Seismically Resilient Building Technology applied in New Zealand since Presented By : Stephen Hogg

Transcription

1 Seismically Resilient Building Technology applied in New Zealand since 2013 Presented By : Stephen Hogg

2 Introduction Resilient Buildings The turning point for resilient design in New Zealand Benefits of Building Resilience Examples of earthquake mitigation devices and resilient mechanisms in use Case study examples of different resilient buildings constructed today Building Resilience Costs Building Resilience Affordability of resilient buildings Presented at Pacific Conference on Earthquake Engineering in 2015 (10PCEE15), updated with additional material for STESSA 2018

3 Earthquake February 22 nd 2011 Christchurch, New Zealand The 2011 Canterbury earthquakes were a turning point in New Zealand for the application of resilient building technologies Prior to 2011 there were a handful of non base isolated resilient building designs primarily in Wellington and Nelson which were developed as demonstration projects for resilient technology rather than driven by seismic risk and asset protection. Following the Canterbury Earthquakes of 2011 there are now in excess of 30 resilient buildings constructed in Christchurch alone. NZ design codes have not been able to keep pace with the resilient technology and the construction boom created by the Christchurch rebuild. New Zealand codes allow alternative design solutions which has allowed resilient design to evolve. A working group has been formed to develop a New Zealand resilient building design guide which is currently work in progress. Base Isolation guidelines are more advanced currently in a DRAFT format.

4 Building Resilience Benefits Facility can function post disaster. Business continuity Early reoccupation Early economic recovery Avoidance of building demolition and time cost for reconstruction Seismic Mitigation systems provide limited structural damage and ease of repair to defined areas ( replacement of plug and play ductility devices) Lower insurance risk for total building damage easier to achieve insurance in an active seismic environment in a seismically aware insurance market Suitability for both infrastructure and multi-level commercial buildings Staff confidence in the building s seismic resilience Access to records immediately after a disaster Improved morale post-earthquake Nelson Marlborough Institute of Technology 2009 using post tensioned rocking timber shear walls

5 Mitigation Systems - Resilient Devices used in New Zealand Examples of replaceable devices designed into non-base isolated resilient buildings to provide plug and play ductility to protect primary structure from earthquake damage Replaceable K Brace Link Compression and tension yielding energy dissipaters U shaped flexural plates Ringfeder Spring Triple friction pendulum bearing One way sliding hinge joint Two way sliding hinge joint Perforated ductile weld plates

6 Isolation Systems Friction Pendulum and Lead Rubber Bearings Two types of bearing are typically used in New Zealand. The selection of bearing type is usually dependent on the displacement availability or Engineer design preference. Image courtesy of Earthquake Protection systems Friction Pendulum Slider Bearings First used in NZ for 151 Cambridge Tce in 2014 to better manage response of irregular building shapes Lead Rubber bearings Traditionally used in New Zealand

7 Resilient Mechanism - Post Tensioned Rocking Walls Rocking wall mechanism Replaceable U shaped flexural plate for energy dissipation Shear wall post tensioned down to foundation beam Shear wall can rock and return to centre under seismic loads Ductile shear wall damage is avoided U shaped flexural plates absorb seismic energy and are replaceable

8 Resilient Mechanism - Rocking Braced Frames with Ringfeder hold-down springs Ringfeder springs post tensioned to foundation Mechanism of a typical rocking braced frame Base hold-down detail Structural Steel prefabricated frames Frames rock to avoid yielding damage Frames are returned to centre by springs at the base Avoids the need to post tension, keeps frames lightweight

9 Resilient Mechanism - Sliding Hinge Joint Frames Structural Steel Two Way Sliding Hinge Joint Frame. Detailed design developed in conjunction with University of Canterbury Sliding Hinge Joints each way using 600 x 600 steel SHS columns in two way bending Structural Steel One Way Sliding Hinge Joint Frame Sliding Hinge Joints one way using conventional Universal beams and Welded I section columns Two way sliding hinge joint frame Expected 90% re-centring system Column Force (b) (c) (a) (e) Displacement (d) One way sliding hinge joint frame

10 Resilient Mechanism K Brace Replaceable Shear Link Active links bolted into K Brace Frames All the proven advantages of standard ductile K Brace frames with easy link replacement if required Most cost effective resilient system available Resilience only for primary structure Non re-centring system

11 Case Study 1 - The Terrace Development Christchurch 2015 Low Damage - Structural Steel Two Way Sliding Hinge Joint Frame Sliding Hinge Joints each way using 600 x 600 steel SHS columns Significant cost in steel plating at the moment joints

12 Case Study Cambridge Terrace - Christchurch 2014 Low damage rocking K Brace frames Ringfedder restoring springs at base of K brace frames Rocking frames are independent of the gravity structure U shaped flexural plates incorporated for energy dissipation

13 Case Study 3 - Knox Church - Christchurch 2014 Seismic bracing piers allowed to rock in each direction Plug and play energy dissipaters are replaceable post earthquake tension compression yielding device

14 Case Study 4 Westpac Building Christchurch Storey K Brace with replaceable link K Braces in two directions Structural steel and Comflor 80 gravity structure 800mm reinforced concrete raft foundation

