Which of the following types of construction offers comparatively better earthquake resistance based on its structural action? Consider that the thickness and length of member to be constructed is constant for any of the following cases.
🔬 Understanding Earthquake Forces and Masonry
During an earthquake, the ground shakes horizontally and vertically. This movement creates powerful lateral (sideways) inertia forces in a building. The key to earthquake resistance is a structure's ability to handle these forces without collapsing.
The Problem with Unreinforced Masonry: Standard masonry (brick or stone with mortar) is very strong in compression (resisting being squeezed) but extremely weak in tension (resisting being pulled apart). The lateral forces from an earthquake induce tension and shear stresses that unreinforced masonry cannot handle, leading to brittle, catastrophic failure.
⚖️ Detailed Analysis of the Options
Let's evaluate each construction type's ability to resist earthquake forces.
(d) Reinforced brickwork
Why it's the best: This system embeds steel reinforcing bars (rebar) within the mortar joints or in cavities of the brickwork. Steel has extremely high tensile strength and is very ductile (it can bend and stretch significantly before breaking). By adding steel, you create a composite material. The brickwork carries the compressive loads, and the steel carries the tensile loads. This gives the entire wall system the ductility it needs to bend and absorb the immense energy of an earthquake without shattering. It is by far the most superior option for earthquake resistance.
(a) Brickwork with English bond
Why it's poor: English bond is a strong pattern for bricklaying, but it is still unreinforced masonry. It has no ability to resist the tensile forces generated by an earthquake and will fail in a brittle manner. Its strength is primarily for vertical, compressive loads.
(b) Random rubble stone masonry & (c) Size stone masonry
Why they're very poor: All stone masonry is heavy, which means it generates very high inertia forces during an earthquake.
• Random Rubble Masonry is particularly dangerous because the irregular stones create numerous weak, thick, and poorly bonded mortar joints. There is no structural integrity, and the wall can easily fall apart.
• Size Stone Masonry (Ashlar) is better than random rubble but is still an unreinforced, heavy, and brittle system that performs poorly under lateral loads.
💡 Study Tips for Earthquake Resistance
- Reinforcement = Ductility = Safety: This is the fundamental principle of earthquake-resistant design. The steel reinforcement is what provides the ability to bend instead of break.
- Unreinforced Masonry is Brittle: Any masonry system without steel (brick or stone) is inherently brittle and performs poorly in earthquakes.
- Heavy and Brittle is the Worst Combination: Stone masonry is the most dangerous because it is both very heavy (creating large forces) and very brittle (unable to resist them).