Patent Grant
10125493
This invention relates to a pre-stressed beam or panel and to a method of manufacturing a pre-stressed beam or panel.
Traditional pre-stressed concrete hollow-core planks are used in the construction of buildings and bridges. While concrete-based construction members are strong and low cost, they are also heavy, expensive to transport and have a high associated environmental cost.
Timber has many advantages over concrete; it has higher strength to weight, is a renewable resource, and wood-based members generally perform better during seismic events due to their reduced mass. Timber is often considered more aesthetically pleasing than concrete and therefore is less likely to necessitate painting or cladding. Despite these advantages, engineered timber structural members are used less often than concrete in large commercial building. This is due to the higher cost of timber and because the on-site construction process is often more complex than for concrete members.
Concrete construction members are available as pre-fabricated and pre-stressed lengths, whereas timber members normally require post-tensioning on site. That requires special skills and equipment and slows construction time.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.
It is an object of at least preferred embodiments of the present invention to provide a pre-stressed beam or panel, and a method for manufacturing a pre-stressed beam or panel that addresses the above mentioned problems and/or that at least provides the public with a useful alternative.
In a first aspect, the invention provides a method of manufacturing a pre-stressed beam or panel. The method comprises: providing a timber-based component; providing a pre-stressing member arranged along the timber-based component; applying a tensile force to the pre-stressing member; providing concrete anchors at locations that are spaced apart along the timber-based component; coupling the pre-stressing member to the concrete anchors; and releasing the tensile force on the pre-stressing member to transfer a compressive force to the timber-based component through the concrete anchors to form a pre-stressed beam or panel.
In a preferred embodiment, the concrete anchors are provided by pouring concrete at locations that are spaced apart along the timber-based component, embedding respective portions of the pre-stressing member. Coupling the pre-stressing member to the anchors comprises allowing the concrete to substantially cure, before the tensile force on the pre-stressing member is released.
Preferably, the concrete is poured at two spaced apart locations positioned at or adjacent the ends of the timber-based component to form end anchors.
In an alternative embodiment, the concrete anchors are pre-cast. The pre-stressing members may be coupled to the pre-cast anchors by grouting, concrete, or mechanical fasteners, for example.
In a preferred embodiment, the method comprises providing and tensioning a plurality of pre-stressing members.
In one embodiment the method comprises pouring concrete at one or more locations between the two end anchors to form one or more intermediate concrete anchors embedding a respective intermediate portion of the pre-stressing member;
allowing the or each intermediate concrete anchor to substantially cure; and
cutting the beam or panel through the or each intermediate anchor and through the respective anchored intermediate portion of the pre-stressing member to form two or more shorter pre-stressed beams or panels. Alternatively, the method may comprise placing at least three discrete pre-cast anchors at spaced apart locations and coupling the pre-stressing member to each of the at least three pre-cast anchors using concrete or grouting. Preferably these three anchors comprise two end anchors and an intermediate anchor positioned between the two end anchors. Once the concrete or grouting has substantially cured, the pre-stressed beam or panel may be cut through the intermediate anchor and through the respective anchored portion of the pre-stressing member, to form two shorter pre-stressed beams or panels.
Using this method, a plurality of shorter pre-fabricated pre-stressed beams or panels, suitable for transport to a construction site, may be pre-stressed at one time.
Some embodiments may comprise pouring or placing two or more intermediate anchors between the end anchors, and cutting the pre-stressed beam or panel through each intermediate anchor.
Preferred forms of the method may be carried out in existing yards currently used for producing precast concrete, with only minor modifications to the yards and equipment. Equipment such as pre-stressing jacks may be used to apply tensile force to the pre-stressing member(s). The tension may be maintained in the pre-stressing member(s) while the concrete cures using any known suitable method.
The pre-stressing member(s) may consist of one or more tendons, which may be rods, bars or cables, for example, or alternatively may consist of one or more plate or sheet members, and could for example be laminates. Preferably the pre-stressing member(s) comprise high tensile steel, but alternatively they may comprise an alloy, carbon composite, glass-aramid, or other composite material.
The timber-based component is preferably an elongate member with one or more elongate hollow portion(s) or channel(s) to receive at least a portion of the pre-stressing member(s). The pre-stressing member(s) may be inserted in a respective hollow portion(s) or channel(s) of the completed timber-based component, for example by being placed in channel(s) extending along an outer surface of the timber-based component. Alternatively the pre-stressing member(s) may be inserted in a respective hollow portion(s) or channel(s) during assembly of the timber-based component, for example by being placed in a channel that is subsequently covered by a timber member such that at least a part of the pre-stressing member(s) is enclosed by the timber-based component.
