BLAST-RESISTANT REINFORCED CEMENTITIOUS PANELS AND REINFORCING STRUCTURES FOR USE THEREIN
Blast-resistant reinforced cementitious panels are disclosed. The panels include reinforcing structures including wire grid assemblies and connecting wires. The reinforcing structures may be pre-formed prior to the addition of the cementitious material to the reinforcing structure.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/722,504 filed Nov. 5, 2012, which is incorporated herein by reference.
FIELD OF THE INVENTIONThe present invention relates to blast-resistant reinforced cementitious panels, and more particularly relates to concrete and other types of cementitious materials containing reinforcement structures that provide improved blast performance.
BACKGROUND INFORMATIONVarious attempts have been made to reinforce concrete building panels in order to withstand explosive forces. However, a need exists for panels having greater blast resistance, particularly when the blasts are of relatively long duration, for example, as experienced during petrochemical explosions.
SUMMARY OF THE INVENTIONThe present invention provides reinforcing structures for concrete and other cementitious material panels that provide improved blast performance. The reinforcing structures may be pre-formed prior to the addition of the cementitious material to the reinforcing structure. The blast-resistant cementitious panels may be pre-cast, cast-in-place or tilt-up panels.
An aspect of the present invention is to provide a reinforcing structure for a blast-resistant cementitious panel comprising a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid, a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid, and a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
Another aspect of the present invention is to provide a reinforced blast-resistant cementitious panel comprising a cementitious material, and a reinforcing structure in the cementitious material. The reinforcing structure comprises a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid, a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid, and a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
A further aspect of the present invention is to provide a method of making a reinforced blast-resistant cementitious panel comprising introducing a flowable cementitious material to a pre-formed reinforcing structure and allowing the cementitious material to cure, wherein the reinforcing structure comprises a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid, a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid, and a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
These and other aspects of the present invention will be more apparent from the following description.
The first wire grid assembly 21 includes an exterior wire grid 22 and an interior wire grid 23. The exterior and interior wire grids 22 and 23 are located relatively close to each other, and lie in planes that are substantially parallel with each other.
As shown in
As further shown in
In certain embodiments, the connecting wires 30 are attached to the various wire grids by welding. For example, the connecting wires 30, exterior and interior wires 22 and 23 of the first wire grid assembly 21, and exterior and interior wires 26 and 27 of the second wire grid assembly 25 may be made of steel that is electro-welded at some or all of the points of contact between the various wires.
As shown in
In accordance with embodiments of the present invention, the configurations, sizes and spacings of the various components of the reinforcing structure 20 are selected in order to produce desirable blast-resistance performance when the reinforcing structure 20 is used in a cementitious panel. In certain embodiments, the wires of the first and second wire grid assemblies 21 and 25 may have typical diameters of from 1 to 7 mm, for example, from 1.5 to 6 mm, or from 2 to 5 mm. In certain embodiments, the connecting wires 30 may have typical diameters of from 1 to 7 mm, for example, from 1.5 to 6 mm, or from 2 to 5 mm. In certain embodiments, the reinforcing rods 42 and 44 may have typical diameters of from 8 to 40 mm, for example, from 10 to 30 mm, or from 12.5 to 25 mm.
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The reinforced blast-resistant cementitious panels of the present invention may be provided in any desired heights and widths. In certain embodiments, the panels may have heights of from 1.5 to 10 m, for example, from 8 to 10 m, or from 2.5 to 7 m. In certain embodiments, the panels may have widths of from 1 to 5 m, for example, from 1.2 to 4 m, or from 1.4 to 3 m. While reinforced panels having substantially flat external surfaces are primarily described herein, it is to be understood that the reinforced panels of the present invention may include other shapes such as rounded or bent surfaces.
