behaviour of tilt-up precast concrete building during the 20102011 christchurch earthquakes

1© 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · Structural Concrete 12 (2011), No. 4

The Christchurch region of New Zealand experienced a series ofmajor earthquakes and aftershocks between September 2010 andJune 2011 which caused severe damage to the city’s infrastruc-ture. The performance of tilt-up precast concrete buildings wasinvestigated and initial observations are presented here. In gen-eral, tilt-up buildings performed well during all three major earth-quakes, with mostly only minor, repairable damage occurring. For the in-plane loading direction, both loadbearing and claddingpanels behaved exceptionally well, with no significant damage orfailure observed in panels and their connections. A limited num-ber of connection failures occurred due to large out-of-planepanel inertia forces. In several buildings, the connections be-tween the panel and the internal structural frame appeared to bethe weakest link, lacking in both strength and ductility. This weak-ness in the out-of-plane load path should be prevented in futuredesigns.

Keywords: tilt-up, precast concrete, connections, earthquakes, seismic design

1 Introduction

Between September 2010 and June 2011, the Christchurchregion of New Zealand was hit by a series of major earth-quakes, including the initial Mw 7.1 earthquake on 4 Sep-tember 2010, a Mw 6.3 aftershock on 22 February 2011and another Mw 6.3 aftershock on 13 June 2011. Theseshallow earthquakes were located in close proximity toChristchurch City and caused extensive infrastructuredamage, particularly the 22 February event. Full details ofthe Canterbury earthquake series have been published ina report by GNS Science [1]. The performance of precastconcrete tilt-up-style buildings has been documented in or-der to assist in identifying both designs that performedsuccessfully as well as design weakness that can be im-proved upon in the future.

Tilt-up is a popular form of precast concrete con-struction that originated in the United States in the early1900s [2]. The concept involves casting large concretepanels horizontally on top of the building’s foundationslab, often with additional panels stack-cast on top of eachother. After the concrete has gained sufficient strength, thepanels are lifted and tilted up vertically into position. The

panels are then connected to one another and to the foun-dation using either bolted or welded steel connections, oran in situ concrete stitch. The tilt-up construction tech-nique is a fast and efficient method due to the construc-tion of large, often full-height, wall panels that wouldotherwise be too large to transport to site. Tilt-up con-struction can also be referred to as site precasting, as op-posed to factory precasting at an offsite location.

Early tilt-up construction in California was observedto perform poorly during the 1971 San Fernando earth-quake. The collapse of many tilt-up buildings was attrib-uted to the lack of strength and ductility in the wall-to-roofconnections, and subsequently led to major changes inseismic design previsions [3, 4]. The 1997 Whittier Nar-rows and 1989 Loma Prieta earthquakes highlighted fur-ther inadequacies in tilt-up construction, especially thewall anchorages and out-of-plane strength [3, 5]. Addition-ally, hundreds of tilt-up buildings were severely damagedduring the 1994 Northridge earthquake [6, 7]. The damageto pre-1973 buildings was not surprising, but the numerouswall anchorage failures in post-1973 code buildings was ofconcern and led to further changes to the design seismicforces and connection details.

2 Tilt-up buildings in Christchurch

Tilt-up construction was first introduced into NewZealand in the 1950s with the construction of one- andtwo-storey buildings [8]. The late consulting Engineer W. J.(Bill) Lovell-Smith successfully implemented several tilt-up concrete buildings in Christchurch throughout the1950s [9]. Tilt-up construction has since become one ofthe dominant building types for low-rise commercial andindustrial buildings, replacing reinforced masonry as theprincipal alternative for such buildings, particularly inChristchurch [10].

There are two main variations of tilt-up buildingsthat exist in Christchurch:– Cladding panels attached to steel or concrete frames– Loadbearing panels that also support the roof trusses

Cladding panels do not carry vertical loads from the roof,but provide a weather and fire barrier and may be used aslateral bracing elements to support in-plane wind or seis-mic loadings in addition to out-of-plane loading from theirown self-weight [11]. Loadbearing walls are used as both

Articles

Behaviour of tilt-up precast concrete buildingsduring the 2010/2011 Christchurch earthquakes

Richard Henry*Jason Ingham

DOI: 10.1002/suco.201100035

Structural Concrete 04/2011:Nr. 035

■■ ready for press ■■ after correction ready for press

date, signature

* Corresponding author: [email protected]

