1. Zheng Li PhD, Assistant Professor Department of Structural Engineering Tongji University Seismic Performance of Timber-Steel Hybrid Structures The Fifth Tongji-UBC Symposium on Earthquake Engineering "Facing Earthquake Challenges Together”

2. Outline 1. Introduction 2. Timber-steel hybrid structure 3. Experimental study 4. Numerical modeling 5. Reliability analysis 6. Summary

3. 1. Introduction Earthquakes!

4. 1. Introduction Christchurch earthquake, M6.3, New Zealand, 2011, Photo by A. Trafford Wenchuan earthquake, M8.0, China, 2008 Kobe earthquake, M6.9, Japan, 1995, Photo by M.Yasumura

5. Murray Grove 8-storey CLT structure in London (2008) 10-storey CLT structure in Melbourne (2012) Timber-concrete hybrid building in Quebec City (2010) Examples of multi-storey timber buildings 1. Introduction

6. 2. Formation of timber-steel hybrid structure Why not hybridization? Hybridization can be an alternative to develop multi-storey timber buildings, because it normally combines the respective benefits of different materials. In this project, a kind of multi-storey timber- steel hybrid structure is proposed. Timber-steel hybrid structure Timber hybrid diaphragm Steel moment resisting frame Suitable for multi-story buildings Good seismic performance Higher degree of industrialization Advantages Light wood-framed shear wall Horizontal system Vertical system

7. Steel frame Infill wood-framed shear wall Bolts Anchor bolts Hold-down  Timber-steel hybrid shear wall system 2. Formation of timber-steel hybrid structure

8. Specimen A : light wood-framed diaphragm single-sheathed infill wood- framed shear wall Specimen B: Timber-steel hybrid diaphragm double-sheathed infill wood- framed shear wall A-1, A-2, A-3 and B-1, B-2, B-3 are timber-steel hybrid shear wall systems in specimen A and specimen B.  3.1 Specimen design 3. Experimental study Layout of specimen A and specimen B

9. Specimen A (light wood-framed diaphragm & single-sheathed infill wood shear wall) Specimen B (timber-steel hybrid diaphragm & double-sheathed infill wood shear wall ) 3. Experimental study  3.3 Installation of the specimen

10. The specimens were first subjected to non-destructive monotonic load to study the initial lateral stiffness of the steel frame before and after the installation of infills. Then fully reversed quasi-static cyclic load was applied and cycled to 80% of degradation in the specimen’s strength. 3. Experimental study  3.4 Test Procedures

11. Nail heads embedding into the sheathing panels Failure of weld Failure modes 3. Experimental study After the tests Fatigue fracture of nails Fall off of the sheathing panels

12. (a) A-1 (c) A-3 (b) A-2 Hysteresis loops (d) B-1 (f) B-3 (e) B-2 3. Experimental study

13. Share of force between timber and steel In a timber-steel hybrid system, the lateral load was resisted by the steel frame and the infill wood shear wall simultaneously. For each specimen, the shear forces carried by the two subsystems were obtained respectively. For instance, the shear force carried by the steel frame and the infill wood shear wall of A-2 are shown below. 3. Experimental study

14. Share of force between timber and steel Based on the test results of the shear force carried by each subsystem, the percentage shear force of each subsystem could be obtained. In the initial loading stage (within 25mm). The single- and double-sheathed infill wood shear walls carried 50-75% and 65-95% of the lateral load of the hybrid system; When damages occurred in the wood shear walls, the percentage shear force in the wood shear walls decreased, and the steel frame became more active. Percentage shear force in the subsystems: (a) specimen with single-sheathed infill light wood- framed shear walls; (b) specimen with double-sheathed infill light wood-framed shear walls 3. Experimental study

15. Numerical model – timber-steel hybrid shear wall 4. Numerical modeling

16. User defined element in ABAQUS 4. Numerical modeling

17. Model validation 4. Numerical modeling Load–displacement relationship Energy dissipations

18. Damage assessment 5. Reliability analysis Test setup Backbone curves Performance level Immediate occupancy (IO) Life safety (LS) Collapse prevention (CP) Drift limit (%)0.72.55.0

19. 5. Reliability analysis Baseline walls:

20. 5. Reliability analysis Earthquake input: According to Chinese code of “Seismic design of building structures”, the probabilities of 50-year exceedance for the earthquakes considered in the IO, LS, and CP limit states are 63%, 10% and 2%, which are in accordance with the average return period of 50, 475, and 2475 years. NO.EventDateStationComponent PGA (g) 1Wenchuan12/05/2008WolongEW0.976 2Tangshan28/071976Beijing HotelEW0.067 3Ninghe25/11/1976Tianjin HospitalNS0.149 4Qian’an31/08/1976M0303 Qianan lanhe bridgeNS0.135 5Chichi-121/09/1999CHY006NS0.345 6Chichi-221/09/1999TCU070EW0.255 7Chichi-321/09/1999TCU106NS0.128 8Chichi-421/09/1999TAP052NS0.127 9Kobe17/01/19950 KJMAKJM0000.821 10Northridge-117/01/19940013 Beverly Hills - 14145 MulholMUL0090.416 11Northridge-217/01/199424278 Castaic - Old Ridge RouteORR0900.568 12Northridge-317/01/199490086 Buena Park - La PalmaBPK0900.139 13Loma Prieta-118/10/198947381 Gilroy Array #3G030000.555 14Loma Prieta-218/10/198957425 Gilroy Array #7GMR0000.226 15Loma Prieta-318/10/198958224 Oakland - Title & TrustTIB1800.195

21. 5. Reliability analysis Hybrid shear wall with K r =0.5 Hybrid shear wall with K r =1.0 Hybrid shear wall with K r =2.5Hybrid shear wall with K r =5.0 Fragility analysis

22. Response surface method 5. Reliability analysis Step 1. Limit state function Step 2. Response surface generation by numerical simulations where K r is a shear wall design factor 15 Spectrum levels (0.10, 0.16, 0.30, 0.45, 0.60, 0.75, 0.90, 1.05, 1.20, 1.35, 1.50, 1.65, 1.80, 2.05 and 2.10 g) 4 K r levels (i.e. 0.5, 1.0, 2.5, and 5.0) 15 historical earthquake records

23. 5. Reliability analysis Step 3. Response surface fitting by polynomial functions Step 4. Failure probability estimation

24. Probabilistic-based design 5. Reliability analysis Performance curves for the hybrid shear wall with K r = 2.5

25. 1.For the hybrid shear wall system, the infill wood-framed shear walls were very effective in the initial stages of loading, while the steel moment resisting frame turned out to be more active around the ultimate limited state of the hybrid system. 2.Reliability analysis and performance-based seismic design of the timber-steel hybrid building systems need robust computer models. Moreover, the definition of the performance criteria and the development of limit state functions are both key issues. 3.Different methods can be used in the evaluation of seismic reliability of timber-steel hybrid systems, which offers effective tools for the development of relative code provisions. 6. Summary

26. Thanks very much for your kind attention! zhengli@tongji.edu.cn