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Emulative design, which requires critical sections to re-

spond under load as they would or cast-in-place concrete,

together with the capacity design philosophy, was crucial

or gaining the acceptance o structural engineers in New

Zealand. In capacity design, the primary structural system

or resisting seismic orces is rst designed to have a

suitable mechanism o accommodating nonlinear lateral

deormation, with the engineer explicitly dening the loca-

tions o plastic hinges. Plastic hinge regions are designed

and detailed or strength and ductility during a severe

earthquake. Then the remainder o the structural system is

provided with sucient strength to avoid other possibleailure modes and maintain ductility ater fexural over-

strength develops at the plastic hinges.

Resisting lateral forcesfrom earthquakes

Moment-resisting rames have been the most common

seismic-orce-resisting system or tall buildings in New

Zealand. A beam sidesway mechanism, in which plas-

tic hinges orm in the beams due to strong columns and

weak beams, is the preerred nonlinear mechanism. To

ensure that fexural hinging does not occur at locations not

Preview of PCIs

New Zealand earthquake

reconnaissance team report

Robert B. Fleischman, Jos I. Restrepo, Joseph R. Maffei,and Kim Seeber

Precast concrete structuraldesign in New Zealand

recast concrete has been used in New Zealand

since the early 1960s and became widely accepted

in the 1980s as an eective construction method

or seismic resistance. Since then, precast concrete

has been extensively used there. Park described the evolution

o precast concrete design in that country.1

During the building boom o the mid- to late 1980s, the speed

o construction and high quality o precast concrete gave itsignicant advantages over cast-in-place concrete. The New

Zealand concrete design standard2 o the time included com-

prehensive provisions or the seismic design o cast-in-place

concrete structures but did not cover all aspects o precast

concrete structures. A study group o the New Zealand

Concrete Society was ormed in 1988 to summarize data on

precast concrete design and construction, recommend best

practices, and identiy areas or urther research. A 1995 revi-

sion o the New Zealand concrete design standard3 included

new provisions or precast concrete structures based on the

research o the early 1990s.1

PCI Reconnaissance Team ReportPhoto:Joseph

R.

Maffei

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designed or ductility, or that shear ailure cannot occur

anywhere in the structure, the maximum actions likely to

be imposed are calculated rom the fexural overstrengths

at the plastic hinges.1 Tall buildings in New Zealand were

typically constructed using perimeter moment rames with

relatively closely spaced sti columns and sti beams.

Interior beams and columns carried gravity load; their

contribution to seismic resistance was neglected.

Structural precast concrete walls (shear walls) have also

been used to provide seismic resistance in medium-rise

buildings in New Zealand. In some cases precast concrete

walls and rames are combined to orm dual systems.

These walls are designed to develop a plastic hinge at the

base. The most important consideration in detailing plastic

hinge regions or ductility is to provide sucient trans-

verse reinorcement, whether rectangular stirrups, hoops,

or spirals. The transverse reinorcement acts as shear rein-

orcement, connes the concrete, and prevents premature

buckling o the longitudinal reinorcement.1

Earthquakeof February 22, 2011

A magnitude 6.3 earthquake struck Christchurch, New

Zealand, at 12:51 p.m. on Tuesday, February 22, 2011. The

epicenter was located 10 km (6 mi) southeast o the city

center.4 The earthquake caused 182 deaths and damaged

thousands o buildings.5

New Zealand lies on the Pacic Rim and has a history

o strong earthquakes. However, Christchurch is about

240 km (150 mi) rom the nearest known major ault, andthus was not expected to experience a large earthquake. It

is in a moderate seismic hazard zone comparable to that o

Portland, Ore. The February earthquake, along with a less-

damaging earthquake the previous September, indicates the

existence o ault lines much closer to Christchurch.

In the February 22 earthquake, an interval o extremely

high-intensity shaking lasted approximately 8 sec. The

average response spectrum o the ground motions recorded

in the city center was approximately equivalent to the

Christchurch maximum considered earthquake and was

stronger or substantial ranges o typical building naturalrequencies. For individual records, the ground motion

contained requency ranges where it was substantially

stronger, similar to the maximum considered earthquake in

Berkeley, Cali.6 The February event was extremely strong

near the epicenter, with vertical accelerations o up to 2g.

Soil liqueaction was signicant and widespread due to the

presence o a high water table in sandy soil. Deep ounda-

tions are airly rare in Christchurch, and several buildings

and bridges showed evidence o support movement or di-

erential settlement.

