TECHNICAL FIELD The present disclosure generally relates to protective structures. In particular the present disclosure relates to protective structures that comprises one or two layers with each layer comprising a plurality of inflatable air beams that are configured to be laterally abutting and where the two layers form at least an inner layer and an outer layer of the structure.
BACKGROUND Explosive events generate blast waves that are often the cause of significant injury to people. The types of human injuries that typically occur due to explosions may be divided into three categories: (i) primary injuries that result directly from blast overpressure and shock-wave effects; (ii) secondary injuries that result from impacts with airborne fragments, debris, structural deformations and the like; and (iii) tertiary injuries resulting from the people being physically propelled by the blast wave. Blast waves can also be transmitted from outside a structure to inside the structure as a shock wave, which can also cause injuries to the structure's occupants.
It is known to construct protective structures from a layer of air beams that are covered with a polymer sheet-material, which is referred to as a fly. These protective structures are designed to protect occupants from the effects of explosive blast-loads. The protective structures are inherently resistant to blast loading as a direct consequence of the flexible properties of the air beams and the fly. These flexible properties allow a significant but controlled flexure in the event of severe blast-loads where deformation of the protective structure absorbs aspects of the blast loads, which ultimately minimizes injury risk to occupants or damage to any material housed within the protective structure.
For example, protective structures that are made with a layer of air beams can reduce the potential for primary, secondary, and tertiary injuries to occupants. The potential for primary and tertiary injuries is reduced by partial mitigation of blast-pulse transmission to the interior of the structure. The possibility of secondary injury is also reduced in comparison to a rigid building that may lose structural integrity and have surfaces fragment or tear away, which can create further hazards.
However, the desirable flexible properties of the air beams may also limit the ability to make pneumatically-supported protective structures beyond a given size, which may limit the applications of such protective structures. Furthermore, even the flexible properties of the air beams does allow some transmission of a shock wave into the interior of the protective structures.
SUMMARY Embodiments of the present disclosure relate to a structure that comprises at least one layer of air beams that define an interior space of the structure wherein laterally adjacent air beams are configured to abut each other.
Some embodiments of the present disclosure relate to a structure that comprises at least a first layer of a plurality of air beams and a second layer of a second plurality of air beams, wherein the second layer is positioned adjacent and interior to the first layer for defining an interior space of the structure.
Inflated structures are comprised of inflated air beams that are made up of fabric the inflation pressure, tube radius, and material stresses are connected through the relationship:
S=pr
where:
-
- S is the fabric hoop stress (in units of Force/Distance vs. Engineering Stress in units Force/[(distance){circumflex over ( )}2];
- p=tube inflation pressure; and
- r=tube radius.
So that for air beams that are inflated at a constant pressure, the stress in the material increases proportionally with radius (likewise, for tubes of constant radius, stress increases proportional to pressure). As the clear span of the structure increases, the air beam diameter (and therefore radius) must be increased to withstand the additional loads especially snow loads and wind loads. As the radius increases, with constant inflation pressure, the stress in the fabric membrane containing the air pressure also increases. Eventually, as the span of a structure is increased, the stress in the fabric due to inflation pressure only, not due to other loading becomes unacceptably high. This may be due to one or more several concurrent constraints:
-
- Due to a complex response of textile fabric under load, the Factor of Safety (FoS) is commonly set quite high typically between 5 and 7 for fabric as compared to about 2 for structural steel. The stress-strain characteristics of fabrics are both nonlinear, and characterized by several discrete loading regimes, in each of which the average modulus of elasticity is significantly different. Therefore, in an effort to avoid troublesome loading regions, the FoS is usually set high.
- The seam strength for heat-fused coated fabrics is lower than the strength of the base material (unlike for steel where the welded connection is typically stronger than the steel) as the fabric stresses increase, the risk of (longitudinal) seam failure increases.
- As the radius of a tube increases, the weight of the air beams increases (due to more fabric being used).
- Increasing fabric stress can be compensated for with heavier fabric, but this also increases weight of the air beams.
At some point, the designer can no longer continue increasing the diameter of the air beams. Without being bound by any particular theory, as the size of the intended structure increases using two or more layers of air beams may be suitable alternative to larger diameter air beams when one or more constraints prevent increasing the diameter any further. This is primarily due to the fact that the primary constraint on using two or more layers of air beams is that it requires twice the material of an equivalent single-layer structure.
Constructing a protective structure with at least two layers of air beams may provide a stiffer structure as compared to a structure that is constructed from a single layer of air beams. A stiffer structure can be built to larger dimensions with larger interior spaces. These interior spaces may be sufficiently large to enclose an already constructed building or structure. Furthermore, when the protective structures have at least two layers of air beams and the air beams within each layer are laterally abutting each other, the protective structure can defeat the transmission of a shock wave through the at least two layers. Defeating the transmission of a shock wave may reduce the primary, secondary and tertiary injuries that can occur when a shock wave is transmitted inside a structure.
