Rock Anchor Design
Rock Anchor Design
(OP)
Is there a minimum unbonded length required for vertical rock anchors utilized for uplift resistance (e.g. shallow foundations on rock resisting uplift).
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RE: Rock Anchor Design
RE: Rock Anchor Design
RE: Rock Anchor Design
PTI 6.4.2 says: Generally, the free stressing length should remain unbonded after stressing, except to satisfy specific structural requirements. PTI C6.4.2 says: Unbonded free stressing lengths allow a more flexible performance of the anchor and the averaging of structure strains resulting in less load shange in individual anchors. Typically, fully bonded and partially bonded free lengths are only applicable in massive concrete structures (dams, diaphragm wall t panels, etc).
PTI 6.8 says: The free stressing length for rock anchors and soil anchors shall not be less than 4.5 m (15 ft) for strand tendons and 3.0 m (10 ft) for bar tendons. PTI C6.8 says: The minimum stressing length recommended is to prevent significant subsequent reductions in transfer load due to seating losses. Shims placed below the wedge plate can compensate for these losses. For more information, the designer should contact the anchor tendon manufacturer.
There is even more about the free stressing (unbonded) length in PTI 6.8.
RE: Rock Anchor Design
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RE: Rock Anchor Design
RE: Rock Anchor Design
RE: Rock Anchor Design
RE: Rock Anchor Design
Not quite sure I followed the example, however thanks for the post. I do follow the idea of initial localized stresses at top of rock (almost always less compentent) gradually being transferred deeper.
RE: Rock Anchor Design
Based on the PTI reference, I would also use a min. unbonded length of 10ft for a threaded bar rock anchor.
Not quite sure I understand the example above, however follow the idea of localized stresses at top of rock (almost always less compentent) working downward.
RE: Rock Anchor Design