Structural Health Monitoring (SHM) of Timber Beams and Girders

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1 Structural Health Monitoring (SHM) of Timber Beams and Girders Dr John C Moore MIEAust MIPWEA Adjunct Lecturer in Civil Engineering, University of New England, NSW. Presentation for: FWPA, 2 April 2014 Gostwyck, NSW (Moore 2013) 1

2 Introduction and Background Bridges Interpret Data Measuring elasticity Prediction of girder failure Understand girder degradation path MoR (MPa) Probability Density Load Distribution Strength Distribution Failure Region Load & Strength Magnitude 14 GPa > Ironbark 1 2A 2B 86 MP 2A, 15 years 2B, 45 years MoE (GPa)

3 3

Built by RTA & Gloucester Shire in 2010 Leslies Bridge,

4 New timber composite bridge New bridge at Bretti, NSW with: Timber girders; Steel piles; and Concrete deck Built by RTA & Gloucester Shire in 2010 Leslies Bridge, The original low level bridge at Bretti NSW over the Manning River. 4

5 Method to determine Safety Index 1. Record all vehicle mid-span deflections 2. Use a vehicle of known mass and determine girder elasticity 3. Convert elasticity to a stress distribution 4. Convert deflection to a stress distribution 5. Compare the two stress distributions 6. Determine the probability of failure and Safety Index 5

6 TSING MA BRIDGE, HONG KONG (Nye, 2013; Wikipedia, 2013; Yau, Chan, & Thambiratnam, 2013) Opened: 1997 Span : 1377 m Sensors: 282 Cost: AUD 1B 6

7 TIMBER BEAM BRIDGES Powers Creek, Armidale Span 9 m c Munsies Bridge, Gostwyck 6 Spans 10 m Opened

8 Timber bridge design (Dare, 1903) 8

9 Modern design (RTA, 2007) 9

10 (Glencross-Grant, c. 1975) Somerton bridge across the Peel river, Tamworth NSW (Ingall, 2008) 10

11 Diagrammatic section through a degraded girder Second moment of Area for a solid circular girder: 11

12 Diagrammatic section through a degraded girder; after excessive loading Second moment of Area for two contiguous girders of semicircular cross-section: And the ratio between the two conditions is: 12

13 Typical girder, Load-v-Deflection curve Applied Load, P (kn Deflection, d (m 13

14 Applied Load, P (kn) Proof load test, 50% ultimate load Measured data 50% load regression 50% prediction limits Deflection, d (mm) 14

15 Applied Load, P (kn) Proof load test, 70% ultimate load Measured data 50% load regression 50% prediction limits Deflection, d (mm) 15

16 Applied Load, P (kn) Proof load test, 80% ultimate load Measured data 50% load regression 50% prediction limits Deflection, d (mm) 16

17 Applied Load, P (kn) Nominal maximum girder load Ultimate load << Nominal maximum girder load Deflection, d (mm) 17

18 SHM: Recording vehicle activity (Moore, 2012) 18

19 Daily vehicle activity (Moore, 2009, 2012) 19

Front axle mass Rear axle mass Measure mid-span

20 Determine girder baseline MoE Measure bridge: Span Girder shape Girder Diameters Decking Weigh vehicle Front axle mass Rear axle mass Measure mid-span deflection of each girder Calculate MoE (Moore, 2012) (Moore, 2012)

21 Traffic load distribution Frequency (X Stress (MPa) 21

22 Girder load tests RTA, 1990 Wilkinson,

23 MoR (MPa) MoE (GPa) Data from 338 girders removed from service (Moore, 2012) 23

24 MoR (MPa) MPa 14 GPa > MoE (GPa) 24

25 MoR (MPa) MPa 14 GPa > 36 GPa > MoE (GPa) 25

26 MoR (MPa) MPa 14 GPa > Data AS 1720:2000/H2.1; 5th percentile MoE (GPa) 26

27 MoR (MPa) MPa 14 GPa > MoE (GPa) 27

28 Girder strength distribution Probability Density Strength Distribution Strength Magnitude (MPa) 28

29 Traffic load and girder strength distributions Probability Density Load Distribution Strength Distribution Load & Strength Magnitude (MPa) 29

30 Failure region Probability Density Load Distribution Failure Region Strength Distribution Load & Strength Magnitude (MPa) 30

31 Frequency (X Applied stress G6-MU MoR Frequency (X Applied stress G6-MU MoR Fmax = 11.6 MPa Failure region Failure rate: in Stress (MPa) Stress (MPa) Failure rate: 2 in 10 7 ; Safety Index =

