Patent Application
20200340244
This invention relates to a composite stud wall assembly.
More specifically, the invention relates to a stud wall assembly, which can be used as protection against blast, ballistic, forced entry, impact, weapons effects, fire and seismic loads. The assembly can be used alone as a blast panel or as a wall or roof panel for modular unit assemblies such as guard booths, trailers and other assemblies for resisting blast, ballistic and/or forced entry loadings.
In general, prefabricated blast or building panels are made of reinforced concrete, which is heavy and subject to fragmentation under extreme loads. An object of the present invention is to provide a stud wall panel assembly which is relatively lightweight and provides greater ballistic protection for a given thickness.
According to one aspect the invention relates to a composite stud wall assembly comprising a frame including a plurality of spaced apart metal studs and metal crossbars interconnecting said studs at locations proximate the ends and at least one location between said ends; and a cementitious aggregate panel, one side of the metal studs being embedded in and permanently connected to the panel along the length of the studs.
The invention is described in greater detail with reference to the accompanying drawings, which illustrate a preferred embodiment of the invention, and wherein:
With reference to the drawings, the composite stud wall assembly includes a frame indicated generally at 1. The frame 1 is defined by a plurality of spaced apart, vertical metal studs 2 partially embedded in a rectangular panel 3 of a composite material. The studs 2 are braced by horizontal metal crossbars 4 extending between the studs 2 and abutting the panel 3. The crossbars 4 can be embedded in the panel 3. The crossbars 4 are located at the centers and proximate the ends of the studs 2. Generally U-shaped metal straps 5 extend between the ends of the studs 2 and are connected thereto by bolts 6 and nuts (not shown). A 0/90°, 1.5×1.5 inch metal or fiber polymer composite mesh 7 reinforcement (
Preferably the studs 2 are steel C-beams, the crossbars 4 are steel C-beams, and the straps 5 are steel. However, other metals can be used for the studs 2, the crossbars 4 and the straps 5. The panel 3 is formed of rubber pieces with embedded fibers in a cementitious matrix. A preferred embodiment of the material comprises, in a dry state, 25% by weight blended cement, 15% by weight rubber pieces with embedded polymeric macro reinforcing fibers, 50% sand and 10% crushed stone (see Table 1, which also lists the ingredients used to produce the panel).
STRUX® BT-50 is a registered trademark for polymeric macro reinforcing fibers, which is included in panels with thicknesses of less than 6 inches. WRDA® PN is a registered trademark for an aqueous solution of polycarboxylate and carbohydrates, and DAREX AEA® is a registered trademark for an aqueous solution of a complex mixture of organic acids. Other reinforcing fibers, water reducers and air entraining agents can be used.
The ingredients can be present in the following percentages by dry weight: cement—20 to 30, rubber—10 to 20, sand—40 to 60 and stone—5 to 15.
The composition of panels used in blast and ballistic testing are listed in Tables 2 and 3.
An eight foot by four foot stud wall panel assembly described above was subjected to blast and ballistic testing. The blast test specimens consisted of four six inch deep vertical cold-formed steel studs 2 (C-beams) embedded in a three inch thick aggregate panel 3 having the composition listed in Table 1. The 0/90 degree, 1.5 inch by 1.5 inch carbon fiber mesh was placed in the panel 3 at mid-depth and tied to the vertical studs 2 using the ¼ inch shear studs 8 spaced twelve inches on center. The vertical studs 2 were braced with horizontal crossbars 4 in the form of 2.5 inch deep steel I-beams located at mid-panel height and approximately ten inches from the top and bottom of the frame. One quarter inch bent steel straps 5 were attached to the top and bottom ends of the studs 2 by two one-half inch diameter bolts 6 on each end and nuts (not shown). The assemblies were connected to steel framing. Ammonium nitrate/fuel oil, a widely used bulk explosive mixture was used as the explosive material to develop blast loads in each test.
Two composite stud wall panel assemblies were subjected to three non-simultaneous explosive shots of the same explosive weight (representative of a car bomb) at varying standoffs. The goal of the three shots was to provide composite panel response data at different blast loading conditions as a means of validating the newly developed blast mitigation composite panel system and to compare the system response to that of conventional wall construction materials utilized in the protective design industry.
