Patent Application
20140144102
The present disclosure relates to building panels, structures comprising building panels, and methods of manufacturing building panels.
Conventional concrete building panels include two outer layers of precast, pre-stressed concrete separated by an inner layer of expanded polystyrene (EPS) or extruded polystyrene (XPS).
Concrete building panels are typically used as wall elements due to their favorable thermal insulation properties, compressive load strength, and out-of-plane flexural strength for wind and seismic loading. However, conventional concrete building panels are not well-suited for use as floor or roof members. More specifically, conventional concrete building panels require thick reinforced or pre-stressed concrete panels in order to withstand the large out-of-plane bending loads typical of floor and roof applications. Moreover, the thickness of the concrete panels needed to achieve the required strength often renders conventional concrete building panels too heavy for floor and roof applications and too thick to meet strict floor and roof zoning requirements and building codes. Conventional concrete building panels also suffer from inadequate water resistance, making them unsuitable for the stringent water resistance requirements of green roof applications.
Other conventional roofing techniques use asphalt roofing, which typically is labor intensive, with labor representing approximately 75% of the total cost whereas materials constitute only about 25% of the total cost. A traditional roof consists of roofing and/or water-proofing materials, an insulation layer, and a supporting structure. Methods in the art concerning this process typically involve either providing the insulation layer above the supporting structure, such as illustrated in
Disclosed herein are various embodiments of a building panel that address limitations associated with prior panels. In a representative embodiment, a building panel comprises a fiber-reinforced polymer layer and an insulative layer disposed adjacent the fiber-reinforced polymer layer. The building panel can further comprise a rigid planar member disposed adjacent the insulative layer such that the insulative layer is located between the fiber-reinforced polymer and the rigid planar member. The building panel can further comprise one or more fiber-reinforced polymer connectors extending through the insulative layer between the fiber-reinforced polymer and the rigid planar member.
In another representative embodiment, a method of making a building panel comprises coupling a rigid planar member with one or more connectors and installing an insulative layer adjacent the rigid planar member. The one or more connectors can be configured to extend through the insulative layer. The method can further comprise coupling a fiber-reinforced polymer layer to the insulative layer and the one or more connectors.
In another representative embodiment, a method comprises providing a building panel and building a structure comprising the building panel.
In another representative embodiment, a structure can include a plurality of walls and a building panel coupled to the plurality of walls. The building panel can comprise a fiber-reinforced polymer layer providing one or more exterior surfaces of the building panel, an insulative layer disposed adjacent the fiber-reinforced polymer layer, and a rigid planar member disposed adjacent the insulative layer such that the insulative layer is located between the fiber-reinforced polymer layer and the rigid planar member. The building panel can further comprise one or more fiber-reinforced polymer connectors extending through the insulative layer between the fiber-reinforced polymer layer and the rigid planar member.
Another representative embodiment of a building panel comprises a first concrete panel and a second concrete panel associated with an insulative core. The building panel can further comprise a fiber-reinforced polymer connector embedded in the first and second concrete panels and extending through the insulative core. The building panel can also comprise at least one fiber-reinforced polymer layer comprising one or more exterior surfaces of the building panel.
Another embodiment concerns a method of making a building panel, comprising associating a fiber-reinforced polymer layer with a formwork, applying a bonding agent to the fiber-reinforced polymer layer, and casting a first concrete panel on top of the fiber-reinforced polymer layer. The method further comprises installing one or more connectors, installing an insulative core, and installing one or more pre-stressing strands or reinforcement bars above the insulative core. The method further comprises casting a second concrete panel on top of the insulative core such that the pre-stressing strands or reinforcement bars are embedded within the second concrete panel.
Another embodiment of the present invention comprises a structure having a plurality of walls and a transverse element. The transverse element comprises an insulative core, a first concrete panel, a second concrete panel, a fiber-reinforced polymer connector, and one or more fiber-reinforced polymer layers. The one or more fiber-reinforced polymer layers comprise one or more surfaces of the transverse element.
Another embodiment of the present invention concerns a method of making a structure, comprising associating a concrete building panel with a plurality of wall structures. The plurality of wall structures are oriented vertically, and the concrete building panel is oriented in a transverse manner adjacent the plurality of wall structures. The concrete building panel comprises an insulative core, a first concrete panel, a second concrete panel, one or more fiber-reinforced polymer connectors, and a fiber-reinforced polymer layer.
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
The following term definitions are provided to aid the reader, and should not be considered to provide a definition different from that known by a person of ordinary skill in the art. And, unless otherwise noted, technical terms are used according to conventional usage.
All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety for all purposes. In case of conflict, the present specification, including explanations of terms, will control.
Although methods and materials similar or equivalent to those described herein can be used to practice or test the disclosed technology, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and are not intended to be limiting.
As used herein, the singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. Also, as used herein, the term “comprises” means “includes.” Hence “comprising A or B” means including A, B, or A and B.
In order to facilitate review of the various embodiments of the disclosure, the following explanations of specific terms are provided:
In some examples, values, procedures, or apparatus' are referred to as “lowest,” “best,” “minimum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections.
As used herein, the term “coupled” generally means physically coupled or linked and does not exclude the presence of intermediate elements between the coupled items absent specific contrary language.
“Acting in a composite manner” or “Composite action”: These phrases refer to the individual components of the building panel acting together and causing the building panel to behave as if it were a member made of a single homogeneous material when subjected to loading. This can allow the building panel to be configured to withstand the loading conditions typical of roof and floor applications without a corresponding increase in weight and thickness.
As used herein, the term “compositely adhered” refers to components of the building panel being adhered or coupled to one another such that the components act in a composite manner when subjected to loading.
FCSR: Fiber-Reinforced Polymer-Confined Sandwich Roof
FRP: Fiber-reinforced polymer
RC: Reinforced concrete
The insulative core 12 can comprise a lightweight material, such as polymer foam, and can act to thermally and/or acoustically insulate the concrete building panel 10. The insulative core 12 can have any desired thickness, such as a thickness of from about two inches to about six inches, depending upon the material and the particular application. Desirably, the insulative core is sufficiently thick to achieve a suitable degree of thermal and acoustic insulation while maintaining a desirable overall thickness dimension of the concrete building panel, such as a thickness of up to at least four inches. The insulative core 12, in combination with the FRP connector 20, provides an efficient thermal barrier due to the lack of thermally conductive materials, such as metals, often used in conventional concrete building panels. This allows the concrete building panel 10 to be used in roof and floor applications without the additional layers of insulation that are typically required in combination with non-insulated structural members. Suitable lightweight, insulative materials that can be used to form the insulative core 12 include, without limitation, polystyrene (e.g., extruded polystyrene, expanded polystyrene), an aliphatic polymer (e.g., extruded polypropylene), polyisocyanurate, or polyurethane. Desirably, the insulative core 12 can be pre-fabricated and installed during construction of the concrete building panel 10.