32 Safety Index Probability of failure Safety Index 1 in in in in in Probability of failure NORMSINV(probability) calculates the inverse of the normal cumulative distribution function 32

33 Frequency (X Applied stress G4-MU MoR Frequency (X Applied stress G4-MU MoR Fmax = 8.6 MPa Failure region Failure rate: in Stress (MPa) Stress (MPa) Failure rate: 1157 in 10 7 ; Safety Index =

34 Interpretation of Safety Index Total cost of system failure = cost of an individual failure x number of failures If the failure cost is small a higher failure rate can be tolerated In such a case a failure rate of 1 in 10 3 and a safety index of 3.1 is generally acceptable A high failure cost necessitates a low failure rate In this type of case a failure rate of 1 in 10 6 and a safety index of 4.8 or higher is expected To achieve a lower failure rate can require excessive design and construction costs 34

Failure examples Small increased deflection of a bridge Condition: Deflection may exceed design standard of 600:1 (No component is expected to break or deform) Limit state: 1 in

35 Failure examples Small increased deflection of a bridge Condition: Deflection may exceed design standard of 600:1 (No component is expected to break or deform) Limit state: 1 in 10 3 ; safety index > 3.1 Large increase in deflection Condition: Structural strength in question (Components may break or deform) Limit state: 1 in 10 6 ; safety index >

36 MoR (MPa) Jarrah Ironbark Tallowwood 86 MP Radiata Pine < 14 GPa MoR (MPa) MoE (GPa) MoE (GPa)

37 Tabulated MoR and MoE data (Bolza & Kloot, 1963, p. 54) 37

38 MoR (MPa) GPa > Radiata Pine Ironbark 86 MP Excised samples 174 Species of timber (CSIRO) MoE (GPa) 38

39 Clustering Ironbark girders Condition State 1. No decay, CS-1 2. Minor decay, CS-2 3. Medium decay, CS-3 4. Advanced deterioration, CS-4 Failure mode MoR (MPa) Mid-span bending failure, FM-1 2. Non mid-span bending failure, FM-2 14 GPa > 86 MPa MoE (GPa)

40 MoR (MPa) GPa > 86 MP Ironbark Girders MoE (GPa)

41 MoR (MPa) GPa > 86 MP Ironbark Girders, CS-1, FM MoE (GPa)

42 MoR (MPa) GPa > 1 86 MP Mean Ironbark,CS-1,FM MoE (GPa)

43 MoR (MPa) GPa > IB,CS-1,FM-1 2 IB,CS-2,FM-1 86 MP MoE (GPa)

44 MoR (MPa) GPa > IB,CS-1,FM-1 2 IB,CS-2,FM-1 3 IB,CS-2,FM-2 86 MP MoE (GPa)

45 MoR (MPa) GPa > MP 1 IB,CS-1,FM-1 2 IB,CS-2,FM-1 3 IB,CS-2,FM-2 4 IB,CS-3&4,FM MoE (GPa)

46 MoR (MPa) GPa > Ironbark 1 86 MP 1 IB,CS-1,FM-1 2 IB,CS-2,FM-1 3 IB,CS-2,FM-2 4 IB,CS-3&4,FM MoE (GPa)

47 MoR (MPa) GPa > Ironbark 1 2A 2B 86 MP 2A, 15 years 2B, 45 years MoE (GPa)

CONCLUSIONS Girder MoE and MoR can be experimentally determined Probability of failure can be calculated A bridge safety limit can be continuously

48 CONCLUSIONS Girder MoE and MoR can be experimentally determined Probability of failure can be calculated A bridge safety limit can be continuously quantified using a SHM system MoR (MPa) GPa > Ironbark 1 2A 2B 86 MP 2A, 15 years 2B, 45 years MoE (GPa) 48

49 END THANK YOU FOR YOUR ATTENTION Please Contact: Dr John C Moore jmoore30@une.edu.au 49

Roadway Grade = m, amsl HWM = Roadway grade dictates elevation of superstructure and not minimum free board requirement.

Roadway Grade = m, amsl HWM = Roadway grade dictates elevation of superstructure and not minimum free board requirement. Example on Design of Slab Bridge Design Data and Specifications Chapter 5 SUPERSTRUCTURES Superstructure consists of 10m slab, 36m box girder and 10m T-girder all simply supported. Only the design of Slab