WO2004014648A2

WO2004014648A2 - Composite structural member

Info

Publication number: WO2004014648A2
Application number: PCT/CA2003/001205
Authority: WO
Inventors: Donald J. Salzsauler; Roy Salzsauler
Original assignee: Saltech Inc
Current assignee: Saltech Inc
Priority date: 2002-08-12
Filing date: 2003-08-12
Publication date: 2004-02-19
Anticipated expiration: 2005-02-12
Also published as: CA2476763A1; EP1532317A2; MXPA05001732A; AU2003257312A1; CA2476763C; US20040103613A1; AU2003257312A8; WO2004014648A3

Abstract

A composite structural panel is provided. The panel comprises a frame having a longitudinal frame axis; a plurality of beam elements (105) mounted in the frame, each of the beam elements (105) has a respective longitudinal beam axis generally parallel to the frame axis; a reinforcing fibre wrapping that extends around each of the beam elements, the wrapping has a fibre direction running generally obliquely to the beam axis; a plurality of wire strands (111) that extend about the wrapping, the wire strands (111) run generally parallel to the beam axis and the frame axis; an outer layer of reinforcing fibre mat (113) that surround the frame, the wrapped beams (105) and the wire strands (111), the mat has a majority of its fibres running generally parallel to the frame axis; and, a solidified epoxy resin (117) that extends throughout and encasing the beam elements (105), beam wrapping, wire strands (111), outer layer and frame.

Description

COMPOSITE STRUCTURAL MEMBER

FIELD OF THE INVENTION:

The invention relates to a structural member, generally. In

particular, the invention relates to a structural member constructed

of composite materials.

BACKGROUND OF THE INVENTION:

Structural members (e.g., columns or beams) may be constructed of

a variety of building materials, such as concrete, wood or steel,

each of which has particularly advantageous or disadvantageous

structural and load bearing properties. For example, concrete alone

has fairly good compressive strength however its tensile and

bending strength can be improved greatly with the use of

reinforcing materials such as hoop steel. Without any

reinforcement, however, transverse and axial loads may cause a

concrete support structure to spall and ultimately fail.

Wood is often used in structural applications because it too has

good load bearing properties. Wood may be described as an

orthotropic material. It .has unique and independent mechanical properties in the directions of three mutually perpendicular axes

(longitudinal, radial and tangential).

When a wooden beam is subjected to a load^' that is perpendicular to

the longitudinal direction of the wood body, the wood fibers

opposite the load are subjected to tension forces and wood fibers

adjacent the load are subjected to compression forces. Under a

heavy load, a wood beam may fail in. either the compressive or

tensile half of the wood beam.

There are drawbacks to using non-reinforced wood as a building

material. For example, wood deteriorates under certain conditions,

such as a high moisture or wet environment. Wood is primarily

composed of cellulose, lignin, hemicelluloses and minor amounts of ■

extraneous materials. Cellulose is a high-molecular-weight linear

polymer consisting of chains of glucose monomers. The cellulose

molecules are arranged in ordered strands, which in turn are

organized into the larger structural elements that make up the cell

wall of wood fibers. Lignin is concentrated toward the outside and

between the cells. It is the cementing agent that binds individual

cells. It is a three-dimensional phenyl-propanol polymer. The

hemicelluloses are associated with cellulose and are branched, low molecular weight polymers composed of several different kinds of

pentose and hexose sugar monomers. As the cellulose, lignan,

hemicelluloses structure deteriorates, the wood fiber strength is

compromised and as a result, so are its load bearing capabilities.

Under this weakened condition, the wood is more prone to failure

under load. Also, despite any environmental deterioration, wood,

under a high load may still experience compression or tension

failure if it is not reinforced.

