A research project at the University of Canterbury’s UC Quake Centre will develop design guides for the seismic retrofit of reinforced concrete buildings in New Zealand – a technical resource currently lacking.
THE FEBRUARY 2011 Christchurch earthquake was one of the most devastating in New Zealand history.
Reinforced concrete buildings badly damaged
While the city’s reinforced concrete (RC) buildings largely survived, apart from the CTV and PGC buildings, most were pushed to their ultimate capacity. This resulted in a building stock with widespread seismic damage that was uneconomic to repair.
These damaged buildings largely date back to the pre-seismic Code era (pre 1970s), but some relatively modern buildings were also damaged.
New Zealand clearly cannot afford similar effects from another earthquake. The economic burden imposed by the complete deconstruction and insurance claims for the most damaged structures has been significant. The economic recovery is expected to take 50 to 100 years.
Widespread retrofits required
Amendments to the Building Act 2004 require territorial authorities to conduct seismic assessments of all non-residential and multi-unit, multi-storey residential buildings. The government is currently revising these timeframes so they vary relative to seismic risk, with high, medium and low-risk areas expected to be allowed 5, 10 and 15 years for assessment and 15, 25 and 35 years for strengthening.
This policy has created significant demand for the assessment and retrofitting of existing RC structures – skills not usually taught in detail in engineering schools.
Most literature on this is in academic publications reporting outcomes for structural subassemblies. They require additional reworking to adapt their analysis and design for multi-storey structures.
Now, a new project at the UC Quake Centre has begun by reviewing relevant research work carried out at the University of Canterbury over the past 10 years.
Design applications being developed
The most viable of the techniques assessed will subsequently be modified or adapted so real-life engineering design applications can be implemented using these methods.
At this stage, the project’s focus is on three topics:
• Assessment of strength hierarchy at RC beam column joints.
• RC beam column joint strengthening using fibre-reinforced polymers.
• RC beam column joint strengthening by steel haunch elements.
Guides for New Zealand use
Ultimately, a series of concise guides will be produced to assist New Zealand engineers and buildings owners with assessing strength hierarchy and retrofit options for existing RC building stock.