Pile size limitations in seismic regions George Mylonakis

Transcription

1 Pile ize limitation in eimic region George Mylonaki Univerity of Britol, UK

2 Acknowledgement Dr Raffaele Di Laora Univerity of Ferrara, Italy Profeor Aleandro Mandolini 2 nd Univerity of Naple, Italy

3 Example of oberved pile head failure Chritchurch, NZ, 20 Niigata, Japan, 964

4 Pile failure Hamada 99 Mizuno 987

5 Kinematic and Inertial Pile Loading

6 Soil Profile & Pile Type

7 Effect of Pile Diameter on Pile Kinematic & Inertial Bending

8 Steel pile, homogeneou oil

9 Kinematic bending teel pile, homogeneou oil / R / kin a M head EpI p / R EpI p / R E p pi p V p d 4 R 2

10 Yield Moment 2 M y EpI p y d P y p f A d 3 P L d N A SF p c u

11 Limit diameter for kinematic loading 2 a L d d 4 T 0 2 V L L q SF f u 2 y A y N, c u T = q A = ( 2t/d) 2 q A SF f y d 2 T T 2 2 V 2 V u kin y a 2 4 y qa SF al f y 2 d 2 kin y V a 2 Maximum diameter!

12 Limit diameter for inertial loading M 4 4 qi a E p in a p 4 g E S P d d Sa a Ep u u din L q I SF T2 y g E E 2q A f y T T qi a E p SaqA 2 g E qi Minimum diameter!

13 Combined kinematic and inertial loading M e M e M tot kin kin in in al d d 4 E u qa qi a p 2 T3 y 2 S a 0 2 V L L qasf E p qi g E d T 2 S 2 4 yv 24 4 al u qa qi a Ep,2 3 2 a a T3 q E A f y y SF qi g E T qe I p u 3 Nc qa SF f y y E E Minimum & maximum diameter!

14 Admiible and inadmiible diameter for different type of loading

15 Admiible pile diameter againt V E /S u = 500, f yk, = 275 MPa, E p = 20 GPa, ν = 0.5, ρ =.7 Mg/m 3, S a = 2.5, FS = 3, t/d = 0.05, α = 0.7, δ =.2, T = 0

16 Limit hear wave velocity V 24 u al 4 qa qi a 2 S 2 a E p qi 3 g,crit 2 qa y SF E E p 2 V d d T 2 2 y a 3 for V<50m/ec, maximum pile diameter d2<m

17 Steel pile, oil with tiffne varying proportional with depth

18 Kinematic bending teel pile, oil with tiffne varying proportional with depth E z E z 4 I p qe M kin 0.85a d E d a u qe I p 5 S L S a M in.6 d SF g E d.8

19 Limit diameter for combined loading I p d I p y d q I p 5 ISu d Sa Su d q E q E q E E L L 64 a L L 6 q SF a L L SF L E L L A d qe 5 I p qi.6sa Su E L A 4 SF q 5 I Ep qi Ep y 6 q a / g 0.85 E L 64 a L Minimum diameter!

20 Homogeneou v Linear Soil Profile a /g = 0.35, E /S u = 500, f yk, = 275 MPa, E p = 20 GPa, ν = 0.5, ρ =.7 Mg/m 3, S a = 2.5, FS = 3, t/d = 0.05, α = 0.5, L = 5 m, E = 2 MPa/m, E =E,L/2 = 5 MPa

21 Admiible diameter: teel pile with depth proportional tiffne a /g = 0.25, E /S u = 500, f yk, = 355 MPa, E p = 20 GPa, ν = 0.5, ρ =.7 Mg/m 3, S a = 2.5, FS = 3, t/d = 0.05, α = 0.5, L =30 m

22 Concrete pile

23 Moment Capacity 3 2 d 3 2 d u u, c u, in ck in yk M M M f c A f in 2 2 k 0 ω = A f yk / (A c f ck ), ν k = W p / (A c f ck ) k /

