Patent Application
20110226166
The invention relates to a protective structure, and in particular to a protective structure built to protect another structure or personnel from harm caused by blasts resulting from explosive shells, rockets, and the like.
Terrorism, war, and other hostile situations are regrettably common around the world. The nature of the threat level often changes, making it difficult to have the proper type of protective structures in place at all locations. For example, military facilities in some locations are built with a relatively low level of hardening because the threat level in the area was not particularly high when the facilities were constructed, or for other reasons. In some instances, facilities originally built by one government or force are taken over by another, and the facilities may not have sufficient protection given the new threat levels faced.
When this happens, the government or other entity operating the facilities must make difficult decisions. It can withdraw key forces from the location to reduce their exposure to threat. That, however, may leave the force unable to respond to the threat in an effective manner. Alternatively, the government or entity may build new facilities that are hardened against incoming blasts to replace the existing unhardened facilities. That is a very expensive and time-consuming approach, but it does yield good results in terms of protecting the force and keeping the force where it needs to be.
An example of the situation described might be a military installation with small to mid-sized aircraft hangers, perhaps hangers for helicopters. If these hangers were not built to withstand the blast of incoming ordinance, they will be at risk if the threat situation changes such that incoming ordinance is a real threat. This is a fairly common situation as more small militia and terrorist groups obtain the firepower to launch offensive attacks on military installations around the world. Even a relatively small militant group may now be able to launch small surface-to-surface missiles at a military facility. Such a missile could pose a serious threat to an unhardened aircraft hanger like those mentioned above.
Something must be done to protect existing, unhardened structures from such damage, and to protect the equipment and personnel within those unhardened structures. The option of constructing entirely new buildings (e.g., new, hardened aircraft hangers) may be too expensive and typically takes a long time to accomplish. Some alternative is needed.
The present invention provides the needed alternative. A protective structure designed to be built around an existing, unhardened structure is disclosed. This retrofit approach is cost-effective, easy to build, and relatively quick to construct. It does not require any change to the existing structure, and in many cases, will allow operation and use of the existing structure to continue without interruption during construction. This latter benefit is important, particularly if the facility being retrofitted is involved in active operations against an enemy threat.
The invention has a support frame that is built outside the existing structure. A blast cover, made of pre-formed concrete panels in a preferred embodiment, is supported by the support frame. The invention is limited in size because the blast cover is heavy and requires substantial support. If the structure is too wide, it is difficult to provide the needed support using only a frame constructed around the existing structure. The present invention works well for situations requiring up to a 20 meter wide support frame, and will work for any length structure.
Once the support frame and blast cover have been constructed, a burster screen is installed an appropriate distance above the blast cover. The burster screen is made of thin, light material. Its function is to create enough resistance to incoming ordinance to cause the ordinance to detonate. By positioning the burster screen away from the blast cover, the incoming ordinance will explode above the blast cover rather than on it. This greatly reduces the destructive force of the ordinance, and allows a relatively modest blast cover to provide adequate protection against most types of ordinance. The burster screens serves to trigger the explosives a fixed distance away from the blast cover.
If a protective structure built in accordance with the present invention comes under attack, the burster screen will be destroyed or heavily damaged. It is intended to be a replacement structure. If a sufficiently large explosion occurs, it is quite possible that some or all of the blast cover might also be damaged and require repair or replacement. Even when that happens, however, the existing, unhardened structure has been protected, and a relatively inexpensive and quick repair will leave the structure protected again. In this sense, the present invention is something of a sacrificial structure, at least in part, designed to fail in order to prevent failure of the protected structure.
There is a further, and related, need for blast protective structures that are small enough to be air lifted to remote locations. Such structures should be easy to assemble by field personnel. The structures should provide protection to personnel from blasts, in the manner summarized above. The present invention meets these needs, too, by providing a smaller version of the blast protection structure. This smaller version is ideally suited to protect individual soldiers or others in harms way.
In a preferred embodiment, the present invention is protective shelter having a support frame positioned exterior to a protected object; a blast cover positioned above the protected object and supported by the support frame; and a burster screen supported by the support frame and positioned a safe blast dissipation distance above the blast cover. Alternatively, the invention embodies a method of constructing a protective bunker, with the steps of constructing a rigid support frame using pre-cut and pre-drilled beams; constructing a blast cover by stacking one or more layers of blocks around the rigid support frame; and, covering the rigid support frame and blast cover with at least one foot of locally obtained fill material. Further embodiments and details are provided in the detailed description below.
Turning to the figures, the present invention can be best understood by starting with a functional diagram. In
The burster screen 18 is positioned about 1-3 meters above the blast cover 16 in a preferred embodiment. The shrapnel, blast wave, and heat created by the detonation of the ordinance 20 dissipates somewhat before making contact with the blast cover 16. These destructive forces are deflected and absorbed by the blast cover 16, and the existing, unhardened structure 12, is thus protected from the incoming ordinance. The particular structural components of the preferred embodiment of the invention are described in more detail below.