BRIEF DESCRIPTION OF THE DRAWINGS These and other features of the present disclosure will become more apparent in the following detailed description in which reference is made to the appended drawings.
FIG. 1 is an isometric view of one embodiment of the present disclosure that relates to a structure;
FIG. 2 is a series of different views of the structure shown in FIG. 1: FIG. 2A is a front elevation, midline, cross-sectional view of the structure shown in FIG. 1; FIG. 2B is a top plan view of a section of the structure shown in FIG. 2A; FIG. 2C is a bottom plan view of the section shown in FIG. 2B; and FIG. 2D is a side-elevation view of the section shown in FIG. 2B;
FIG. 3 is a schematic illustration of embodiments of the present disclosure that relate to various configurations of air beams: FIG. 3A shows a first configuration; FIG. 3B shows a second configuration; FIG. 3C shows a third configuration; and FIG. 3D shows a fourth configuration;
FIG. 4 is a schematic illustration of embodiments of the present disclosure that relate to various further configurations of air beams: FIG. 4A shows the first configuration; FIG. 4B shows the second configuration; FIG. 4C shows a variation of the second configuration; FIG. 4D shows another variation of the second configuration; FIG. 4E shows a variation of the fourth configuration; FIG. 4F shows another variation of the second configuration; FIG. 4G shows another variation of the fourth configuration; and FIG. 4H shows another variation of the second configuration;
FIG. 5 shows an example of a shock-tube assembly and example configurations of target samples tested therein: FIG. 5A is a side elevation, midline schematic of a shock-tube assembly that was used for acquiring data from a target sample; and FIG. 5B is a top plan schematic of the example configurations of air beams and flys that were used as target samples within the shock-tube assembly;
FIG. 6 is a line graph that shows an example of overpressure vs. time data that was captured within a shock-tube assembly without a target sample;
FIG. 7 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a test-sample was present;
FIG. 8 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-sample was present;
FIG. 9 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-sample was present;
FIG. 10 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-sample was present;
FIG. 11 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-sample was present;
FIG. 12 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-specimen was present;
FIG. 13 is a line graph that shows an example of overpressure vs. time data that was acquired at a second sensor and a third sensor within the shock-tube assembly when a different test-specimen was present;
FIG. 14 is a bar graph that compares the peak overpressure data from the data provided in FIG. 6 through to FIG. 13;
FIG. 15 is an isometric view of a schematic of one example of a shear control system according to embodiments of the present disclosure;
FIG. 16 is an isometric view of a schematic of another example of a shear control system according to embodiments of the present disclosure;
FIG. 17 is an isometric view of a schematic of another example of a shear control system according to embodiments of the present disclosure;
FIG. 18 is an isometric view of a schematic of another example of a shear control system according to embodiments of the present disclosure;
FIG. 19 is a dot plot that shows an example of experimental data that compares the collapse load (“breakpoint”) of air beams in bending, using various shear control systems;
FIG. 20 is a combined side elevation view and isometric view of a schematic of an example of a connection system according to embodiments of the present disclosure;
FIG. 21 is a top plan view of two parts of the connection system shown in FIG. 20;
FIG. 22 is a top plan view of the connection system shown in FIG. 20; and
FIG. 23 is a top plan view of the connection system shown in FIG. 20 for use with multiple air beams in two layers.
DETAILED DESCRIPTION Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
As used herein, the term “about” refers to an approximately +/−10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.
Embodiments of the present disclosure relate to a structure that can be rapidly deployed proximal a site of interest. The structure may at least partially protect the site of interest from an explosion. Alternatively, or complimentarily, the structure may be large enough to provide a large interior space with various commercial uses, industrial uses, recreational uses and combinations thereof. The structure comprises multiple air beams that may also be referred to as fabric beams, pneumatic beams, pneumatic columns, pneumatic arches or pneumatic tubulars. The air beams may be arranged in one or more configurations to form ribs of the structure with multiple ribs forming a frame of the structure. A fly that is made of a sheet material may be incorporated into or on top of the ribs to enclose the frame. Connection systems may also be employed to connect the air beams to each other to form the structure and optionally to incorporate the fly. The configuration of the air beams determines the type of protection the structure provides to the site of interest and the overall size that the structure can be.
Embodiments of the present disclosure relate to a structure that is made up of at least two layers of air beams. Each layer comprises a plurality of air beams that substantially abut a laterally adjacent air beam so that a plurality of abutting air beams within a layer form part of or all of a wall of the structure. One layer of air beams forms an inner layer and one layer of air beams forms an outer layer. Some embodiments of the present disclosure relate to structures with more than two layers of air beams that comprise an inner layer, an outer layer and one or more intermediate layers therebetween.
