Compressive and diagonal shear tests of masonry

Compressive strength test

• A wall panel or prism (at least 400 mm high, $h/t$ between 2 and 5) is loaded vertically in a compression machine till failure.
• $f_m = \dfrac{P}{A}\times k$, with $k$ from IS 1905 Table 12; basic compressive stress $f_b=0.25f_m$.
• Failure mode: vertical splitting cracks in units. Gives compressive strength and modulus of elasticity.

   P                    P (along diagonal)
   v                     \
 +-----+               +--\--+
 |     |               |    \|
 |prism|               |wall /|
 +-----+               +----/+
 compressive test      diagonal shear test

Diagonal shear test

• A square wall panel (about 1.2 m $\times$ 1.2 m) is loaded in compression along one diagonal through steel shoes at opposite corners.
• Shear strength $\tau = \dfrac{0.707P}{A_n}$, with $A_n=\dfrac{w+h}{2}t$; diagonal tensile strength $f_t=0.5P/A_n$.
• Failure mode: diagonal tension cracking along the loaded diagonal.

Basic difference