The mode of failure of a very short masonry member having h/t ratio of less than 4 is by:
🔬 Understanding Failure Modes vs. Slenderness
The way a masonry column or wall fails under a compressive load is directly related to its slenderness ratio (h/t), which is the ratio of its effective height (h) to its effective thickness (t). This ratio determines whether the member is "short" (stocky) or "long" (slender).
Short Members (Low h/t ratio, e.g., < 4): These members are very stable against sideways movement. Their failure is governed by the material's intrinsic strength.
Slender Members (High h/t ratio): These members are susceptible to geometric instability. They tend to fail by bending or bowing sideways long before the material's crushing strength is reached.
⚖️ Detailed Analysis of the Options
The question specifies a "very short" member with an h/t ratio less than 4. This immediately tells us the failure mode will be a material failure, not a stability failure.
(b) Vertical tensile splitting
Why it's correct: This is the classic crushing failure mode for a short, brittle member under compression. Due to the Poisson's effect, as the member is compressed vertically, it expands horizontally. Since masonry (like concrete and stone) is very weak in tension, this lateral expansion creates vertical tensile stresses. These stresses cause vertical cracks to form, and the member fails by splitting apart. This is the ultimate material failure in compression.
(a) Shear
Why it's incorrect: Shear failure typically occurs when there is a significant lateral (sideways) load in addition to the vertical load. For a member subjected to pure axial compression, shear is not the primary mode of failure.
(c) Buckling
Why it's incorrect: Buckling is a stability failure mode that only occurs in slender members with a high h/t ratio. A short, stocky member with an h/t ratio of less than 4 is not slender and will crush long before it has a chance to buckle.
💡 Study Tips for Masonry Failure
- Short and Stocky = Splits and Crushes: Associate a low slenderness ratio with a material crushing failure, which manifests as vertical splitting.
- Long and Slender = Buckles: Associate a high slenderness ratio with a stability failure, which is buckling.
- Visualize the Poisson Effect: Imagine squashing a marshmallow. As you press down, it bulges out to the sides. This sideways bulge is what creates the tensile stress that splits a brittle material like masonry.