Embodiments of the present disclosure will now be described by reference to FIG. 1 to FIG. 14.
FIG. 1 shows one example of a structure 10. The structure 10 may include one or more doors 200 to provide access to an interior space 12 of the structure 10 (shown in FIG. 2A). While FIG. 1 shows a specific arrangement of four doors 200, this is provided merely as an illustrative example and it is not intended to be limiting. For clarity, the structure 10 is shown in FIG. 1 without a fly 218, which is discussed further herein below.
FIG. 2A shows a midline cross-section of the structure 10 that is taken perpendicular to the longitudinal axis of the structure 10 (the direction of the longitudinal axis is shown as line X in FIG. 1). The structure 10 comprises as least a first layer 10A and a second layer 10B. Each layer 10A, 10B comprises one or more air beams 14, with air beams 14A forming the first layer 10A and air beams 14B forming the second layer 10B. The air beams 14 are made of a fluid tight material so that a desired volume and pressure of an inflating fluid, such as air or other mixtures of gases, can be contained within each air beam 14.
As shown in the non-limiting depiction of the structure 10 in FIG. 2A, one or more air beams 14 may extend from one side of the structure 10 to the other side to form a rib 15, which may also be referred to as an arch. Multiple ribs 15 are arranged in an abutting relationship to form a frame of the structure 10 in the shape of a barrel vault. Alternatively, multiple air beams 14, of successively smaller span, may be connected with each other to enclose the open ends of the barrel vault portion of the structure 10 in a manner similar to that shown in the region of rib 15. In some embodiments of the present disclosure, a first portion (shown as X2 in FIG. 2A) of the structure 10 may be defined by one or more air beams 14 that extend away from the ground upon which the structure 10 is deployed. In some embodiments of the present disclosure the structure 10 may be constructed without a first portion X2. In some embodiments of the present disclosure the structure 10 may be tethered to the ground by various approaches, including a tethermast and/or a frag wall, as described in the Applicant's patent application WO 2011072374 entitled Tethermast and Frag Wall, the entire disclosure of which is incorporated herein by reference. In some embodiments of the present disclosure, the rib 15 includes the first portion X2. In some embodiments of the present disclosure, the ribs 15 are dimensioned to provide a total span (shown as Y1 in FIG. 2B) of about 200 meters. In some embodiments of the present disclosure, the ribs 15 are dimensioned to provide a span that is selected from a group of about 175 meters, about 150 meters, about 125 meters, about 100 meters or less. In some embodiments of the present disclosure the ribs 15 are dimensioned to provide a span that is between about 35 meters to about 125 meters. In some embodiments the total span may be smaller or larger than the range provided above. The peak height (shown as X1 in FIG. 2A) of the structure 10 may fall between a range of 2 and 100 meters. In some embodiments the peak height may be smaller or larger than the range provided above.
In some embodiments of the present disclosure, the structure 10 may define a large enough interior space 12 so that another building or structure will fit therein. In this fashion, the structure 10 could be deployed about an existing building, either as a temporary protective-structure or as a longer-term protective structure or for providing a large enough interior space 12 so that various commercial, industrial and/or recreation activities can occur therein. As described further below, when the structure 10 is constructed with at least two layers 10A, 10B, the ribs 15 are sufficiently stiff enough to support the large spans. Furthermore, the at least two layers 10A, 10B provide further protection from blast waves and transmitted pressure waves when compared to when similar structures are constructed of a single layer of air beams and subjected to similar blast waves.
The air beams 14 within and among the layers 10A, 10B may be similar to each other, or not. In some embodiments of the present disclosure the air beams 14A, 14B can be filled with a fluid, such as air, to a range of desired pressures. An air beam 14 may have a diameter between about 0.01 meters and about 2.5 meters or other broader ranges.
Within the embodiments of the present disclosure that are shown in FIG. 2B and FIG. 2C, there are three air beams 14A with each air beam in an abutting relationship with a laterally adjacent air beam 14A of the first layer 10A. While in an abutting relationship with a laterally adjacent air beam, there is substantially no gap between the adjacent air beams. In this abutting relationship, the laterally-adjacent air beams may be direct contact with each other and they may be physically coupled together by a connection system, or not. In other embodiments of the present disclosure there may be a gap so that there is no contact between laterally-adjacent air beams when the air beams are static. FIG. 2A shows the first layer 10A as an outer layer and the second layer 10B as being an inner layer, which may also be referred to as an interior layer. The second layer 10B may define the dimensions of the interior space 12.
