other regions. Recent field measurements indicate that these forces should be increased [71]. Thus, a foundation system designed to prevent sliding, overturning and separation of the mobile home from its supports must have the capability of resisting horizontal and uplift forces. Since most mobile homes are supported by piers which rest on top of the ground, have relatively little weight and generally have no ties to connect them with the supporting piers, uplift and horizontal forces must be resisted by soil anchors. Industry recognized the need for providing anchoring systems for mobile homes and developed a variety of products which are readily available and can be installed inexpensively. However, data on the performance of these anchoring systems are relatively scarce, are not very well correlated with soil properties, and have not been systematically compiled. The purpose of this study was to compile available information, assess our ability to predict the pull-out capacity of anchors in various soils, and determine what additional information or standards could improve the reliability of anchoring systems. Background information on the need for anchoring and anchoring standards and procedures is provided in Chapter 2; Chapter 4 gives an overview of available anchoring hardware; the state of knowledge with respect to theoretical prediction of anchor pull-out capacity is discussed in Chapter 5; Chapter 6 provides information on empirical methods presently used to predict pull out capacity; load test data that could be located by the authors are presented and analyzed in Chapter 7; environmental effects on anchor pull-out capacity are discussed in Chapter 8; and needed research to fill most important information gaps is discussed in Chapter 9. Facing page: Mobile home damaged by wind upset. All areas of the United States at one time or another are subjected to winds of sufficient intensity and duration to cause damage to mobile homes [39, 46, 71, 78]. Areas adjacent to the oceans and the Gulf of Mexico may be subjected to hurricane-force winds. Furthermore most areas, particularly those in the interior of the U.S., may be subjected to tornadoes. Wind forces on mobile homes situated in open areas generally exceed those acting on mobile homes sheltered by trees and surrounding structures (other mobile homes) [46]. A discussion on windstorm characteristics related to mobile home damage was presented by Vann and McDonald, 1978 [Ref. 102a]. The soil anchor is an important component of the foundation system which provides structural stability for an installed mobile home. It is part of a structural chain of components that includes the mobile home structural frame and floor, roof-wall, and wall-floor joints, foundation blocking, anchor straps, connecting hardware between the anchor straps and anchor, and finally the anchor embedded in the soil and/or rock. Failure of any one of these components could result in damage to the mobile home and its contents and injury to its inhabitants during windstorms. Data on the actual percentages of anchored and unanchored mobile homes that were damaged during severe windstorms are very scarce. Several insurance companies and state agencies active in mobile home programs in one way or another were contacted. Although all parties concerned agreed that anchoring a mobile home is very beneficial, significant data substantiating the effects of anchors on the behavior of mobile homes during windstorms could not be produced. The following references provide limited information: In the November 12-13, Pickard (1978) [84a] reported the following: In the same storm in the same county at Whispering Oaks Mobile Home destroyed and 3 were severely damaged. The damage to the anchored mobile homes was primarily caused by flying debris from the destroyed mobile homes. In the Amber Mobile Home Park, in a different location in the same storm and county, 6 units were subjected to the windstorm. The 4 mobile homes that were tied down suffered nominal damage, while the 2 units that were not tied down were completely destroyed; one rolled over and one blew away. One June 12, 1972, in Hurricane Cecilia, in Del Rio, Texas, 15 mobile homes [in one park] were subjected to strong winds. Of the 7 mobile homes that were anchored, 1 was destroyed (the unit was hit by an unanchored mobile home), 2 suffered minor damage and 4 escaped injury. Of the 8 mobile homes that were unanchored, 6 were totally destroyed and 2 suffered minor damage. The following mobile home damage report on Hurricane Eloise in Florida, in 1975, was prepared by Wayne Haddock of Minuteman Anchors, Inc., in East Flatrock, North Carolina: In the Reids Trailor Park and Sea Gull Trailer Park in Panama City, Florida, in almost every instance, those mobile homes that had no anchors were blown over or were destroyed in the September 23, 1975, Hurricane (Eloise). In the Fort Walton area, approximately 300 mobile homes were located in the Shalimar Mobile Home Park located approximately 15 miles (24 Km) inland. The only home that blew over was not tied down. The remaining homes were predominantly anchored according to the Florida state code and showed very little damage. In Dothan, Alabama, where wind speeds reached 88 mph (140 Km/h), 75 percent of the 70 mobile homes in the Ridgewood Estates Mobile Home Park were blown off their blocks and 4 homes None of the (anchored) mobile homes [in the park] were destroyed. were moved. In the March 24, 1975, tornado at Traveler's Rest, South Carolina, a total of 8 mobile homes were hit by high winds. Six of the 8 mobile homes were not anchored; 2 were completely demolished and the remaining 4 were damaged. Those 2 remaining mobile homes were anchored and suffered no damage. 2.2 NATIONAL AND STATE STANDARDS Besides the National Standard [10, 34, 69], there are various state rules, regulations and laws regarding the anchoring of mobile homes. Some states (for example, Alabama, [7, 8]) require that any new mobile home occupied after a certain date, (January 1, 1976, in Alabama), must be tied down in accordance with ANSI Standard A119.1/NFPA 501B [69]. These standards, summarized by Cooke, et al. [29], and Waldrip [105], are intended to protect the occupants and are advocated by the companies who insure mobile homes against loss due to high winds. Specific recommendations for anchoring equipment are given in paragraph 4.4. of the "Standard for the Installation of Mobile Homes" Manufactured Housing Institute and National Fire Protection Association [69] [NFPA 501A; ANSI 119.3]. The basic provision is that the anchoring equipment should be capable of resisting an allowable working load equal to or exceeding 3150 lb (14.0 kN) when installed. The term "allowable working load" means that the anchor capacity should be greater, providing a factor of safety. The provision stipulates a factor of safety by stating that the anchor should be capable of withstanding a 50 percent overload (which comes out to be 4725 lb (21kN), total) without failure of either the anchoring equipment or the structural hardware which anchors the mobile home or which ties the mobile home to the soil anchor itself. Section 5.5.1 of the NFPA Standard, entitled "Capacity of Anchors," defines failure as the condition when the point of connection between the tie and the anchor moves more than two inches (50 mm) at the 50 percent overload or 4725 lb (21kN) in the vertical direction. In addition, it is further prescribed that in the event the load is other than from the vertical direction, the anchor shall withstand 3150 lb (14kN) at an angle of 45° from the horizontal |