This shift impacts engineers working on NZTA projects, particularly in how PGA values are sourced and how VS30 classifications are applied.

WHAT'S CHANGED?

Previously, seismic design in New Zealand largely followed NZS 1170.5, where site classification was based on geotechnical parameters like soil class. Now, the NSHM hazard map uses VS30 (time-averaged shear wave velocity over the top 30m of subsurface profile) as the primary metric for site classification. However, VS30 evaluation remains a challenge, as:

• It requires geotechnical data that may not always be readily available.
• The probability of exceedance framework differs from NZS 1170.5, requiring engineers to adapt their methodologies.

HOW DOES ENVIROCALC HELP?

Envirocalc allows engineers to seamlessly integrate the new seismic hazard model into their workflow by offering two key functionalities:

1. Automated kh Calculation – Engineers can input their selected PGA value, and Envirocalc will compute kh following Module 6.
2. Manual kh Input – If an engineer prefers to adjust kh based on project-specific data, they can override the automatically calculated value with a custom input.

This flexibility ensures that engineers can maintain control over seismic assessments while aligning with NZTA’s evolving standards.