Christchurch Town Hall Briefing to Councillors August 28, 2013

Introduction What happened –Settlement –Lateral Spread –Measurements Analysis –Current capacity Repair and strengthenign –Foundation options and implications –Superstructure strengthening Relevelling Peer Review

Damage sustained

Level Survey 300mm 210mm 150mm 90mm

Verticality Survey 50 mm 30 mm 55 mm 20 mm 16 mm 35 mm

Analysis Full 3D computer anlaysis model developed –Non-linear, ie models strength and then determines outcomes Quake records run –From major Canterbury earthquakes –Scaled to reflect code demands Performance assessed –Compared to current code, IL3

Computer Modelling

Computer Analysis – Canterbury earthquake sequence

Computer Analysis – Code comparison

Current Seismic Status 45%NBS 14%NBS 45%NBS 63%NBS 27%NBS

Repair and Strengthening Repair –Reinstate as nearly as practical to original condition Accept or reinstate concrete damage where no structural implications Strengthen –Upgrade of foundations critical to prevent future damage Option 1 – Piles Option 2 – Grouting –CCC policy is to achieve 100%NBS

Option 1 - Piles

Option 2 - Grouting

Beneficial effect Movement under moderate earthquake –Piles: 10mm lateral, 15mm vertical –Grouting: 0mm lateral, 15mm vertical Movement under design level earthquake –Piles: 150mm lateral, 30mm vertical –Grouting: 50mm lateral, 75mm vertical Conclusions: Jet Grouting selected as preferred option as: –Less intrusive construction process –Superior resistance to lateral spread –Easier waterproofing detailing

Structural Work Summary Upgrade foundations first –Primary need before any other work –Jet grouting Re-level (Limes Room) Strengthen Repair & refurbish

Strengthening Minimal strengthening required to Auditorium, James Hay Theatre and Kitchen Foyer –Columns too flexible and under-strength: rebuild –Bracing excluded as too intrusive –Steel frame alternative under consideration Limes Room/restaurant –Columns too flexible and under-strength: add bracing below level1

Peer Review

End