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  • Masonry Structural design 
    See Masonry Structural design page: Masonry Structural design

    Masonry accessory materials include reinforcement, connectors, sealants, flashing, coatings, and vapor barriers and moisture barriers. Each of these is described further below.

    Reinforcement
    Reinforcement consists of the following:
    • Steel deformed reinforcing bars meeting the requirements of ASTM A615 (billet steel) or A996 (rail and axle steel), or ASTM A706 (low-alloy weldable steel)
    • Joint reinforcement (ASTM A951)
    • Deformed reinforcing wire (ASTM A496)
    • Steel welded wire reinforcement for concrete (ASTM A497)
    • Steel prestressing strand (ASTM A416)
    Typical uses of each type of reinforcement are shown in Figs. 2.5 through 2.8. Figure 2.5 shows deformed reinforcing bars in a grouted masonry wall. Figure 2.6 shows joint reinforcement. Figure 2.7 shows welded wire reinforcement in the topping of a floor slab connected to a masonry wall. Figure 2.8 shows posttensioning tendons in a masonry wall.

    Connectors
    Connectors are addressed by the following ASTM specifications:
    • ASTM F1554 (plate, headed and bent bar anchors)
    • ASTM A325 (high-strength bolt anchors)
    • ASTM A1008 (sheet steel anchors and ties)
    • ASTM A185 (steel wire mesh ties)
    • ASTM A82 (steel wire ties and anchors)
    • ASTM A167 (stainless steel sheet anchors and ties)
    • ASTM A193-B7 (high-strength threaded rod anchors)
    • ASTM A641, A153, or A 653 (galvanized steel connectors)
    Typical uses of each type of connector are shown in Figs. 2.9 through 2.11. Figure 2.9 shows typical veneer ties. Figure 2.10 shows typical adjustable pintle ties. Figure 2.11 shows typical connectors.

    Adjustable ties are useful for accommodating differences in elevation of bed joints. As shown in Fig. 2.12, adjustable ties can be very flexible if they are used at large eccentricities (difference in elevation of bed joints).

    Sealants

    Sealants are used to prevent the passage of water at places where gaps are intentionally left in masonry walls. Three basic kinds of gaps (joints) are used
    • Expansion joints are used in clay masonry to accommodate expansion
    • Control joints are used in concrete masonry to conceal cracking due to shrinkage
    • Construction joints are placed between different sections of a structure

    Sealants are most commonly formulated using synthetic polymers such as silicone, neoprene, latex, or butyl rubber. Their elastic properties include compressibility, expressed as the ratio of minimum thickness to original thickness. Because the polymers comprising them deteriorate under exposure to ultraviolet light and ozone, the normal life of sealants in exterior exposures is about 7 years. Sealants should be replaced at intervals approximately equal to their expected life.

    Flashing

    Flashing is a flexible waterproof barrier, intended to permit water that has penetrated the outer wythe to re-exit the wall. It is placed at every interruption of the vertical drainage cavity, including the following locations: at the bottom of each story level (on shelf angles or foundations, as shown in Fig. 2.13), over window and door lintels, and under window and door sills. Flashing is made of stainless steel, copper, plastic-coated aluminum, plastic, rubberized asphalt, EPDM (ethylene-propylene-diene monomer), or PVC (polyvinyl chloride). Metallic flashing lasts much longer than plastic flashing. Nonmetallic flashings are subject to tearing. Modern self-adhering flashing of rubberized asphalt is a good compromise between durability and ease of installation. Flashing should be applied above shelf angles, above door and window openings, and below door and window openings. Flashing should be lapped, and ends of flashing should be defined by end dams (flashing turned up at ends). Directly above the level of the flashing, weepholes should be provided at 24-in. spacing.

    Coatings

    Coatings include paints and water-repellent coatings.

    • Paint is less durable than the masonry it covers.

    • Water-repellent coatings cannot bridge wide cracks. They tend to trap water behind them, causing freeze-thaw damage behind the coating, and also crypto-florescence. They are generally unnecessary for clay masonry, and generally less effective than integral waterrepellent admixtures for concrete masonry.

    Vapor Barriers

    Vapor barriers are waterproof membranes (usually polyethylene or PVC). They are intended to prevent the passage of water in vapor or liquid form, and thereby prevent interstitial condensation within the air space of a drainage wall. In warm climates, warm air from the outside of the building can pass through the outer wythe of a cavity wall and condense within the interior wythe. The vapor barrier is therefore placed against the exterior face of the interior wythe. In cold climates, warm air from the inside of the building will pass through the inner wythe of a cavity wall and condense within the cavity. The vapor barrier should therefore be placed against the interior face of the exterior wythe. In practice, this conflicts with the above requirements for warm climates. As a result, vapor barriers are often placed on the exterior face of the interior wythe anyway, as a compromise. 2.8.7

    Moisture Barriers

    Moisture barriers are membranes that prevent the passage of water in liquid form, but permit the passage of water in vapor form. One example is Tyvek®. They are intended to keep liquid water out of walls. They do not prevent interstitial condensation within the air space of a drainage wall. 2.8.8

    Movement Joints

    Three basic kinds of movement joints are used in masonry construction: expansion joints, control joints, and construction joints.

    1. Expansion joints, shown in Figs. 2.14 and 2.15, are used in clay masonry to accommodate expansion. In these figures the backer rod is shown separated from the sealant, so that they can be distinguished. In reality, they are in contact.

    2. Control joints, shown in Fig. 2.16, are used in concrete masonry to conceal cracking due to shrinkage.

    Control joints are placed at openings in concrete masonry. As shown in Fig. 2.17, the joints are “dog-legged” so that the lintel can be supported by the masonry on both sides of the opening, and also so that it can be restrained against uplift by vertical reinforcement at the edges of the opening.
    3. Construction joints are placed between different sections of a structure.


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