In one embodiment, the concrete for the anchors is poured into hollows or boxed regions defined by the timber-based component. In an embodiment having three or more anchors, in which the initial beam or panel is cut into a plurality of shorter beams or panels, the timber-based component is preferably sufficiently elongate that the plurality of shorter beams or panels are also elongate.
The timber-based component may be a single integrally formed member or may comprise a plurality of members or sub-components assembled or arranged together.
The timber sub-components may be arranged, for example, end-to-end, but not connected. Alternatively, the sub-components may be connected. In that embodiment, the pre-stressing member is arranged to extend along all of the individual sub-components, and the or each intermediate concrete anchor is poured between the ends of two adjacent individual sub-components to join the sub-components. The intermediate concrete anchor(s) may then be cut to separate the beam or panel into shorter beams or panels.
The timber-based component may further comprise a transverse channel or hollow portion for receiving a transverse pre-stressing member for pre-stressing the beam or panel in a second transverse direction. The transverse pre-stressing member may be one of the type described above, and may be the same or different from the longitudinal pre-stressing member(s).
In one such embodiment, the method further comprises inserting a transverse pre-stressing member into the transverse channel or hollow portion, applying a tensile force to the transverse pre-stressing member, pouring concrete at spaced apart locations along the transverse pre-stressing member, allowing the concrete to substantially cure to anchor respective portions of the transverse pre-stressing member, and releasing the tension from the transverse pre-stressing member to pre-stress the beam or panel in the transverse direction. These steps to pre-stress the beam or panel in the second direction may be carried out on the pre-fabricated beam or panel, after the beam or panel has been pre-stressed in the first direction, and optionally after the initial beam or panel is cut into shorter lengths. Alternatively, the beam or panel may be pre-stressed in the second direction at the same time it is pre-stressed in the first direction.
In an alternative embodiment pre-stressed in a transverse direction, the method may further comprise coupling pre-cast anchors at spaced apart locations along the transverse pre-stressing member, inserting transverse pre-stressing member into the transverse channel or hollow portion, applying a tensile force to the transverse pre-stressing member, coupling the tensioned pre-stressing members to the pre-cast anchors, and releasing the tension from the transverse pre-stressing member to pre-stress the beam or panel in the transverse direction. The pre-stressing member may be coupled to the pre-cast anchors by grouting, concrete, or by mechanical fasteners.
In an embodiment, the timber-based component comprises an engineered timber laminate such as LVL (laminated veneer lumber), glulam (glued laminated timber), or Cross-lam/CLT (cross laminated timber). Alternatively or additionally, the timber-based component may comprise a wood-based composite, for example manufactured by binding strands, particles or veneers of wood together with adhesive to form a composite, and/or sawn hard wood. The timber-based component may also comprise one or more other structural materials such as steel, composite carbon fibre reinforcement, or glass reinforcing members. As one example, a timber-based component having one or more webs may comprise composite CFRP (carbon fibre reinforced polymers), GFRP (glass fibre reinforced polymers), or steel reinforcing in the webs.
The timber-based component may also comprise a concrete topping layer on a top side of the timber-based component, for fire, seismic, acoustic and/or vibration performance, for example. The concrete topping layer may be reinforced, for example with steel or mesh reinforcing and may be prefabricated or poured in-situ or at the same time as the concrete anchors. The topping layer may be bonded to the timber-based components, so to contribute to the strength of the beam or panel. In one embodiment, the concrete topping layer is bonded to the timber-based component by way of fasteners protruding from a top side of the timber-based component. The fasteners become at least partly embedded in the concrete when the topping layer is poured. Alternatively the topping layer may be unbonded from the timber-based component.
The timber-based component may further comprise a transverse channel or hollow portion for receiving a transverse pre-stressing member. In such an embodiment, the timber-based component may comprise cross laminated timber. In such embodiments, the method may comprise inserting a transverse pre-stressing member into the transverse channel or hollow portion; applying a tensile force to the transverse pre-stressing member; pouring concrete at spaced apart locations along the transverse pre-stressing member; allowing the concrete to substantially cure to anchor respective portions of the transverse pre-stressing member; and releasing the tension from the transverse pre-stressing member to pre-stress the beam or panel in the transverse direction.
Alternatively the method may comprise attaching pre-cast anchors to the timber-based component at spaced apart locations along the transverse channel or hollow portion; inserting a transverse pre-stressing member into the transverse channel or hollow portion; applying a tensile force to the transverse pre-stressing member; coupling the tensioned transverse pre-stressing member to the respective pre-cast anchor; and releasing the tension from the transverse pre-stressing member to pre-stress the beam or panel in the transverse direction.
