Masonry Magazine October 2003 Page. 21
Figure 10
Tendon Layout
Figure 11
THIS IS ONE of the most critical elements of post-tensioning construction. The actual tendon layout is dictated by the openings in the walls. The tendons must be placed away from the edges of the openings.
It is recommended to grout the edges of the openings and place the closest tendon at approximately two feet away. This does not create any special problems because it is common to grout and reinforce the jambs of openings.
Bottom Anchor Selection
THE CHOICE of which anchor is used has an impact upon constructability and placement tolerances. Three options are possible.
A cast-in-place anchor (Figure 10) provides the strongest and most reliable anchorage. However, installation tolerances are difficult to control and preplanning is needed during the foundation construction to determine the masonry coursing. If the foundation contractor installs these anchors, coordination with the mason contractor is essential.
A second option is the mason contractor can install an adhesive anchor as the masonry layout occurs. This reduces the concern over placement tolerances. The disadvantage to this anchor is the strength is dependent upon the quality of the adhesive and the care taken during installation. However, there are concerns over long-term creep and the fire resistance of adhesives.
The bottom anchor method (Figure 11) also gives the mason full control over installation. The anchorage does not have to be embedded in the foundation as long as it's not part of a shear or cantilever wall. It is also ideal for post-tensioning interior partitions that are braced at the top. An additional doweled connection, identical to that used in reinforced masonry and separate from the post-tensioning, will lock in the bottom of the wall.
Top Anchor Location
THE ANCHOR and the position of the anchor should be considered in planning a project. Figure 12 shows a design detail for new construction.
Providing accessibility to the top anchor for the future is advisable wherever possible. Usually it is not necessary for masons to go back and re-tension the tendons, however, the tendons have to be loosened prior to cutting into the walls for future renovations.
Figure 12
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