Figure 6.7

Basic Wind Speed in Miles Per Hour (mph). Annual
Extreme Fastest Mile Speed 30 ft above ground,
50-year Mean Recurrence Interval [10]

Figure 6.8 Recommended Wind Velocity - Anchorage Requirement Curve by Harris [46]

Figure 6.9 Relationship Between Anchor Spacing and Anchorage Requirement for the Pull on One Anchor [46]

Figure 6.10 Anchor Spacing Chart, Type A and AA Anchors (6-inch Helix and 10-inch Arrowhead Shaped Anchors, Respectively) [46]

Instead of the generic description of soil types, N values from the Standard Penetration Tests or torque readings from the Soil Test Probe could be used. Recently, Marshall [71] has provided design pressures for 70 mph and 90 mph windstorms. These design pressures, based on measurements on a prototype mobile home, could be used to update the anchor load requirements.

6.3 USE OF LOCAL EXPERIENCE

Local experience can play an important part in assisting local installers in meeting the needs of the mobile home community. Over a period of months or perhaps years, individual installers become experienced in predicting the pull-out capacity of certain types of anchors installed in soils with which they are familiar. These installers may know little of the theory behind anchor pull-out capacity prediction, but they have demonstrated adequate know-how to choose and install anchors which perform successfully. However, the know-how had to be initially gained by some experiments, such as anchor pull-out tests.

6.4 THE USE OF PROTOTYPE PULL-OUT TESTS

The only conclusive way to establish the pull-out capacity as well as the load-displacement curve for an anchor is to run a prototype load test at the mobile home site in the soil where the anchor is going to be installed. This is usually beyond the resources and the skill of the mobile home owner but it is the only way to obtain a true indication of anchor behavior.

There are generally two types of load test results that are found in the unpublished literature available either from anchor manufacturers or, with permission, from field or laboratory data acquired by testing firms. The load tests will either be presented in terms of (a) pull-out capacity for a given soil class or (b) a complete load versus displacement curve.