Page 120 - Design of Reinforced Masonry Structures

3.14 CHAPTER THREE

FIGURE 3.4 Construction of masonry prisms according to ASTM
C1314-03b. (Courtesy: National Concrete Masonry Association.)

The prisms should be kept in airtight bags and should not be disturbed until 48 h prior
to testing. After the initial 48 h, the bagged prisms should be maintained in an area with
a temperature of 75 ± 15°F. The prisms are to be tested after 28 days or at the designated
period. The moisture-tight bags containing the prisms are to be removed 2 days prior to

testing and storing the prisms at 75 ± 15°F.
Calculation of the compressive strength of masonry from masonry prism tests is a three-
step process. First, the masonry prism strength is calculated by dividing each prism’s com-
pressive load sustained by the net cross-sectional area of that prism (express the result to
nearest 10 psi). Next, the compressive strength of masonry is determined based on the
aspect ratio of the masonry test prisms. For masonry prisms having aspect ratio (h /t ) of 2,
p p
the compressive strength of masonry is taken to be equal to the strength of masonry prism.
For masonry prisms having aspect ratios between 1.3 and 5.0, the compressive strength
of masonry is obtained by multiplying the masonry prism strength with correction factors
listed in Table 3.3 [3.24]. Interpolation may be used for obtaining the correction factor for
the aspect ratios not listed in the table. And finally, the compressive strength of masonry,
f , is obtained by averaging the values so obtained.
mt