Lessons from the Field; Steel Structure Performance in Earthquakes in New Zealand from 2010 to 2016 Paper by G Charles Clifton, University of Auckland and Gregory A MacRae, University of Canterbury Presentation by Charles Clifton STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
Scope of Talk • The earthquakes; location, intensity • Special focus on Christchurch earthquake series • Overview of building performance • Damage observed and lessons learned • Multi-storey steel buildings • Light steel framed buildings • Assessment of multi-storey steel framed buildings damaged by earthquake • Conclusions STESSA ’1 8
Geological Setting Wellington Christchurch STESSA ’1 8
Christchurch – between the sea and the hills: NZ’s second largest city Christchurch, population 400,000 STESSA ’1 8
New Zealand Geology Auckland eruption (artist’s impression) Mt Ruapehu 1995 eruption Christchurch Feb 2011 Lake Taupo, earthquake Rhyolite Caldera STESSA ’1 8 Volcano
How well do we learn from the past? By the early 1900’s we were back to building unreinforced masonry BUT: In 1876, following the 1848 and 1855 Wellington earthquakes, this seismic-resistant masterpiece was opened. (Old Govnmt Bldg.) We have done much better since the 1931 Napier earthquake that killed 285 people, but • In life safety, not mitigating economic impact STESSA ’1 8 • This is the lesson to be learned from Christchurch and Wellington
Christchurch Earthquake Series Timing, Intensity, Expected Building Performance STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
The Earthquake Sequence: Impact on Christchurch CBD Magnitude and Intensity of damaging events: 4 Sept 2010: M 7.1, MM 7, ≈ 0.7 x DLE * 26 Dec 2010: M 5.5?, MM 7 to 8 22 Feb 2011: M 6.3, MM 9 to 10, ≈ 1.8 x DLE * 13 June, 2011: M 5.4?, MM 7 to 8 13 June 2011: M 6.3, MM 8 to 9, ≈ 0.9 x DLE * 23 December 2011: M 5.5, MM 6 to 7, ≈ 0.6 x DLE * DLE * = design level event for ultimate limit state (ie the design “big one”) Cumulative effect ≡ close to maximum considered event (step above DLE) STESSA ’1 8
22 February Earthquake – Intensity of Shaking and Duration Figure 1 NZS 1 1 7 0 .5 Spectra and Largest Horizontal Direction Recorded from the CBD Strong Motion Records Notes: 1 . The long dotted black line is the ULS design spectrum for norm al im portance buildings for the soft soil type, Class D, generally considered in the CBD, Z = 0 .2 2 2 . The short dotted black line is the Maxim um Considered Event design spectrum for norm al im portance buildings for Class D soil in the CBD, Z = 0 .2 2 3 . The solid thick black line is the average from the 4 recording stations all of w hich are w ithin 1 km of the CBD and in sim ilar ground conditions STESSA ’1 8
Aftershocks more intense than main event Very good strong motion records • Large number and good quality PGA from February earthquake very intense • 0.5g to 1.2g Hor PGA within CBD (cf: 0.22g for ULS DLE) • Up to 1.8g Hor and Ver PGA in hill suburbs STESSA ’1 8
Columbo St looking South, September 2010 earthquake Columbo St looking South, February 2011 earthquake STESSA ’1 8
• Worcester Street September 2010 earthquake • PGA ≈ 0.15 to 0.2g Retrofitted buildings to 0.15g Worcester Street Feb 2011 earthquake PGA ≈ 0.5 to 0.8g Note vulnerability of street corner building compared with adjacent buildings STESSA ’1 8
Seddon Earthquake 16 August 2013 STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
2013: Key Points Summary • Intensity approx 50 to 70% ULS • See details opposite • Widespread minor damage in Wellington • Some loss of masonry in older buildings • Cracking of masonry and concrete in older buildings • Cracks of drywall construction in new buildings • Structural damage in some new buildings; two subsequently demolished. STESSA ’1 8
Intensity of event in CBD and suburbs • PSA up to 1g at Karori and in hill suburbs • PSA 0.5g at Te Papa • PGA = 0.4PSA approx • PGA = 0.26g recorded Te Puni Village (65% 500 year RP value for Wellington) STESSA ’1 8
Kaikoura Earthquake 11 November 2016 STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
Details and Intensity • M7.8; second most powerful earthquake in NZ’s history • Over 6 faults ruptured • Approx 30 seconds strong ground motion shaking • Intensity under 50% ULS most sites (500 year RP) but exceeding ULS in soft soil basins in Wellington city; soil periods of around 1.5 seconds. STESSA ’1 8