Case study:PricewaterhouseCoopersoffice building

The 21-story PricewaterhouseCoopers oce building was

constructed in the 1980s (Fig. 1). It was designed with

an exterior moment-resisting rame and constructed us-

ing a detail in which the precast concrete joint (Fig. 2) is

placed over the column below. Vertical ducts in the precast

concrete joint allow the vertical reinorcement rom the

column to be threaded through and into the column above.

The ducts are grouted once the joint is in place.1

Figure 3 shows the perimeter moment-resisting rame

(background) and the interior gravity rame (oreground)

ollowing the earthquake o February 22. As can be seen,

the columns are more closely spaced in the perimeter

rame.

A visual survey o this building by the authors showed a

pattern o damage consistent with capacity design (Fig. 4).

The lowest two foors, situated above a parking garage and

undergoing less deormation, showed no plastic hinging.

The lower- to midlevel foors showed the greatest beam de-

Figure 1. PricewaterhouseCoopers building under construction in Christchurch,

New Zealand.

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3/5Winter 2012 |PCI Journal4

ormation and damage, and the upper foors less damage.

Figure 4 shows the damage to the perimeter rame on the

interior o the 10th foor. The north-south beam exhibits

fexural-torsional cracks rom earthquake displacement

perpendicular to the rame, while the east-west beam

exhibits fexure cracks. The authors judge that the fexural

cracking observed does not reduce the strength o the

beams and does not substantially diminish their continueddeormation capacity or the ability o the structure to resist

uture earthquakes.

The exterior moment-resisting rame o the Pricewater-

houseCoopers building perormed as intended, orming the

desired fexural plastic hinges at the ends o the beams. No

structural damage was observed in the columns. Where the

damage was greatest, cracking and fexural torsion were

associated with these hinges. The extent o the damage

is not surprising given the extreme intensity o the earth-

quake motions. The authors judge the oce building to

have met or exceeded its design requirements to avoid col-

lapse in the maximum considered earthquake.

Final report

A ull report covering the perormance o a number o

other types o precast concrete structural systems during

the February 22, 2011, New Zealand earthquake, some

Figure 3. Corner joint in rst-level parking podium area ater February 22, 2011, earthquake in New Zealand. Photo courtesy o Franz Kahn.

Figure 2. Typical precast concrete corner unit being installed in perimeter

moment rame o the PricewaterhouseCoopers building.

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5. The Canterbury Earthquakes Royal Commission.canterbury.royalcommission.govt.nz.

6. Earthquake Engineering Research Institute (EERI).

2011.Learning from Earthquakes: The M 6.3 Christ-

church, New Zealand, Earthquake of February 22,

2011. EERI Special Earthquake Report. Oakland, CA:

EERI.

o which suered serious damage, will be published in auture issue o the PCI Journal.

References

1. Park, Robert. 2002. Seismic Design and Construction

o Precast Concrete Buildings in New Zealand. PCI

Journal, V. 47, No. 5 (SeptemberOctober): pp. 6075.

2. Standards Association o New Zealand. 1982. Code of

Practice for the Design of Concrete Structures. NZS

3101:1982. Wellington, New Zealand: Standards As-

sociation o New Zealand.

3. Standards Association o New Zealand. 1995. The

Design of Concrete Structures. NZS 3101:1995. Wel-

lington, New Zealand: Standards Association o New

Zealand.

4. GNS Science. 2011. The Canterbury Earthquake

Sequence and Implications or Seismic Design Levels.

Consultancy report 2011/183 to Canterbury Earth-

quakes Royal Commission. Compiler: T. H. Webb.

Figure 4. Corner joint in upper foor indicated damage suered in February 22, 2011, earthquake in New Zealand. The north-south beam (upper let) exhibits fexural-

torsional cracks, while the east-west beam (upper right) exhibits fexure cracks.

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5/5Winter 2012 |PCI Journal6

About the authors

Robert B. Fleischman, PhD, is anassociate proessor in the Depart-

ment o Civil Engineering and

Engineering Mechanics at the

University o Arizona.

Jos I. Restrepo, PhD, is a

proessor in the Department o

Structural Engineering at the

University o Caliornia at San

Diego.

Joseph R. Maei, S.E., PhD,

LEED AP is a principal at

Rutherord & Chekene Engineers

in San Francisco, Cali.

Kim Seeber, P.E., FPCI, is a

senior vice president at Seaboard

Services o Virginia Inc. in

Taylors, S.C.

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