A plurality of pre-fabricated beams that have been pre-stressed in the first longitudinal direction may be placed side-by-side and pre-stressed in the second direction together to form a panel member. This step may be carried out on a construction site. For example, a plurality of pre-fabricated pre-stressed beams each comprising a transverse channel or hollow portion may be placed side-by-side so the channels or hollow portions on the beams are aligned, and the transverse pre-stressing member arranged to extend through the transverse channels or hollow portions in the plurality of side-by-side beams.
In one embodiment, two side members each comprising a transverse opening aligned with the transverse channels or hollows may be placed one on either side of the plurality of side-by-side beams. Concrete is poured into the transverse opening in each side member to form the anchors for the transverse pre-stressing member. Alternatively, pre-cast anchors may be attached to opposite sides of the timber component and the transverse pre-stressing member tensioned and coupled to those pre-fabricated anchors. The pre-stressing member may be coupled to the pre-cast anchors by grouting, concrete, or mechanical fasteners.
The concrete anchors may be made from light weight concrete, or may comprise hollow regions or timber cores to reduce weight. The method may comprise placing timber, polystyrene or other filler material at the location for each anchor, before pouring the concrete, to create a lightweight core, region, or void in the anchors.
The concrete anchors may comprise steel reinforcing, for example stirrups and bars. For example, the method may comprise placing one or more steel reinforcing members at the location for each anchor, before pouring the concrete, to reinforce the concrete anchors.
In embodiments in which the concrete anchors are poured, shear or axial connectors may protrude from part of the timber-based component into one or more of the anchor locations, such that the connectors become at least partly embedded in the concrete anchors when the anchors are poured. The concrete then cures around the connectors, strengthening the connection between the anchors and the timber-based component.
In a second aspect, the invention provides a pre-stressed beam or panel manufactured according to the method outlined in relation to the first aspect above.
In a third aspect, the invention provides a pre-fabricated pre-stressed beam or panel comprising: a timber-based component; spaced apart concrete anchors operatively connected to the timber-based component; and at least one pre-stressing member extending between the spaced apart concrete anchors. The pre-stressing member comprises portions coupled to the concrete anchors to apply a compressive force to the timber-based component to pre-stress the beam or panel.
The concrete anchors are preferably discrete anchors and preferably comprise two end anchors recessed in opposite ends of the timber-based component. The beam or panel may comprise one or more intermediate anchors positioned between the two end anchors. The intermediate anchors preferably have a length about twice the length of the end anchors.
The beam or panel may comprise one or a plurality of pre-stressing members. The pre-stressing member(s) may consist of one or more tendons, which may be rods, bars or cables, for example, or alternatively may consist of one or more plate or sheet member(s), and could for example be laminates. Preferably the pre-stressing members comprise high tensile steel, but alternatively may comprise an alloy, carbon composite, or glass-aramid or other composite material, for example.
The pre-stressing member(s) preferably comprise portions embedded in the discrete anchors.
The timber-based component is preferably an elongate member with one or more elongate hollow portion(s) or channel(s) to receive the pre-stressing member(s). The pre-stressing member(s) may be positioned in the hollow portion(s) or channel(s) of the timber-based component, for example they may be positioned in channel(s) extending along an outer surface of the component or within internal hollow portion(s) in the timber-based component such that at least a portion of the pre-stressing member(s) are enclosed by the component. The timber component may comprise a transverse wall adjacent each anchor, the wall comprising one or more apertures through which the pre-stressing member(s) extend. Preferably, the cross sectional area of each concrete anchors is much larger than the cross sectional area of the channel, hollow or wall aperture(s) immediately adjacent the anchor. For example, the cross sectional area of each concrete anchors may be at least twice or at least three times the cross sectional area of the channel, hollow or wall aperture(s) immediately adjacent the anchor.
In an embodiment having three or more anchors, the timber-based component is preferably sufficiently elongate that a plurality of shorter beams or panels that are also elongate may be formed by cutting through the intermediate anchor(s). The timber-based component may comprise a plurality of individual timber-based sub-components arranged end-to-end. In such an embodiment, the pre-stressing member(s) may extend along all of the individual sub-components, and the intermediate concrete anchor(s) are positioned between the ends of two adjacent individual sub-components connecting the sub-components.
In one embodiment, the timber-based component comprises an engineered timber laminate, a wood-based composite and/or sawn hard wood, and may comprise other structural materials or topping layers, as described with above with respect to the first aspect.