FIG. 3 shows a cross-sectional, top plan view of a number of different configurations of air beams 14 that may be useful in making the ribs 15 of the structure 10. The structure 10 may comprise ribs 15 of the same configuration or the ribs 15 may be of different configurations. FIG. 3A shows a first configuration with a single air beam 14 with a diameter of about 0.8 meters. FIG. 3B shows a second configuration of air beams with a first layer 10A that includes two air beams 14A and a second layer 10B with two air beams 14B, the air beams 14 in the second configuration have a diameter of about 0.4 meters. FIG. 3C shows a third configuration of air beams with a first layer 10A with a single air beam 14A and a second layer 10B with a single air beam 14B. The air beams 14 in the third configuration have a diameter of about 0.8 meters. FIG. 3D shows a fourth configuration of air beams that includes a first layer 10A, a second layer 10B and an intermediate layer 10C, each layer in the configuration has a single air beam with a diameter of about 0.8 meters. Within the second, third and fourth configurations, the air beams 14A of the first layer 10A are substantially aligned centrally with the air beams 10B of the second layer 10B. As used herein, the expression “aligned centrally” refers to the relative position of an air beam in one layer compared to one or more air beams in another layer. The aligned centrally means that the center point of an air beam of one layers is aligned with the center point of an air beam in another layer so that if a straight line was drawn that extends from the center point of one of the air beams being referred to—where the line extends substantially orthogonal to the respective layer of the air beam being referred to—that line may also extend through the center point of an air beam in another layer (see line Z1 in FIG. 4B).
FIG. 4 shows a top plan view of a number of different configurations of air beams 14 that also may be useful in making ribs 15 of the structure 10. FIG. 4A shows the first configuration of FIG. 3A. FIG. 4B shows the second configuration with a first layer 10A and a second layer 10B, wherein the air beams 14A of the first layer 10A are substantially aligned with the air beams 10B of the second layer 10B.
FIG. 4C shows a fifth configuration of air beams 14 with a single air beam 14A from the first layer 10A for every two air beams 14B of the second layer 10B with the air beam 14A aligned offset and in between the two air beams 14B. As used herein, the expression “aligned offset” refers to a central point of an air beam in one layer being offset relative to the central point in an air beam in an immediately adjacent layer. If a straight line was drawn that extends from the center point of one of the air beams being referred to—where the line extends substantially orthogonal to the respective layer of the air beam being referred to—that line will not extend through the center point of an air beam in the immediately adjacent layer (see line Z2 in FIG. 4C). Rather that line will extend through a lateral edge region of an air beam in the immediately adjacent layer. In some embodiments of the present disclosure, when air beam 14A (in layer 10A) is of equal diameter to air beams 14B (in layer 10B) (as shown in FIGS. 4C and 4D) a line be drawn to connect the centers of these three air beams and this line will define an equilateral triangle.
FIG. 4D shows a sixth configuration with a single air beam 14B from the second layer 10B for every two air beams 14A of the first layer 10A. The single air beam 14B is aligned approximately in between the two air beams 14A of the first layer 10A.
FIG. 4E shows a seventh configuration with an intermediate layer 10C that is made up of a single air beam 14C that is positioned in the middle of and aligned approximately in between the two air beams 14A of the first layer 10A and two air beams 14B of the second layer 10B.
FIG. 4F shows an eighth configuration with two air beams 14A of the first layer 10A is aligned approximately in between and three air beams 14B of the second layer 10B.
FIG. 4G shows a ninth configuration that includes a single air beam 14A of the first layer 10A, two air beams 14C of the intermediate layer 10C and three air beams 14B of the second layer 10B. The air beams 14 in this ninth configuration are all aligned approximately in between the air beams of an adjacent layer.
FIG. 4H shows an tenth configuration that includes three air beams 14A of the first layer 10A that are each aligned approximately in between three air beams 14B of the second layer 10B.
While the description of these air beam configurations include specific dimensions of air beams 14, it is understood that these diameters are examples only and the embodiments of the present disclosure are not limited to these specific dimensions.
Some embodiments of the present disclosure include connection systems for connecting air beams 14 within a configuration of two or more layers 10 of air beams 14. Some embodiments of the present disclosure relate to connection systems that act as shear control systems for controlling or reducing shear forces between air beams 14A in one layer and air beams 14B in an adjacent layer.
