon 220 (Fig. 6) . After the various layers of ribbon 220 have been wound about the mandrel 200 with profile members 202 to form the structural assembly, the curing process takes place, after which the actuators 550 and 552 are actuated to cause a collapse of the mandrel 500.

After the structural assembly has cured to sufficient hardness on the mandrel 500, the actuators 550 and 552 are actuated to retract, and thus release the produced structural assembly. Fig. 10 further indicates that the faces 502 in an embodiment may have an outwardly rounded surface, as opposed to being flat. The retractable corners 506 have a cross sectional shape of a "v" .

Fig. 11 represents a side view along the length of the mandrel 500, where the channels 512 and one retractable corner 506 are visible along the length

of the mandrel 500. The channels 512 are both for the spiral pattern and axially fixed patterns at intervals along the length 504.

In a simplistic configuration of the mandrel 500, only one faceplate is provided between a pair of the retractable corners 506. In such a case, the channel 512 in the face 502 is sufficient to ensure the desired positioning of the ribbon with respect to the profile members. Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified without departing from the spirit and nature of the subject invention, as defined in the appended claims.