Previous attempts to reinforce concrete, wood or steel support

structures (e.g., Michalcewiz US5,505,030) involve using pre-made

reinforcing layers which are attached or fitted to the element being

reinforced, thereby increasing the reinforced element's

compressive, shear or load bearing capacity. Solutions of this type,

however, are merely prophylactic because they do not address the

underlying problem of using a building material that is susceptible to

load failure. The effective use of casing reinforcing materials, such

as described by Michalcewiz, is further limited by the fact that they

are merely surface treatments. It may not be possible to apply

reinforcing materials to parts of a structure that are not readily

accessible. There remains a need for a composite structural member with

increased resistance to failure under load.

SUMMARY OF THE INVENTION:

The present invention provides a structural panel comprising a

frame having a longitudinal frame axis; a plurality of beam elements

mounted in the frame, each of the beam elements has a respective

longitudinal beam axis generally parallel to the frame axis; a

reinforcing fibre wrapping that extends around each of the beam

elements, the wrapping has a fibre direction running generally

obliquely to the beam axis; a plurality of wire strands that extend

about the wrapping, the wire strands run generally parallel to the

beam axis and the frame axis; an outer layer of reinforcing fibre

mat that surround the frame, the wrapped beams and the wire

strands, the mat has a majority of its fibres running generally

parallel to the frame axis; and, a solidified epoxy resin that extends

throughout and encasing the beam elements, beam wrapping, wire

strands, outer layer and frame. The reinforcing fibre mat of the beam wrapping may be a woven

mat having about the same quantity of fibres extending in each of

two generally orthogonal directions.

The beams may be made up of a plurality of panels having adjacent

faces laminated together and having a grain running along the beam

axis.

The structural panel may be a bridge deck having an upper face

coated with a road surfacing material.

The upper face may be canted with a longitudinally extending

centre section higher than and sloping toward opposite side edges

of the structural panel to promote drainage.

BRIEF DESCRIPTION OF THE DRAWINGS:

Preferred embodiments of the present invention are described

below with reference to the accompanying drawings in which:

Figure 1 is a schematic view illustrating a composite structural

member according to the present invention; Figure 2 is a schematic view illustrating a beam according to the

present invention and the beam's grain orientation relative to its

longitudinal axis;

Figures 3a - b are schematic views illustrating alternate orientations

of a fibrous material in sheet form and its orientation as it extends

about and between a plurality of beams according to the present

invention;

Figures 4a - b are schematic views illustrating the use of a fibrous

material in cord form and its orientation as it extends about and

between a plurality of beams according to the present invention;

Figures 5a - b are schematic views illustrating the use of a fibrous

material in both sheet and cord form in a structure according to the

present invention.

Figures 6 is a perspective cross-sectional view of a composite

structural member according to an embodiment of the present

invention;

Figure 7 is a cross-sectional view of a bridge and its associated

components assembled using a composite structural member

according to an embodiment of the present invention; Figure 8 (a) is a schematic plan view of a structural panel according

to an alternate embodiment of the present invention;

Figure 8 (b) is a schematic cross-sectional view of the structural

panel of Figure 8 (a);

Figure 9 is a plan view of a frame element of the structural panel of

Figure 8 (a) according to the present invention;

Figure 10 (a) is a longitudinal cross-sectional view of the frame of

Figure 9 according to an embodiment of the present invention;

Figure 10(b) is a longitudinal cross-sectional view of the frame of

Figure 9 according to an alternate embodiment of the present

invention;

Figure 10 (c) is a cross-sectional view of the frame of Figure 9

according to an embodiment of the present invention;

Figure 11 is a. partial plan view of an end portion of a beam element

of the structural panel of Figure 8 according to an embodiment of

the present invention; Figure 12 is a perspective view of an end portion of a beam element

of the structural panel of Figure 8 according to an embodiment of

the present invention;

Figure 13 is a perspective cross-sectional view of a bridge deck

according to an embodiment of the present invention;

Figure 14 is a perspective view- of a beam element of the structural

panel of Figure 8 according to an embodiment of the present

invention;

Figure 15 is an exploded view of the constituent components of the

structural panel of Figure 8 according to an embodiment of the

present invention; and,

Figure 16 is a perspective cross-sectional view of the structural

panel of Figure 8 according to an embodiment of the present

invention.