The insulative core 12 can be variably sized. In some embodiments, the insulative core 12 is sized such that it is shorter than the overall length of the concrete building panel 10 and thus terminates before first and second ends 70, 72 of the concrete building panel, as shown in
The first concrete panel 14 can comprise conventional or high-strength concrete (i.e., the compressive strength of the concrete can be greater than or equal to 5,000 psi), and can be located adjacent a top surface 22 of the insulative core 12. The first concrete panel 14 can achieve composite action with the FRP layer 18, and therefore the first concrete panel need not be reinforced (i.e., no reinforcing bar need be embedded in the first concrete panel) or pre-stressed (i.e., tensioned pre-stressing strand or cable need not be embedded in the first concrete panel). Thus, the first concrete panel 14 can have any suitable or desired thickness, such as a thickness of from about one-half inch to about five inches, depending on the application, because pre-stressing strand and reinforcing bar need not be accommodated. Desirably, for certain disclosed embodiments, the first concrete panel 14 can have a thickness of about one inch to adequately balance the need for load-bearing strength with the need for weight reduction.
The composite action between the FRP layer 18 and the first concrete panel 14 thereby allows the concrete building panel 10 to achieve the same or greater load-bearing capacity as compared to conventional building panels without the corresponding increase in weight. Additionally, the reduced thickness of the first concrete panel 14 can lower the cost of the concrete building panel 10 as compared to conventional building panels by reducing the quantity of concrete required. The reduced thickness of the first concrete panel 14 can also contribute to an overall reduction in thickness of the concrete building panel, which can be critical for conforming to strict zoning requirements or other building standards for roof and floor applications. However, although the first concrete panel 14 can achieve composite action with the FRP layer 18, a person of ordinary skill in the art will appreciate that the first concrete panel 14 can comprise additional materials than those described, such as pre-stressed concrete or reinforced concrete, for additional strength.
The second concrete panel 16 can comprise conventional or high-strength concrete, as discussed above, and can be located adjacent a bottom surface 24 of the insulative core 12. The second concrete panel 16 can comprise pre-stressed or reinforced concrete such that it can withstand the out-of-plane bending and internal shear forces associated with floor and roof applications. The second concrete panel 16 can have a suitable or desired thickness, such as a thickness of from about two inches to about five inches, depending on the application. Desirably, the second concrete panel 16 can have a thickness of about three inches to adequately balance the need for load-bearing strength with the need for weight reduction.
The FRP layer 18 can comprise one or more woven fiber mats or sheets embedded in a polymer resin, and can be located adjacent a top surface 42 of the first concrete panel 14. Woven fiber sheets can be layered one on top of another until the desired strength properties and thickness are achieved. Suitable fibers include, for example, carbon fibers, glass fibers, or aramid fibers. In some embodiments, one or more of the woven fiber sheets can be layered such that the fibers are arranged in a particular orientation (i.e., at an angle θ) with respect to the edge of the concrete building panel, where θ typically is from zero degrees to ninety degrees. In this manner, the FRP layer 18 can be optimized for loading conditions in which a force or forces act in a particular direction on or within the concrete building panel 10.
Due to the desirable water resistance qualities of FRP materials, the FRP layer 18 can also act as a water or moisture barrier. When configured as the exterior-facing surface of the concrete building panel 10, such as, for example, when the FRP layer 18 is configured to comprise the exterior surface of a building into which the concrete building panel is incorporated, the FRP layer 18 can protect the other components of the concrete building panel from moisture-related degradation. Thus, the FRP layer 18 eliminates the need for a separate moisture barrier membrane. Elimination of the moisture barrier membrane can dramatically reduce the cost of the concrete building panel 10 over conventional building panels. Additionally, elimination of the separate moisture barrier can reduce the overall thickness of the concrete building panel 10, which can allow it to meet strict zoning requirements and other building regulations for roof and floor applications.
The bottom surface 26 of the FRP layer 18 can include a thin layer of polymer concrete (i.e., concrete utilizing a thermosetting resin to bind the aggregate). During construction of the concrete building panel 10, a bonding agent can be applied to the polymer concrete before the first concrete panel 14 is cast. When the first concrete panel 14 is cast on top of the polymer concrete, the bonding agent facilitates the forming of a bond between the first concrete panel 14 and the polymer concrete of the FRP layer 18. In this manner, the FRP layer 18 can achieve full composite action with the first concrete panel 14 when subjected to loading. The bond between the FRP layer 18 and the first concrete panel 14 can also reduce the incidence of crack formation in the first concrete panel 14, extending the life span of the concrete building panel 10 over conventional building panels. The FRP layer 18 can have any suitable or desired thickness, such as a thickness of from about 0.05 inch to about 0.2 inch, depending upon the design load and the type of fibers used. Desirably, using glass fibers embedded in a polymer resin, certain disclosed embodiments of the FRP layer 18 have a thickness of about 0.1 inch. Alternatively, the FRP layer 18 and the first concrete panel 14 may be bonded together with a bonding agent without the use of polymer concrete.
As best shown in
In the embodiment shown, the projections 30 can extend into the second concrete panel 16 up to or beyond a midpoint 46 of the cross-section of the second concrete panel 16. In this manner, the FRP connector 20 transfers shear forces between the FRP layer 18, the first concrete panel 14, and the second concrete panel 16. This, in turn, allows the concrete building panel 10 to act in a composite manner when subjected to loading. Desirably, the elongate member 28 and projections 30 can be integrally fabricated from single a piece of FRP material. Alternatively, the projections 30 and elongate member 28 can be separately fabricated and joined together to create the FRP connector 20.