In addition, a ballistic resistance testing evaluation of the precast panel assembly was conducted within an indoor range at Oregon Ballistic Laboratories in Salem, Oreg. for various thicknesses of the precast panel in accordance with UL 752 and NIJ-STD-0108.01 testing standards. The muzzle of the test barrel was mounted at selected distances from the target and positioned to produce 0-degree obliquity impacts.
US Army Corps of Engineers Protective Design Center Technical Report PDC-TR 06-08 (Revision 1 dated 7 Jan. 2008—APPROVED FOR PUBLIC RELEASE) describes damage levels and levels of protections (LOPs) that can be used to classify the responses for each test. Table 4 provides descriptions for each component damage level and the corresponding building LOP considering the component as a secondary (i.e., non-load bearing) structural element.
The results for three blast test, 1-3 using the same quantity of ammonium nitrate/fuel oil (ANFO) representative of a car bomb, at standoffs varying between 40 feet (12.2 m) and 100 feet (30.5 m) are summarized in Table 5.
The ballistic resistance testing evaluation was conducted within an indoor range at the Oregon Ballistic Laboratories for various thicknesses of the precast panel in accordance with UL 752 and NIJ-STD-0108.01 testing standards. The muzzle of the test barrel was mounted at selected distances from the target and positioned to product 0-degree obliquity impacts.
All panel assemblies tested for both ballistic testing standard had overall dimensions of 3 feet (910 mm) wide by 3 feet (910 mm) tall with thickness ranging from 3 inches (76 mm) to 10 inches (254 mm). The two panel composition listed in Tables 2 and 3. For panels with thicknesses less than 6 inches (152 mm), a synthetic macro fiber reinforcement labeled as STRUX BT50® was utilized in the design of the panel assemblies. For panels with thicknesses of 6 inches (152 mm) or greater, carbon-fibre reinforced polymer (C-FRP) rebars labeled as C-BAR® were utilized instead.
Tables 6 and 7 summarize the performance ballistic ratings for the ProtectiFlex precast systems evaluated. Based on the ballistic testing results, a 3-inch (76 mm) thick ProtectiFlex precast panel (as used for the blast-tested composite stud wall system) is rated as UL 752 Level 2 and NIJ-STD-0108.01 Level II.
Unified Facilities Criteria (UFC) 4-023-7 (dated 7 Jul. 2008 with Change 1 from 1 Feb. 2017—APPROVED FOR PUBLIC RELEASE) provides design guidance to resist direct fire weapons effects. A UL 752 Level 5 rating can be satisfied with approximately 4 inches (102 mm) of reinforced concrete or 8 inches (203 mm) of fully grouted CMU or brick.
As described above, the stud wall panel assembly of the present invention responded with a High Level of Protection (HLOP) at a standoff of 100 feet (30.5 m), a Medium Level of Protection (MLOP) at a standoff of 60 feet (18.3 m), and Low Level of Protection (LLOP) at a standoff of 40 feet (12.2 m) for the same car bomb-sized explosive charge. As a basis of comparison, UFC 4-010-01 presents conventional construction standoff distances (CCSDs) for various common construction types that would be capable of achieving an LLOP for a similarly sized explosive threat (W I). Representative CCSDs for no-load bearing walls are provided in Table 5.
It can be observed that the standoff required to achieve an LLOP for the stud wall panel assembly of the present invention is similar to that of reinforced concrete (26 feet/8 m) and reinforced masonry (30 feet/9 m), noting that the 40-ft (12.2 m) tested standoff is not necessarily an upper limit for LLOP panel response).
With reference to Table 8 below, comparing the minimum wall weights in Table 8 to the 34 psf (160 kg/m2) for the tested panel, the stud wall assembly provides a 60% weight reduction compared to reinforced concrete (based on a 6-inch/150 mm thick wall with 10-psf/50-kg/m2 insulating materials) and a 40% weight reduction compared to reinforced masonry (based on an 8-inch/200-mm thick wall grouted every fourth cell with 10-psf/50-kg/m2 insulating materials). Excluding the insulating materials, these weight reductions are 55% and 28%, respectively. This significant weight reduction for the stud wall assembly can be advantageous in construction to meet non-blast design requirements. In any case, the tested performance of the study wall assembly is a significant improvement over conventional unreinforced masonry or metal stud construction, which would require a standoff of well over 100 feet (30.5 m) to achieve an LLOP. Therefore, the testing stud wall assembly can be considered to be a viable construction option for blast design applications.
