Priority

This application claims priority to and the benefit of Australian Patent Application No. 2018900717, filed March 6, 2018, and Australian Patent Application No. 2019201225, filed February 21, 2019, the entire contents of each of which are incorporated herein by reference.

This invention relates to insulated concrete sandwich panels and methods of manufacturing such panels.

Prefabricated concrete panels are particularly useful for modem building construction as they allow for simplified on-site building construction by lifting, erection and installation as a single piece. The concrete panels may advantageously be fabricated in an off-site factory, although in some cases, fabrication of the panels on site delivers simplicity benefits too. For improved thermal insulation properties, prefabricated concrete panels may have a 'sandwich' structure in which the panel has two layers of concrete with a layer of insulative material therebetween. Certain insulated panels provide an internally facing concrete wall for meeting structural requirements, an insulation layer for limiting the flow of heat energy through the panel, and an external concrete cladding which protects the insulation layer. Although the thickness of each of these layers can be varied to achieve different structural and thermal properties, in general only one of the concrete layers provides the structural (e.g. load-bearing) requirements and, therefore, is often thicker than the other concrete layer which has a primarily protective purpose.

The structure of a concrete sandwich panel may typically include a plurality of connector pins that extend between the two concrete layers, through the insulation layer, to secure the layers together. The connector pins are installed perpendicular to the plane of the panel at evenly spaced intervals. An example of such pins is the Nirvana™ connector pins which are precision manufactured from a high strength pultruded ECR-Glass reinforced epoxy- backboned vinylester resin. This double-headed pin spans the insulation layer of the sandwich panel, with each tip securely anchored in each concrete wythe. The connector pins are made from a material that is not thermally conductive, rather than metal, so as to minimise heat transfer through the insulation layer from one concrete layer to the other. Following further analysis, it has been found that by altering the orientation of some of the pins, it is possible to substantially improve the composite action of the assembled panel, such that both of the concrete layers work as one panel to resist loads.

According to a first aspect of the present invention, there is provided a concrete sandwich panel comprising first and second concrete layers with a layer of thermal insulation material therebetween, the panel including an array of first connector pins extending between the first and second concrete layers through the insulation layer substantially perpendicular to the plane of the insulation layer, and further including a plurality of second connector pins extending between the first and second concrete layers through the insulation layer at an angle to the perpendicular.

The second connector pins preferably form an angle to the perpendicular between 40 and 50 degrees. In one form of the invention the second connector pins form an angle of substantially 45 -degrees to the perpendicular. The angle of the second connector pins may advantageously be in the vertical dimension with respect to the panel when in use. Half of the second connector pins may be angled 'up' and the other half angled 'down'

The array of first connector pins may be arranged in a plurality of rows and columns across the plane of the panel. The second connector pins may comprise additional pins arranged across one or more rows. In embodiments, the second connector pins may be arranged across the 'top' and 'bottom' rows of the panel for greatest structural benefit.

According to a second aspect of the present invention, there is provided a method of assembling concrete sandwich panels, comprising:

inserting a plurality of first connectors through an insulation layer such that the first connectors are installed perpendicular to the insulation layer;

inserting further connectors through the insulation layer adjacent the first connectors and oriented at angles relative to the first connectors; and

installing the insulation layer with the first and further connectors between two layers of poured concrete such that opposed ends of each of the first and further connectors are embedded in the two layers of concrete.

According to one embodiment of the invention, a first layer of concrete is poured, insulation layer is placed on top and then the first and second connector pins are pushed through the insulation and into the underlying concrete before the concrete has set. Then, a second layer of concrete is poured on top of the insulation layer.

According to a third aspect of the present invention, there is provided a concrete sandwich panel assembled according to the method of the second aspect.

There is also disclosed herein a device for forming pilot holes in the insulation layer for use in the method of the second aspect of the invention.

Advantageously, the provision of connectors at an angle to the perpendicular connectors may allow for a reduction in thickness of the first layer of concrete by distributing the structural load over both layers of concrete, which significantly reduces material costs. For example, a conventional building panel as described above might have a first, structural concrete layer of l50mm and a second concrete layer of 50mm, whereas an embodiment of the present invention designed for the same application could have two concrete layers each having a thickness of 70mm. Considering the same 50mm insulation layer between the two concrete layers, the total thickness of the concrete sandwich panel resulting from the present invention is l90mm, as compared with a thickness of 250mm for the conventional panel. Alternatively, the thickness of the insulation layer may be increased with the reduction of concrete wythe thickness, thereby maintaining the same overall panel thickness but with enhanced thermal properties.