As shown in
In some embodiments, the FRP connectors 20 can comprise one or more reinforcement holes 56 and/or one or more flow-promoting holes 58, as shown in
Alternatively, the concrete building panel 10 can comprise the FRP shell 60 of
In an alternative embodiment of the concrete building panel 10, a second FRP layer 38 can be associated with the second concrete panel 16 as shown in
Desirably, the FRP members 104 can be embedded in the first concrete panel 14 such that they extend beyond the midpoint 44 of the thickness of the first concrete panel 14 without reaching the top surface 42 of the first concrete panel 14. Similarly, the FRP members 104 can be embedded in the second concrete panel 16 such that they extend beyond the midpoint 46 of the thickness of the second concrete panel 16 but do not reach the bottom surface 40. In this manner, the plurality of FRP members 104 transfer shear stress between the FRP layer 18, first concrete panel 14, and second concrete panel 16, thereby contributing to the composite action of the concrete building panel 100. Alternatively, the concrete building panel 100 can comprise an additional FRP layer (not shown) associated with the second concrete panel 106 in the manner of the concrete building panel 10 of
Alternatively, the one or more elongated FRP members 204 can be arranged such that the curves 206 propagate in a direction substantially perpendicular to the top surface 50 of the concrete building panel 200, as shown in
Turning now to methods of making a concrete building panel, the concrete building panel described herein lends itself to fast, efficient, low-cost construction. The first and second concrete panels can be cast in a controlled environment to help ensure structural quality, and the completed concrete building panel or panels can be transported to a job site with less labor than is required to make an in-situ roof or floor. A FRP layer 18 can be associated with a formwork 52 having a bed 54 (
With respect to the embodiment of
Once the FRP connectors 20 are installed, the insulative core 12 can be installed adjacent a bottom surface 48 of the first concrete panel 14. The insulative core 12 can be pre-fabricated, and can be installed such that the FRP connector 20 extends through the entirety of the cross-section of the insulative core 12. With the insulative core 12 in place, pre-stressing strand or cable can be installed in the formwork 52 and tensioned. A concrete mixture or slurry may then be poured on top of the insulative core 12 to cast the second concrete panel 16 such that the pre-stressing strand is embedded within the second concrete panel 16. After the second concrete panel 16 has reached the required release strength (i.e., the concrete has attained sufficient compressive strength such that the tension of the pre-stressing strand may be released), the pre-stressing strand may be cut or released, placing the second concrete panel 16 into a pre-stressed state. Alternatively, reinforcing bar can be placed in the formwork 52 and the concrete mixture can be poured such that the reinforcing bar is embedded within the second concrete panel 16. Once the second concrete panel 16 has cured or hardened, the completed concrete building panel 10 can be removed from the formwork 52.
Turning now to methods of constructing a building incorporating a concrete building panel, one or more completed concrete building panels 10 can be associated with a plurality of wall structures 56 to form a roof structure or a floor structure in a building 58, as shown in
Turning now to additional embodiments of building panels, the building panels disclosed herein address the deficiencies of traditional panels, such as the traditional roof panels illustrated in
The disclosed building panel may comprise at least one FRP layer, an optional concrete panel, one or more connectors, an insulative layer, and combinations thereof. In particular disclosed embodiments, the building panel comprises both a top FRP layer and a bottom FRP layer (i.e, a rigid planar member), which are typically placed at the outermost portions of the building panel. The building panel components may be configured such that the optional concrete panel, the FRP layer, the insulative layer, and the one or more connectors (e.g., FRP connectors) all act in a composite manner when subjected to out-of-plane bending and internal shear forces.
In particular disclosed embodiments, the FRP layer comprises high-strength fibers, such as, but not limited to, glass, carbon, aramid, or combinations thereof. In particular disclosed embodiments, the FRP layer can comprise one or more woven fiber mats or sheets embedded in a polymer resin. Woven fiber sheets can be layered one on top of another until the desired strength properties and thickness are achieved. In some embodiments, the woven fiber sheets can be pre-impregnated with resin. In alternative embodiments, resin can be applied to fiber sheets that have been arranged in the desired shape and thickness. In some embodiments, one or more of the woven fiber sheets can be layered such that the fibers are arranged in a particular orientation (i.e., at an angle θ) with respect to the edge of the building panel, where θ is from zero degrees to ninety degrees. In this manner, the FRP layer can be optimized for loading conditions in which a force, or forces, act in a particular direction on, or within, the building panel. In particular disclosed embodiments, the high-strength fibers may be embedded in a polymer resin. In particular disclosed embodiments, the polymer resin may be selected from polyester, vinyl ester, or combinations thereof. Embodiments of the FRP are high strength given the types of fibers contained therein. The FRP also is lightweight and may exhibit high durability.
In particular disclosed embodiments, one or more of the FRP layers may comprise a polymer-concrete interior surface, which may be suitable for bonding to fresh concrete. In additional embodiments, a bonding agent may be applied to the polymer concrete surface in order to achieve full composite action with a concrete panel when it is applied. The FRP layers may have a thickness of from about 0.05 inch to at least about 0.2 inch, depending upon the design load and the type of fibers used. Using glass fibers embedded in a polymer resin, the FRP layers can have any desired or suitable thickness, such as a thickness of about 0.1 inch for certain disclosed embodiments.
Due to the desirable water resistance qualities of FRP materials, the FRP layers can also act as a water or moisture barrier. When configured as an exterior-facing surface of the building panel, such as, for example, when an FRP layer is configured to comprise the exterior surface of a building into which the building panel is incorporated, the FRP layer can protect the other components of the building panel from moisture-related degradation. Thus, the FRP layer eliminates the need for a separate moisture barrier membrane. Eliminating the moisture barrier membrane can dramatically reduce the cost of the building panel or of building a structure in comparison to conventional building panels. Additionally, eliminating the separate moisture barrier can reduce the overall thickness of the building panel, which can allow the building panel to meet strict zoning requirements and other building regulations for roof and floor applications. The disclosed building panel therefore is suitable for use in high moisture applications, such as water tanks, fish tanks, under-water rehabilitation, and the like. Also, the FRP material is easy to repair by bonding on-site additional FRP strips on top of the damaged area.
The insulative layer can comprise a lightweight material, such as polymer foam, and can act to thermally and/or acoustically insulate the building panel. The insulative layer can have any desired or suitable thickness, such as a thickness of from about two inches to about twelve inches in certain embodiments, depending upon the material and the particular application. Desirably, in certain embodiments, the insulative layer can be about four inches thick to achieve a suitable degree of thermal and acoustic insulation while maintaining a desirable overall thickness dimension of the building panel. The insulative layer, in combination with the one or more connectors (e.g., FRP connectors), provides an efficient thermal barrier due to the lack of thermally conductive materials, such as metals, often used in conventional building panels. This feature allows the building panel to be used in roof and floor applications without the additional layers of insulation that are typically required in combination with non-insulated structural members. Suitable lightweight, insulative materials that can be used to form the insulative layer include, without limitation, polystyrene (e.g., extruded polystyrene, expanded polystyrene), an aliphatic polymer (e.g., extruded polypropylene), polyisocyanurate, or polyurethane. In some embodiments, the insulative layer can be pre-fabricated and installed during construction of the building panel.
