cyclic loading in Germany

Transcription

1 Note to actual al design of micropiles under axial cyclic loading in Germany according to DIN 1054 and further guidelines Jennifer Kleih 9th International Workshop on Micropiles London 13th May 2009

2 Outline Motivation Definitions Design guidelines in DIN 1054: and EA-Pfähle Conclusion and outlook

3 Motivation Micropiles il are often subjected to cyclic loads 13th May th IWM London 3

4 Motivation Wind Buoyancy Traffic Wind Tide Wind 13th May th IWM London 4

5 Motivation Micropiles il are often subjected to cyclic loads Field tests: Accumulation of deformations or sudden failure after a certain number of load cycles - although cyclic loads are far away from static capacity of the micropile 13th May th IWM London 5

6 Motivation Number of load cycles log N Steadily increasing displacement (decreasing strain rate) Pilehead displacements Sudden failure (increasing strain rate after a certain number of load cycles) Tests of e.g. NGI (1980s) Schwarz ( ) Lehane (2003) 13th May th IWM London 6

7 Motivation Micropiles il are often subjected to cyclic loads Field tests: Accumulation of deformations or sudden failure after a certain number of load cycles Capacity of micropiles under cyclic loads decreases depending on Number of load cycles Load amplitude / load range of cyclic loads Type of soil 13th May th IWM London 7

8 Definitions Tension Tensile and Compressive Alternating ti Load (Two-Way Loading) One-Way Loading Tension Load Range Load Amplitude stat. F zykl. F zykl. F^ N stat. F N stat. F Compression Load Cycle Compression 13th May th IWM London 8

9 Definitions R 2t,k = 0,5 R 1t,k R 1t,k Tensile Load Former global safety concept static pile load test or experienced data: shaft friction * shaft surface area He eave of Pil le 13th May th IWM London 9

10 Design guidelines DIN 1054: / EA-Pfähle General: valid for: grouted micropiles in Consideration of cyclic loads if non-cohesive soils load amplitude > 20 % of R 2t,k above groundwater level only regulation of axial cyclic loads Serviceability Limit State: Expected number of load cycles N Characteristic load range 1 1,00 R 2t,k (1) zykl. F x R 2t,k 100 0,80 R 2t,k ^ ,68 R 2t,k (2) stat. F + zykl. F R 2t,k ,56 R 2t,k ,40 R 2t,k 13th May th IWM London 10

11 Design guidelines DIN 1054: / EA-Pfähle Ultimate t Limit it State: t not yet regulated Proposal: (1) zykl. F γ cyclic,load Range x R 1,k / γ t,cyclic ^ (2) stat. F γ G + zykl. F γ Q R 1,k / γ t Partial factors have to be defined d based on field testst 13th May th IWM London 11

12 Conclusion and Outlook Capacity of micropiles il under cyclic loads decreases Design guidelines for micropiles under cyclic loads are necessary Up to now: Only regulation of Serviceability Limit State for axial cyclic loads Reference values only for grouted micropiles in non-cohesive soils above groundwater level Outlook: Regulation of Ultimate Limit State Reference values for different type of soils for both limit states 13th May th IWM London 12

13 Outlook TUM Research Project 2009 / 2010: Capacity of axial cyclic loaded micropiles in cohesive soils Test area with 8 micropiles in clay 13th May th IWM London 13

14 Example (design with experienced data) Pile diameter: Tension D s = 0,2 m Soil: Sand shaft friction q s1,k = 0,15 MN/m 2 stat. F = kn kn zykl. F = 300 kn ^ zykl. F = 150 kn Number of load cycles: kn N 13th May th IWM London 14

15 Example Serviceability Limit it State: t (1) zykl. F x R 2t,k Pile Length, R 1,k = q s1,k π D s l R 2t,k = 0,5 R 1,k R 2t,k = 0,5 150 π 0,2 l (former global security concept) x = 056(N= 0, ) 000) 300 0,56 0,5 150 π 0,2 l l 11,4 m 13th May th IWM London 15

16 Example Serviceability Limit it State: t ^ (2) stat. F + zykl. F R 2t,k ,5 150 π 0,2 l l 9,6 m Maximum of (1) and (2) decisive: necessary pile length l = 11,4 m 13th May th IWM London 16