DETAILED DESCRIPTION:

Figure 1 illustrates a composite structural member (CSM) 10 made

in accordance with a preferred embodiment of the invention. Referring to Figures 1 - 2 and 6, the CSM 10 has a plurality of

beams 20, each beam having a longitudinal axis 22 and at least one

side 24 generally parallel to and facing at least part of a side 26 of

at least one adjacent beam 20. A fibrous material 30 extends about

and between the beams 20. A potting material 40 permeates the

fibrous material 30 and encases the beams 20. The fibrous material

30 and potting material 40 are selected to yield a resistance to

bending in the CSM 10 that is greater than the combined individual

resistance to bending of the beams 20.

Each beam 20 has a grain direction 28 that is generally aligned with

the longitudinal axis 22. and is preferably a member selected from

the group consisting of wood and wood composites. In an alternate

embodiment, the beams 20 may be constructed of concrete,

fiberglass, and possibly other materials with properties similar to a

wooden beam.

In a preferred embodiment, the surfaces of the wooden beams 20

and the fibrous material 30 should be treated to clean and prepare

the surfaces for bonding. To enhance the bonding between the

wooden beams 20 and the fibrous material 30, the wooden beams

should be dry with their surfaces relatively free from grease, excessive dust, etc. Preferably the surfaces should be rough to

enhance adhesion. A water proofing treatment might also be

considered, particularly where the CSM 10 is to be used in a

submersed or partially submersed environment and there is a risk of

the encapsulating material being damaged so as to expose the

wooden beams 20 to water.

Referring to Figures 3 - 5, the fibrous material 30 is constructed of

engineering materials having a high tensile .strength. In alternate

embodiments, a fibrous material 30 having higher or lower tensile

strength and modulus properties may be used depending on the

particular application of the invention.

Referring to Figure 5a, an embodiment of the fibrous material 30 is

in sheet form 32. In an alternate embodiment depicted in Figure 5b,

the fibrous material is in cord form 36. The fibrous material 30 in

the sheet form 32 may have variety of fiber architectures. In a

preferred embodiment, the fibers 34 are woven. Alternately, the

fibers 34 may be braided or knitted. The majority of the fibers 34

in the sheet form 32 are preferably unidirectional in the longitudinal

direction of the sheet form. Referring now to Figure 3a, the fibers 34 of the sheet form 32 are

preferably aligned generally transversely (i.e. non-parallel) relative

to the longitudinal axis 22 of the beams 20. Figure 3b illustrates an

alternate embodiment where the fibers 34 of the sheet form 32 are

aligned generally diagonally relative to the longitudinal axis 22 of

the beams 20,

Figure 4a illustrates a further embodiment. The fibers 34 of the

cord form 36 run generally transversely relative to the longitudinal

axis 22 of the beams 20. Figure 4b illustrates a still further

embodiment where the fibers 34 of the cord form 36 run generally

diagonally relative to the longitudinal axis 22 of the beams 20.

Figure 6 depicts a still further embodiment wherein the fibrous

material 30 extends around an individual beam 20, but does not

extend around any adjacent beams 20.

In a preferred embodiment of the invention, the fibrous material is a

member selected from the group consisting of glass, carbon,

Kevlar™, aramids, nylon, possibly natural fibers (e.g. hemp) and

combinations of the foregoing. Referring now to Figure 1, the potting material 40 is "a curable resin

such as vinyl esters, poly esters, urethanes, BMIs, phenolics,

acrylics, epoxies, cynate esters and thermoplastics. The potting

material is preferably an epoxy that has exceptional adherence to

steel, such as the Jeffco 4101-08 epoxy resin and Jeffco 4101-18

epoxy hardener as manufactured by Jeffco Ltd; of San Diego,

California.

