L18: Earthquake-prone Buildings Flashcards
What was the catalyst for change in earthquake-prone buildings?
The Christchurch earthquakes;
1350 CBD buildings lost
3rd most expensive disaster globally
How has seismic design changed? (1931, 1935, 1965, 1976, 2004)
1931 - Napier earthquake
1935 - First earthquake design standard created
1965 - Banned new multi-storey unreinforced masonry buildings
1976 - Major improvement to design standards
2004 - General design standards created (not just URM) and specific standards for concrete/steel frame
What are earthquake-prone buildings?
Those likely to collapse during/following a moderate earthquake (below 34% NBS)
Moderate earthquake - one that would generate level of shaking that would be used to design new building at the site
What are the three risk classes and how are they measured?
Low risk - 67%+ NBS
Moderate risk - 34-66% NBS
High risk - below 34% NBS
Measured as the % of strength and ability to resist seismic loads compared to new building standards
What were the EQP Building policy approaches adopted by councils?
Passive approach - do nothing until building consent required
Active approach - identify and assess potential EQP buildings
What are the EQP building assessments?
Initial Evaluation Process - report aimed to determine % NBS
Detailed Engineering Evaluation Report - more detailed version done if IEP found to be below 34% NBS
What could local authorities do if buildings were deemed to be earthquake-prone
Issue section 124 notice which must be completed between 10-20 years; if owners do not comply building is condemned
What was the level of required strengthening?
Some councils require 67% NBS but Courts held Councils cannot demand strengthening above 34% NBS
What did the Canterbury Earthquake Royal Commission policy review do?
Recommended improving regulations
What did the DBH policy review do?
Public consultation; better information, strengthening required, timeframes, exemptions for low risk, heritage buildings, disabilities
What did the Amendment Bill policy review do?
Shift from uniform approach to targeting areas and timeframe based on location (risk), 10yr extension to heritage buildings, reduced cost, timeframe depending on building type (shorter for schools)
How were residential buildings impacted?
Standards apply to buildings on good ground; other standards apply for sites susceptible to liquefaction and reclaimed land
What is liquefaction?
Soil where water can flow up through strata resulting in sand boil and settlement
What are the costs associated with strengthening EQP buildings?
Varies depending on building
Soft costs include assessment, design and consent
Hard costs estimated at $300-416/m2
What are retrofit solutions and what are some examples?
Can be aesthetic, not visible, interior, exterior
Eccentric bracing, buttressing, seismic dampers, shotcrete/GFRP, independent structural frame, floor diaphragm, seismic base isolation