Submitted for review: 04 August 2011Revised: 05 October 2011Accepted for publication: 13 October 2011

rhenry

Text Box

the main structural and cladding elements, and must sup-port vertical gravity loads in addition to resisting in-planeand out-of-plane seismic and wind loads [11]. Low-rise tilt-up buildings are typically stiff structures with a fundamen-tal period of < 0.4 s and are usually designed to resist seis-mic loads within the elastic limit, or with a limited ductileresponse (ductility factor μ < 3), in accordance with NewZealand concrete design standards [10, 12]. However, thedesign of tilt-up walls can often be governed by either fireor construction loads instead of seismic actions [9], and soextensive damage to panels and connections should notbe expected following a design level earthquake. Capacitydesign principles are only considered when the building isdesigned for a ductile response and may have also beenneglected when considering a building’s resistance to out-of-plane panel inertial forces. Additionally, older tilt-upbuildings were often designed with non-ductile weldedsteel connections that cannot easily withstand panel de-formations, and cracking at connections can even arisedue to temperature and shrinkage movement. The tilt-upbuilding stock in Christchurch includes a large number ofgenuine site-cast tilt-up buildings as well as factory-castprecast panel buildings of the same style. Due to the simi-larities in the design and connection details, both site- andfactory-cast tilt-up panel buildings were examined withinthe scope of this investigation.

There are several geographical areas in Christchurchwith a significant number of low-rise commercial and in-dustrial tilt-up buildings. In the Hillsbrough and HeathcoteValley suburbs to the south-east of the Central BusinessDistrict (CBD) there is a cluster of recently constructed tilt-up buildings. These buildings are located within a few kilo-metres of the epicentre of the most damaging 22 February2011 earthquake, but are also located on firm ground at thebase of Port Hills. There are also a number of tilt-up build-ings of varying age in the CBD and in the suburb of Brom-ley located to the east of the CBD. These two locations al-so experienced high ground accelerations during the22 February 2011 earthquake, and were located on groundthat experienced severe liquefaction during all three majorearthquakes. Lastly, a number of industrial and commer-cial tilt-up buildings to the south-west of the CBD were sub-jected to less severe ground accelerations during each ofthe major earthquakes. Response spectra calculated fromground motion records in each of these areas have beenpublished by GNS Science [1].

3 Performance of tilt-up buildings

In general, tilt-up buildings performed well during all theChristchurch earthquakes, with mostly only minor dam-age observed which is easily reparable. The most severedamage to tilt-up buildings occurred in areas where lique-faction occurred. The buildings were not designed to ac-commodate the ground settlements that occurred due toliquefaction and therefore examination of these failureswas not considered relevant to the structural performanceof tilt-up buildings. Additionally, the performance of tilt-upbuildings was comparable with other forms of precast con-crete construction. Details of the performance of rein-forced and precast concrete structures during the Canter-bury earthquakes has been published separately [13].

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R. Henry/J. Ingham · Behaviour of tilt-up precast concrete buildings during the 2010/2011 Christchurch earthquakes

Structural Concrete 12 (2011), No. 4

In most cases, the tilt-up panel response in the in-plane loading direction did not result in any significantdamage or failures. This finding is attributed to a combi-nation of several factors:– Ground motion records indicate that for the fundamen-

tal period of typical tilt-up buildings (< 0.4 s), the de-mand during the 22 February earthquake did not great-ly exceed a design level event in the Christchurch CBD.

– All the earthquakes had a short duration.– Tilt-up buildings are designed for an elastic or limited

ductile response.– Construction or fire loads can govern the design of tilt-

up buildings, instead of seismic actions.

More noticeable damage to both panels and connectionswas observed in the out-of-plane loading direction, whichis consistent with observations made following the 1994Northridge earthquake in California [6]. Due to longerfundamental periods, the slender wall panels may have ex-perienced accelerations in excess of the maximum earth-quake loading considered in the out-of-plane loading di-rection.

3.1 Panel performance

With the exception of only a few buildings, damage to theconcrete panels was confined to narrow cracks. Typicalpanel damage that was observed is shown in Fig. 1. Sever-al panels were found to have diagonal cracks, indicative ofin-plane diagonal shear effects, whereas other panels hadhorizontal cracks running along the length of the panel.These horizontal cracks were typically close to the mid-height of the panel and were most likely caused by out-of-plane bending of the panels because panels are usually on-ly supported at foundation and roof levels. In some casesthe horizontal cracks were located adjacent to interior


Fig. 1. Four examples of minor cracking in panels (photos: Hossein Derakhshan, Dmytro Dizhur, John Marshall)

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floor diaphragms that would have contributed to the out-of-plane loads the panels were subjected to. There was oneexample of significant out-of-plane buckling of a panel, asshown in Fig. 2. However, buckling of a slender wall dueto in-plane loading was not observed in any building,which confirmed the findings of previous testing that hasbeen conducted in New Zealand to confirm the panelslenderness limits [14–17].