Overview of building performance STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
Performance requirements of modern buildings in > DLE event For normal importance buildings to conventional ductile design, they: 1995 • Shall remain standing under Reinforced Concrete DLE, should also under MCE Building • Structural and non structural damage will occur • Building will probably require replacement STESSA ’1 8
What Types of Damage Occurred? All possible types, singularly and in combination: • Structural damage or collapse • Ground instability: liquefaction, lateral spreading • Damage to external cladding and internal wall linings • Collapsed suspended ceilings , shelving and contents • Damage from landslides, slope instability and rockfalls STESSA ’1 8
Structural Damage STESSA ’1 8
STESSA ’1 8 Structural Damage
Ground instability, liquefaction STESSA ’1 8
Damage to suspended ceilings, shelving, contents STESSA ’1 8
Damage from landslides and STESSA ’1 8 rockfalls
Building Performance; Christchurch Feb 2011 • Houses performed well for life safety • Multi-storey buildings did not collapse • Old buildings did not kill occupants but rather those outside • Newer buildings that collapsed killed occupants • Fire suppression systems worked extremely well STESSA ’1 8
Building Performance; Wellington 2016 • Houses performed well for life safety including near epicentre, PGA> 1g • Old buildings Wellington performed well (low PGA H and PGA V ) • Damage most evident in ductile modern buildings on soft ground • One new building partial collapse; building unoccupied at time of earthquake • Fire suppression systems worked extremely well STESSA ’1 8
Damage to Multi-Storey Steel Framed Buildings and Subsequent Studies into Their Behaviour STESSA ’1 8 1 4 - 1 7 February 2 0 1 8 STESSA ’1 8 Christchurch, New Zealand
Strength and Stiffness: Actual versus Predicted • Steel buildings typically 2 to 2.6 times stronger and stiffer than the models predicted: why: we are working on reasons – slab, non structural elements, HSBC Tower: SFSI • Open plan office building • Design drift 1.3% under • This determined from extent of DLE observed response versus Actual drift ≅ 1% under 2.0 • predicted response from model DLE • Most steel buildings effectively • Ratio of stiffness self-centred without need for real/ model = 2.6 Source: measurement of scuff marks on specific devices to ensure this stairs; details from Design Engineer STESSA ’1 8
Damage and Disruption to Contents and Non-Structural Components • Minimal in buildings that performed well • most contents still in place • Proportional to observed drift • more effects in buildings with higher drift (compare PWC and HSBC tower) • EBFs showed less damage than MRFs • Some effects of vertical acceleration seen, eg • doors off hinges STESSA ’1 8
Contribution of Composite Floor Slab to Steel Concrete Buildings’ Strength and Stiffness • Excellent diaphragm action • Ability to resist beam elongation • Out of plane resistance of some 20 kN/ mm and 25mm elastic threshold • Assists with self centering STESSA ’1 8
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Contribution of composite slab to stiffness Slab spans perpendicular Slab spans parallel to active link to active link Active Link Active Link Active link was omitted from the models in Vulcan, to only capture the out of plane stiffness of the concrete slab Also investigate the effects of: • Secondary beam spacing; 2 beams & 4 beams • Different mesh reinforcement; A142, A193, A252, A393 STESSA ’1 8
Inelastic behaviour of of composite slab this case provides m uch B. Slab parallel to active link higher out of plane stiffness 2 secondary beam s 4 secondary beam s More secondary beams Higher out of plane stiffness STESSA ’1 8
EBF building model + out of plane stiffness of floor slab • Arcelik • Duzce • Elcentro Nonlinear tim e history analysis Ground m otioned • Hokaido Of 1 0 -story EBF building in Ruaum oko scaled to NZS1 1 7 0 .5 • LaUnion • Lucerne • Tabas Typical elevation Typical floor plan STESSA ’1 8
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