As shown in
Although only two wire grid assemblies 21 and 25 are shown in the embodiments of
In accordance with embodiments of the present invention, the cementitious material 12, 112 and 114 may comprise any known type of cementitious material such as Portland cement, pozzolanic cement, coal fly ash, ground granulated blast furnace slag, and the like. The cementitious material may comprise concrete, mortar, and other known types of materials. In certain embodiments, the cementitious material may include sand, stone, aggregate and other materials that are conventionally added to cement.
In certain embodiments, the cementitious material may be reinforced with fibrous materials. For example, the reinforcing fibers may include carbon fibers, aramid fibers, polymeric fibers, nylon fibers, polypropylene fibers, kevlar fibers, basalt fibers or any other known type of fibrous material. In certain embodiments, the fiber reinforcements are discontinuous and may have typical lengths of 1.25 to 15 cm, or from 2 to 10 cm. Alternatively, continuous fiber reinforcement materials may be used in place of, or in addition to, discontinuous fiber reinforcements. For example, continuous fibers may be provided in the form of woven fiber applied to the various components of the reinforcing structure 20, e.g., the continuous fibers may be wound around, or woven between, the various wires and/or reinforcing rods of the reinforcing structure 20. The amount of fiber reinforcements contained in the cementitious material may be varied as desired. For example, when discontinuous fibers are used, they may be present in an amount of from 0.05 to 2.5 weight percent, or from 0.1 to 2 weight percent, based on the total weight of the cementitious material. In certain embodiments, effective amounts of discontinuous fiber reinforcements may be less than 2 weight percent, or less than 1 weight percent, while providing sufficient blast-resistance properties.
In accordance with embodiments of the present invention, the reinforced panels have desirable compressive strengths for improved blast-resistance. For example, the reinforced panels may have compressive strengths of greater than 5,000 psi, for example, greater than 10,000 or 12,000 psi. In certain embodiments, the reinforced panels may have compressive strengths ranging from greater than 15,000 psi up to 20,000 psi, 24,000 psi, or higher.
The following examples are intended to illustrate various aspects of the invention, and are not intended to limit the scope of the invention. Two different types of foam core panels were tested with varying reinforcement ratios and panel thicknesses, and compared against the performance of a solid pre-cast concrete panel under similar test conditions. Experimental and analytical findings of the tests conducted on these panels are described below.
EXAMPLESThree panel types were assessed as follows:
1. PSM HP 80: 8-inch thick Single Polystyrene High Performance structural wall panel consisting of a 4-inch thick EPS foam core straddled with 2-inch thick concrete on each face. Both concrete layers were reinforced with two layers of electro-welded 3 mm wire mesh having an approximate spacing of 2.8 inches.
2. PSM HP 160—RB#5: 11⅜-inch thick Single Polystyrene High Performance structural wall panel consisting of a 6-inch thick EPS foam core straddled with 2.5-inch thick concrete on each face. Each concrete layer was reinforced with the same two layers of electro-welded 3 mm wire mesh and #5 longitudinal reinforcing bars spaced 5 inches on center placed between the wire mesh reinforcement.
3. PC HP 80—RB#5: 6-inch thick Precast High Performance structural wall panel with electro-welded 3 mm wire mesh with an approximate spacing of 2.8 inches. #5 longitudinal rebar was placed between the wire mesh at 6 inches on center, which is slightly more than the 5-inch spacing for the PSM HP 160 panels. The concrete in this panel was reinforced with two different types of short and long synthetic fibers.
Table 1 summarizes the panel dimensions and properties used for the structural analysis.
Dynamic testing of the prepared panel test specimens was conducted at a shock tube facility. The shock tube is a compressed air-driven test apparatus that consists of two major sections, a driver section and an expansion section. Blast pressures are generated when an aluminum rupture disk placed between the two sections fails, due to pressure in the driver section. A shock wave then travels down the expansion section and loads the test specimen at the end of the expansion section. The driver was baffled to reduce the effects of reloading by the reflections that exist in the shock tube.
Each flat wall panel was mounted into a reaction structure that provided simple supports to the panel while allowing for reaction load measurement at the bottom support. In the test specimen installation, the specimen spans vertically 8 feet. Load cells are used to measure support reactions at the bottom of the specimen. The load cells provide the only lateral restraint of the bottom channel that supports the panel.