For example, one embodiment comprises a concrete topping layer on a top side of the timber-based component. The beam or panel may further comprise fasteners attached to the top side of the timber-based component and at least partly embedded in the concrete topping layer. The topping layer may comprise steel or mesh reinforcing.
The timber-based component may further comprise a transverse channel or hollow portion for receipt of a transverse pre-stressing member. Spaced apart transverse concrete anchors may be operatively connected to the timber-based component. In one such embodiment, the beam or panel further comprises spaced apart transverse concrete anchors and a transverse pre-stressing member arranged in the transverse channel or hollow portion and extending between the transverse concrete anchors, applying a compressive force to the timber-based component to pre-stress the beam or panel in the transverse direction. The transverse pre-stressing member may be one of the type described above, and may be the same or different from the longitudinal pre-stressing member(s).
The beam or panel may comprise a plurality of the above beams each comprising a transverse channel or hollow portion arranged side-by-side with the channels or hollow portions aligned and further comprising two side members, one on either side of the plurality of side-by-side beams. In such an embodiment, the side members each comprise a concrete anchor aligned with the transverse channels or hollows, and a transverse pre-stressing member arranged in the transverse channels or hollow portions and extending between the transverse concrete anchors, such that the transverse pre-stressing member pre-stresses the beam or panel in the transverse direction.
The concrete anchors may be made from a light weight concrete, or may comprise hollow regions or timber cores to reduce weight.
In some embodiments, the beam or panel comprises shear and/or axial connectors that protrude from the timber-based component into one or more of the anchor regions, such that the shear connectors are at least partly embedded in the concrete anchors. This strengthens the connection between the anchors and the timber-based component. The shear and/or axial connectors may comprise timber-based protrusions on the or each timber-based component. Alternatively, the timber-based component may comprise recesses in the anchor regions, such that the concrete anchors protrude into the recesses to strengthen the connection between the anchors and the timber-based component.
One embodiment beam or panel comprises: a plurality of side-by-side timber-based components; spaced apart transverse concrete anchors; and a transverse pre-stressing member extending between the transverse concrete anchors and coupled to the transverse concrete anchors, the transverse pre-stressing member applying a compressive force to the timber-based component to pre-stress the beam or panel in the transverse direction.
In one embodiment, the anchors are at least partly pre-cast. The pre-cast anchors may comprise attachment features and the timber-based component may comprise a series of complementary attachment features for attaching the anchors to the timber-based component. In one embodiment the attachment features on the anchors comprise a plurality of protruding rods, bars, or screws, and the attachment features on the timber-based component comprise a plurality of complementary holes for receiving the rods, bars, or screws. Alternatively the timber-based component may comprise protruding rods, bars, or screws, and the anchors may comprise a plurality of complementary holes. The holes may contain epoxy, grouting, concrete, or an adhesive to improve the connection between the anchors and the timber-based component.
In one embodiment the anchors are partly pre-cast and each comprise a duct that receives the pre-stressing member. The duct comprises concrete or grouting, coupling the pre-stressing member to the anchors. In an alternative embodiment, the anchors are pre-cast and the pre-stressed beam or panel comprises mechanical fasteners that mechanically couple the pre-stressing member to the anchors.
In a fourth aspect, the invention provides a method of manufacturing a panel. The method comprises placing a plurality of pre-fabricated beams or panels as outlined in relation to the second or third aspects of the invention, side-by-side. The method further comprises providing a transverse pre-stressing member arranged transversely across the side-by-side timber-based components, applying a tensile force to the transverse pre-stressing member, providing transversely spaced concrete anchors, coupling the transverse pre-stressing member to the transversely spaced concrete anchors, and releasing the tensile force on the transverse pre-stressing member to transfer a transverse compressive force to the timber-based components through the transverse concrete anchors to pre-stress the panel in the transverse direction.
Each pre-fabricated beam or panel may comprise a transverse channel or hollow portion, the pre-fabricated beams or panels being arranged side-by-side so the channels or hollow portions of the beams are aligned. In such an embodiment, the transverse pre-stressing member is preferably arranged to extend through the aligned transverse channels or hollow portions.
The term ‘comprising’ as used in this specification and claims means ‘consisting at least in part of’. When interpreting statements in this specification and claims which include the term ‘comprising’, other features besides the features prefaced by this term in each statement can also be present. Related terms such as ‘comprise’ and ‘comprised’ are to be interpreted in a similar manner.
It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. As used herein the term ‘(s)’ following a noun means the plural and/or singular form of that noun.
As used herein the term ‘and/or’ means ‘and’ or ‘or’, or where the context allows both.
The invention consists in the foregoing and also envisages constructions of which the following gives examples only.
