Patent Application
20070151186
The invention relates to a method for the assembly of protective wall panels suitable for retrofitting an existing room to provide improved resistance to impact loads such as generated by severe storm events and explosive blasts.
Storm and blast shelters are necessary to provide a safe haven for civilian protection against severe storm events in regions prone to tornado or hurricane activity and military protection from explosive blast events. Protective wall and building designs are known in the art and take on various forms. Wall designs proposed for severe storm events are detailed in various reports developed for, or by, the Federal Emergency Management Agency (FEMA). Various wall designs for blast resistant shelters are detailed in patent art.
In Taking Shelter from the Storm (FEMA Publication 320) and Design and Construction Guidance for Community Shelters—(FEMA Publication 361) design for construction of walls and buildings to resist tornado generated wind loads and debris impact are described. Wind impact resistant walls of other designs are detailed in a report dated May 31, 2000 by Clemson University submitted to the Federal Emergency Management Agency entitled “Enhanced Protection for Severe Wind Storms. While these designs do not meet Tornado Impact criteria, they do provide enhanced protection from less severe storms.
U.S. Pat. No. 3,994,105, U.S. Pat. No. 4,143,501, U.S. Pat. No. 4,566,237, U.S. Pat. No. 4,691,483, U.S. Pat. No. 4,748,790 and U.S. Pat. No. 4,937,125 each detail some of the various forms for blast and bullet resistant walls and buildings.
Many of these engineered wall systems provide the capability to produce modular wall systems that are subsequently assembled in the field for use. When such modular approaches are used, a simple field joint that enables easy assembly provides for structural load transfer and yet provides impact resistance is desirable.
It is well known in the art that if some flexibility can be engineered in the direction of impact, that such flexibility will improve overall impact resistance. The various wall designs in the art that have such flexibility must be joined together in a manner that does not restrain the movement of these wall systems, especially near the point of attachment. This is most critical near joints where walls abut one another at corners or other non-planer joints where one wall can substantially restrain the movement of the other.
A substantial need exists for a method for the assembly of protective wall systems for wind and blast resistance within confined spaces. A particular need exists for a wall panel assembly suitable for retrofitting an existing room.
The present invention is directed to an assembly of wall panels particularly suitable for protection against wind blown debris or an explosive blast comprising;
In the present invention it is necessary to employ at least one wall panel capable of withstanding a force generated from a sudden impact such as wind blown debris of from an explosion. The types of wall panels are varied and can be formed from a metal such as steel, from wood or from a composite of several different materials. Although typically there will be wall damage due to an impact, the purpose of the wall is to maintain its integrity such as to protect a person within a room of a building. Although only one impact resistant wall panel can be employed to protect against an external force, it is desirable for greater protection to employ two adjacent wall panels to have impact resistance.
The protection from a wall panel will depend on its construction. The greater the ability to withstand force will in turn offer a greater protection. An example of a test procedure to determine impact resistance is ASTM procedure E 1886-97. Illustratively a 33 kilogram (15 pound) 2×4 lumber projectile is employed to impact a wall. The ability of the wall to withstand a projectile speed is a measure of determining its resistance. A desirable resistance is an at an impact speed of 161 kilometers (100 miles) an hour. Less resistance would be at failure at impact speeds above 80 or 90 miles an hour.
In similar fashion to determining resistance in accordance to ASTM procedure E 1886-97 test procedures to obtain a desired resistance to a force generated from an explosion can be used to determine the type of wall panel to be employed.
For windblown debris a suitable wall constructions are described in U.S. patent application Ser. No. 09/977,648 filed 15 Oct. 2001 and Ser. No. 10/308,492 filed 3 Dec. 2002 incorporated by reference herein. An example of a construction is a composite comprising in order:
A necessary portion of the construction of the wall assembly is the use of a strap to connect adjacent wall panels. As employed herein the term strap means a band or plate for holding an object in a fixed position. Although the strap may be of metal construction, such as steel or aluminum, other materials are suitable such as plastic or a composite of different materials.
