Patent Application
20050262998
1. Field of the Invention
This invention is directed to a protective structure and to a protective system for protecting buildings, streets, and other areas from explosions caused by an explosive device such as a bomb. More particularly, the protective structure and protective system employ a membrane-like mesh structure made up of, for example, steel wire. The mesh structure surrounds a concrete fill material such as reinforced concrete. The protective structure deflects in response to and absorbs the energy associated with the blast load of an explosion, and the mesh structure prevents concrete fragments from injuring people or property in the vicinity of the explosion. The protective structure is sacrificial in nature: i.e. its sole purpose is to absorb the energy from the explosive shock wave and contain concrete debris caused by the explosion. Accordingly, this results in reduction in personal injury and property damage due to the explosion.
2. Background Information
Protection of people, buildings, bridges etc. from attacks by car or truck bombs, remote controlled explosives, etc. is of increasing importance and necessity. The explosive force or pressure wave generated by an explosive device such as a car bomb may be sufficient (depending on the size of the explosive device used) to disintegrate a concrete wall, thereby causing shrapnel-like pieces of concrete to be launched in all directions, and causing additional personal injury and property damage.
Conventional reinforced concrete structures such as reinforced concrete walls are well known to those skilled in the art. Such conventional structures typically employ steel reinforcement bars embedded within the concrete structure or wall. However, in the case of an explosion or blast load which may generate a pressure wave in excess of tens of thousands of psi, a conventional reinforced concrete structure will be ineffective in providing sufficient protection, and the blast load will cause disintegration of the concrete, thereby causing shrapnel-like pieces of concrete to be launched in all directions, and causing additional personal injury and property damage.
One example of a proposed solution for this problem is the Adler Blast Wall™ which is described, for example, at www.rsaprotectivetechnologies.com. The Adler Blast Wall™ is made up of front and back face plates which contain a reinforced concrete fill material. According to the developers of the Adler Blast Wall™, if an explosion occurs proximate to the front face plate, the back face plate will catch any concrete debris which results from the explosion. However, if the back face plate of the Adler Blast Wall™ is sufficiently displaced in the horizontal or vertical direction due to the explosion, small pieces of concrete debris traveling at high velocities may escape, thereby causing personal injury or property damage. Accordingly, there is a need for a protective structure which further minimizes the possibility that such small pieces of concrete debris traveling at high velocities will escape the protective structure employed.
It is a first object of this invention to provide a protective structure which minimizes the possibility that small pieces of concrete debris traveling at high velocities will escape the protective structure in the event of an explosion or blast load proximate to the structure.
It is one feature of the protective structure of this invention that it employs a membrane-like mesh structure made up of, for example, steel wire. The mesh structure is compressible in all three dimensions, and surrounds a concrete fill material such as reinforced concrete. In the event of an explosion proximate to the protective structure of this invention, the mesh structure advantageously prevents concrete fragments produced due to disintegration of the concrete fill material of the protective structure from injuring people or property in the vicinity of the explosion.
It is another feature of the protective structure of this invention that, in the event of an explosion proximate to the protective structure of this invention, the protective structure deflects in response to and absorbs the energy associated with the blast load of the explosion.
It is a second object of this invention to provide a protective system which employs a number of the above described protective structures which are joined together via a number of support members, thereby providing a protective wall of sufficient length to provide more complete protection of a given area as well as additional ease of construction and use.
It is a feature of the protective system of the invention that the support members be capable of receiving the respective ends of the protective structures to provide an integrated wall structure.
It is another feature of the protective system of the invention that the support members may also employ a mesh structure made up of, for example, steel wire. The mesh structure may surround a concrete fill material such as reinforced concrete. Thus, in the event of an explosion proximate to the protective system of this invention, the mesh structure prevents concrete fragments produced due to disintegration of the concrete fill material of the support members from injuring people or property in the vicinity of the explosion.
Other objects, features and advantages of the protective structure and protective system of this invention will be apparent to those skilled in the art in view of the detailed description of the invention set forth herein.