FIG. 15 shows a shear control system 1 that comprises at least one set of a strap 100 and a pocket 102. The pocket 102 can be secured to the outer surface of one air beam 14A in the first layer 10A and the strap 100 can be wrapped around both air beams 14A and 14B and through the pocket 102. The pockets 102 can be secured by the use of suitable adhesives and/or attachment techniques such as sonic welding, thermal polymer-welding and the like. In some embodiments of the present disclosure the strap 100 can be a webbing ratchet strap and the pocket 102 can be made of a vinyl fabric. There can be multiple sets of straps 100 and pockets 102 along the length of the air beams 14A, 14B. As will be appreciated by one skilled in the art, the layer 10A, 10B in which the pocket 102 is secured can be the same or different between different sets of straps 100 and pockets 102 that are distributed along the length of the air beams 14A, 14B. Furthermore, each set of the shear control system 1 may include more than one strap 100 and more than one pocket 102. For example, there may be a pocket 102 secured to an air beam 14 in each layer 10, or not. While FIG. 15 shows two layers, it is understood that the shear control system 1 may be used in configurations that have more than two layers.
FIG. 16 shows a shear control system 2 that comprises one or more sets of a first hug strap 104, a second hug strap 106 and a length of webbing 108. The first hug strap 104 is secured about the outer surface of one air beam 14A and the second hug strap 106 is secure about the outer surface of an air beam 14B in an adjacent layer 10. Each hug strap 104, 106 may have a loop extension (not shown) that is positioned in the contact area between the two air beams 14A and 14B. The hug straps 104, 106 can be positioned in an offset manner (as shown in FIG. 16) so that the loop extensions are positioned proximal each other so that the hug straps 104, 106 are configured for receiving a portion of the length of webbing 108 therethrough for connecting the air beam 14A to air beam 14B. As will be appreciated by one skilled in the art, in configurations that have more than two layers 10, the hug straps 104, 106 may each have more than one extension loop positioned at each contacting surface between the layers 10 of the configuration.
FIG. 17 shows a shear control system 4 that comprises one or more sets of a pair of fixed point connectors 109 and bracing straps 110. In this shear control system, each of the fixed point connections 109 can be loop or circular members, such as O rings or D rings, and one of the pair of fixed point connections is secured to the outer surface of air beam 14A and the other fix point connection of the pair is secure to the outer surface of air beam 14B. The bracing straps 110 are connected at opposite ends to the fixed point connection 109 that make up a pair. The bracing straps 110 can have an adjustable length so that when they are shortened a tension load acts on the fixed point connections 109 to restrict or prevent movement of air beam 14A relative to air beam 14B. As shown in the non-limiting example of FIG. 18, the fixed point connection 109 can be positioned so that the bracing straps 110 are oriented in a pattern of alternating direction. As will be appreciated by one skilled in the art, the number of fixed point connection 109 and bracing straps 110 utilized in this example of the shear control system can be variable based upon the length of the air beams 14 used and the number of layers 10 in a given configuration.
FIG. 18 shows a shear control system 5 that is similar to the system shown in FIG. 17. The primary difference in the system of FIG. 18 is that there are only two sets of fixed point connections 109 and bracing straps 110 and each set is positioned near an end of the air beams 14A and 14B.
Not shown in the drawings is a shear control system (Ctrl) that comprises paired strips of hook and loop portions of a hook and loop fastener that are secured to the outer surface of two air beams 14 and each portion extends along the entire axial length of each air beam and each portion is positioned within the contacting area so that when the two air beams 14 are brought close enough together the hook and loop portions connect to form the hook and loop fastener.
FIG. 20 shows a shear control system 3 that is similar to the system (Ctrl) but the paired strips of a hook portion 120A and a loop portion 120B are not continuous along the entire axial length of air beams. Rather the portions 120A and 120B are smaller lengths that do not extend the entire axial length of the air beams 14. Each air beam 14 may have multiple pairs of laterally displaced hook portions 120A or loop portions 120B that are positioned along the length of the air beam 14.
FIG. 19 shows examples of experimental data obtained from four-point bending experiments where air beams with 65 cm diameters were connected into a two layer configuration using each of the shear control systems 1 through 5. The bending experiments were conducted with the air beams inflated to a low pressure (1 psi) and a high pressure (2 psi). As shown in FIG. 19 the system (Ctrl) and system 3 had the highest breakpoint results (with minimal differences between the two hook and loop fastener based systems), which is an indication of the ability of these systems to restrict movement of the air beams of one layer relative to another layer.