The disclosed building panel may comprise a single concrete panel having a thickness that is suitable for particular loading conditions, and in particular disclosed embodiments, the concrete layer need not be present. The concrete panel can comprise conventional or high-strength concrete (i.e., the compressive strength of the concrete can be greater than or equal to 5,000 psi), and can be located adjacent a top surface of the insulative layer. The concrete panel can achieve composite action with the FRP layer, particularly a top FRP layer, and therefore the concrete panel does not need to be reinforced (i.e., no reinforcing bar need be embedded in the concrete panel) or pre-stressed (i.e., tensioned pre-stressing strand or cable need not be embedded in the concrete panel). Thus, the concrete panel can have a thickness of from about 0.5 inch to at least about five inches, depending on the application, because pre-stressing strand and reinforcing bar need not be accommodated. In some embodiments, the concrete panel can have a thickness of from about 0.5 inch to about twelve inches. In some embodiments, the concrete panel can have a thickness of about one inch to adequately balance the need for load-bearing strength with the need for weight reduction.
Referring to
Referring to
In some embodiments, one or both of the first and second FRP layers 302, 304 may be pre-manufactured with one or more of the insulative layer 306 and/or the concrete panel 308 of the building panel 300. Solely by way of example, the second FRP layer 304 may be pre-manufactured with one or more connectors 310 and an insulative layer 306 to form a building panel shell assembly 324, as shown in
Suitable insulative material may then be added. For example, a liquid styrene formulation can be poured to produce a foam which, when cured, can form the insulative layer 306. In some embodiments, the thickness of the foam can be controlled using a mold. The insulative layer 306 can compositely adhere to an embedded portion (e.g., the valleys 318 and the angled portions 314) of the one or more connectors 310. The insulative layer 306 can also compositely adhere to the second FRP layer 304. In some embodiments, the one or more connectors 310 need not be totally encapsulated within the insulative layer 306. This can allow the one or more connectors 310 to interact with an optional concrete panel 308, as further described below.
This particular pre-manufactured combination 324 may be used with an optional pour-in-place concrete panel 308. For example, wet concrete can be poured on top of the insulative layer 306 and around the angled portions 314 of the one or more connectors 310. The concrete can be configured such that the cured concrete panel 308 compositely adheres to the angled portions 314 and the peaks 316 of the one or more connectors 310. Once the concrete panel 308 is cured, the first FRP layer 302 may be applied to the building panel shell 324 and cured such that the first FRP layer 302 is securely coupled to the peaks 316 of the one or more connectors 310 to form a finished building panel 300, as shown in
The first FRP layer 302 can include a layer of polymer-concrete on its interior surface to allow bonding to fresh concrete (i.e, to allow the first FRP layer 302 to compositely adhere to the concrete panel 308). In embodiments of the building panel 300 that do not comprise concrete, the first FRP layer 302 can be bonded directly to the insulative layer 306 and the one or more connectors 310 of the building panel shell assembly 324.
The concrete layer 308 can work compositely with the first and second FRP layers 302, 304 through, for example, shear transfer via the one or more connectors 310. Applying a polymer-concrete composition on the interior surface of the first FRP layer 302 can provide a strong interface bond and allow composite action with the concrete layer 308. Accordingly, in particular disclosed embodiments, the building panel 300 can work as a composite structure. In some embodiments, the first and second FRP layers 302, 304 can provide a confinement effect and structural reinforcement. For example, the second FRP layer 304 can take tensile forces and the one or more connectors 310 can take shear forces, which can eliminate the need for steel reinforcement in the concrete panel 308. In particular disclosed embodiments, the first FRP layer 302 can provide a water barrier and also protect the concrete panel 308 below the first FRP layer 302, thereby eliminating the need for additional roofing materials, such as water-proofing materials known in the art.
Referring to
In some embodiments, the first FRP layer 302 can comprise a layer of polymer concrete on the surface in contact with the concrete layer 308. The first FRP layer 302 can be installed such that the polymer concrete layer of the first FRP layer 302 is in contact with the wet concrete of the concrete panel, and the peaks 316 of the connector are in contact with respective portions of the interior surface of the first FRP layer 302. In this manner, the first FRP layer 302 and the concrete panel 308 can be compositely adhered to one another, which can allow the building panel to achieve composite action when subjected to loading. In some embodiments, polymer concrete can be applied to all interior surfaces of the building panel, including the first and second FRP layers 302, 304, and the one or more connectors 310, to allow composite action between the respective components of the building panel 300. In embodiments where more than one building panel 300 is employed, FRP strips (not shown) can be bonded to the first FRP layers 302 of adjacent building panels 300 and extending across the longitudinal joint between the building panels.
In particular disclosed embodiments, the FRP material of the first and second FRP layers 302, 304 can have a thermal resistance R value of about 3.26° F.-ft2-hr/Btu-in. This thermal resistance value is comparable to that obtained from other materials typically used for energy efficient structures, such as Expanded PolyStyrene foam (EPS, which has an average R-value of 3.8° F.-ft2-hr/Btu-in).
The insulative layer 306 of the disclosed building panel 300 can increase the building panel's stiffness and strength, and can also improve the thermal resistance of the building panel 300 for improved comfort and reduced energy consumption. For example, a building panel 300 having an overall thickness of about ten inches and including an insulation layer 306 having a thickness of about six inches can have an R-value approximately 30 times greater than a conventional concrete panel of the same thickness. Additionally, the steel-free building panel 300 disclosed herein not only eliminates the potential corrosion problem associated with metal components such as steel rebars and pre-stressing strand, but can also reduce deterioration of the concrete layer 308. This can increase the service life of the structure in which the building panel is used by as much as two times.
In particular disclosed embodiments, the compressive strength and ultimate strain of the confined concrete panel 308 of the disclosed building panel 300 can be much higher than an unconfined concrete panel, such as a regular reinforced concrete panel. The strength and ductility of the building panel 300 can thereby provide improved seismic/blast resistance and safety by containing debris and spall.