The term "resin" refers to any substance, or combination of

substances, of a suitable viscosity, such that they can be used to

impregnate the fibrous materials and surround the plurality of

beams and ultimately undergo a physical state transformation from a

low viscosity fluid to a rigid solid state wherein said transformation

can occur via various means such as chemical reactions, a thermal

cycle, etc. and acts as a binding matrix of the fibrous material and

beams to create a final composite material.

A "Vacuum Assisted Resin Transfer Method" (VART) may be

utilized to encase the beam/fibrous material structure in resin. This

is a known method of impregnating fibers with resin.

SAMPLE APPLICATIONS: Bridge construction is a sample application of the CSM 10 of the

present invention that illustrates its unique and enhanced load

bearing properties over prior generation composite structural

materials.

Referring to Figure 7, a bridge 70 consisting of a substructure and a

superstructure is illustrated. Substructure elements include

abutments 72, piers or pilings. Superstructure elements, which sit

atop the substructure, include stringers and or a deck 74. These

structural elements experience compression and tension forces

from several potential sources. For example, an abutment 72, pier

or piling, would experience compression forces 76 from the weight

of the superstructure, the weight of any body positioned on the

superstructure and the weight of the abutment 72 pier or piling

itself. Superstructure elements, such as the decking 74, may

experience compression forces 77 and tension forces 78 from the

weight of the decking 74 itself as well as any body 79 sitting on the

decking. The combined, compression and tension forces may cause

the bridge structural elements to buckle (in the areas experiencing

compression forces) and or snap (in areas experiencing tension). A composite structural member of the type described in the present

invention dissipates the compression and tension forces over the

whole of the structural member, unlike individual structural

members, such as wooden beams or glue-laminated timber (glulam).

This load dissipating property of the CSM 10 permits the

construction of bridges of greater scale and enhanced load-bearing

properties. This is because the load-bearing versus weight ratio of

the composite structural member of the present invention is several

times that of concrete or steel.

Bridge construction using the CSM 10 creates an integrated

structure where the decking is self-supporting, rather than simply

used as cladding. The structural strength of the CSM 10 stems from

the fact that the combined strength of the CSM 10 components

exceeds that of the beams and the potted encasement elements on

their own, in the configuration in which they are present.

ALTERNATE EMBODIMENT:

Referring to Figure 8 (a) - (b), 15 and 16, a composite structural

member according to a preferred embodiment of the present

invention is illustrated. The composite structural member or structural panel 100 ^' is comprised of a frame 101 having a

longitudinal frame axis 103. A plurality of beam elements 105 are

mounted in the frame 101, each of the beam elements 105 has a

respective longitudinal beam axis 107 that is generally parallel to

the frame axis 103. The beam elements 105 are wrapped in a beam

wrapping 109 of reinforcing fibre mat that extends around each of

the beam elements 105, the beam wrapping 109 has a fibre direction

running generally on a bias with (or obliquely to) the beam axis 107.

The structural panel 100 further includes a plurality of wire strands

111 that extend about the wrapping 109. The wire strands 111 run

generally parallel to the beam axis 107 and the frame axis 103.

There may also be transverse wire strands 151. The frame 101,

wrapping 109, beams 105 and wire strands 111 are further wrapped

and surrounded by an outer layer of reinforcing fibre mat 113 that

has a majority of its fibres 115 extending longitudinally generally

parallel to the frame axis 103. A solidified epoxy resin 117 extends

throughout and encases the beam elements 105, beam wrapping

109, wire strands 111, outer layer 113 and frame 101.

