Diagonal shear test of masonry wall

Diagonal shear (diagonal compression) test

Purpose: to find the shear strength (diagonal tensile strength) and shear modulus of masonry; used for in-plane shear design (ASTM E519, RILEM TC 76).

Specimen: a square wall panel about 1.2 m $\times$ 1.2 m (or the actual wall in situ), built with the same unit, mortar, bond and workmanship as the structure, cured 28 days.

Set-up and procedure

1. The panel is turned so that one diagonal is vertical. Steel loading shoes are fixed with plaster or mortar at the two opposite corners on that diagonal.
2. A hydraulic jack and load cell apply a compressive load $P$ along the diagonal, at a uniform rate.
3. Displacement gauges (LVDTs) on both diagonals measure shortening and elongation to get shear strain.
4. The load is increased until the first diagonal crack and failure; the maximum load $P$ is recorded.

        P (jack)
         |
      +--v-----+
      |\       |
      |  \     |   diagonal crack
      |    \   |   parallel to the load
      |      \ |
      +-------^+
           reaction

Calculation

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

where $\tau$ is the shear strength, $f_t$ the principal (diagonal) tensile strength, $w$, $h$ and $t$ the width, height and thickness of the panel. Shear modulus $G = \tau/\gamma$, with $\gamma=(\Delta_v+\Delta_h)/g$ from the diagonal deformation.

Failure: diagonal cracking through the joints and units, giving the diagonal tension capacity used in design of shear walls.