In particular disclosed embodiments, the FRP material of the first and second FRP layers 302, 304 may be modified to promote fire resistance, energy performance, UV resistance, and combinations thereof. For example, nano-size silicate or alumina trihydrate can be mixed with the resin of the FRP material to increase its fire resistance. Also, different colors of pigment can be added to the resin to change the Solar Reflectance Index (SRI), which can in turn reduce roofing-related thermal load to optimize the energy performance. Also, UV inhibitors can be mixed with resin to increase its UV resistance.
Although the following discussion proceeds with reference to the building panel 300, the methods and apparatus described can be used in combination with any of the building panels described herein. The disclosed building panel 300 may be used in any suitable industry. In particular disclosed embodiments, the building panel 300 is used in roofing and/or construction, such as in flat-roof construction in commercial, public, and/or residential buildings. In particular disclosed embodiments, the building panel 300 can be used for residential building roofs and/or floors, and may optionally be free of the concrete layer 308. State-of-art technology of roof systems includes advanced roof and attic design, including above-deck ventilation, radiant barriers, insulation, and near infra-red reflective pigment. The disclosed building panel 300 can be used in such systems without the need to treat different components separately (e.g., roofing, insulation, and supporting structure), as is currently done in the art. The disclosed building panel 300 provides an energy efficient, durable, and steel-free structure with ease of construction. Accordingly, the disclosed building panel 300 provides the ability for fast construction and lower construction labor costs, thermal resistance, and high strength. In additional disclosed embodiments, the building panel 300 may be used in any application in which a combination of FRP, such as FRP layers 302, 304, and insulation, such as the insulative layer 306, are useful. Such applications can include truck-doors, wall panels, bridge decks, abutment enclosures, and connector pin assemblies (e.g., for continuous track or tread, such as employed on construction equipment and military vehicles).
In particular embodiments, the disclosed building panel 300 can be installed in one step, and no additional insulation layers or materials (e.g., waterproofing materials) are required. Additionally, the disclosed building panel 300 and/or the building panel shell assembly 324 can be suitable for transport in large sections and for easy on-site assembly, as described above.
Development of FRP and Foam Materials: Polymers with suitable fire resistance for use in the first and second FRP layers 302, 304 can be produced by dispersing nano-clay and/or alumina trihydrate in a polymer matrix. Nano-clays are typically mineral silicates, such as montmorillonite, modified with surface active agents to permit their dispersion and mixing in polymer matrices.
The nano-clay can enhance the heat capacity and resistance of the resin, by forming glassy silicon-oxy-carbides at surfaces exposed to direct flame. As the polymer burns away, it leaves the silica content behind, which consolidates into a protective surface film. The incorporation of nano-clay, nano-silica, and pigments can be accomplished by melt-mixing the components. Also UV inhibitors can be mixed with the resin to increase its UV resistance. Multiple compositions can be prepared and evaluated.
The choice of proper material for the insulative layer 306, such as a foam material, possessing a high R-value and enough strength to act as a stay-in-place formwork, also is desired. The density of the foam can be varied to meet the thermal requirement for roof insulation and the stiffness and strength requirements for a stay-in-place formwork.
Evaluation of FRP and Foam Materials: Extensive evaluations can be conducted, including energy, structural, and applicability of the FRP layers 302, 304 as roofing materials. The material properties obtained from these evaluations can be used to prototype and optimize the building panel 300 in subsequent embodiments.
Material Manufacturing: In particular embodiments, the first and second FRP layers 302, 304 may be obtained from 4.5 ounces of Chopped Strand Mat (ChSM) with glass fiber and polyester resin, which cures to a 0.09 inch wall thickness when saturated. For material testing, the thickness of the first and second FRP layers 302, 304 can be approximately 0.25 inch. In some embodiments, the first and second FRP layers 302, 304 can be from about 0.01 inch to about one inch thick.
Thermal Evaluations of FRP and Foam: To evaluate the thermal performance of the building panel 300, the thermo-physical properties such as density, specific heat, thermal conductivity, and thermal diffusivity of the FRP and foam materials can be obtained using a thermal conductivity instrument (e.g., LaserComp FOX314). The procedure typically can follow ASTM C518 standards. The thermal properties of the building panel 300 can be evaluated based on the heat flux through the building panel 300. In addition, other thermo-physical properties such as density and length changes can be obtained using scales and transducers with high accuracy.
Evaluation of SRI of FRP Laminates: A large amount of building cooling and heating loads come from the sun through the building roof. One of the most effective approaches to reducing building thermal load is to increase the roof surface's ability to reflect solar radiation and emit thermal radiation. This can be measured by the SRI, which includes solar reflectance and thermal emissivity of the material. To improve the SRI of the surface of the building panel 300, the first FRP layer 302 can contain pigments of selected colors to reflect the near-infrared component of the sunlight. The SRI of first FRP layers 302 with different color pigments can be measured and their thermal performance for different simulated climates can be evaluated. A solar spectrum reflectometer can be used to determine the solar reflectance and thermal emissivity of the first FRP layers 302, in accordance with ASTM C1549 and ASTM E408. The SRI of the building panel 300 can be calculated according to ASTM E 1980-01.
Structural Evaluations of FRP Laminates and Foam: In some embodiments, sample FRP material can be employed in the first and second FRP layers 302, 304, and the one or more connectors 310, can be tested. The stiffness and strength properties of the FRP material can be evaluated. The testing protocol for coupon samples to obtain stiffness and strength can consist of tension, bending, compression, and shear, following modified ASTM guidelines supplemented by proven methods. For tension, sample FRP material having dimensions 10 inches by 1 inch can be tested to failure (ASTM D 638-99) to record longitudinal and transverse strains and load-displacement to failure. For bending, sample FRP layers having dimensions of 15 inches by 2 inches can be tested to failure under 3-point loading (ASTM D 790-99), to record mid-span strains and deflections as function of load. For compression, a testing tool can be used and the sample FRP material can have dimensions of 2 inches by 1 inch, with strain gages bonded to opposite sides to attain alignment and eliminate bending. Finally, for shear, the Iosipescu test (ASTM D 379-88) method can be used with notched butterfly specimens instrumented with strain gages; the testing tool and the equipment for precise cutting and polishing of specimens are available.
The prediction models for stiffness and strength can be calibrated using the data obtained from embodiments disclosed herein, which will permit making predictions for other possible laminates to recommend optimum materials, and also to guide the manufacturing of the connectors 310 and the first and second FRP layers 302, 304.
