IEP, DEE & Seismic Evaluation of Commercial Buildings

December 16, 2013

Today building owners and investors could be left bewildered by the array of earthquake assessments and reporting available to them and it may be difficult to determine what is appropriate.  Suddenly “IEP“, “DEE” and “%NBS” have become part of everyday vocabulary for those in the construction industry and property investors.  The impact of these assessments can be significant and extensive.  The risk has been transformed from that of harm or death to a premium that will be paid in insurance and lessor difficulties in leasing earthquake prone buildings.

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The first step in the seismic evaluation of a building is usually the Initial Evaluation Procedure (IEP).  This is an evaluation procedure devised by the New Zealand Society for Earthquake Engineering (NZSEE) in 2006.  The purpose of the IEP is to identify earthquake prone buildings.  Earthquake prone buildings are defined as being less than 33%NBS (33% New Building Standard).  The Building Act 2004 requires Territorial Authorities (TA) to adopt policies on earthquake prone buildings.  Section 124 outlines the powers of TAs in respect of dangerous, earthquake prone, or insanitary buildings.  The powers include hoardings around and warning signs on the building and significant fines.

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Why would a Detailed Engineering Evaluation (DEE) be required?  There are two reasons a DEE is carried out.  Firstly, to provide a more accurate assessment of the building strength if it is found to be on the threshold of earthquake prone and secondly, to provide a more accurate assessment of the buildings capacity to resist a ‘moderate’ earthquake with a view to strengthening.  The IEP report is intended to be used as a broad brush approach to quickly identify earthquake prone buildings using minimal resources.  A DEE may be required to establish whether the building is above the 34%NBS threshold.  Given the conservative nature of the IEP procedure, which relies heavily on engineering judgement, the results are far less definitive than a DEE.  The DEE requires calculations and analysis and also gauges the strength of structural elements and systems.  This information may provide a methodology for strengthening the building.  Often a building owner may already be aware of the limited seismic resisting capacity of their building and may rather direct resources towards a more detailed analysis, with a view to structural strengthening, from the outset.

Once a building owner enters the realms of structural strengthening, the issue becomes how close to NBS is an appropriate goal.  NZSEE recommends 67%NBS as the minimum that should be considered for the improvement of structural performance, particularly when major alterations or refurbishments are contemplated.  The seismic capacity of a building must now become an important consideration for all building owners.  We recommend an IEP assessment is carried out when undertaking technical due diligence pre purchase.  Having comprehensive knowledge of your building puts you in a more powerful position.  A building that has a high %NBS and grading is a highly marketable investment and conversely understanding a low %NBS and grading may be used for planning future improvements.

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