Masonry Structural design

Properties of Masonry Assemblages

The following characteristics of masonry assemblages are covered by ASTM Specifications E72, C1072, C1388, C1389, C1390, C1391, C1357, and C1314:

1. Compressive strength: This is often denoted by fm . Using ASTM C1314, it is measured using stack-bonded prisms whose maximum ratio of height divided by least lateral dimension is between 1.3 and 5. For example:

a. Hollow concrete masonry units measuring 8 × 8 × 16 in., tested as a 2-high prism, would have a height of about 16 in. and a minimum lateral dimension of about 8 in., for a ratio of height to least lateral dimension of about 2.

b. Modular clay units measuring 4 × 2-2/3 × 8 in., tested as a 6-high prism, would have a height of about 16 in. and a minimum base dimension of about 4 in., for a ratio of height to least lateral dimension of about 4. The compressive strength of a clay masonry prism is less than that of the mortar or the unit tested alone. This is because clay masonry prisms typically fail due to transverse splitting. The mortar is usually more flexible than the units. Under compression perpendicular to the bed joints, it expands laterally, placing the units in transverse biaxial tension. The prism cracks perpendicular to the bed joints (parallel to the direction of the applied load). Because concrete masonry prisms typically have mortar and units of similar strengths and elasticity, these tend to fail like a concrete cylinder. 2. Tensile bond strength can be measured by tests on wall specimens (E72), by modulus of rupture tests on masonry beams (E518), by bond wrench tests (C1072), or by crossed-brick couplet tests. Results from these tests are not equal. Strict protocols for bondwrench testing are specified in C1357.

3. Shear strength can be measured by diagonal compression tests (E519).

4. Water permeability is measured in terms the amount of water passing through a wall under a standard pressure gradient, simulating the effects of wind-driven rain (E514).

Related Articles

Close