Earthquake Strengthening

Since the Christchurch earthquakes seismic strengthening has become a priority across the country, and nowhere more so than in Wanganui with its large collection of historic commercial buildings.

We have completed many Detailed Seismic Assessments in recent years as well as strengthening design work on several major projects including:

History of Seismic Design in New Zealand

The need for a building to be able to resist seismic loads in an earthquake was realised after the Napier earthquake of 1931. Seismic design is now an important part of the design process for buildings in New Zealand.

Since 1931, the government has refined the standards around earthquake design. First in 1965, where they split the country into areas of greater or lesser risk of an earthquake occurring. They also categorised buildings by importance, differentiating between public and private buildings.

The next changes happened during 1976 when a significant development in earthquake resistance design took place. This development, known as capacity design, significantly reduced the risk of catastrophic failure.

The Seismic Assessment Process

The most common way for a building to be assessed is by the IEP (Initial Evaluation Procedure). This process makes an initial assessment of the performance of an existing building against the design standard required for a new building. The result is presented as a percentage of New Building Standards (%NBS).

This process bases the percentage on parameters such as, the building age, geometrical features, general condition, and by the identification of any critical structural weaknesses. The process involves a survey of the building and gathering of relevant information such as construction drawings.

BPL Group have carried out IEP Reports for buildings and have thereafter been engaged by the clients to produce a DSA (Detailed Seismic Assessment). This report outlines what remedial work may be done to improve the buildings performance and gives the owner a more detailed %NBS rating for the building.