The present invention will now be described by way of example only and with reference to the accompanying drawings in which:
Pre-Tensioned, Multiple Beams/Panels
At the opposing ends of the timber-based component 1, adjacent webs 4 define a number of spaces 5a, 5b between the webs 4 that are open at least on an upper side to receive poured concrete for forming a respective discrete end anchor. In the embodiment in
In a second stage illustrated in
The opposing ends of the tendons 9 are connected to tensioning equipment and a tensile force is applied to the tendons 9. The ends 9a, 9b of the tendons may comprise enlarged portions or attached blocks or other features, as shown in
As a further alternative, one or more transverse steel plates connected to the timber-based component 1 may be positioned in or adjacent an end of the open anchor regions 5a, 5b, 7. The pre-stressing member(s) 9 would extend through apertures or notches in the plate(s) and may be tensioned against the plate(s), for example using a thread and nut arrangement or a pre-stressing cone or wedge, such that the steel plate(s) bear against a portion of the timber-based component to transfer the pre-stressing force. In embodiments with a steel plate positioned within one or more of the anchor regions 5a, 5b, 7, the poured concrete would at least partially embed the plate(s). In those embodiments, the steel plate may form the boxing for the respective anchor, to contain the poured concrete. The plate may also reduce the required length of the concrete anchor by bearing some of the pre-stressing load.
Methods of tensioning tendons are known to a person skilled in the art. For example, from Collins M. P. and Mitchell D, Prestressed Concrete Structures, Prentice Hall, Englewood Cliffs, N.J., USA 1991, Response Publications, Toronto 1997, ISBN 0-9681958-0-6.
In a third stage illustrated in
When the concrete is poured, the portions of the tensioned tendons 9 positioned within the anchor regions 5a, 5b, 7 are embedded in the concrete. The concrete is then cured to form end anchors 11a, 11b and intermediate anchors 13 that fixedly couple the tendons 9 to the timber-based component 1. In embodiments where the timber-based component 1 comprises a plurality of shorter members or sub-components 1a, 1b, 1c, the intermediate cavities 7 are each defined between the ends of the respective two adjacent sub-components. When the concrete poured into those intermediate cavities 7 cures, it joins the adjacent sub-components 1a/1b, 1b/1c together.
In a fourth stage illustrated in
The anchors may comprise any suitable concrete including, but not limited to, high strength concrete, light weight concrete, fibre reinforced concrete, or self-compacting concrete. The concrete may additionally contain small aggregates. To reduce weight, the anchors may comprise hollow portions or a timber core. To form an anchor having hollow portions, a core comprising a material such as polystyrene or PVC may be inserted into the anchor region and the concrete poured around the inserted core. The core may be removed when the concrete has been cured. Steel reinforcing may also be used in the anchor region to reinforce the concrete anchor.
The initial pre-stressed beam 14 in
The anchors are preferably cut using a saw capable of cutting concrete and steel. Alternatively, a polystyrene divider may be placed along the intermediate plane 17 in the intermediate cavities 7 before the concrete is poured. In stage 3, concrete is then poured on both sides of the polystyrene divider. In the final stage, the initial pre-stressed beam 14 may then be cut along intermediate transverse cutting planes 17, through the polystyrene and the tendons 9. This enables faster cutting of the beam. In one example, the polystyrene divider is 10 mm thick.
It can be seen that once cut, the concrete anchors 11a, 11b, 18a, 18b are recessed in the ends of the beams or sub-beams, and preferably do not project outwardly beyond the ends of the timber-based component or sub-components.
The cut pre-stressed beams 14a, 14b, 14c may then be transported to a construction site for use. The beams may be used for constructing suspended floors, roofs, walls or some bridges, for example.
This process has the advantage that a plurality of final beams 14a, 14b, 14c can be pre-stressed at the same time, making more efficient use of tensioning equipment for high volume production.
Pre-Tensioned, Single Beam
An alternative preferred embodiment method for producing a single pre-stressed beam is shown schematically in
Once the concrete anchors 111a, 111b have substantially cured, tension is released from the tendons and protruding portions of the tendons 109 are removed to form a final pre-stressed beam 119. This embodiment differs from the above method in that the beam formed cannot be cut into shorter lengths, so only a single pre-fabricated beam or panel is produced. This process may be used where there is insufficient space for a plurality of beams to be pre-stressed end-on-end, where there are only low-volume requirements, or for beams or panels with custom dimensions, for example. The method and formed pre-stressed beam may have any one or more of the features described above in relation to the embodiment of
The embodiment of
Pre-Fabricated Anchors
Rather than pre-tensioning the pre-stressing cables and pouring the anchors as described above, the concrete anchors 32 may be at least partially pre-cast, and the cables post-tensioned.
