Glossary
Base Shear
Plain-Language Definition
The total horizontal seismic force acting at the base of a building during an earthquake, calculated as a function of the building's weight, seismic zone factor, soil type, and structural system.
Technical Context
Base shear V = Cs × W, where Cs is the seismic response coefficient (depends on zone factor Z, importance factor I, response modification R, and spectral acceleration) and W is the effective seismic weight. Higher base shear = more force the structure must resist. BNBC 2020 specifies zone factors for Bangladesh: Zone I (Z=0.12) to Zone IV (Z=0.36).
Why It Matters
Base shear determines the minimum structural resistance a building must provide against earthquakes. A building designed for Zone I base shear is structurally inadequate if located in Zone III. Understanding base shear is essential for evaluating whether an existing building meets current seismic code requirements.
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