Seismic Performance of Timber-Steel Hybrid Structures

Transcription

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

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 Wenchuan earthquake, M8.0, China, 2008 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 1. Introduction Examples of multi-storey timber buildings 10-storey CLT structure in Melbourne (2012) Murray Grove 8-storey CLT structure in London (2008) Timber-concrete hybrid building in Quebec City (2010)

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 timbersteel hybrid structure is proposed. Timber-steel hybrid structure Timber hybrid diaphragm Steel moment resisting frame Light wood-framed shear wall Horizontal system Vertical system Advantages Suitable for multi-story buildings Good seismic performance Higher degree of industrialization

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

8 3. Experimental study 3.1 Specimen design Specimen A : light wood-framed diaphragm single-sheathed infill woodframed shear wall Specimen B: Timber-steel hybrid diaphragm double-sheathed infill woodframed shear wall Layout of specimen A and specimen B 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.

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

10 3. Experimental study 3.4 Test Procedures 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.

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

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

13 3. Experimental study 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.

14 3. Experimental study 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. Percentage shear force in the subsystems: (a) specimen with single-sheathed infill light woodframed shear walls; (b) specimen with double-sheathed infill light wood-framed shear walls 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.

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

16 4. Numerical modeling User defined element in ABAQUS

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

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

19 5. Reliability analysis Baseline walls: Kr kinfill / kbf, 0.5,1.0, 2.5, 5.0

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. Event Date Station Component PGA (g) 1 Wenchuan 12/05/2008 Wolong EW Tangshan 28/ Beijing Hotel EW Ninghe 25/11/1976 Tianjin Hospital NS Qian an 31/08/1976 M0303 Qianan lanhe bridge NS Chichi-1 21/09/1999 CHY006 NS Chichi-2 21/09/1999 TCU070 EW Chichi-3 21/09/1999 TCU106 NS Chichi-4 21/09/1999 TAP052 NS Kobe 17/01/ KJMA KJM Northridge-1 17/01/ Beverly Hills Mulhol MUL Northridge-2 17/01/ Castaic - Old Ridge Route ORR Northridge-3 17/01/ Buena Park - La Palma BPK Loma Prieta-1 18/10/ Gilroy Array #3 G Loma Prieta-2 18/10/ Gilroy Array #7 GMR Loma Prieta-3 18/10/ Oakland - Title & Trust TIB

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

22 5. Reliability analysis Response surface method Step 1. Limit state function G ( S, K, ) where K r is a shear wall design factor a r Step 2. Response surface generation by numerical simulations 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 Kr 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 5. Reliability analysis Probabilistic-based design Performance curves for the hybrid shear wall with Kr = 2.5

25 6. Summary 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.

26 Thanks very much for your kind attention!