In a second phase of the method, illustrated in
The timber-based component 31 comprises a plurality of ducts 33 which extend along the length of the component 31 for receiving pre-stressing members 39. The pre-cast anchor 32 also comprises a series of ducts or apertures 38 that align with the ducts 33 in the timber-based component 31 when the anchor and timber component 31 are assembled.
A single pre-stressing member 39 is placed through each duct 33 in the timber-based component 31, and the corresponding duct 38 in the anchor 32. Alternatively, several pre-stressing members 39 may be placed in each duct 33, 38. In a third phase, shown in
In addition to two end anchors 32, the method may also comprise placing one or more intermediate pre-cast anchors between the ends of two timber-based sub components in a similar manner to the embodiment of
Once the grouting has substantially cured, the initial pre-stressed beam or panel may be cut along intermediate transverse cutting planes through the intermediate anchors and the pre-stressing members 39, forming a plurality of shorter beams or panels. Because the tendons are grouted along the length of intermediate anchors, they are also embedded along the length of the resulting new end anchors so that the pre-stress is maintained in the shorter beams. As described with respect to the embodiment of
Instead of the starter rods 37 and drilled holes 33, other suitable fasteners may be used. For example, the timber-based component 31 or the concrete anchors 32 may comprise metallic ducts for receiving rods or screws attached to the other of the concrete anchors 32 or the timber-based component 31. The rods or screws may be screwed, bolted or epoxied into the other of the timber-based component 31 or the anchors 32.
As a further alternative, rather than using concrete or grouting to couple the pre-stressing members to the pre-cast anchors 32, the pre-stressing members 39 may be mechanically coupled to the pre-cast anchors 32. For example, the pre-stressing members may be threaded members and may be post-tensioned by tightening a nut that then abuts the end of the pre-cast anchor 32 or a plate at the end of each end anchor 32. The concrete anchors diffuse the stresses from the mechanical coupling to the timber-based component 31 and offer a lower-cost solution than coupling the pre-stressing members to the timber-based component using a steel plate, which would need to be thick to diffuse the stresses.
Concrete Topping Layer
Any of the beam or panel embodiments described above may optionally comprise a concrete-based topping layer.
In a first phase shown in
In a second phase shown in
In a third phase, shown in
In a fifth stage shown in
Preferably the concrete topper does not cover the two webs 4a, 4b on the sides of the timber-based component 1, and hooked ends 43a, 43b protrude from the concrete topping layer.
In two further stages illustrated in
In embodiments where the concrete topping layer is poured in situ, the steps of
The fasteners 41 in the above described embodiments bond the concrete topping layer to the timber-based component.
Once the pre-stressed panels are at the construction site, the panels may be placed side-by-side to form a large supporting surface such as a floor.
The hooked ends 43a, 43b of the transverse reinforcing bars in the concrete topping layers protrude into the spaces between topping layers 51a, 51b, 51c and overlap with the hooked ends 43a, 43b of the reinforcing bars in an adjacent panel. In a final step, concrete 57 is poured into the spaces between the adjacent slabs 51a, 51b, 51c, embedding the protruding, hooked portions 43a, 43b of the steel reinforcing to form a continuous surface.
Optionally, fasteners 55 may also be attached to the timber-based component 1 in the spaces between adjacent topping layers 51a, 51b, 51c. Those fasteners are then embedded in the strips of concrete 57 that are poured to join the slabs to improve the connection between the topping layer and the timber based component 1.
In alternative embodiments, the concrete topping layer may not be bonded to the timber-based component or may only be partially bonded. For example, the step of attaching fasteners to the timber-based component 1 (
As a further alternative, the concrete topping layer may comprise pre-cast reinforced slabs that are placed on the timber-based component 1 on site and attached by fasteners.
The concrete topping layer improves the fire, acoustic, and vibration performance of a given beam or panel. The topping layer also may improve performance of the beam or panel during a seismic event by helping to transfer inertial forces to frames and walls supporting the beam or panel.
An unbonded concrete topping layer may be cheaper and/or easier to manufacture than a fully bonded layer, but still provide most of the advantages mentioned above.
However, an unbonded concrete topping layer acts as a dead weight that must be supported by the pre-stressed timber beam or panel, in contrast, when the concrete topping layer at least partially bonded to the timber-based component, the topping layer contributes to the strength of the pre-stressed beam or panel. Therefore, a smaller beam or panel is required for a given application if the topping layer is at least partially bonded.
