Introduction to Earthquake Engineering Behaviour of structures under earthquakes

Transcription

1 Introduction to Earthquake Engineering Behaviour of structures under earthquakes Prof. Dr.-Ing. Uwe E. Dorka Stand: September 2013

2 Conventional rc-frame structure under Kobe earthquake 2

3 Non-linear cyclic behaviour of frames Plastic hinge From Petersen (9) Failure in soft storey From Müller, Keintzel (2) 3

4 Non-linear cyclic behaviour of walls flexural failure shear failure sliding failure rotation of foundation 4

5 Behaviour of reinforced concrete structures Flexural cyclic behaviour in plastic hinges j From Earthquake Spectra (10) 5

6 Concrete columns Buckling of longitudinal reinforcement From Earthquake Spectra (10) 6

7 Concrete columns Behaviour under combined bending and axial load: From Petersen (9) 7

8 Short columns 8

9 Short columns Extreme pinching of hysteresis loop and failure in shear 9

10 Rc frame corners pinching effect and deterioration due to large shear 10

11 Complicated details in rc-frames: From Müller, Keintzel (2) 11

12 Shear walls Brittle behaviour, but large capacity! 12

13 Coupled shear walls Brittle failure in shear! From Earthquake Spectra (10) 13

14 Coupled shear walls Large shear in connecting beam leads to Impossible detailing requirements for an rc-solution! Better: steel beam, but special attention must be paid to the connection! From Müller, Keintzel (2) From Müller, Keintzel (2) 14

15 Pre-cast structures Domino effect due to sudden connection failure often leads to total collapse! From Earthquake Spectra (10) 15

16 Behaviour of steel structures Conventional steel structure under Kobe earthquake: soft storey 16

17 Steel beams Plastic hinges From DGEB (8) Local buckling under cyclic loading 17

18 Steel beams Moment-rotation hysteresis loop of a steel beam 18

19 Steel columns Hysteresis of column with P-D effect Instable load bearing due to negative post-yield stiffness can lead to total collapse of structure Rapid deterioration due to local buckling Columns should not yield, only beams! Strong column weak beam concept! From Petersen (9) 19

20 Steel struts Cyclic buckling of struts From Earthquake Spectra (10) 20

21 Braced steel frames Braced full-scale portal frame under constant vertical load and cyclic horizontal load. Combined action of beam plastic hinges and cyclic strut behaviour: stiff but ductile! H P= 0,5*N pl P= 0,5*N pl H 21

22 Steel connections Brittle fracture in welds Both Pictures from earthquake Spectra (10) 22

23 Steel connections Brittle fracture in welds and rupture of bolts Both Pictures from earthquake Spectra (10) 23

24 Steel connections Seismically sound connections in frame corners 24

25 Behaviour of timber structures Modern Japanese residential structure under Kobe earthquake: 25

26 Behaviour of timber structures Insufficient connections can lead to brittle failure 26

27 Timber wall with cladding 27

28 Timber wall with cladding Load-deflection relationship for a timber wall with cladding under cyclic shear 28

29 Behaviour of masonry structures Typical crack pattern between openings and at corners 29

30 Behaviour of masonry structures Typical crack pattern between openings and at corners 30

31 Behaviour of masonry structures Collapse of chimneys and out-of-plane failure of roof gable walls due to insufficient lateral support From Earthquake Spectra (10) 31

32 Masonry walls Horizontal load-deflection relationship for a wall subjected to cyclic shear and constant vertical load showing rapid deterioration of hysteresis loop 32

33 Masonry in-filled rc-frames Non-linear mechanism with compression strut developing in masonry wall causing shear failure in rc-columns 33

34 Behaviour of historic structures Many old historic structures behave well having sustained several earthquakes during their history Intact historical structural systems are usually quite safe, sometimes with surprising effects From Earthquake Spectra (10) 34

35 Behaviour of historic structures 35

36 Behaviour of historic structures New (18 th 20 th century) historic structures are often derived from non-seismic countries like Britain or Germany with modern structural systems not capable of resisting large earthquakes 36

37 Behaviour of historic structures Modern alterations often lead to a change in behaviour and collapse Car parking or shops create soft storeys Rc- additions change historic load paths etc. 37

38 Behaviour of bridges Horizontal shear failure in deck due to differences in deformations of supporting frames (short frame vs. long frame) Both Pictures from Earthquake Spectra (10) Relative motion of singlespan deck caused drop-off 38

39 Behaviour of bridges Brittle shear failure in columns (short column effect) and frame corners Both Pictures from Earthquake Spectra (10) 39

40 Behaviour of bridges Toppling due to P-D effect From Petersen (9) Both Pictures from Earthquake Spectra (10) 40

41 Behaviour of bridges Both Pictures from Earthquake Spectra (10) Bearing failure due to large mass effect 41

42 Behaviour of bridges Both Pictures from Earthquake Spectra (10) Insufficient retrofit due to neglect of differential motion between large masses: band-aid solution! 42

43 References (1) Wakabayashi Design of Earthquake-Resistant Buildings McGraw-Hill Book Company (2) Müller, Keintzel Erdbebensicherung von Hochbauten Verlag Ernst & Sohn (3) Deutsche Gesellschaft für Erdbebeningenieurwesen - DGEB Schriftenreihe der DGEB, Heft 2 Elsevier (4) Petersen Statik und Stabilität der Baukonstruktionen Vieweg (5) Jack P. Moehle Earthquake Spectra April