The test load was measured using a total of three dynamic pressure transducers located on each side wall and the floor of the shock tube adjacent to the target end of the shock tube. The load reported for each test is the average of the three gauges and represents the load applied to the wall specimen. Two quartz force ring dynamic load cells were used to measure panel end reactions. Initially, the dynamic mid-span displacements were monitored using a laser distance meter positioned at mid-span and offset from the panel. However, due to damage sustained to the gauge during the initial tests as a result of significant deflections, accelerometers were subsequently used and mounted to the panel at mid-span to capture the panel acceleration, which was differentiated to obtain the mid-span displacement. High speed video was focused on a mid-span scale background to confirm the active measured panel displacement data.
Pre-test analytical models were derived for each panel type based on single-degree-of-freedom (SDOF) methodology in order to predict the flexural response of each panel prior to testing. Initial estimates of the first test load were selected to obtain a low to moderate damage response. After each test was conducted, the experimental response was compared to the predicted response and the model was then adjusted to represent the observed response. The revised model was then used to determine the magnitude of blast loads for subsequent tests with increasing levels of damage. The objective of this process was to obtain experimental results for varying pressure and impulse combinations in order to define acceptable response limits with respect to peak applied pressure and impulse.
Table 2 presents a summary of the test program providing the panel type, specimen number, peak pressure, impulse, and test duration for each test. The resulting panel response is reported using: (i) Δpeak=peak mid-span displacement with corresponding time of occurrence; (ii) Rpeak=peak support reaction with corresponding time of occurrence; (iii) Support=support rotation based of peak displacement; and (iv) response of panel in accordance with ASCE damage response criteria based on measured deflection. The observed damage was qualitatively less than what was designated by ASCE response criteria. For example, Test 3 for the PSM HP 80 Panel II, would be characterized as failure whereas the panel achieved a maximum deflection and survived the applied blast loading without failure.
Three tests were conducted on two PSM HP80 panel specimens ranging from 3.9 psi to 5.1 psi with impulses of 160 psi-ms to 210 psi-ms, respectively. All tests exhibited a typical flexural response with horizontal cracks evenly distributed along the height of the non-loaded tension face as shown in
Five tests were conducted on four PSM HP160—RB#5 panel specimens ranging from 4.2 psi to 21.9 psi with impulses of 222 psi-ms to 445 psi-ms, respectively. All tests primarily responded in flexural with the formation of single hinge at mid-span, coupled with concrete spalling on the compression face as shown in
Test 16 applied a blast load similar to Test 3 (PSM HP80) in order to obtain a direct correlation between the two panel types. The panel responded elastically to the blast load with a peak deflection of 0.36 inches and had no residual surface cracking, thus exhibiting a significant increase in blast resistance in comparison to the PSM HP80 panels. Test 17 was a retest of Specimen I with in increased blast load of 10.7 psi resulting in a peak deflection of 2.8 inches as shown in
Tests 18 and 19 subjected new test panels to peak applied blast pressures of 15.3 psi and 21.9 psi, respectively, and both resulted in heavy damage approaching incipient failure. In addition to the primary flexural hinge formed at mid-span, each panel also sustained significant shear failure at their supports causing the panels to unseat from the supports as shown in
Four tests were conducted on two PC HP80—-RB#5 panel specimens ranging from 5.2 psi to 23.6 psi with impulses of 224 psi-ms to 496 psi-ms, respectively. All tests exhibited a typical flexural response with horizontal cracks evenly distributed along the height of the non-loaded face as shown in
The structural performance of the PSM HP foam core panels is largely dependent on the interaction between the two concrete layers and the corresponding level of composite behavior.
