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Background

The Seismic Load Calculator allows engineers to calculate base shear and distribute lateral seismic forces across multiple stories based on site and building parameters. It supports Earthquake Design Categories (EDC) I and II, with a focus on residential and small commercial structures. This guide walks you through key sections of the calculator and highlights how calculations are performed under the AS 1170.4:2024 standard.

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Key sections of the calculator

The calculator has three main input areas:
  1. Site & Building Parameters
  2. Lateral Load Distribution
  3. Summary

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1. Site & Building Parameters

This section collects all relevant information to determine seismic category, building importance, and hazard levels. Seismic Analysis Interface

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Housing vs. Non-Housing

For domestic housing structures under 8.5 m tall, the calculator automatically assigns the appropriate classification and simplifies compliance under Clause A.2 of AS 1170.4.

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Building Height and Story Info

Use the Building Stories table to enter the number of stories, their individual heights, and seismic weights. This helps determine how lateral loads are distributed through the structure.

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Site Class and Hazard Factors

Specify the sub-soil class and hazard design factor (Z) according to the building’s location. The calculator uses this to determine seismic zone compliance, in combination with probability and importance factors.

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2. Lateral Load Distribution

Depending on your selected EDC, the calculator automatically switches between:
  • Cl. A.2 simplified static method (for EDC I or housing structures)
  • Cl. 5.4 and Section 6 equivalent static method (for EDC II)
Enter the building stories and seismic weights, and the calculator distributes base shear across the height of the building according to AS 1170.4 provisions. Lateral Loads Pn Each storey’s lateral force and resulting shear is displayed in a table. You can also export these forces for diaphragm or wall design workflows.

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3. Summary

The Summary shows total base shear and lateral forces. These values are derived from:
  • Building mass and seismic weight
  • Hazard factor and probability
  • Sub-soil conditions
  • Story-by-story lateral load calculations
These forces can then be used in downstream wall, diaphragm, or column designs.

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What’s not supported (yet)

  • EDC III structures, typically those over 50 metres in height or requiring dynamic analysis
  • Structures with torsional irregularities or those requiring site-specific ground motion assessments

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Try it in your next project

Use the Seismic Load Calculator to simplify AS 1170.4 checks and speed up lateral load modelling across residential and small commercial buildings. Try the calculator now →