FIG. 20 also shows an example of a connection system that includes the shear control system 3 and a lateral connection system that comprises straps 122 and 126 that each extend laterally from an air beam 14A in layer 10A. Strap 122 can include a first portion 124A of a fastener 124, such as a hook portion 124A of a hook and loop fastener 124 and strap 126 can include a second portion 124B of the fastener, such as an associated loop portion 124B of the hook and loop fastener 124. The person skilled in the art will appreciate that there is no requirement that the fastener 124 is a hook and loop fastener 124, rather the first portion 124A merely needs to be mateable with the second portion 124B to form a completed (fastened) fastener 124. Further examples of the fastener 124 include buckles, press fit fasteners and the like. Air beam 14A also includes non-continuous hook portion 120A that are positioned axially along the length of air beam 14A. Air beam 14B has loop portions 120B that are positioned axially along the length of the air beam 14B and positioned to mate with the hook portions 120A of air beam 14A. FIG. 21 also shows the components of the connection system on each of air beam 14A and air beam 14B. The person skilled in the art will appreciate that FIG. 21 is not limiting and the hook portions 120A, 124A and the straps 122 and 126 can be part of air beam 14B and the loop portions 120B, 124B can be part of the air beam 14B.
FIG. 22 shows how the hook portion 120A can be positioned proximal to the loop portion 120B to mate and form a complete (fastened) hook and loop fastener 120 (as shown within the hash lined circle of FIG. 22). FIG. 22 also shows one example arrangement whereby the strap 122 of one air beam 14A can be positioned around an outer portion of air beam 14B and the strap 126 can also be positioned around the outer portion of air bean 14B so that hook portion 124A can mate with loop portion 124B to make a complete (fastened) hook and loop fastener 124 (as shown within the hash lined circle in FIG. 22). As one skilled in the art will appreciate, the drawings show the straps 122 and 126 as extending from air beams 14A and the air beam 14B as including the fasteners 120B but this is but one example that may provide easier access to the straps 122 and 126 for mating the fasteners to make the completed hook and loop fasteners 124. In some embodiments of the present disclosure, the straps 122 and 126 may extend laterally from the air beam 14B and the air beam 14A may include fastener portion 120B.
FIG. 23 shows one example of the connection system used to interconnect multiple air beams 14A of one layer with air beams 14B of another layer by using the portions of the hook and loop fasteners 120, 124 described herein above to restrict or reduce shear between layers of air beams and to provide a configuration with any gap between laterally adjacent air beams of one layer.
While FIG. 23 shows a configuration where the layers are aligned offset, the person skilled in the art will appreciate that the positioning of the hook portions 120A, 124A and the loop portions 120B, 124B can be adjusted so that the air beams of the two (or more) layers are aligned centrally. Without being bound by any particular theory, when air beams in two or more adjacent layers are aligned centrally, there can be increases in the structural strength of the structure, which means that larger spans can be contemplated. In contrast, when air beams in two or more adjacent layers are aligned offset and the air beams within each layer are laterally abutting, there may be improved blast-related properties (e.g. a further attenuation of any transmitted pressure through the layers of air beams) and this may be because the respective air beams are in a somewhat nested position relative to each other.
EXAMPLES Example 1: Material-Property Analysis The inventors performed an initial analysis that illustrates the benefit of a multilayer configuration of air beams 14. This analysis was based on comparing the first configuration (FIG. 3A) and the second configuration (FIG. 3B). This is a useful comparison, because it allows a comparison of stiffness and load-bearing properties on the basis of the same width, depth, and area of wall section (as shown by the dotted squares shown in FIG. 3A and FIG. 3B).
A complication arises, however, in the case of inflated fabric structures such as air beams. For conventional engineering materials, the material properties are not dependent on the arrangement; for fabric structures, the effective material properties are highly dependent on prestress loading (among other parameters), and there is a tight relationship between prestress loading, inflation pressure, and tube diameter. In order to compare the first and second configurations on an equitable basis, the air beams of the second configuration must be inflated at precisely twice the pressure as the air beam in the first configuration. This is referred to as the “constant prestress” (versus “constant pressure”) condition.
Table 1 provides theoretical stiffness properties and predicted span length of the first, second, third and fourth configurations of air beams.
TABLE 1
Theoretical stiffness and span values for four configurations of air beams.
Configuration Type
First Second Third Fourth
Configuration Configuration Configuration Configuration
Stiffness 100% 75% 300% 633%
relative to (constant
First Configuration pressure)
150%
(constant
prestress)
Low estimate 100% n/a 173% 252%
High estimate 100% n/a 200% 300%
Testing focused on four-point flexural tests to determine the overall structural response of an air beam within each of the first, second, third and fourth configurations to a bending load, and to determine an appropriate value for the modulus of elasticity, E (also known as Young's Modulus).
Briefly, the four-point flexural tests were performed as follows:
Load was applied continuously using a winch system with the load measured by a load cell and the displacement was measured by a draw-wire sensor attached to the bottom of the air-beam configuration being tested. The load and displacement data were recorded using a computer data-acquisition system.