For example, one embodiment of a panel has an unbonded concrete topping layer between 65 and 75 mm thick. In a comparable panel with a bonded topping layer of the same thickness, the thickness/depth of the timber-based component would be less than for the timber-based component in the panel with the unbonded topping layer, resulting in a lighter panel. The span of the beam generally determines the thickness of the timber-based component. For example, a panel having an 8 m span may be 360 mm deep, including a 65 mm concrete topping layer. Whereas a panel with a 6 m span may be only 210 mm deep, including a 65 mm concrete topping layer. If the concrete layer is included as a ‘diaphragm’ for seismic events, the thickness of the concrete topping layer in a bonded panel may be less than for an unbonded panel.
The timber-based component 1′ comprises a channel section 40 on one side, having a top flange 40a and a bottom flange 40b. The hooked ends 43b′ at one end of the transverse reinforcing bars in the concrete topping layer protrude over the top flange 40a. A plurality of the beams shown in
In a similar manner as described above in relation to the embodiments of
The bottom flange 40b is cosmetic, to provide a flat surface if looking at the beam from below.
Alternative Cross Sections
The timber-based components 1, 101, 301 shown in
As illustrated, the timber-based component 1 may comprise either hollows (
Aspects of the cassette-based, solid, and T-shaped cross-sections may be combined to produce any number of alternative cross-sections. For example the panel shown in
Different cross-sections provide different advantages. For example, a T-section may be light weight, but a cassette-type or solid construction such as those in
Any of the panels shown in
In embodiments having a concrete topping layer 71, the concrete topping layer 71 primarily resists compression, while the timber-based construction 1 resists tension and bending. The connection between the timber-based construction 1 and the concrete topping layer 71 transmits the shear forces between the two components. Advantages over timber floors include increased load-carrying capacity, higher stiffness (which leads to reductions in deflections and susceptibility to vibrations), improved acoustic and thermal properties, and higher fire resistance.
The exemplary timber-based components 1 illustrated in
As an example, the embodiments shown in
In the embodiments shown, the tendons 9 are offset below the vertical mid-point of the beam or panel. This produces an upward deflection or pre-camber to balance deflection from downward loading on the beam or panel in use. For example, loading when the panels form a floor. Offsetting the pre-stressing members 9 to deflect the beam or panel towards the anticipated loading enables longer span beams or panels and/or shallower depth beams or panels when compared to an equivalent beam or panel with centrally positioned tendons.
A pre-stressed panel or beam produced using the above method is typically between 6 and 12 m long. However, shorter and longer beams and panels are possible. Longer lengths require increasing the depth and width of the panel or beam accordingly.
Bi-Directional Panels
Timber-based components 201 with transverse ports, such as those shown in
In a first step shown in
After arranging the beams 200a, 200b, 200c and side members 223a, 223b, transverse tendons 209 are arranged in the transverse hollow portions, as shown in
The tendons 209 are then tensioned using suitable tensioning machinery, for example hydraulic jacks. The tendons 209 are then kept in tension, for example by reacting the tensile force in the tendons against an anchor block or plate. The anchor block or plate may be positioned in or adjacent an end of the open anchor regions 229a, 229b, with the pre-stressing members 209 extending through apertures or notches in the block or plate. Alternatively the anchor block or plate may be externally fixed, for example anchored to the ground. The tendons are then fixed against the block or plate using any mechanical anchoring means, for example a thread and nut arrangement or a pre-stressing cone or wedge. In a third step shown in
Alternatively, the concrete side anchors may be at least partially pre-cast, and the cables post-tensioned. The pre-cast anchors would be attached to the sides of the arranged pre-stressed beams of panels in a similar manner to the pre-cast anchors described above with respect to
After the transverse pre-stressing members 209 are tensioned, they may be fastened to the pre-cast side anchors either by injecting concrete or grouting in the ducts and allowing that to cure, or by mechanically fastening the tensioned pre-stressing members to the anchors for example, by tightening a nut.
In a final step, the portions of the tendons 209 protruding from the sides of the side anchors are removed by cutting through the cutting planes 231a, 231b shown in
This process forms a panel 233 that is pre-stressed in two directions. Such a panel may have application as a suspended floor, for example, where it is advantageous to transfer load in two directions. This arrangement would typically be suitable for covering long spans, as the panel can be lower depth than a beam that needs to span the same distance. Because the panels are either pre-tensioned prior to delivery to site, or only need to be post-tensioned in the transverse direction on site, not in both directions, this method significantly reduces the on-site labour required to construct a large bi-directionally stressed panel.