A protective structure such as a protective wall for protecting buildings, bridges, roads and other areas from explosive devices such as car bombs and the like comprises:
A protective system such as a protective wall for protecting buildings, bridges, roads and other areas from explosive devices such as car bombs and the like comprises:
This invention will be further understood in view of the following detailed description. Referring now to
It has previously been suggested, for example, in Conrath et al., Structural Design for Physical Security, p. 4-46 (American Society of Civil Engineers-Structural Engineering Institute 1999) (ISBN 0-7844-0457-7), that wire mesh may be employed on or just beneath the front and rear surfaces of structural elements to mitigate “scabbing” (i.e. cratering of the front face due to the blast load) and “spalling” (i.e. separation of particles of structural element from the rear face at appropriate particle velocities) for light to moderate blast loads. However, in the protective structure of the present invention, the wire mesh structure employed does not merely mitigate scabbing and spalling for light to moderate blast loads. Instead, the wire mesh structure both prevents spalling at all blast loads (including high blast loads which generate a pressure wave in excess of tens of thousands of psi)), and also enables the protective structure to deflect both elastically and inelastically in response to the blast load, as further discussed herein with respect to
The embedded depth for the support member portions 315a and 325a in the ground will be determined according to the subsurface soil conditions, as will be recognized by those skilled in the art. For example, in one preferred embodiment, the embedded length of the support member portions in the soil will be a minimum of about one-third of the total length of each support member.
In another preferred embodiment, the support members comprise a mesh structure. The mesh structure of the support members may preferably comprise a plurality of interconnected steel wires. Such steel wires will be selected based upon the assumed maximum blast load, the length of the protective structure, the grade strength of the steel employed in the mesh, and other factors. For example, steel wires having a thickness of 8 gage, 10 gage, 12 gage, or 16 gage may be employed. The mesh structure, if employed, preferably comprises a plurality of mesh unit cells having a width in the range of about 0.75 to 1.75 inches, and a length in the range of about 0.75 to 1.75 inches, although the opending size of the mesh structure may be optimally designed depending upon the properties of the concrete fill material. The mesh structure, if employed, preferably surrounds a concrete fill material such as reinforced concrete. The concrete fill material preferably protrudes through the mesh structure on all sides to provide a concrete face material for the support member.
While not wishing to be limited to any one theory, it is theorized that the deflection of the protective structure of this invention in response to a blast load may be analogized or modeled as wires in tension. Upon explosion of the explosive device and delivery of the blast load to the protective structure, the steel wires of the mesh structure absorb the energy of the blast load. Employing this model, the membrane stiffness of the mesh wire (K) is defined as:
K=Pe/De
where Pe is the load corresponding to the elastic limit of the wire mesh structure and De is the deflection corresponding to Pe, and the time period of oscillation of the wire mesh structure (T) (in milliseconds) is defined as:
T=1000/ω
where ω is the frequency of oscillation in cycles per second (cps), which is defined as
ω=(½Π)(K/m)1/2
where m is the mass per foot-width of the mesh structure.
Using the above equations, various design parameters such as the wire gage, size of the mesh unit cell opening, steel grade, etc. may be selected for various blast loads, as set forth in Table 1 below:
where:
ΣA is the sum of the area of the wires per 1 foot-width of mesh structure
Ru is the ultimate load capacity of the wire mesh per foot
Fy is the yield stress of the wire
Lm is the span of the wire mesh structure
As set forth in Table 1, the time period T is a critical design parameter which may be designed for in the protective structure of this invention. For a given explosion or blast load, it is expected that the time duration of the blast load (td) will be in the order of a few milliseconds, say 5-10 milliseconds. The mesh structure employed in the protective structure of this invention will be designed such that it will have a time period T much greater than td; typically T is of the order of 5-20 times greater in duration than td.
It should be understood that various changes and modifications to the preferred embodiments herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of this invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