Water Resistance Test of the FRP Layers: This test follows ASTM D 7281-07 to determine the water migration resistance of the first FRP layer 302 as a roof membrane, resulting from a standing head of water when pressurized with air from the underside. The test apparatus can be manufactured to comprise top and bottom sections, with the sample placed as a diaphragm between the two sections. Both controlled samples and conditioned samples exposed to UV radiation and moisture can be tested, with two specimens for each type.
Smoke and Toxicity Test of FRP Layers: This test can be conducted based on ASTM E84-12: Standard Test Method for Surface Burning Characteristics of Building Materials. The test can expose building panels 300 having dimensions of 24 ft long by 20 inches wide to a controlled air flow and flaming fire adjusted to spread the flame along the entire length. During the 10-minute duration, flame spread over the specimen surface and density of the resulting smoke can be measured and recorded. Test results can be calculated relative to red oak, which has a rating of 300, and fiber-reinforced cement board, which has a rating of 0, and expressed in terms of Flame Spread Index and Smoke Developed Index. Based on these results, the building panel 300 can be graded as A, B, or C, corresponding to Type I, II, or III as specified in the building code.
Fire Resistance of FRP Layers: Two types of tests can be conducted: flame-spread and high-temperature exposure tests. Three kinds of flame-spread tests can be conducted: the limit oxygen index (LOI) test (ASTM D2863-00), the horizontal flame spread test, and the vertical flame spread test. The property of flame spread from top to bottom can be evaluated using the LOI test, which determines the oxygen concentration at which sustained combustion occurs using a vertically mounted specimen FRP layer ignited at the upper end. All tests can be carried out according to ASTM D2863. The high-temperature exposure test can be conducted by exposing the specimen to 260° C. for 2 hours. An oven can be preheated to 260° C. to simulate the effects of a real fire on the structural elements.
UV Resistance of FRP Layers: The long-term use of FRP composites in outdoor or exposed conditions is dependent on the resistance of the resins to ultraviolet light. A QUV accelerated weathering tester equipped with UVB-313 lamps can be used to perform the test in accordance with ASTM D4329-84 to determine the UV resistance of the first and second FRP layers 302, 304. The cycle can be an alternating eight hours of UV exposure at 60° C. and four hours of condensation at 50° C. Test specimens can be exposed on one side to UV radiation. Multiple specimens from each material can be used in the test and removed at periodic intervals for evaluation.
Configuration Optimization: The goal of the disclosed building panel 300 roof system is to minimize building thermal load, life cycle cost, and installation time, as well as to maximize structural strength and stiffness and to improve the overall performance of the building panel 300. Multi-objective optimization methods can be adopted to analyze and optimize the design and configuration of the building panel 300. The parameters in the optimization study include the thickness and ingredient combinations of the first and second FRP layers 302, 304, the concrete panel 308, and the insulative layer 306, as well as the configuration and spacing of the one or more connectors 310.
Evaluation of Scaled Specimens: Once the optimal design and configuration of the building panel 300 are completed, scaled specimens can be produced and their performance can be evaluated in terms of energy, structural performance, fire resistance and durability.
Manufacturing of Building Panel Shell Assembly: A hand lay-up method can be used for constructing a building panel shell assembly 324. Once it is determined that the building panel 300 can be commercialized, a mechanized production line can be constructed for mass production. The one or more connectors 310 can be manufactured in large pieces and cut into strips, as shown in
FRP layer 302 can be fabricated by applying polymer concrete at its surface when the resin of the first FRP layer 302 is still wet.
Thermal Evaluation: The thermal properties of the building panel 300 can be evaluated for a prediction of the overall building energy reduction. The LSCS can be configured to measure heat flow across a 12 ft by 12 ft large test building panel 300 in accordance with ASTM C1363, which is the standard for testing thermal performance of large building materials and envelope specimens by means of a hot box apparatus. The metering chamber of the LSCS acts over an 8 ft by 8 ft FCSR section in the center of the 12 ft by 12 ft building panel 300. Heat flow in or out of the meter chamber can be recorded and used to determine the steady-state heat flux through the building panel 300, which can be tested for both winter and summer conditions. The building panel 300 can have arrays of thermocouples installed during production at the top of the first FRP layer 302, the top of the concrete layer 308, the top of the insulative layer 306, and at both surfaces of the second FRP layer 304. The temperature difference of the metering chamber and the exterior of the climate side can be measured. The thermal resistance of the building panel can be calculated, and the thermal properties of the building panel can be compared to the reference roof systems to determine the performance of the building panel 300.
A heat transfer model can be validated by the testing data from the embodiments disclosed herein and can be continuously used in the analyses and evaluations for demonstration houses.
Structural Evaluation: Half-scaled building panels can be fabricated based on the optimization results obtained from embodiments disclosed herein. The building panels can be 12 ft long and 4 ft wide. Two thicknesses can be considered for concrete to be potentially used for regular roofs (including snow load and other roof live load) and green roof (including load from overburdened soil and vegetation). The third group can be reference reinforced concrete panels reinforced with horizontal rebars, which can be designed to be comparable to the other two groups, based on strength properties obtained herein. Two building panels for each group can be tested. Four-point bending tests on scaled building panels can be conducted to study the behavior of the building panels under roof loads. Strain gages can be bonded to the first and/or second FRP layers 302, 304 and the concrete panel 308 to study the composite action. Load-displacement relations can be recorded to study the stiffness. All building panels can be tested until failure to study the strength and failure modes.
Creep test: Creep tests can be conducted to study long-term deflection of the building panel 300 under sustained loads. Particular embodiments can be subjected to a four-month creep in bending at 40% of the static capacity.
Fire Test: The fire test can be in accordance with ASTM E119/UL 263. The procedures used to measure the fire resistance and integrity of the building panel 300 can consist of two phases: a fire endurance (furnace) test, using the standard time-temperature curve specified in ASTM E119, which is considered to represent a severe building fire. The fire endurance test can immediately be followed by a water hose stream test, which subjects the building panel 300 to the cooling impact and erosion effects of a stream of water to evaluate the ability of the panel construction to resist disintegration under adverse conditions. The building panel 300 should sustain the applied load during the fire endurance and hose stream test with defined limited passage of flame or gases. The performance of the exposure can be expressed as in terms of the fire duration, e.g., “2-hour,” etc.