The actual response of these panels will be a partially composite response that is a function of the ratio between the shear flow and flexural capacities; where the shear flow capacity is provided by the wire dowels and foam core connecting the concrete layers, and the flexural bending capacity is provided by the longitudinal reinforcement. A simplified modeling approach was initially adopted for the analytical modeling of these panels using a Single-Degree-of-Freedom (SDOF) model to evaluate the nonlinear dynamic response of each panel when subjected to the averaged blast pressure-time history from each test. The following section describes the SDOF model used for each panel, and compares the SDOF model results to the experimental results. A summary of the peak displacements (Δpeak) and peak reactions (Rpeak) for the experimental and SDOF analytical results are provided in Table 3.
PSM HP 80 Panel: The flexural capacity is provided by the longitudinal mesh only and was relatively balanced with the shear flow capacity provided by the wire dowel connectors and foam core. Therefore, the blast capacity was better captured by the full-composite model; however, because the wire dowel connectors are embedded in the foam, the stiffness was better captured using the non-composite model. The SDOF model results were within 16% agreement with the experimental results, which was reasonable considering the level of complexity involved with modeling these panels.
PSM HP 160—RB#5: In comparison to the PSM HP 80 Panels, the flexural capacity of the PSM HP 160 Panels is significantly increased with the inclusion of the #5 rebar; however, the shear flow resistance provided by the wire dowel connectors remained unchanged. Post-experimental analysis concluded that the blast capacity of the panel was on the order of halfway between the full- and non-composite model due to the fractional amount of shear flow transferred by the dowel wires and foam core. This approximation resulted in comparisons within 43% of the experimental results regarding the measured reactions; however, the observed displacements had a much greater deviation. The deflections measured for Tests 18 and 19 are not representative of the flexural response anticipated, due to the shear failure sustained at the panel supports.
PC HP 80—RB#5: The SDOF model for this panel was derived using a moment-curvature relationship of the doubly reinforced concrete section, assuming standard flexural theory. Standard concrete constitutive material models were assumed for this model as no material test data was available for the fiber reinforced concrete used in the construction of these panels. When compared to the experimental results, the analytical model consistently over predicted the deflections up to 13%, and under predicted the reactions no more than 38%. One possible explanation for these differences may be due to the additional stiffness provided by the concrete fibers under high strain-rate effects.
In order to further investigate the level of composite interaction between the two layers of reinforced concrete outer layers in the PSM HP 80 and PSM HP 160—RB#5 panels, DYNA-3D Finite Element Models (FEM) were developed for these two panel types. Hexahedral (solid brick) elements were used to represent the concrete and foam core, while structural beam elements were used to model the reinforcing steel. Strength Increase Factor (SIF) and Dynamic Increase Factor (DIF) were applied to all material strengths per guidelines in the Unified Facilities Criteria (UFC). Concrete element size was generally 0.50×0.50×0.40 inch in the PSM HP 160—RB#5 model, and 0.50×0.50×0.30 inch in the PSM HP 80 model. The reinforcing steel beam elements shared nodes with the concrete and foam mesh (i.e., no provision for bond-slip between rebar and concrete). Physical properties for the foam were not available, so typical properties were assumed. A contact surface was applied over the top and bottom 2 inches of the panels providing a free span of 96 inches between simple supports. The panels were not allowed to develop vertical in-plane deflection resistance at the supports such that no arching or membrane behavior could occur.
The concrete was modeled using the Applied Engineering Cap Model with Three Invariants (AEC-31, implemented into DYNA-3D). The AEC-3I models material plasticity with a unified shear yield and cap surface that can harden from an initial yield position to ultimate strength and then soften to residual surfaces under continued loading. Decohesion algorithms model the formation of crack planes with defined orientation and controlled growth based on material fracture energy, which is specified as a user input. Crack growth is represented with decohesion strain components resulting in anisotropic material behavior. Orientation of crack plane initiation is based on principal-stress Rankine criteria that are characteristic of brittle-fracture materials.
