Christchurch Town HallChristchurch Town Hall

November 27th, 2013November 27th, 2013

Introduction

• What happened– Settlement– Lateral Spread– Measurements

• Analysis– Current capacity

• Repair and strengthening– Foundation options and implications– Superstructure strengthening

• Relevelling• Peer Review

Damage sustained

Damage sustained

Level Survey

300mm

210m

m

150mm

90mm

Verticality Survey

50 mm

50 mm

30 mm

55 mm 20 m

m

16 m

m

35 mm

Analysis

• Full 3D computer analysis model developed– Non-linear, i.e. 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

Relevelling Consideration

• All of ground floor slab must be removed to complete foundation work

• Relevelling of structure– Must be done, in case of Limes Room– Could be accommodated by careful

detailing in case of Auditorium, Foyer, James Hay Theatre

Peer Review

End