Referring to Figure 9, the frame 101 defines and determines the

approximate size and shape of the structural panel 100. In a preferred embodiment, the frame 101 is comprised of two side

members 119 positioned opposite each other and running generally

parallel to the longitudinal frame axis 103. The side members 119

are connected to each other via two end members 121, which are

positioned opposite each other and generally orthogonal to the side

members 119. In an alternate embodiment, the frame 101 is a

unitary structure. Any other frame configuration known to those

skilled in the art that defines and determines the approximate size

and shape of the structural panel 100 may be employed.

The frame 101 may be comprised of steel. In a preferred

embodiment, the frame 101 is comprised of a mild steel, such as a

44W High Strength Low Alloy steel, although any standard grade

steel that can be flame cut, formed, drilled, welded and/or machined

by any normal means may be employed.

Referring to Figure 10(a), cross-sectional view of the frame 101

along the frame axis 103 according to a preferred embodiment of

the present invention is illustrated. The frame 101 of structural

panel 100 is configured to receive at least opposite ends of the

beams 105. The end members 121 are recessed or cut out along

their respective lengths in order to provide a beam receiving surface 123 for receiving opposite ends of the beam 105. The

recess 125 may be of any shape known to those skilled in the art

(e.g. flat, bevelled or curved) that defines a beam receiving surface

123. An alternate embodiment of the end members 121 is

illustrated in Figure 10(b). In this embodiment, the end members

121 are not cut out, but rather, the end members 121 have at least

one hole or passage 127 passing through the end members 121. A

fastener 129 passes through the respective end members and

secures the beams 105 to the frame 101.

In a preferred embodiment, the frame 101 has longitudinally

extending edge flanges 131 that are generally parallel to the frame

axis 103.

Referring to Figure 16, a perspective cross-sectional view of the

structural panel 100. is illustrated. The frame 101 preferably has a

plurality of spars 133 extending across the frame between the edge

flanges 131 and the spars 133 have sockets 135 formed therein for

receiving the opposite ends of the beam elements 105.

Referring to Figure 11, an end section 137 of the beam 105

according to a preferred embodiment of the present invention is illustrated. The beam 105 is wrapped in a beam wrapping 109

comprised of reinforcing glassy fibres 139. In a preferred

embodiment the glassy fibre is standard fibreglass as sold by Dow

Corning of Corning, New York. In an alternate embodiment, the

glassy fibre is basalt based.

In a preferred embodiment, the beam wrapping 109 is a woven mat

having about the same quantity of fibres 139 extending in each of

two generally orthogonal directions (i.e., approximately 50% of the

fibres 139 running in each direction). This is achieved by wrapping

the beam wrapping 109 on a bias relative to the beam axis 107.

The beam 105 is further wrapped with wire strands 111. In a

preferred embodiment, the wire strands 111 are incorporated in the

beam wrapping 109. Alternately, the wire strands 111 may be an

element of an additional wire strand wrap 141, which is applied over

top the beam wrapping 109. In either case, the wire strands 111

run generally parallel to the beam axis 107 (Figure 14).

The wire strands 111 are comprised of steel. In a preferred

embodiment, the wires 111 are comprised of high tensile strength

steel. Referring to Figures 8(b) and 12, a beam end portion 137 is

illustrated according to a preferred embodiment of the present

invention. The beams 105 are comprised of wood, with each of the

beams being made up of a plurality of laminae 143 having adjacent

faces 145 laminated together and having a grain 147 running along

the beam axis 107. In a preferred embodiment, the laminae 143 are

aligned with the adjacent faces 145 generally parallel to the upper

face 149 of the panel 100.

In a preferred embodiment, the wood laminate beam 105 is

comprised of kiln dried spruce, which provides a high tensile

strength per unit weight. The wood laminae 143 are dried to

approximately 16% moisture or less and fixed to each other using

an adhesive. In a preferred embodiment, the adhesive is

manufactured by Borden Chemical Ltd. of Montreal, Canada,

although any adhesive known to those skilled in the art that is as

strong as or stronger than the wood may be employed.