Comparisons of the peak displacements (Δpeak) and peak reactions (Rpeak) for the experimental and DYNA-3D FEM results are provided in Table 4. The peak deflections represent complicated interactions of concrete damage (cracking and compressive shear), foam crushing, and flexural/buckling behavior of the through-thickness shear steel. An example of the resulting crack pattern at the moment of peak deformation from Test 17 is shown in
The test program provided test data showing reasonable blast capacity of the reinforced foam core panels when compared to the tested solid core panels, although significantly less blast damage was observed for the solid panels under similar blast loading. For example, the PSM HP 80 Panel II (Test 3) showed moderate to heavy damage when subjected to 5.1 psi/210 psi-ms compared to the PC HP 80—RB#5, Panel I (Test 7) that showed light damage when subjected to 5.2 psi/224 psi-ms. Note that the PSM HP 80 panel had much less flexural reinforcement and was a third lighter compared to the PC HP 80—RB#5 panel. Another example was the PSM HP 160—RB#5 Panel III (Test 19) that showed heavy damage when subjected to 21.9 psi/445 psi-ms and the PC HP 80—RB#5 Panel V (Test)) that show moderate damage when subjected to 23.6 psi/496 psi-ms. Although both panels had similar reinforcement, the PSM HP 160—RB#5 panel was almost 20 lighter than the PC HP 80—RB#5 panel.
Both SDOF and FEA models of the panel responses produced reasonable comparisons with the test results, with the FEA models showing better agreement. These models were able to capture the failure mechanisms associated with the foam core panels with respect to diagonal shear of the concrete layers as well as the in-plane shear capacity at the foam-concrete surface. These models can be reasonably be used to better define the response limits of specific foam-core designs ranging in concrete and foam thickness, and reinforcement combinations.
The reinforced cementitious panels of the present invention provide several advantages. Lighter inexpensive cladding building systems can be implemented into building blast hardened construction. A cost-effective reinforced concrete foam core panel may take advantage of increased section depth with minimal effect on panel weight. The reinforced panels may use high-strength concrete specifically designed for in-situ applications either before or after installation of the panel units, and the connecting wires provide shear reinforcement. The present system may improve constructability for applications where access is difficult, as well as providing enhanced thermal characteristics.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
Claims
1. A reinforcing structure for a blast-resistant cementitious panel comprising:
- a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid;
- a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid; and
- a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
2. The reinforcing structure of claim 1, wherein the first wire grid assembly is substantially planar, the second wire grid assembly is substantially planar, and the planes of the first and second wire grid assemblies are substantially parallel with each other.
3. The reinforcing structure of claim 2, wherein the second wire grid assembly further comprises an interior wire grid, and each of the plurality of connecting wires is attached to the exterior and interior wire grids of the first wire grid assembly and the exterior and interior wire grids of the second wire grid assembly by welding.
4. The reinforcing structure of claim 3, wherein the plurality of connecting wires are substantially perpendicular to the planes of the first and second wire grid assemblies.
5. The reinforcing structure of claim 3, further comprising a first plurality of reinforcing rods located between the exterior and interior wire grids of the first wire grid assembly.
6. The reinforcing structure of claim 5, further comprising a second plurality of reinforcing rods located between the exterior and interior wire grids of the second wire grid assembly.
7. The reinforcing structure of claim 6, wherein the exterior and interior grids of the first and second wire grid assemblies comprise wires having diameters of from 1 to 7 mm, the plurality of connecting wires have diameters of from 1 to 7 mm, and the first and second pluralities of reinforcing rods have diameters of from 8 to 40 mm.
8. The reinforcing structure of claim 6, wherein the first and second wire grid assemblies are spaced apart from 1 to 20 mm.
9. The reinforcing structure of claim 6, wherein the exterior and interior wire grids of the first wire grid assembly are spaced apart substantially the same distance as a diameter of the first plurality of reinforcing rods located therebetween, and the exterior and interior grids of the second wire grid assembly are spaced apart substantially the same distance as a diameter of the second plurality of reinforcing rods located therebetween.
10. The reinforcing structure of claim 6, wherein the first and second pluralities of reinforcing rods are held in position by frictional engagement with the wire grids.