One of the few examples of tilt-up wall panels thatfailed catastrophically is shown in Fig. 3. In this building,the top section of the wall panel appears to have detachedfrom the steel frame and folded in half. However, this re-sponse is most likely attributable to initial failure of theconnections, which is discussed in more detail below.

3.2 Connection performance3.2.1 Foundation connections

All types of moment-resisting connections at the wall-to-foundation interface appear to have performed exception-ally well. In some buildings it was evident that there hadbeen movement and uplift of the panel, but the resultingdamage was restricted to minor spalling or cracking at thebase of the wall. This damage was in accordance withwhat should be expected for a tilt-up panel designed for anelastic or limited ductile response.

3.2.2 Panel joints

On the strength of visual inspections, the vertical jointsbetween concrete wall panels also performed reasonablywell. In most cases there was evidence of relative defor-mations at the joints between panels, which was identifiedby the joint sealant condition and minor cracking of thepanel edge as shown in Fig. 4. Additionally, irregularities

in structural form contributed to the poor performance ofseveral buildings, and this is highlighted in Fig. 5, whichshows damage at a joint between two sections of a build-ing having different heights. The different dynamic char-acteristics of the two sections with different heightscaused excessive demand at the joint which was revealedby the permanent opening and localized crushing andspalling of the concrete. The cast-in connection betweenthe two panels was subjected to large deformations, butappeared to be largely intact.


Fig. 2. Out-of-plane panel buckling (photos: Liam Wotherspoon)

Fig. 3. Panel failure (photos: Rick Henry)

Fig. 4. Movement at a vertical joint between panels (photos: Rod Fulford)

Fig. 5. Excessive joint demand due to different heights (photos: Rick Henry)

Fig. 6. Edge cracking at insert/connector location (photos: Pia Abercromby,Dmytro Dizhur)

No catastrophic failures were observed for mechani-cal connections between precast panels. However, Fig. 6shows an example of a threaded insert and an embeddedsteel plate connection that had cracks propagating out tothe panel edge. The threaded inserts should be placed fur-ther from the panel edge to avoid this problem and pre-vent potential pull-out of the insert due to the out-of-planeseismic demand. Conversely, the embedded steel plate ap-pears to have sufficient anchorage to prevent the connec-tion pulling out abruptly.

As with the in-plane panel joints, the corner jointsbetween panels had also undergone significant deforma-tion. As shown in Fig. 7, some minor spalling and crack-ing was typically observed at corner connections. How-ever, anchorage of the bolted connections was generallysufficient to ensure that the steel angle yielded in acontrolled manner as opposed to pull-out failure of thebolts.

3.2.3 Connection to portal frames

As stated earlier, only a small number of buildings had tilt-up panels that completely failed and/or collapsed. Threesuch failures are shown in Fig. 8, where the panels becamedetached from the steel portal frames and subsequentlycollapsed. It is suspected that all three failures are attrib-utable to large out-of-plane inertia forces acting on thepanel and subsequent failure of the panel-to-steel frameconnections. Detailed inspection of the failed connectionswas difficult due to the prompt removal of partially col-lapsed panels for safety reasons. However, the building inFig. 8a had an in situ concrete connection around thesteel columns, and the stirrups tied into the in situ stitchappear to have pulled out cleanly from the concrete panel.Additionally, for the building in Fig. 8c, the panel was con-nected to the steel portal frame using four expansion bolts.These bolts appear to have pulled out from the panel, asseen in the close-up insert.

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Where the tilt-up panels were not loadbearing andwere used as cladding panels only, failure of the panelconnections did not result in collapse of the entire build-ing. However, collapse of the large panels themselves stillposes huge safety risks and is unacceptable in terms ofseismic performance. The strength hierarchy of the com-ponents should be considered and the connections be-tween the panel and the steel portal frame should eitherbe designed with sufficient ductility and robustness or in-stead be designed to be stronger than the panel itself usingcapacity design principles. Using this design approach, ifout-of-plane seismic inertia forces exceed the design levelloads, as was probably the case during the 22 February2011 earthquake, the panel should respond in a ductilemanner rather than causing catastrophic failure of theconnections and collapse of the entire cladding panel.

