Building Design and Construction Handbook - Merritt - Ventech!

11.24 SECTION ELEVEN
with metal anchors or by keying the top of the partition to overhead work. Suspended
ceilings may be considered as lateral support if ceilings and anchorages are
capable of resisting a horizontal force of 200 lb/lin ft of wall.
11.9 DETERMINATION OF MASONRY
COMPRESSIVE STRENGTH
Allowable stresses are based, for the most part, on the ultimate compressive strength
ƒ�m psi, of masonry used. This strength may be determined by prism testing, or may
be based on the compressive strength of the bricks and the type of mortar used.
Compressive strength tests of brick should be conducted in accordance with ASTM
‘‘Standard Methods of Sampling and Testing Brick,’’ C67.
Prism Tests. When the compressive strength of the masonry is to be established
by preliminary tests, the tests should be made in advance of construction with
prisms built of similar materials, assembled under the same conditions and bonding
arrangements as for the structure. In building the prisms, the moisture content of
the units at the time of laying, consistency of the mortar, thickness of mortar joints,
and workmanship should be the same as will be used in the structure.
Prisms. Prisms should be stored in an air temperature of not less than 65�F and
aged, before testing, for 28 days in accordance with the provisions of ASTM ‘‘Standard
Method of Test for Compressive Strength of Masonry Assemblages,’’ E447.
Seven-day test results may be used if the relationship between 7- and 28-day
strengths of the masonry has been established by tests. In the absence of such data,
the 7-day compressive strength of the masonry may be assumed to be 90% of the
28-day compressive strength.
The value of used in the standard, ‘‘Building Code Requirements for Engi-
ƒ� m
neered Brick Masonry,’’ is based on a height-thickness ratio h/t of 5. If the h/t of
prisms tested is less than 5, which will cause higher test results, the compressive
strength of the specimens obtained in the tests should be multiplied by the appropriate
correction factor given in Table 11.2. Interpolation may be used to obtain
intermediate values.
Brick Tests. When the compressive strength of masonry is not determined by
prism tests, but the brick, mortar, and workmanship conform to all applicable requirements
of the standard, allowable stresses may be based on an assumed value
of the 28-day compressive strength ƒ�m computed from Eq. (11.1) or interpolated
from the values in Table 11.3.
TABLE 11.2 Strength Correction Factors for Short Prisms
ƒ� � A(400 � Bƒ�) (11.1)
m b
Ratio of height to thickness h/t 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Correction factor 0.82 0.85 0.88 0.91 0.94 0.97 1.00