11. The reinforcing structure of claim 6, wherein the first and second pluralities of reinforcing rods are attached to the wire grids by welding and/or mechanical fasteners.
12. The reinforcing structure of claim 6, wherein the exterior and interior wire grids of the first wire grid assembly are spaced apart from 8 to 40 mm, and the exterior and interior wire grids of the second wire grid assembly are spaced apart from 8 to 40 mm.
13. The reinforcing structure of claim 6, wherein the exterior and interior wire grids of the first and second wire grid assemblies comprise perpendicular wires forming substantially rectangular openings with heights of from 20 to 200 mm and widths of from 20 to 200 mm.
14. The reinforcing structure of claim 6, wherein the first and second pluralities of reinforcing bars are substantially parallel with each other.
15. The reinforcing structure of claim 6, wherein the structure has an overall thickness of from 6.5 to 30 cm, a height of from 1.5 to 10 m, and a width of from 1 to 5 m.
16. The reinforcing structure of claim 6, wherein the first and second wire grid assemblies, the plurality of connecting wires, and the first and second pluralities of reinforcing rods comprise steel.
17. The reinforcing structure of claim 1, further comprising a third wire grid assembly between the first and second wire grid assemblies.
18. The reinforcing structure of claim 1, further comprising a layer of foam between the first wire grid assembly and the second wire grid assembly.
19. The reinforcing structure of claim 1, wherein the reinforcing structure is pre-formed prior to addition of a cementitious material to the structure.
20. A reinforced blast-resistant cementitious panel comprising:
- a cementitious material; and
- a reinforcing structure in the cementitious material, wherein the reinforcing structure comprises: a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid; a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid; and a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
21. The reinforced cementitious panel of claim 20, wherein the first wire grid assembly is embedded in the cementitious material a distance of from 0.25 to 7.5 cm from a first planar surface of the panel, and the second wire grid assembly is embedded in the cementitious material a distance of from 0.25 to 7.5 cm from a second planar surface of the panel opposite from the first planar surface of the panel.
22. The reinforced cementitious panel of claim 20, wherein the cementitious material comprises Portland cement, pozzolanic cement, coal fly ash and/or ground granulated blast furnace slag.
23. The reinforced cementitious panel of claim 20, wherein the cementitious material comprises concrete.
24. The reinforced cementitious panel of claim 20, wherein the cementitious material includes reinforcing fibers dispersed therein comprising carbon fibers, aramid fibers, polymeric fibers, nylon fibers, polypropylene fibers, kevlar fibers and/or basalt fibers.
25. The reinforced cementitious panel of claim 24, wherein the reinforcing fibers comprise nylon.
26. The reinforced cementitious panel of claim 24, wherein the reinforcing fibers have lengths of from 1.25 to 15 cm and are present in the cementitious material in an amount of from 0.05 to 2.5 weight percent based on the total weight of the cementitious material.
27. The reinforced cementitious panel of claim 20, wherein the reinforced panel has a compressive strength of greater than 10,000 psi.
28. The reinforced cementitious panel of claim 20, further comprising a layer of foam embedded in the cementitious material between the first wire grid assembly and the second wire grid assembly.
29. A method of making a reinforced blast-resistant cementitious panel comprising introducing a flowable cementitious material to a pre-formed reinforcing structure and allowing the cementitious material to cure, wherein the reinforcing structure comprises:
- a first wire grid assembly comprising an exterior wire grid and an interior wire grid spaced from the exterior wire grid;
- a second wire grid assembly spaced from the first wire grid assembly comprising at least an exterior wire grid; and
- a plurality of connecting wires attached to the wire grids of the first and second wire grid assemblies.
Type: Application
Filed: Nov 5, 2013
Publication Date: May 22, 2014
Inventor: Michael A. Riley (Towson, MD)
Application Number: 14/072,497
International Classification: F41H 5/04 (20060101); F41H 5/02 (20060101);