Durability Test: The lifetime of the building panel 300 can be evaluated by a durability test. The two types of tests can include accelerated aging and cyclic freeze-thaw, which can be conducted on ¼ scaled specimens of the building panel 300 measuring 6 ft long and 2 ft wide.
Accelerated Aging Test: Combined water immersion and elevated temperature can be effectively used for accelerated aging, where the elevated temperature can accelerate the degradation of the building panel 300. Three temperatures can be considered, namely, T1=20° C., T2=40° C., and T3=60° C., by conditioning two building panels 300 for each temperature in deionized water in custom-built temperature-controlled tanks for four months. The same bending test as disclosed herein can be conducted on the conditioned building panels 300 and two control specimens, and any decay in the ultimate load can be used as an indication of the effect of accelerated aging. The test results can be further used to develop a model to predict the long-term behavior of the interface based on Arrhenius relation.
Cyclic Freeze-Thaw Test: Embodiments of any of the building panels described herein can be conditioned for 100 cycles in a Z-16 environmental chamber. In particular disclosed embodiments, the building panel 300 can be subjected to freeze-thaw conditioning in an environmental chamber, and two companion embodiments of the building panel 300 can be placed in an environmental room maintained at 28° C. and 50% relative humidity. The conditioned building panels 300 can be subjected to a total of 400 cycles. A typical freeze-thaw cycle will consist of ramping the temperature from 20° C. to −20° C. in two hours; maintaining the temperature at −20° C. for two hours and ramping back to 20° C. in another two hours. At the end of the conditioning, the building panel 300 can be removed and a bending test can be conducted.
Evaluation of Connections: Two types of connections should be evaluated: a building panel to building panel connection, and a building panel to supporting structure (e.g., a wall or column) connection. A typical dowel connection can be used to connect a building panel, such as the building panel 300, to a supporting structure, such as the supporting structure 326, as illustrated in
Referring to
The building panel 400 can be made by constructing first and second building panel shell assemblies 412, 414, as shown in
Once the first and second building panel shell assemblies 412, 414 are properly arranged, the concrete layer 408 can be poured over both building panel shell assemblies 412, 414, and one or more first FRP layers 402 can be installed over the concrete layer 408. In this manner, the components of the building panel 400 can achieve composite action because the concrete layer 408 inside the building panel 400 is solid and continuous. Diaphragm shear can thereby be transferred through the concrete layer 408, which can be superior to a precast concrete roof, whose strength relies heavily on panel connections.
In some embodiments, longitudinal interfaces 416 of adjacent first FRP layers 402 can be offset from longitudinal interfaces 418 of adjacent second FRP layers 404. This can increase the water migration resistance of the building panel 400 by eliminating the direct path between the respective first and second FRP layers 402, 404 through the building panel 400. In some embodiments, FRP strips 420 can be applied over the longitudinal interfaces 416 of two adjacent first FRP layers 402 of respective first and second building panel shell assemblies 412, 414, as described above.
Thermal Evaluation: Although the following discussion proceeds with reference to the building panel 400, the methods and apparatus described can be used in combination with any of the building panels described herein. Building panels 400 can be constructed, and a thermal flux transducer, such as the HFP01 from Hukseflux, along with thermocouples, can be used to measure heat flux and temperature at each layer of the building panel 400. Those measurements can be used to calculate thermal resistance (R-value) and thermal transmittance (H-value) according to ASTM C1046 and ASTM 1155 standards.
Evaluation of Water Resistance: A similar water resistance test as disclosed herein can be conducted on first and second FRP layers 402, 404 with connections.
Evaluation of Full-Scale Specimens: Based on findings from the configuration optimization embodiments and evaluations of scaled specimens, full-scale embodiments (24 ft long and 8 ft wide) of the building panel 400 can be constructed. The performance can be evaluated and the failure modes can be characterized.
Thermal Evaluation: For an increased roof-span, the building panel 400 typically will require a greater depth (i.e., thickness) to support the roof structure. The same facility and approach can be used as is employed for thermal evaluation of the scaled specimens. The only difference is that the specimens in this evaluation have a larger depth.
Structural Evaluation: Four-point bending tests can be conducted to study the behavior of the full-scale embodiments of the building panel 400 under roof loads. Strain gages can be bonded to the first and second FRP layers 402, 404 and the concrete layer 408 through the thickness of the building panel 400 to study the composite behavior. Load-displacement relations can be recorded to study the stiffness. All panels can be tested until failure to study the strength and failure modes.
Evaluations of Demonstration Houses: Referring to
The building panel 400 configured as a roof can be applied to the house 500, and a conventional roof can be applied to the house 502 for thermal performance comparison. The one or more building panel shell assemblies 410, 412 can be installed, followed by concrete for the concrete layer 408 and the first FRP layer 402. The building panel 400 and the conventional roof can be installed with arrays of thermocouples at the top of each layer and the bottom of the lowest layer of the respective roof systems. A reflectometer can be used to measure the SRI of the building panel 400. The demonstration houses 500, 502 can serve as labs for performance analysis in terms of heat transfer, thermal properties, peak energy, and energy consumption, to illustrate the advantages of the building panel 400. Each house can also be subjected to dead load, rain, snow, and wind load to ensure its safety and resistance to leakage. The test can last a year, and the two houses 500, 502 can be moved to other locations for additional climate-related thermal performance evaluation of the building panel 400.
A heat transfer model can be validated and used for the roof thermal analysis and performance evaluation under the actual outdoor condition. The weather station located close to the site of the demonstration houses will provide the necessary data of the weather conditions for analysis. Additionally a building simulation model can be developed in Energy Plus to show the favorable thermal performance of the building panel 400. This analysis helps to quantify the thermal performance of the building panel 400 when it is applied to multi-story buildings. In alternative embodiments, the above procedure can be conducted with any of the building panels disclosed herein, such as the building panel 300 of
The following examples are provided to illustrate certain features of working embodiments. A person of ordinary skill in the art will appreciate that the scope of the present invention is not limited to the scope of the features exemplified by these examples.