Cross-laminated timber is particularly suitable for bi-directional pre-stressing due to their bi-directional built-up. Cross-laminated timber provides relatively high in-plane and out-of-plane strength and stiffness in both directions, giving embodiments such as those shown in
The pre-stressed beams of
The timber component of
Anchors
Force from the pre-stressing members may be transferred from the concrete anchors to the timber-based component as a predominantly compressive or shear force, or as a combination of compressive and shear forces. The end anchor regions and any intermediate anchor regions on the timber-based component 1, 101, 201 may comprise features to enhance the shear or axial connection between the timber-based component 1 and the concrete anchors 11a, 11b, 13, 18a, 18b, 111a, 111b, 211a, 211b.
Instead of rods 19, other features may be provided to improve the shear connection between the concrete anchors 11a, 11b, 13, 18a, 18b, 111a, 111b, 211a, 211b and the timber-based component 1. For example, one or more plate members 21 such as those shown in
In another embodiment, one or more of the side walls or top or bottom walls of the timber-based component in the anchor regions may be provided with undulations, projections or recesses, to provide an uneven surface to interface with the concrete and enhance the shear connection.
The pre-stressed beams or panels may comprise longitudinal reinforcing.
The embodiment shown in
In the embodiment of
The timber construction 501 comprises one side timber web 508 with a top lip 508a, and one side timber web 508 with a complementary recess 508b. This enables shear force to be taken by the timber webs 508 when beams 500 are placed side-by-side, without the need to connect the webs using bolts.
The force from the pre-stressing tendons 509, 609 is transferred from the concrete anchor 511, 611 to the timber-based component 501, 601 as a combination of compressive and shear forces. The compressive pre-stressing is transferred to the timber deviators 504, 604 defining the end of the anchor 511, 611. Shear stress is transferred at the interface between the timber-based component and concrete by the timber webs 502, 602 between pre-stressing members 509, 609 and the shear connectors 506, 606 and reinforcing bars 512, 612.
The beam embodiment shown in
In the embodiment shown in
The anchor regions further comprise transverse stirrups 618 (
To reduce the total weight of the pre-stressed beams or panels, polystyrene blocks 616 are embedded in the concrete anchor 611 and attached, for example glued, to the timber shear keys 606. Each polystyrene block 616 has two recesses that receive two respective adjacent timber keys such that polystyrene surrounds three sides of each timber key 606, with a web 616a of the polystyrene block 616 extending between two adjacent timber keys 606. The embodiment shown comprises six pre-stressing tendons, six timber shear keys 606 and three spaced apart polystyrene blocks 616. To form the anchor 611, concrete is poured into a boxed anchor region, embedding the polystyrene blocks 616 pre-stressing tendons 609, and reinforcing members 612.
Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention. For example, rather than providing central hollow chambers in the timber-based component for receiving reinforcing members, the timber-based component may comprise one or more open channels along one or more of the sides of the component. For example, a plurality of channels may be provided on the top and bottom surfaces of the timber-based component.
The features in any of the above described embodiments can be combined or replaced by features from other embodiments without departing from the scope of the invention. The dimensions, numbers of components, and described arrangements described for the preferred embodiments are by way of example only. For example, rather than each sub-beam 14a, 14b, 14c being the same length, the concrete anchors 13 could be spaced unevenly so as to form sub-beams of lengths that differ from each other. Typically, longer beams or sub-beams would require a greater beam depth than shorter beams or sub-beams.
As another example, while the embodiment of
As another example, the timber-based components could have one, two, three, or more pre-stressing members positioned in each hollow.
Other modifications are outlined in the ‘summary of the invention’ section.
The above described preferred embodiment pre-stressed timber-based beams and panels provide a high strength to weight ratio in comparison to other commonly used alternatives such as reinforced concrete. This enables longer span floors for architectural design purposes, reduces the cost of supporting beams, columns and foundations (due to lowered strength requirements), and reduces the cost of transport and lifting of the beams or panels and their supporting structures. A manufacturer is also able to supply a larger geographic region due to lower transport costs. The lower weight of the preferred embodiment timber-based beams and panels also means that in a seismic event, less energy is transferred through inertia to the supporting structures, resulting in less damage.
By being pre-fabricated, the preferred embodiment beams and panels are also more accessible to end users, meaning builders and other users are more likely to readily adopt the beams and panels. The preferred embodiment timber-based beams and panels also have a lower carbon footprint than many other construction materials such as concrete-based beams and other commercial flooring alternatives. This means the above described beams and panels may be an attractive option in ‘green building’ projects.
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| Number | Date | Country | |
|---|---|---|---|
| 20180058070 A1 | Mar 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61819724 | May 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14888679 | US | |
| Child | 15590304 | US |