The invention may be better understood from the following detailed description of embodiments thereof, presented by way of example only, and with reference to the accompanying drawings, in which:

Figure 1A is a diagrammatic illustration of a building structure incorporating a concrete sandwich panel;

Figure 1B is a diagrammatic perspective view of the concrete sandwich panel of Figure 1A, shown in isolation;

Figure 1C is a sectional view through X-X of the concrete sandwich panel of Figure 1B;

Figure 2 shows an example of a connector pin for use in assembling concrete sandwich panels;

Figure 3A is a diagrammatic perspective view of a concrete sandwich panel according to an embodiment of the present invention; Figure 3B is a sectional view through Y-Y of the concrete sandwich panel of Figure 3 A;

Figures 4A, 4B and 4C are diagrammatic perspective, vertical-section and horizontal-section views, respectively, of a concrete sandwich panel according to an embodiment of the invention;

Figure 5 is a flow chart diagram of a procedure for fabricating a concrete sandwich panel according to embodiments of the invention;

Figures 6A and 6B are top and end elevation views, respectively, of a jig for use in fabrication of a concrete sandwich panel according to embodiments of the invention; and

Figures 7A and 7B are side and end elevation views, respectively, of the jig of Figure 6, showing internal features thereof.

With reference to Figure 1A, a building structure 10 is diagrammatically illustrated incorporating a concrete sandwich panel 20 in a vertical side wall, the panel having external facing layer 22. Figure 1B shows the concrete sandwich panel 20 in isolation in horizontal orientation with the layer 22 facing upward. Figure 1C illustrates the concrete sandwich panel 20 in sectional view through X-X of Figure 1B, fabricated according to conventional principles. As shown, the concrete sandwich panel 20 includes a structural concrete layer 26, a non-structural concrete layer 22 and an insulation layer 24 situated between the two concrete layers. In the sectional view (Figure 1C) it can be seen that the layers of the concrete sandwich panel 20 are held together with a series of regularly spaced connector pins 30, which extend normal to the plane of the concrete sandwich panel. In a concrete sandwich panel of this form the first, structural concrete layer 26 has a greater thickness (e.g. l50mm) as compared to the second, non-structural concrete layer 22 and the insulation layer 24 (each 50mm in thickness, for example).

Surprisingly, it has been found that by fabricating a concrete sandwich panel in which some of the connector pins have a different orientation, it is possible to produce a concrete sandwich panel with substantially improved composite action properties compared to conventional panels, particularly if pins with different orientation are located in rows close to the edges of the panel. In other words, the modified panel construction facilitates both of the concrete layers to work in unified fashion to resist loads, with the result that a panel of the same total thickness will be stronger, or a panel of the same strength may be thinner.

In particular, it has been found that by placing two additional pins at equal and opposite angles (e.g. 45°) relative to selected perpendicularly installed pins, composite action of up to 100% can be achieved.

Figures 3A and 3B, and Figures 4A-4C show a concrete sandwich panel 50 fabricated in accordance with an embodiment of the invention. As with a conventional sandwich panel, the panel 50 has first and second concrete layers (52, 56) with a layer of an insulative material (54) therebetween. Embedded within the sandwich layer construction of the panel 50 is an array of connector pins, each of which extends through the insulation layer 54 and has respective ends secured in the concrete layers 52, 56. The connector pins are generally evenly spaced from one another across the two major dimensions of the panel. Most of the connector pins (i.e. those labelled 60 in the Figures) are oriented substantially normal to the plane of the panel 50. A selection of the connector pins, however, have angled orientations, such as those indicated at 70 in the Figures. As seen best in Figures 4A and 4B, in the panel 50 the top and bottom rows of connector pins (with respect to how the panel will be oriented in use) include additional pins that are angled at approximately +45° and -45°.

Due to the improved resistance to differential axial and rotational displacement using the angled pins, it is possible to reduce the thickness of the first, structural concrete layer (e.g. layer 56) to 70mm (as compared to l50mm for layer 26 in the conventional panel structure), and increase the thickness of the other concrete layer (52) to 70mm (as compared to 50mm for conventional structure layer 22) while maintaining approximately the same load bearing capacity of the panel. In other words, using this arrangement both concrete layers act as structural layers and the panel can be made significantly thinner, saving on material and cost.

A procedure 200 for fabricating a concrete sandwich panel according to embodiments of the invention is illustrated in the form of a flow chart diagram in Figure 5. The panel fabrication process begins with operation 202, wherein a formwork mold is constructed according to the desired dimensions of the panel to be fabricated. The next operations 204- 210 involve preparation of the insulation layer sheet, which should be done before pouring of the first concrete layer. First the sheet material that will be used for the insulation layer is cut to size for the desired panel dimensions (operation 204). The insulation layer may comprise one or more of a range of insulative sheet materials, preferably a form of closed cell polymer foam such as expanded or extruded polystyrene. With the insulation layer sheet cut to appropriate size, one face of the sheet is then marked as a guide for connector pin placements (operation 206). For ease of fabrication the connector pin location markings may comprise a regular grid, for example, with normal pin placings at the grid vertices.