The strap is rigidly connected to adjacent wall panels and holds the panels in place. To facilitate assembly connection of the strap to the wall panels in confined spaces, such as, when retrofitting an existing room, connectors can be premounted on the external face of the straps to allow for the strap to be connected to the panels from the opposite face of the panel. Suitable connectors is a blind threaded fasteners. A blind threaded fastener is any threaded sleeve, plate or nut, that is affixed to the backside (or blind side) of a bolted connection, to allow the torquing of the bolted joint, without a wrench or other holding tool on the backside. The threaded sleeve, plate or nut is attached to the backside, for example, by riveting, clinching, welding, brazing, or gluing of the threaded fastener itself, or by attachment of a retaining cage or housing which holds the threaded piece. These fasteners are commonly referred to as cage nuts, weld nuts, rivets nuts, aircraft nut fasteners or the like. Examples can be found in the patent art in such as U.S. Pat. No. 2,243,923, U.S. Pat. No. 2,443,752, U.S. Pat. No. 2,815,789, U.S. Pat. No. 2,971,425 and U.S. Pat. No. 3,695,324. Preferably, the connectors are blind threaded rivet nuts, weld nuts, or floating nut fasteners. More preferably the connectors are floating plate self-locking nuts or cage nuts. Most preferably the connectors are floating plate self-locking nuts as detailed in military specification sheet MS21059 Rev J. However, the strap is capable of flexing due to a force on a wall panel. It is directly understood that the amount of flex of the strap will be determined by its end use. Illustratively, a need for a greater resistance to an impact will determine a greater resistance to flex. Also the amount of stap flex will be determined by the number of straps connecting adjacent wall panel. The greater number of straps, the lesser is a need for resistance to flexing.
For purposes of illustration both single and double straps are suitable. An example of a suitable thickness for a metal strap is from 0.06 inches (1.5 mm) to 0.375 inches (9.5 mm) such as 0.075 inches (0.19 mm) to 0.150 inches (3.8 mm).
Although a strap may be employed on only an inner or outer wall portion, preferably individual straps are present to connect adjacent wall panels on inner and outer walls. As employed the term inner means portions of wall which face one another, such as walls that form the interior of a room. The term outer means portions of a wall which do not face one another, such as walls that form the exterion of a room. The strap or straps connect walls in a non-planer orientation, i.e. the walls are at an angle to one another. For purpose of illustration most walls are joined at an angle of 90 degrees. An example of two walls joining one another is an angle within a range from 30 to 120 degrees. Also generally there will be an air gap between adjacent wall since if the wall touch there may be an inability for the strap to flex properly upon a sudden impact. A typical air gap is considered to be at least 3 mm (0.125 inches). In a preferred construction a wall capable of withstanding a sudden impact is joined to two adjacent wall with straps on both on inner and outer wall surfaces connecting adjacent walls.
In the above disclosure the combination of a wall assembly with use of straps has been describe in relationship to resistance and protection of a sudden impact such as from wind blown debris and an explosion. However it is within the scope of the present invention that a wall assembly need not possess such resistance. Therefore, wall panels can be employed with such resistance to an excess sudden impact. In turn the staps would have the ability to flex under a minimum amount of force upon one of the wall panels.
In the Figures,
To further illustrate the present invention the following example is provided.
A shelter system shown in
The panels were assembled as shown in
The shelter was impacted in several locations with a 15-lb 2×4 (inches) timber projectile traveling at 100 mph, to access ability to meet the “Windborne Missile Impact Resistance on Shelter Wall and Ceiling” provisions of the National Performance Criteria for Tornado Shelters, First Addition, FEMA, May 28, 1999. Cannon set-up and firing was done in accordance with ASTM E 1886-97.
All projectiles fired at the shelter were stopped from passing through it, as required by the FEMA provisions, and the projectile was rebounded back. High speed photography taken during the event showed the joints to flex inwardly upon impact, helping to absorb a portion of the energy from the projectile. The plywood layer on the backside showed only very minor cracking around the impact point. The shelter assembly was deemed compliant with the provisions of the National Performance Criteria for Tornado Shelters.
