Seismic Base Shear Calculator (BNBC 2020)

Basis of Calculation: This application calculates the Seismic Base Shear (V) utilizing the Equivalent Static Analysis Procedure as outlined in Bangladesh National Building Code (BNBC) 2020, Part 6, Chapter 2, Section 2.5.7. The Fundamental Translation Period (T) is calculated using the approximate method (Eq. 6.2.38).

Limitations & Scope (Strictly for Regular, Low-to-Medium Rise Structures): In accordance with BNBC 2020 Section 2.5.6 and Section 2.5.8.1, this static calculation method is limited to specific structure types. This tool should NOT be used for:

• High-Rise Buildings: Structures where the building period (T) exceeds 2.0 seconds, or buildings exceeding 40 meters in height in Zones 2, 3, and 4 (or 90 meters in Zone 1), where Dynamic Analysis is mandatory.
• Irregular Structures: Buildings possessing Vertical Irregularities (e.g., soft story, mass irregularity, weak story) or Plan Irregularities (e.g., torsional irregularity, re-entrant corners >15%, non-parallel systems) as defined in Sec 2.5.5.3.
• Complex Soil Conditions: Sites classified as S1 (Soft Clay/Muck) or S2 (Susceptible to failure/collapse), which require site-specific response spectrum analysis.
• Flexible Diaphragms: The distribution logic assumes rigid floor diaphragms.

User Responsibility: This tool provides the total Lateral Force (Base Shear) only. The user is responsible for the vertical distribution of this force across the building height (F_x) and the subsequent horizontal distribution to shear walls or frames. The user must verify that the structure meets the "Regular Structure" criteria defined in BNBC 2020 Sec 1.3.4 before relying on these outputs.