The burster screen 18 may be made of any material with sufficient rigidity to detonate incoming ordinance. The needed separation between the burster screen 18 and the blast cover 16 will vary depending upon the type of ordinance expected, the size and strength of the blast cover, and possibly the hardness of the structure being protected. The required distance between the burster screen 18 and the blast cover 16 can be defined as a safe blast dissipation distance, which is the amount of distance required to ensure that incoming ordinance do not compromise the structure or object being protected by the shelter. The safe blast dissipation distance will vary somewhat, but typically will be at least one meter, and rarely will exceed three meters. For the bunker embodiment of the invention discussed below in connection with
The blast cover 16 is shown just above the top of the existing hanger 12 in
The burster screen 18 is shown supported by an upper support frame 24 in
The lower support frame 14 is shown with optional cross supports 26. These supports enhance the rigidity and strength of the lower support frame 14. The blast cover 16, upper support frame 24, and burster screen 18 are also shown in
The pre-formed slabs 34 are preferred, however, because they may make construction easier and it eliminates the need for a full lower structure for the blast cover 16. The pre-formed slabs 34 used in this preferred embodiment are somewhat similar to the slabs used to construct bridges and other road structures. The slabs 34 may be up to about 20 cm in thickness and made of concrete. When a protective structure 10 is made in the manner show in
The burster screen 18 is positioned about 1-3 meters (about 3-10 feet) above the blast cover 16. The burster screen 18 is sufficiently strong and rigid to trigger a contact fuse on incoming ordinance. This causes the ordinance to detonate when it strikes the burster screen 18, rather than the blast cover 16. A good part of the explosive energy of the ordinance is thus dissipated in the air before making contact with the blast cover 16. This key feature of the present invention allows the use of sufficiently light materials for the blast cover to allow for a retrofitted structure that will cover many existing unhardened structures. If larger charges are expected, the burster screen 18 can be positioned farther above the blast cover 16, thus allowing for more of the force to dissipate.
The present invention will not protect all existing unhardened structures and it will not protect against all threats. Some buildings are simply too large, and some threats are simply too destructive. In addition, some threats are not delivered through the air. For example, a suicide bomber may enter a facility and detonate a charge. The present invention is not designed to protect against that type of threat. It is expected, however, that the present invention can protect 90% or more of existing unhardened structures from about 90% of the incoming ordinance threats. The present invention offers a cost-effective means of retrofitting many structures in harm's way.
The present invention also may be used with new construction. A new facility may be built in the normal manner, without additional hardening. The present invention may then be built around the new facility. The simplicity of the present invention may allow the protective structure 10 to be completed even before the interior of the protected structure is completed. This approach may be just as cost-effective as adding hardening features to the design of the new facility, and also might allow for removal of the protective structure if the situation changes and such protection is no longer needed.
The method of protecting an unhardened structure, therefore, is applicable in almost any situation. It does not require much additional space, is easy to construct, and is cost-effective. This process offers many advantages over retrofitting in the traditional manner.
The present invention is also quite versatile. It can be used in a scaled-down version to protect personnel (e.g., soldiers) in the field. Soldiers traditionally have used fox holes or dug out trenches for protection from incoming blasts. In some areas, it is not practical to use this type of protection, and even where possible, these traditional techniques do not provide enough protection from overhead blasts or falling objects. The present invention can be used to provide an alternate personnel protection structure.
The embodiment shown in
In place of the burster screen shown in
In the personal bunker embodiment, it is convenient to use a mass fill 60 as a burster screen. The outer surface of the mass fill provides a contact surface capable of detonating incoming ordinance. By using a sufficient thickness of locally obtained fill material (e.g., earth, sod, etc.) placed over the impermeable membrane 56, the mass fill 60 becomes a burster screen, while also providing additional protection. If used, the mass fill 60 should be at least one foot thick, and preferably is about two feet thick. The outer surface of the mass fill 60 serves as a burster screen, in much the same way as the screen described above. In addition, the mass fill 60 provides additional blast protection because the fill 60 typically will be a relatively solid material. It is important to use a reasonably thick mass fill 60 so that the blast of an incoming round will burst some distance away from the primary blast cover 54. This separation of the actual blast from the blast cover 54 remains a key feature of the present invention. If a separate burster screen is used (e.g., of wood, sheet metal, or other material), it is preferable to locate the screen about one meter above the blast cover.
To help hold a thick layer of mass fill 60 in place, boxed supports or anchoring material 68 may be placed at the base of each side of the bunker 50. For example, Hesco-type structures, filled with local material, may be placed a few inches away from the bottom edges of the blocks that make up the blast cover 54. The mass fill 60 may then be placed over the entire bunker 50, with the anchoring material 68 helping to hold the mass fill 60 in place, and allowing use of a thicker layer of fill 60.
The structural frame 52 is preferably bolted together in the field. It can be anchored in place using anchor pins 62, and anchoring stones 64 or other anchoring objects. The two base ends of the frame 52 may be connected using a cross brace line 66. In a preferred embodiment, the cross brace line 66 is a wire rope that is connected at its ends with clevis plates and pins. A turn buckle may be used to tighten the wire rope. The cross brace line 66 helps hold the structural frame 52 in place and helps prevent flattening of the bunker 50 by an incoming blast.
The key components of the personal bunker embodiment may be air lifted to remote locations and dropped to soldiers in the field. The structural frame components, the blast cover blocks, and the anchoring hardware are all that are needed for construction of the bunker 50. Other materials are locally sourced. Using the present invention, field personnel are able to construct safe, secure personal bunkers in relatively little time. These bunkers are stable, will last as long as needed, and provide better protection than more traditional alternatives.
While the preceding description is intended to provide an understanding of the present invention, it is to be understood that the present invention is not limited to the disclosed embodiments. To the contrary, the present invention is intended to cover modifications and variations on the structure and methods described above and all other equivalent arrangements that are within the scope and spirit of the following claims.