Load was applied to the air-beam configuration being tested through two 30 cm (12″) wide load straps that were draped over the air-beam configuration and attached to an aluminum frame hanging below the configuration. The straps were located at about ⅓ of the span of the air-beam configuration for the majority of the tests. For this series of tests the span between the supports was about 4.65 m (load strap spacing 1.55 m for ⅓ span loading). A number of tests were also performed with the straps near the center of the configuration (strap spacing 66 cm (26″)).
The air-beam configurations were supported by yokes that matched the curvature of the air beams within the configurations to minimize any deformation of the air beams at the supports. The yokes were hinged and set on casters to allow for rotation and horizontal displacement as the configuration bent under the influence of the load.
-
- Table 2 summarizes experimental results from four-point bending tests on single layers of air beams and on double layers of air beams to assess structural properties of the air beam layers.
TABLE 2
A summary of experimental results from four-point bending tests
performed on single layers of air beams with diameters of 50 cm,
65 cm and 80 cm and on double layers of air beams with each
layer having air beams with diameters of 50 cm or 65 cm.
Data Source k Fc
Configuration (Study No.) (N/mm) (N)
Single-Layer 50 cm ø 2 6.47 624.06
65 cm ø 3 11.78 1439.97
80 cm ø 1, 2 17.30 2742.93
Dual-Layer 100 cm S.D. 4A, 4B 16.87 2274.29
(2 × 50 cm ø)
130 cm S.D. 4B 29.39 4060.07
(2 × 65 cm ø)
In Table 2, Fc represents the mean collapse load of each configuration of air beams. The dual-layer configurations tested both show substantially higher Fc values as compared to the single-layers made up of air beams with the single layers.
Applying the empirical result factor of 93% to actual span data, and assuming a maximum practical span of a structure that is constructed with ribs 15 of the first configuration is about 33.5 meters (about 110 feet), this provides low and high estimates for the maximum predicted span of dual-layer and triple-layer structures, as shown in Table 3 below.
TABLE 3
A summary of calculated span lengths for the first, third and
fourth configuration of air beams.
Configuration Type
First Third Fourth
Configuration Configuration Configuration
Maximum Low 33.5 m (110′) 56.0 m (184′) 81.4 m (267′)
predicted span High 67.1 m (220′) 100.6 m (330′)
Example 2: Blast-Tube Testing A blast tube 200 is a type of shock tube, an example of which is shown in FIG. 5A. Briefly, the blast tube 200 comprises a driver section 202 in which an explosive event 204 is triggered. The pressure wave, which may also be referred to as a blast wave, shock wave or a blast pulse, generated by the explosive event 204 travels through a transition section 206 and into a driven section 208. The driven section 208 includes an upstream wall-mounted pressure sensor 210 and a front pressure-sensor 212. Adjacent the front pressure-sensor 212 is positioned a test sample 216 that may include a fly 218. Behind the test sample is a rear pressure-sensor 214. The pressure sensors 212, 214 were disc-type pressure sensors. During these experiments, the front pressure-sensor 212 was positioned about 0.5 meters (about 20 inches) away from the fly 218 and the rear pressure-sensor was positioned about 2.13 meters (about seven feet) from the front pressure-sensor 212. The pressure information captured by the pressure sensors was transmitted to a computer run software program for analysis and display.
FIG. 5B shows the configurations of air beams 14 that were tested in the blast tube 200 as test samples 216. All of the air beams 14 tested in the blast tube 200 had a diameter of about 0.6 meters. Test sample 216B includes two individual air beams 14 with a fly 218, a fly 218 and a gap 213 between the two air beams, this is a further example of the first configuration. The fly 218 may be made of polyvinyl chloride, polyester or a combination thereof. Test sample 216B1 is the same as test sample 216B except the fly 218 is made from an auxetic material, this is another example of the first configuration. In certain configurations where there is no gap 213 between laterally adjacent air beams 14, those laterally adjacent air beams 14 are configured to be in an abutting relationship or position. Test sample 216C includes three individual air beams 14 with a fly 218 and no gap 213 between the air beams 14. Test sample 216C is another example of the first configuration. Test sample 216D includes three air beams 14A that are positioned adjacent the fly 218 to form the first layer 10A and three air beams 14B that form the second layer 10B. The three air beams 14B are adjacent to and aligned centrally with the air beams 14A of the first layer 10A. Test sample 216E includes the first layer 10A of three air beams 14A, the second layer 10B of three air beams 14B and the intermediate layer 10C of three air beams 14C. All of the air beams 14 in test sample 216E are aligned centrally with adjacent air beams 14.
FIG. 6 through FIG. 13 show examples of overpressure data that was captured in the blast tube 200. FIG. 6 shows three lines of captured data from: the upstream pressure sensor 210, shown as line 210A; the front pressure sensor 212, shown as line 212A and the rear pressure sensor 214, shown as line 214A when there is no target sample present, which may be referred to herein as a reference shot. The reference shot allowed an examination of the characteristics of the blast pulse, and how the blast-pulse profile changes as the blast wave transits the length of the blast tube 200. Without a specimen in the test section, the incident pulse is undisturbed by target reflections.