In an alternate embodiment, the panel 100 may be used in low

stress or low load bearing applications, such as a wall panel. The

load bearing capabilities and weight of a panel 100 that incorporates

wood laminate beams may be neither required, nor desired. The beams 105 may be comprised of a low density material, such as a

foam material, which is both light weight and able to bear a load.

Any low density material that can bear a load, which is known to

those skilled in the art, may be employed.

Referring to Figures 8(a) and (b), the frame 101, beam wrapping

109, beams 105 and wire strands 111 are further wrapped and

surrounded by an outer layer of reinforcing fibres 113 comprised of

mat reinforcing fibres 115, thereby creating a wrapped structure. In

a preferred embodiment, the reinforcing fibre 115 is a glassy fibre,

such as a standard fibre glass as sold by Dow Corning of Corning,

New York. In an alternate embodiment, the glassy fibre is basalt

based.

In a preferred embodiment, the outer fibre wrap 113 has about 90%

of its fibres extending longitudinally and generally parallel to the

frame axis 103. The relative ratio of the fibres 115 as well as the

relative directions in which the fibres 115 extend may vary with the

particular use to which the structural member 100 is put and the

direction and magnitude of the resultant forces exerted on the

structural panel 100. For example, if the structural panel 100 is

used as a roof panel, the fibres 115 may extend equally in all directions. If the panel 100 is employed as a bridge deck, then

approximately 80% of the fibres 115 extend longitudinally

(generally parallel with the frame axis 103) and approximately 20%

of the fibres 115 run generally orthogonal to the longitudinally

extending fibres 115.

After the outer fibre mat 113 is applied, the wrapped structure is

permeated with and encased in an epoxy resin that extends

throughout the frame 101, beam wrapping 109, beams 105, wire

strands 111 and outer wrap 113. The epoxy resin impregnates the

fibrous material and surrounds the frame 101 and plurality of beams

105, ultimately undergoing a physical state transformation from a

low viscosity fluid to a rigid solid state and thereby acting as a

binding matrix of the fibrous .material (109, 113), frame 101 and

plurality of beams 105 to create a final composite material. In a

preferred embodiment, the epoxy has exceptional adherence

(without the use of special primers) to steel, such as the Jeffco

4101-08 epoxy resin and Jeffco 4101-18 epoxy hardener as

manufactured by Jeffco Ltd. of San Diego, California.

A vacuum assisted resin transfer method (V.A.R.T.) may be used to

encase the wrapped structure in epoxy resin, although any other method of impregnating and encasing a wrapped structure that is

known to those skilled in the art may be used.

The wire strands 111 act as a flow medium for the epoxy resin,

thereby ensuring that the resin sufficiently permeates and

surrounds the wrapped structure. The wire strands' 111 function as

a flow medium for the epoxy resin also obviates the need to cut

flow channels into the wrapped structure or any of its components.

The components of the panel 100 (i.e., the frame 101, beams .105,

wraps 109 and 113, and epoxy 117) are selected to have physical

properties that do not vary to such a degree that separation of the

components of the composite panel occurs when the panel 100 is in

use; i.e., tensile and compressive forces exerted on the panel 100.

are distributed over the whole of the panel and no one component of

the panel 100 bears a disproportionate degree of load bearing

stress, which would result in separation of the panel 100

components.

Sample Applications:

The structural panel 100 may be used in many different

applications, such as building panels, piles, floor panels, wall panels, roof panels, box culverts and retaining walls. Referring to Figure

13, a preferred application of the structural panel 100 as a bridge

deck 500 is illustrated.

The bridge deck 500 has an upper face 501 that is coated in a road

surfacing material 503. In a preferred embodiment, the coating 503

is a latex asphalt, such as manufactured by TJ Pounder Inc. of

Brampton, Ontario, Canada. Latex asphalt is preferred because it

can be applied cold, thereby obviating the need to apply a hot

asphalt mixture, which may potentially compromise the structural

integrity of the structural panel 100. A primer is applied first to the

upper surface and then an approximately one -half inch

(approximately 1.25 cm) layer of latex asphalt is applied. The

opposite face or underside 505 of the deck 500 is painted with UV

stabilised polyurethane.