24 Admiible diameter: concrete pile in homogeneou oil a /g = 0.25, E /S u = 500, E p = 30 GPa, ν = 0.5, ρ =.7 Mg/m 3, S a = 2.5, FS = 3, A /A c = 0.05, f ck = 25 MPa, f yk = 450 MPa, α = 0.5, L = 30 m

25 Admiible diameter: concrete pile with depth proportional tiffne a /g = 0.2, E /S u = 500, E p = 30 GPa, ν = 0.5, ρ =.7 Mg/m 3, Sa = 2.5, FS = 3, A /A c = 0.05, f ck = 25 MPa, f yk = 450 MPa, α = 0.5, L = 30 m

26 Steel v Concrete Pile in Homogeneou and Linear Soil Profile a /g = 0.25, E /S u = 500, f yk, (teel) = f yk (concrete reinforcement) = 450 MPa, f ck = 25 MPa, E p = 30 GPa or 20 GPa (for concrete and teel, repectively), ν = 0.5, ρ =.7 Mg/m 3, S a = 2.5, FS = 3, t/d = A /A c = 0.05, α = 0.5, L = 30 m

27 Concluion Concrete pile poe a narrower range of admiible diameter to withtand eimic action over hollow teel pile. Thi can be attributed to the higher bending tiffne of the concrete pile cro-ection (which attract higher kinematic moment), a well a the inability of the concrete material to carry tenion. For oft oil of contant tiffne with depth, kinematic interaction dominate eimic demand. A a reult, admiible pile ize are eentially over-bounded by a critical diameter which, in ome cae, may be quite mall (~ m) and, hence, may affect deign. Under thee circumtance, adding more pile or increaing pile length will not improve afety, a uch remedial olution do not affect kinematic demand. In tiffer oil, inertial interaction i prominent due to the heavier load carried by the pile under a contant FS. Thi yield a minimum admiible pile diameter which, in region of moderate to high eimicity, may be quite large (~ m).

28 Concluion (cont d) Soil with tiffne increaing proportionally with depth eentially enforce only a lower bound on pile diameter, which may be rather large (> 2 m), epecially for trong tiffne gradient. Note that the abence of an upper limit i not due to weak kinematic demand. On the contrary, in uch oil the ratio of kinematic over inertial moment may be larger than unity, yet the kinematic moment doe not trongly depend on diameter. The range of admiible diameter decreae with increaing deign ground acceleration, pectral amplification, oil trength and pile length, wherea it increae with increaing oil tiffne, pile afety factor and amount of reinforcement (or wall thickne). On the other hand, pile material trength play a minor role in controlling pile ize.

29 Concluion (cont d) There i alway a critical oil hear wave velocity or tiffne gradient below which no pile diameter i admiible for a given deign ground acceleration. Below thi threhold, a fixed-head pile cannot tay elatic regardle of diameter or material trength. In the extreme cae where V = 0 (e.g., a pile in water), no diameter i apparently admiible. Thi behavior hould not be viewed a paradoxical, ince then a would alo be zero. Exploring the interplay between V and a lie beyond the cope of thi tudy. Pile-oil contact tree due to kinematic interaction are not expected to be important at low frequencie and do not induce major nonlinearitie into the oil. The Author alo recognize the lack of documented cae hitorie demontrating the effect dicued herein. Thi may be attributed to an inufficient number of obervation involving multiple pile diameter under retraining cap in oil with ufficiently low hear wave propagation velocitie (<00m/) to trigger thi effect.

30 Reference Di Laora R, Mylonaki G, Mandolini A. (203) Pile-head kinematic bending in layered oil. Earthquake Engineering & Structural Dynamic, 42: Mylonaki G, Di Laora R, Mandolini A. (204) The role of pile diameter on earthquake induced bending. 5 th European Conference on Earthquake Engineering, Itanbul, Augut In Percpective on European Earthquake Engineering and Seimology Springer Di Laora R, Mylonaki G, Mandolini A. (206) Size limitation for pile in eimic region. Earthquake Spectra (under review).

31 Thank you!!! Ευχαριστώ!!! Grazie!!!