Diagonal shear and push shear tests

Diagonal shear test (of a masonry panel)

Aim: shear (diagonal tensile) strength and shear modulus of masonry.

• A square wall panel (about 1.2 m $\times$ 1.2 m) is rotated so a diagonal is vertical; steel shoes at the two opposite corners.
• A jack applies compression along the diagonal at a steady rate to failure; the diagonal crack and the load $P$ are noted. LVDTs on the diagonals measure the deformation.

$$\tau = \frac{0.707P}{A_n},\qquad f_t=\frac{0.5P}{A_n},\qquad A_n=\frac{w+h}{2}\,t$$

       P
       |
    +--v----+
    |\      |
    |  \    |  crack along the
    |    \  |  loaded diagonal
    +-----^-+

Push shear test (in situ)

Aim: shear strength of bed joints of existing wall.

• A brick is isolated by removing a head joint at one end and the brick at the other end is removed to place a small jack and load cell.
• The jack pushes the brick horizontally along the bed joints; the load $F$ at first slip is recorded.

$$\tau = \frac{F}{2A_b},\qquad c=\tau-\mu\,\sigma_v$$

where $A_b$ is the bed area of the brick (two joints), $\sigma_v$ the vertical stress at the joint and $\mu$ the friction coefficient (about 0.4 to 0.65).

 +----+----+----+
 |    |[jack]->[brick]   F pushes brick along bed joint
 +----+----+----+

The diagonal shear test is a laboratory test on a panel (destructive); the push-shear test is done on the actual wall with little damage.