In a first working example, a first concrete building panel having an overall length of approximately nine feet and an overall width of approximately two feet was constructed and loaded to failure in a three-point bending test. The overall thickness of the first concrete building panel was about ten inches, wherein the FRP layer had a thickness of about 0.085 inch, the first concrete panel had a thickness of about three inches, the insulative core had a thickness of about four inches, and the second concrete panel had a thickness of about three inches. The second concrete panel was reinforced with two #5 (5/8 inch) longitudinal reinforcement bars and #4 (1/2 inch) transverse reinforcement bars placed at intervals of 18 inches as measured from the centers of the reinforcement bars (i.e, “18 inches on center”). The insulative core was made from expanded polystyrene. The first concrete building panel was fabricated to include a solid concrete zone twelve inches in length at each end of the first concrete building panel (i.e., the insulative core terminated twelve inches from each end of the first concrete building panel and the volume otherwise occupied by the insulative core was occupied by concrete). The concrete from which the first and second concrete panels were fabricated reached a compressive strength of 4,000 psi after curing for 28 days. The first concrete building panel was fabricated with the FRP connector of
The first concrete building panel was placed on a strong floor and supported with pin and roller supports (i.e., one end of the first concrete building panel was supported by a cylindrical roller and the other end was supported by a steel pad). Sensor elements, including strain gages and linear transducers, were placed on and within the first concrete building panel, and a load was applied to the center of the first concrete building panel by a hydraulic press. The loading sequence proceeded in load increments of one thousand pounds. A load reduction of about 150 pounds was experienced prior to each load increase as the hydraulic press relaxed. At each incremental load, crack formation and propagation in the first concrete building panel were measured. Deflection of the first concrete building panel was measured by the strain gages at a sample rate of 10 Hz. The incremental loading sequence continued until the first concrete building panel failed.
The data from the first working example are plotted in the load-displacement curve of
In a second working example, a second concrete building panel having an overall length of approximately nine feet and an overall width of approximately two feet was constructed and loaded to failure in a three-point bending test. The overall thickness of the second concrete building panel was about ten inches, wherein the FRP layer had a thickness of about 0.085 inch, the first concrete panel had a thickness of about three inches, the insulative core had a thickness of about four inches, and the second concrete panel had a thickness of about three inches. The second concrete panel was reinforced with two #5 (5/8 inch) longitudinal reinforcement bars and #4 (1/2 inch) transverse reinforcement bars placed at intervals of 18 inches as measured from the centers of the reinforcement bars (i.e., “18 inches on center.”). The insulative core was made from expanded polystyrene. The second concrete building panel was fabricated to include a twelve-inch solid concrete zone at each end of the second concrete building panel (i.e., the insulative core terminated twelve inches from each end of the concrete building panel and the volume otherwise occupied by the insulative core was occupied by concrete). The concrete from which the first and second concrete panels were fabricated reached a compressive strength of 4,000 psi after curing for 28 days. The second concrete building panel was fabricated with the FRP connector of
The second concrete building panel was placed on a strong floor and supported with pin and roller supports (i.e., one end of the concrete building panel was supported by a cylindrical roller and the other end was supported by a steel pad). Sensor elements, including strain gages and linear transducers, were placed on and within the second concrete building panel, and a load was applied to the center of the second concrete building panel by a hydraulic press. The loading sequence proceeded in load increments of one thousand pounds. A load reduction of about 150 pounds was experienced prior to each load increase the hydraulic press relaxed. At each incremental load, crack formation and propagation in the second concrete building panel were measured. Deflection of the second concrete building panel was measured by the strain gages at a sample rate of 10 Hz. The incremental loading sequence continued until the second concrete building panel failed.
The data of the second working example are plotted in the load-displacement curve of
Cost and Installation: The following discussion proceeds with respect to the building panel 400 of
Assume that a roof has a simply-supported span of 16 ft and will be subjected to a snow load of 30 psf. Following IBC 2009 and ACI 318, the roof can be designed as a 10 inch solid concrete slab with bottom reinforcement of 5 pounds at 12 inches on center in the main direction and 4 pounds at 12 inches on center in the other direction. This will be used as a reference roof slab.
Next, a building panel 400 can be designed and configured as a roof based on the same span and loading condition as the reference roof. For material properties, values from previous studies can be adopted. The tensile strength of the first and second FRP layers 402, 404 is 18.5 ksi and the elastic modulus is 939 ksi. Assume the concrete panel 408 is 4 inches thick and the insulative layer 406 is 6 inches thick, and the concrete panel 408 has a compressive strength of 4,000 psi. Based on an analysis of the first and second building panel shell assemblies 412, 414 as formworks, a thickness of 0.18 inch for the first and second FRP layers 402, 404 and the one or more connectors 410 allows a maximum un-shored span of 4 feet. This will significantly reduce the installation time and labor associated with the formwork. Based on the building panel 400 configuration, the dead load of the 4 inch concrete panel 408 is 48.3 psf. The dead load of the first and second building panel shell assemblies 412, 414 and others is approximately 8 psf. Therefore, the total dead load is 56.3 psf (for the RC slab this is 133 psf). The live load is 30 psf as mentioned above. The total factored load can be calculated as 1.2×56.3+1.6×30=115.6 psf. If a 1 ft strip of the slab is taken for analysis, the ultimate moment and shear can be calculated as 3.7 ft-kips and 0.92 kips, respectively.
Following the analysis procedures in ACI 440, the moment and shear capacity provided by the building panel 400 is 32.03 ft-kips and 5.2 kips, giving a safety factor of 8.7 and 5.7 for moment and shear, respectively. The live load deflection and total load deflection is calculated to be L/1584 and L/408, respectively, which satisfies the requirement of L/360 (live load) and L/240 (total load) based on ACI Building Code.
Therefore, the building panel 400 as described above can be superior to a 10 inch solid concrete slab. This can be used for a cost analysis and energy analysis. It is estimated that 20% cost reduction can be achieved for the building panel 400 compared to a RC panel. The cost reduction for the building panel 400 comes from a) elimination of the formwork (which represents 40-60% of total construction cost) and the steel reinforcement; b) reduced concrete material; and c) elimination of roofing and insulation. The added cost from the first and second FRP layers 402, 404 can be offset by these cost reductions.
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
This application is a continuation-in-part of International Patent Application No. PCT/US2012/069291, filed on Dec. 12, 2012, which claims the benefit of the earlier filing date of U.S. Provisional Patent Application No. 61/570,167, filed on Dec. 13, 2011, both of which are incorporated herein by reference in their entirety. This application also claims the benefit of the earlier filing date of U.S. Provisional Application No. 61/759,841, filed on Feb. 1, 2013, which is also incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61759841 | Feb 2013 | US | |
| 61570167 | Dec 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2012/069291 | Dec 2012 | US |
| Child | 14171195 | US |
