After the cavity wall has been designed to meet the structural requirements, connections between the precast concrete plank and the masonry wall must be detailed. Other details, such as flashing, must

also be developed. The wall/floor connections provide the wall with lateral bracing against wind loads. This connection should also assist in the transfer of shear stresses, and in the case of bearing walls, transfer gravity loads to the foundation

FIG 4. Typical Bearing Wall Section

CONNECTION FOR LOAD BEARING

One way to anchor precast concrete plank into load bearing concrete masonry is to create a positive tie with reinforcing bars bent at 90 degree angles, see Figure 5. A structural engineer should determine the size and spacing of the reinforcement required.

The reinforcing bar is set into the layway formed between the concrete planks and grouted solid. The exposed portion of the reinforcement fits into the cell of the concrete masonry unit. In the next course, a positive connection is formed when the cell is grouted.

If lateral forces are low, an alternative connection should be considered,see Figure 6. This connection bonds the precast concrete planks to the masonry with a solidly grouted joint. Plugging the cores of the precast concrete planks creates a continuous grout cavity. When the grout is poured it flows into the grout pocket formed at the end of the planks. After the grout cures a positive key connection is formed between the planks and the concrete masonry units. All the precast planks should be in place and the grout fully set before the wall construction continues. Because this detail relies on the bearing pad's frictional resistance to help transfer shear stresses, a structural engineer should determine when this connection is
 

Fig 7 - Lateral Bracing Option 1

Fig 8 - Lateral Bracing Option 2

CONNECTION FOR NON-BEARING

Non-bearing walls (which span parallel to the floor planks) must also be laterally braced by the concrete plank floor system. One method requires holes to be broken in the top of the plank at designated intervals, see Figure 7. Specify the plank adjacent to the wall to bear on the wall a minimum of 3 inches. The cures of the plank are plugged on both sides of the hole with inserts to form a grout packet. A strap anchor is installed so that one end projects down into the grout pocket and the other end projects up into the cell of a concrete masonry unit. The grout pocket and cell of the concrete masonry unit are grouted solid. This connection transfers sear stresses through the floor diaphragm to interior shear walls while providing lateral support for the exterior wall. An alternative connection requires cutting or breaking the precast concrete plank continuously and butting the plank against the wall,see Figure 8.

Reinforcement is aligned and set into the head joints of the concrete masonry and bent at 90 degrees into the core of the precast plank. The core of the precast plank is then grouted solid when the grout cures it forms a positive connection. The significance of base flashing can never be over emphasized. The success of any cavity wall system depends on proper flashing details at the base of the wall. Figure 9 illustrates a properly flashed cavity wall at the foundation. Weepholes are required at 16" or 24" on center to divert moisture from the cavity to the exterior of the building.

Figure 10 suggests one method of construction for a window-head condition. A bond beam is used in lieu of a steel angle lintel. Flashing should be extended beyond the jamb lines with both ends damned. Solid masonry jambs should be avoided. However, for steel windows, the jamb must be partially solid to accept most standard jamb anchors. Stock sizes of windows may be used in cavity walls, although sometimes additional blocking is needed for anchorage. Window spans may be limited for this type of construction.
 

FIG 9 -Base Flashing Detail - Cavity Wall

FIG 10 -Lintel Detals

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