The performance of different connection types wasalso investigated. In general, panel connections that in-cluded an in situ concrete encasement around the steelcolumn performed in a robust manner, as shown in Fig. 9.Minor spalling occurred due to the movement of paneland column, but in most cases the connections remainedundamaged. Steel bolted connections appeared to be lessrobust and a number of failures were observed. Fig. 10shows a building with several failed bolted connectionsthat led to the precast cladding panels leaning out fromthe building. Some of the bolts had torn out of the steelplate due to insufficient edge distance, whereas other ex-pansion bolts had partially pulled out of the concretepanel due to insufficient anchorage. As discussed above,these types of bolted connections appear to be the weakestlink in the out-of-plane load path, and should instead bedesigned to be stronger than the panel. Another poor “clip-plate” connection detail was observed in several buildings,as shown in Fig. 11. The “clip-plate” detail uses a small L-shaped steel plate to hold the precast cladding panel on-to the steel column, and is secured using a single bolt inthe panel. During the earthquakes, the panel and column


Fig. 7. Three examples of deformations at panel corner joints (photos: Pia Abercromby, Dmytro Dizhur)

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movement caused the bolt to loosen, which allowed theplate to rotate downwards, as shown in Fig. 11b. Luckily,this deformation did not result in the panel detachingfrom the building, but the detail could easily be mademore robust by using two bolts instead of one to preventrotation of the steel clip.

3.2.4 Connection to roof diaphragms

In general, the performance of loadbearing tilt-up panelsand their connections to roof diaphragms was good. As


Fig. 8. Three examples of connection failures causing complete panel collapse (photos: Rick Henry, Dmytro Dizhur)

(a)

(b)

(c)

Fig. 9. Concrete-cased steel column (photos: Jamie Lester)

Fig. 10. Failure of bolted connections (photos: Hossein Derakhshan)

Fig. 11. Failure of “clip-plate” connection (photos: Pia Abercromby)(a) as-built, (b) rotated

(a) (b)

with other types of connection, there was indication of rel-ative movement that caused some localized damage to thepanels, but no catastrophic failures were reported. Exam-ples of observed damage are shown in Fig. 12, where roofbeams and cross-bracing are attached to tilt-up panels.

3.3 Partially constructed building

An unusual situation occurred with a tilt-up building thatwas under construction at the time of the earthquake. Asshown in Fig. 13, a number of the tilt-up panels were inplace and temporarily propped, but the first floor and roof

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diaphragms had not yet been constructed at the time ofthe 22 February earthquake. Owing to the lack of supportat roof level, several of the connections between the pan-els failed, but the temporary props were sufficient to pre-vent the panels collapsing.

4 Conclusions

Initial observations from an investigation into the perfor-mance of tilt-up precast concrete buildings during theChristchurch earthquakes have been presented. Tilt-up isa popular form of concrete construction in Christchurchfor low-rise commercial or industrial buildings, and in gen-eral this class of building behaved well during all three ma-jor earthquakes and subsequent aftershocks. Significantdamage occurred in only a small proportion of tilt-upbuildings, and details of these failures are described.

Tilt-up buildings behaved exceptionally well in the in-plane loading direction. Mostly, only minor cracking wasobserved in the wall panels and no significant damage oc-curred at the wall-to-foundation moment-resisting connec-tions. The level of damage observed was consistent with adesign level event and an elastic or limited ductile designphilosophy.

Several connection failures were reported, with themajority of these failures being associated with the out-of-plane loading of non-loadbearing cladding panels. In sev-eral cases the connections between panels and steelframes appeared to be the weakest link, which in a fewcases resulted in catastrophic collapse of the wall panel. Itis recommended that the ductility and strength hierarchyof the load paths be considered to ensure that the connec-tions do not fail in a brittle manner prior to a more ductilefailure of the panel occurring. Additionally, connections ofthe “clip-plate” variety between panels and steel columnsshould be avoided in future designs as they can potential-ly lead to the loss of the panel-to-frame connection duringan earthquake.


Fig. 12. Examples of failure of roof truss-to-panel connections (photos:Hossein Derakhshan, Pia Abercromby)

Fig. 13. Partially constructed tilt-up building (photos: Rick Henry)

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Acknowledgements

The authors would like to acknowledge the assistance ofseveral engineers in Christchurch who helped gather in-formation and photos. These include: Pia Abercromby,Hossein Derakhshan, Dmytro Dizhur, Rod Fulford, JamieLester, John Marshall, Len McSaveney and Liam Wother-spoon.

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University of AucklandCivil & Environmental EngineeringPrivate Bag 92019Auckland Mail CentreAuckland 1142New Zealand

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behaviour of tilt-up precast concrete building during the 20102011 christchurch earthquakes

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