The upper face 501 of the deck 500 is preferably canted with a

longitudinally extending centre section 507 higher than and sloping

toward opposite side edges 509 of the deck 500 to promote

drainage. In a preferred embodiment, the deck 500 is thicker at the opposite

side edges 509 than at the centre section 507 thereby providing a

curb 511 at the side edges 509. Having a deck 5O0 with curbs 511

at the opposite side edges 509 results in overall enhanced stiffness

of the deck 500, thereby allowing it to be thinner at the centre

section 507 than would be required of a panel having the same load

bearing capacity but of generally constant thickness.

The present invention is defined by the claims appended hereto,

with the foregoing description being illustrative of the preferred

embodiments of the invention. Those of ordinary skill may envisage

certain additions, deletions and/or modifications to the described

embodiments, which, although not explicitly suggested herein, do

not depart from the scope of the invention, as defined by the

appended claims. For example, the beams may be of non

rectangular cross-sectional configuration (such as circular,

elliptical, triangular etc.) and the beams need not have their

respective longitudinal axes coplanar. Furthermore in some

applications curved rather than straight beams may be desirable.

Claims

We claim:

1. A structural panel comprising:

a frame having a longitudinal frame axis;

a plurality of beam elements mounted in said frame, each of said

beam elements having a respective longitudinal beam axis

generally parallel to said frame axis;

a reinforcing fibre wrapping extending around each of said beam

elements, said wrapping having a fibre direction running

generally obliquely to said beam axis;

a plurality of wire strands extending about said wrapping, said

wire strands running generally parallel to said beam axis and

said frame axis;

an outer layer of reinforcing fibre mat surrounding said frame,

said wrapped beams and said wire strands, said mat having a

majority of its fibres running generally parallel to said frame

axis; and, a solidified epoxy resin extending throughout and encasing said

beam elements, beam wrapping, wire strands, outer layer and

frame.

2. The structural panel of claim 1 wherein:

said frame is configured to receive at least opposite ends of said

beams; and,

said reinforcing fibre mats of said beam wrapping and said outer

layer are of a glassy fibre.

3. The structural panel of claim 2 wherein:

said reinforcing fibre mat of said beam wrapping is a woven mat

having about the same quantity of fibres extending in each of two

generally orthogonal directions; and,

said reinforcing fibre mat of said outer layer has about 90% of its

fibres extending longitudinally generally parallel to said beam

axis.

4. The structural panel of claim 3 wherein:

said beams are of wood; and, said wire strands are of steel.

5. The structural panel of claim 4 wherein:

each of said beams is made up of a plurality of panels having

adjacent faces laminated together and having a grain running

along said beam axis; and,

said wires are of high tensile strength steel.

6. The structural panel of claim 5 wherein:

said structural panel is a bridge deck having an upper face

coated with a road surfacing material; and,

said planks are aligned with said adjacent faces generally parallel

to said upper face

7. The structural panel of claim 6 wherein:

said upper face is canted with a longitudinally extending centre

section higher than and sloping toward opposite side edges of

said structural panel to promote drainage.

8. The structural panel of claim 7 wherein:

said structural panel is thicker at said opposite side edges than

at said centre section thereby providing a curb at said outer

edges with enhanced stiffness to allow said structural panel to be

thinner at said centre section than would be required of a panel

having the same load bearing capacity but of generally constant

thickness.

9. The structural panel of claim 8 wherein:

said frame has longitudinally extending edge flanges generally

parallel to said frame axis;

said frame has a plurality of spars extending there across

between said edge flanges;

said spars have sockets formed therein toward said upper face

for receiving said opposite ends of said beam elements.