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Load Combinations according to BNBC-2020 & BNBC-2006

 Load Combinations 





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Load Combinations According to BNBC – A Guide for Structural Engineers

When designing a safe and code-compliant structure in Bangladesh, following the Bangladesh National Building Code (BNBC) is essential. One of the most important aspects of structural design is defining the right load combinations—the various scenarios in which different loads act together on a building.

This guide walks you through the BNBC-prescribed load combinations and their significance.

🔹 What Are Load Combinations?

Load combinations represent possible scenarios where various types of loads—dead load (DL), live load (LL), wind load (WL), and earthquake load (EL)—act simultaneously or in sequence. These combinations ensure that the structure can handle the most demanding loading conditions it may encounter during its lifetime.

🔹 Why Follow BNBC Load Combinations?

The BNBC 2020 provides standardized combinations to:

  • Ensure safety under extreme conditions

  • Account for uncertainty in load actions

  • Help engineers design in compliance with local regulations

📋 BNBC 2020 Load Combinations

Here are some typical load combinations based on BNBC recommendations:

  1. 1.4 DL

    • For strength design under dead load only

  2. 1.2 DL + 1.6 LL

    • Commonly used in residential and commercial buildings

  3. 1.2 DL + 1.6 WL

    • Wind-sensitive structures (e.g., high-rise buildings)

  4. 1.2 DL + 1.0 LL + 1.6 WL

    • Combines occupancy and wind effects

  5. 1.2 DL + 1.0 LL + 1.0 EL

    • Used for seismic zones under earthquake loading

  6. 1.2 DL + 1.0 LL + 0.5 WL

    • Wind effects under partial occupancy

  7. 0.9 DL + 1.6 WL

    • Critical case for overturning (e.g., for cantilever structures)

  8. 0.9 DL + 1.0 EL

    • Minimum load with seismic action

💡 Note: These combinations may be adjusted based on occupancy type, building height, soil conditions, and zone-specific factors. Always cross-check with the latest BNBC version and project specifications.

🔧 Application in ETABS or STAAD

Most structural design software like ETABS or STAAD allows you to enter these load combinations manually or generate them automatically. When setting up combinations:

  • Use clear naming (e.g., COMB_DL_LL, COMB_DL_EL)

  • Ensure unit consistency

  • Validate the load direction and factors