Masonry Magazine April 1988 Page. 22
As shown, adjustable tie deflections become large as the adjustment eccentricity becomes large. These values were calculated assuming that no mechanical play existed in the tie system. Mechanical play must be added to these values to determine the total deflection of the exterior wythe. Typical adjustable ties have values of mechanical play ranging from approximately 0 to 0.3 in. (0 to 8 mm). Some adjustable ties may have an extreme amount of mechanical play when not properly installed (see Fig. 12). If satisfactory performance is to be expected, total tie and backup deflections must be maintained within the working range of the masonry facade under full design loads.
Recommendations. At present, analysis techniques that accurately model metal-tied wall systems are still in the developmental stage and require further refinement and verification through testing. Until more accurate methods are available, the Brick Institute of America feels that acceptable strength and deformation characteristics can be achieved by one or more of the following measures: 1) Reduce or eliminate lateral mechanical play in adjustable tie systems. Limit the total mechanical play to 0.02 to 0.05 in. (0.5 to 1.2 mm), see Fig. 12. 2) Reduce or eliminate adjustment eccentricity in adjustable tie systems. This can be accomplished by installing ties as facing wythes are constructed or by using starter courses or ledges when facing wythes are constructed over masonry backup. 3) Eliminate possible disengagement of adjustable ties by providing positive vertical movement limitations. 4) Provide additional ties within 8 in. (200 mm) of openings and discontinuities, i.e., windows, shelf angles, verticial expansion joints, etc. 5) Do not specify ties with formed drips.
Testing has shown that drips can reduce the ultimate buckling load by approximately 50 percent. 6) Reduce tie spacing, as shown in Table 1, based on the tie system and wall system. 7) Specify stiff ties. This can be accomplished by specifying ties with maximum deflections of less than 0.05 in. (1.2 mm) when tested at an axial load of 100 lb in tension and compression. When adjustable ties are specified, the deflection limit should be satisified at the eccentricity expected in the field. See Table 2 for minimum tie gage and diameter recommendations. 8) Select an appropriate tie system for the wall system (see Table 3).
96 IN.
88 IN.
72 IN.
56 IN.
40 IN.
24 IN.
8 IN.
10
WALL MODEL
LATERAL LOAD 1 psf
PINTLE ECCENTRICITY
A) STEEL STUD BACKUP
B) CONCRETE BACKUP
C) MASONRY BACKUP
D) WOOD STUD BACKUP
Masonry Re-Anchoring Systems
FIG. 10
DEFLECTION (IN. X 1/1000)
TIE LOAD (LB)
24
56
72
TIE LOCATION (IN.)
LATERAL LOAD 1 psf
24
56
72
TIE LOCATION (IN.)
A
STANDARD
DOUBLE EYE AND
PINTLE,
1/2 IN.
DOUBLE EYE AND
PINTLE, 1 IN.
SINGLE EYE AND
PINTLE,
1 IN.
SINGLE EYE AND
PINTLE, 1/2 IN.
Calculated Tie Loads and Deflections
FIG. 11