1. Technical Field
The present invention relates generally to protective shelters, and more particularly to redeployable mobile aboveground shelters.
2. Description of the Related Art
The construction of storm shelters, safe rooms and blast resistant modules is well known and thoroughly documented, for example, in FEMA 320, Third Edition and FEMA 361, Second Edition, both available from the Federal Emergency Management Agency (FEMA), as well as in ICC/NSSA 2008 “Standard for the Design and Construction of Storm Shelters,” published jointly by the International Code Council (ICC) and the National Storm Shelter Association (NSSA) and in Section 6, Wind Loads, of “Minimum Design Loads for Buildings and Other Structures,” SEI/ASCE 7-05, 2005, ISBN: 0-7844-0809-2, published by the American Society of Civil Engineers. To meet safety standards, conventional shelters require either burial below ground or, for one common aboveground shelter design, secure fastening of the shelter by numerous metal bolts or adhesives to heavy foundations or concrete “pads”. For pad-anchored aboveground shelters, the combined weight of the shelter plus its foundation or pad is often the primary factor relied upon to resist movement of the shelter (and thus provide protection of its occupants) during high velocity wind events. In many instances non-residential aboveground shelters are designed to be permanently installed at one location.
If a redeployable or mobile protective shelter is unavailable, personnel that are temporarily located where severe wind events may occur remain at risk. Those working on oil well drilling rigs, pipeline construction, wind turbine erection, petroleum refineries, compressor station repair, and road construction and repair are examples of personnel at risk. One of the challenges of providing severe wind event protection for such personnel is the need for the shelter to be able to be easily, quickly and inexpensively relocated to different work sites as the crews frequently relocate.
Conventional pad-anchored aboveground protective shelters depend almost completely upon the total weight of the shelter and its attached concrete foundation to resist movement. To a lesser degree, the large width of the required concrete foundation also helps the assembly resist overturning. To resist wind induced overturning, uplift and sliding, some shelters require the use of expensive subterranean concrete footings in addition to the wide width and massive weight of the foundational pads. Although pre-cast concrete community and industrial shelters are available, their immense weight (approximately 75,000 lbs. or more) requires the use of specially permitted and oversized trucks to haul them and heavy cranes to lift them into place, which renders their temporary redeployment impractical. Some conventional metal shelters can be unbolted from their heavy concrete bases and moved more easily. However, each new location requires the preparation of another heavy concrete pad to which the shelter can be bolted. In most instances the cost and inconvenience of pouring of a new pad (and the attendant environmental impact of their subsequent demolition and removal) renders impracticable the redeployment of a pad-anchored protective shelter for temporary use.
A second design of aboveground shelter is an “anchored box” that utilizes one or more exposed wire-lines, chains or cables to provide stability in high wind loads to a lightweight metal enclosure, such as an intermodal shipping container. In a typical installation, the securing lines are either looped over or attached to the metal enclosure and also anchored to the ground using any of a variety of anchoring devices, such as helical earth screws, driven piles, or bored holes filled with cement fitted with “eyes” to which a turnbuckle or other similar attachment mechanism can be affixed. Although the anchored box shelter design affords a greater degree of shelter mobility than pad-anchored shelter designs, anchored box shelter designs place shelter occupants at high risk of injury as a result of impact induced failure of the exposed anchoring elements.