For some 'soft' insulation layer materials the connector pins can be pressed into the sheet material at the placement locations without prior preparation. However, where a 'hard' material is used, such as extruded polystyrene, it may be desirable to first create pilot holes at the placement locations for the pins to be inserted into (operation 208). For example, for placement of the angled connector pins it is possible to first create pilot holes using a guide jig to ensure consistent spacing and angular orientation. One particular example of a guide jig 100 for this purpose is shown in Figures 6 and 7 and described below.

The jig 100 as seen in Figures 6A and 6B has a generally rectangular block-shaped body that may be made from molded or printed polymer material, for example. The jig has opposed, flat top and bottom surfaces 110, 120 and spiked feet 125 centrally located at the bottom edge of each of the sides. In use, the feet 125 can be aligned with grid markings on the insulation sheet whereupon a central passage 112 will be aligned with the grid vertex. When the jig located on the insulation sheet and pressed into the surface, spikes on the underside of the feet 125 engage the sheet material to hold the jig temporarily in place whilst pilot holes are formed. The jig 100 has three passages formed through the body that extend from the top surface 110 to the bottom surface 120. The centrally located passage 112 is oriented perpendicular to the flat bottom surface 120 which lies against the insulation sheet in use. Two additional passages 114 and 116 are angled and offset with respect to the central passage 112, as seen best in Figures 7A and 7B which reveal the internal structure of the jig.

To create pilot holes for pins in the insulation layer sheet, the jig 100 is placed to the sheet surface in the desired location using the feet 125 to align with grid markings and to hold the jig in place. Then, a drill or other sharp implement can be inserted into each of the passages 112, 114 and 116 in turn to bore or pierce through the insulation layer sheet underneath in line the respective passages. The pilot holes thus formed will comprise a central normal hole with two angled, offset holes, one to each side.

Referring again to Figure 5, once the pilot holes have been created in the insulation layer sheet, respective connector pins are inserted into the pilot holes from one side, but not extending all the way through (operation 210).

In operation 212 the first concrete layer is poured in the panel form, which may also include installation of reinforcing steel before pouring the concrete. Before the concrete has set, the insulation layer sheet with fitted connector pins is laid onto the top surface of the first concrete layer (operation 214). Once the insulation layer sheet is correctly positioned, the connector pins are pressed through into the wet concrete. Referring to Figure 2, the pins 30 may have a flange 32 that provides a physical stop, or at least a visual indication of when the pin has been inserted to the correct extent. Preferably the connector pins that are inserted at an angle (e.g. pins 70) are somewhat longer than those that are inserted perpendicular (e.g. pins 60) so that the ends are embedded to the same overall depth into the concrete layer. After the connector pins have all been fully seated into the first concrete layer, including those inserted at respective angles to the perpendicular, the equivalent extent of the pins remain projecting from the top surface of the insulation layer. Reinforcing steel (if necessary) can then be installed on top of the insulation layer and the second concrete layer is poured (operation 216). When the concrete has sufficiently cured, the completed concrete sandwich panel can be removed from the form.

The angled pins are preferably inserted at approximately 45°, slanting in the vertical dimension of the panel when considered in its intended orientation in use. The angled pins are preferably of a greater length than the pins provided perpendicular to the plane of the panel. For example, a concrete sandwich panel constructed in accordance with an embodiment of the present invention may have two concrete layers each 70mm thick on either side of an insulation layer 50mm thick, interconnected by perpendicular pins l50mm in length and angled pins 200mm in length. The angled pins may be of a length such that, when installed at ±45° angles, the ends of the pins are roughly aligned with the ends of the perpendicular pins.

Although the embodiments of the invention described hereinabove utilise rows of angled pins 70 at the top and bottom of the panel, it is also possible to distribute the locations of the angled panels across the height and width of the panel in different patterns.

Experiment results

Comprehensive testing of panels fabricated according to embodiments of the present invention has been conducted by Dr. Marc Maguire at Utah State University, with pertinent results outlined below.

Eight full-scale precast concrete sandwich panels were tested to failure in flexure. The purpose of the testing was to obtain the composite action of the panels with connectors arranged in a“star pattern”, where one connector is placed perpendicular to the plane of the panel and two connectors are placed adjacent the perpendicular connector at 45° angles. The“star pattern” was concentrated on the outer edges of each panel. The goal was to determine if an arrangement using perpendicular and angled connectors could create a partially composite sandwich panel.

Eight full scale concrete sandwich panels were cast in two lengths, two concrete wythe thicknesses and two insulating wythe thicknesses. Concrete wythe thicknesses were 70 and 90mm. Insulating wythe thicknesses were 50mm and lOOmm. Panel lengths were 3.3 and 4.2m. All panels were l.8m in width.

Analysis of the test results compared observed ultimate moment from the testing with a fully composite and non-composite ultimate moment calculation for the tested panels. From this analysis it has been determined that nominal strength composite action was found to be between 90% and 142% for the panels tested. These calculated moments neglect strain hardening of the steel, to which may be attributed the measured percentage composite action results above 100%

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.