15 Case Study Cambridge Terrace Christchurch 2014 Triple friction pendulum bearing manufactured by Earthquake Protection Systems (EPS) in the USA. First use in New Zealand Overall size 914mm x 323mm Displacement capacity 572mm 500 Year Earthquake Force transfer 0.13g 254mm displacement at a period 2.8 seconds 2,500 Year Earthquake Force transfer 0.20g, Displacement 520mm displacement at a period 3.3 seconds

16 Case Study 6 Lucas House- Nelson 2013 Seismic bracing walls are able to rock Post tensioned rocking wall with compression and tension yielding energy dissipaters Walls are post tensioned to provide stability and restoring Plug and play energy dissipaters are replaceable post earthquake

17 Case Study 7 Elevate Apartments - Wellington Storey rocking braced frame Nth Sth direction. 15 Storey sliding hinge joint frame East West direction

18 Building Resilience Cost Based on recent experience we see these cost premiums for resilient structures built in New Zealand Resilient Building additional 1% - 3% cost premium compared to code minimum ductile building Base Isolated Building additional 5% - 7% cost premium compared to code minimum ductile building Te Puni Student Accommodation using concentric braced rocking frames and Ringfedder hold down springs and sliding hinge joints

19 Building Resilience Affordability Consider a notional six storey code minimum commercial office building with car parking in Christchurch (NZ) Allow 5% additional cost for building resilience Building Costs Development Cost For code minimum building Development Cost For resilient plus 5% resilient cost Land Acquisition 2.5M 2.5M Total Construction 19.5M 20.5M (plus 5%) Cost Professional Fees 2.7M 2.7M Consent fees 1.2M 1.2M development contributions and sundries Bank Charges 50K 50K Interest 600K 600K Development contingency Total Development Cost 1.0M 1.0M 27.5M 28.6M

20 Building Resilience Affordability Target Financial Return = 7.5% of the rental income per year Development Cost for code minimum building Development Cost for resilient plus 5% resilient cost Total Development Cost 27.5M 28.6M 2017 Christchurch market rental income of $425/m2 = 2.2M Rental Income per year Building Value = Rental Income / 7.5% return Margin = Building Value Total Development Cost 2.2M 2.2M 2.2M/7.5% = 29.3M 2.2M/7.5% = 29.3M 29.3M 27.5M = 1.8M (6%) 29.3M 28.6M = 700K (2%) small margin available feasibility is Minimal margin available marginal Resilient building not feasible

21 Building Resilience Affordability Target Financial Return = 7.5% of the rental income per year Development Cost for code minimum building Development Cost for resilient plus 5% resilient cost Total Development Cost 27.5M 28.6M 2017 Christchurch market rental income of $425/m2 = 2.2M Rental Income per year Building Value = Rental Income / 7.5% return Margin = Building Value Total Development Cost 2.2M 2.2M 2.2M/7.5% = 29.3M 2.2M/7.5% = 29.3M 29.3M 27.5M = $1.8M (6%) 29.3M 28.6M = $700K (2%) small margin available feasibility is Minimal margin available marginal Resilient building not feasible Insufficient margin Target is 20%

22 Building Resilience Affordability Target Financial Return = 7.5% of the rental income per year Development Cost for code minimum building Development Cost for resilient plus 5% resilient cost Total Development Cost 27.5M 28.6M 2017 Christchurch market rental income of $425/m2 = 2.2M Rental Income per year Building Value = Rental Income / 7.5% return Margin = Building Value Total Development Cost 2.2M 2.2M 2.2M/7.5% = 29.3M 2.2M/7.5% = 29.3M 29.3M 27.5M = $1.8M (6%) 29.3M 28.6M = $700K (2%) small margin available feasibility is Minimal margin available marginal Resilient building not feasible The rental needs to increase - Lets try $500/m2 per year

23 Building Resilience Affordability Target Financial Return = 7.5% of the rental income per year Development Cost for code minimum building Development Cost for resilient plus 5% resilient cost Total Development Cost 27.5M 28.6M 2017 Christchurch market rental income of $500/m2 = 2.2M Rental Income per year Building Value = Rental Income / 7.5% return Margin = Building Value Total Development Cost 2.6M 2.6M 2.6M/7.5% = 34.7M 2.6M/7.5% = 34.7M 34.7M 27.5M = 7.2M (20%) 34.7M 28.6M = 6.1M (17.6%) Margin OK development feasible Margin OK resilient building feasible Note $520/m2 achieves 20% margin Depending on market forces a developer may want a higher rental for the additional cost of a resilient building tenant pays Or a tenant may demand a resilient structure if a tenant is to agree to lease the building for market rental!!! developer pays

24 Building Resilience Key Point Summary 1. A working group is developing a New Zealand low damage design guidance document which will provide a standardised framework for industry to design and specify resilient buildings 2. There are plenty of benefits for resilient structures to be preferred building types in seismic areas 3. Resilient design adds a premium to the build cost between 1% and 7% on the total development cost 4. The additional cost of a resilient building is equivalent to a rental of $20/m2 per year (4% increase in floor rental) 5. The developers margin is reduced by 2.4% for a resilient building (20% reduces to 17.6%) Therefore. Any commercial building that is financially feasible can stack up as a resilient building if the rent is right!

25 Thankyou Presented By: Stephen Hogg Technical Director Aurecon