Table 4 shows the characteristics of the reference shot.
TABLE 4
A summary of the reference shot characteristics.
Measurement Location PSO (Peak), psig
Upstream pressure sensor 6.81
Front pressure sensor 6.59
Rear pressure sensor 5.91
FIG. 7 shows the overpressure-data captured when the target sample 216B (first configuration with the gap 213) was present. Line 212B shows the pressure data captured from the front pressure sensor 212 and line 214B shows the pressure data captured from the rear pressure sensor 214. The line 214B shows and incident-peak pressure that represents the maximum value of blast overpressure (psig) associated with the initial shock wave caused by the explosive event 204. Subsequent pressure peaks are shown in line 214B that have higher values, but these are associated with reflections that occur when the blast wave encounters the target sample 216 (shown as reflection peaks in FIG. 7). While these pressure values are real and do act on the test sample, a more accurate assessment of the reduction of transmitted blast overpressure requires that the pressure wave transmitted through the structure be compared to the peak that would exist if the structure were not present. Therefore, in the present analysis the transmitted peak shown in line 214B was compared to the incident-peak pressure shown in line 212B, and not the reflected peaks. In FIG. 7, the transmitted pressure shown in line 214B was about 30.7% lower than the incident-peak pressure shown in line 212B. The transmitted pulse retained a shock front.
FIG. 8 shows the overpressure data captured when the target sample 216B1 (first configuration with the gap and an auxetic fly) was present in the blast tube 200. The transmitted pressure shown in line 214B1 was about 35.3% lower than the incident-peak pressure shown in line 212B1. The transmitted pressure retained a shock front.
FIG. 9 shows the overpressure data captured when the target sample 216C (first configuration with no gap) was present in the blast tube 200. The transmitted pressure shown in line 214C1 was about 67.2% lower than the incident-peak pressure shown in line 212C1. The incident pressure in this run was higher than for others (8.10 psig vs. approximately 6.0 psig). The transmitted pulse appears to have a short, finite rise time, but still retained a shock-like characteristic.
FIG. 10 shows the overpressure data captured from a second explosive event (shot) when the target sample 216C (first configuration with no gap) was present in the blast tube 200. The transmitted pressure shown in line 214C2 was about 46.8% lower than the incident-peak pressure shown in line 212C2. The transmitted pulse retained a shock front.
FIG. 11 shows the overpressure data captured when the target sample 216D (second configuration) was present in the blast tube 200. The transmitted pressure shown in line 214D1 was about 78.5% lower than the incident-peak pressure shown in line 212D1. The transmitted pulse did not have an associated shock front; the shock is completely absent in the transmitted pulse. The maximum transmitted pressure also did not occur in the first peak of the transmitted wave.
FIG. 12 shows the overpressure data captured when a second explosive event 204 occurred (second shot) and the target sample 216D (second configuration) was present in the blast tube 200. The transmitted pressure shown in line 214D was about 76.9% lower than the incident-peak pressure shown in line 212D. The transmitted pulse did not have an associated shock front. It was determined that the pressure spikes shown in line 212D at about t=11.0 milliseconds (indicated with * in FIG. 12) are anomalies and can be disregarded.
FIG. 13 shows the overpressure data captured when the target sample 216E was present in the blast tube 200. The transmitted pressure shown in line 214E was about 79.9% lower than the incident-peak pressure shown in line 212E. The transmitted pulse did not have an associated shock front.
FIG. 14 shows a comparison of the peak-incident pressure data and transmitted overpressure data captured when the various target samples 216 were present within the blast tube 200.
The first configuration 216B with the gap 213 between laterally adjacent air beams 14 reduces the overpressure transmitted through the target sample 216 by about 30-35%. This finding is highly representative of blast resistance at full structural scale. Approximately the same degree of overpressure reduction was detected in all of the applicant's previous free-field blast studies on single-layer inflated structures with a gap between laterally adjacent inflated air beams.
Without being bound by any particular theory, if the inflation pressure and tube diameter are kept constant, when the structure 10 has no gap between adjacent air beams, the structure 10 is stiffer and capable of carrying a greater load than a structure 10 with a gap. When the structure 10 has at least two layers 10A, 10B of air beams 14 with an equivalent tube-diameter and inflation pressure, the structure 10 will be stiffer and stronger than a structure 10 with only one layer of air beams 14. Furthermore, the configurations of air beams 14 that had at least two layers 10A, 10B fully defeated the transmission of a shock wave.
