Anchor Uplift Capacity

This chapter is organized into sections on loadings, pile structures, gravity platforms, anchor uplift capacity, jack-up platforms, and hydraulic filled islands. 

Industrial and military needs have placed greater emphasis on improved anchor systems as operations are performed in deeper wafer and with some positioning accuracy. Additionally, anchor requirements include high anchor capacity/weight ratio, reliability, efficiency, and ease of handling and deployment These demands have led to the development of a large number of new anchor types and an assortment of theories to predict the uplift capacity of fhese anchors in differenf sedimenf fypes (Figure 10.39). This section will contain a review of fhese new anchor types and some anchor capacity theories. While the uplift pile remains an important anchor type, it was discussed in some detail earlier in this chapter. 

The holding capacity equation for an anchor is similar to the bearing capacity equation for a deep foundation. The general uplift capacity, f, of an anchor is often expressed as the following ... 

A Vs-in. thick preformed plain elastomeric pad or fabric pad placed atop the concrete bearing surface or grout pad most economically compensates for any minor surface irregularities. Fully threaded anchor rods can be either cast into the concrete or drilled and grouted into place. An anchor plate can be either bolted or welded to the bottom of the anchor rod to augment uplift capacity in the concrete. If no uplift capacity is required, a swedged rod may be substituted for a threaded one. The swedged rod may be terminated just below the top of the masonry plate and the void filled with a flexible sealant. 

Anchors are special foundation elements that are designed to take uplift loads. Anchors can be added if an existing foundation lacks uplift capacity, and competent layers of soil or rock are shallow and easy to reach. Anchors, however, cannot take lateral loads and may be sheared off if combined lateral capacity is not enough. 

Design ctirves of holding capacity factor versus relative embedment depth (D/B). (From Taylor, R.J. et al.. Handbook for Uplift Resisting Anchors, U.S. Navy, Civil Engineering Laboratory, Port Hueneme, CA, 1975.)... 

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