Displacement-based calculation method on soil-pile interaction of PHC pipe-piles

Transcription

1 Seattle, WA Displacement-based calculation method on soil-pile interaction of PHC pipe-piles Dr. Huang Fuyun Fuzhou University 31 st May, 217

2 Outline Background ing introduction ing results Simple calculation Conclusions

3 1.Background Deck slab Pavement Approach slab Backfill Abutment Girder Pier Abutment Backfill Pile Approach slab Soil spring Abutment Girder Pier F N M Friction Piles Soil spring Soil spring Soil spring

4 1.Background Deck slab Pavement Approach slab Backfill Abutment Girder Pier Abutment Backfill Piles sum T E Under temperature and seismic load, displacement of superstructure is absorbed by piles and piles are under cyclic load. To satisfy demand of superstructure deformation, flexible piles are used most frequently. H-steel piles have been widely used under Integral Abutment in North America and Europe, because of good flexural property and ductility.

5 1.Background Deck slab Pavement Approach slab Backfill Abutment Girder Pier Abutment Backfill Piles Researchers of Iowa State University used PC piles in IJB and did researches on behavior of these piles and field monitoring on IJB using PC piles. 24, researches on behavior of prestressed concrete square piles were conducted by Prof. Edwin from Tennessee University, which proved that PC piles can be used in IJB.

6 1.Background Deck slab Pavement Approach slab Backfill Abutment Girder Pier Abutment Backfill Piles m method is linear and elastic with a limit 8-1mm in Chinese Code. p-y method is complex or accurate enough for RC piles?

7 2. ing introduction PHC model piles C8 concrete (has a compressive strength of 82.1 MPa) With a diameter of 155mm,length of 2.75m 7-wires prestressed steel strand with a diameter of 11.1mm Labeled as PHC-1 to PHC-4 t Number Diameter (mm) Pile Length (m) Wall Thickness (mm) Prestressed Degree λ Stirrup Spacing (mm) Deformation Coefficient a Calculate Pile Length(m) PHC PHC PHC PHC

8 2. ing introduction Soil Container (rigid box) Circular Height of m Diameter of m Wall thickness of 1mm 4 diagonal braces Soil (medium dense sand) Sand from Min River Water Content (%) Density (g/cm 3 ) void ratio Internal friction angle ( ) Average SPT blow count

9 ing introduction Sensor arrangement Strain gages Soil surface S1 S8 S2 S9 S3 S4 S5 S1 S11 S12 14 strain gages were installed on piles with an equal spacing of 35mm, labeled as S1 to S14. S6 S13 S7 S14

10 ing introduction Sensor arrangement Earth pressure cells Soil surface T1 T2 T3 T4 T7 T8 T9 T1 12 earth pressure cells were installed on piles with an equal spacing of 35mm, labeled as T1 to T12. T5 T6 T11 T12

11 2. ing introduction Sensor arrangement Displacement meters D1 Soil surface 4 D2 D3 D4 D5 D6 D7 D displacement meters were installed, labeled as D1 to D8. 1

12 2. ing introduction Method of displacement meters placement

13 2. ing introduction Loading(Displacement loading method) Displacement load (mm) Initial stage: 2 mm, 5mm, 8mm and 1mm. 1mm to 3mm: increase by 5mm. After 3mm: increase by 1 mm, and the test end until the lateral force decreases to 85% of peak value. Load.. speed: mm/s. 3 cycles every load grade

14 3. ing Results 3.1 Failure modes PHC-2 PHC-4

15 3. ing Results 3.2 Displacement soil surface Embedded depth (m) soil surface Displacement (mm) Embedded depth (m) 2mm 5mm 8mm 1mm 15mm 2mm 25mm 3mm 4mm 5mm 6mm 7mm 8mm 9mm 1mm 11mm Displacement (mm) PHC-4

16 3. ing Results 3.3 Hysteretic curve and skeleton curve Load kn Load kn PHC-2 PHC-2 P cr =5.4kN Displacement mm y cr =1mm -P u =-12.4kN -y u =-19.6mm -P cr =-5.5kN -y cr =-9.9mm Displacement mm P u =1kN y u =11mm Load kn Load kn PHC-4 Displacement mm P cr =5.3kN Y cr =9.9mm -5 -P u =-16.3kN -1 -Y u =-119.1mm -P cr =-5.1kN -15 -Y cr =-9.2mm Displacement mm PHC-4 P u =15.9kN Y u =119.4mm

17 3. ing Results 3.4 Strain distribution and strain history Embedded depth (m) PHC-2 21 PHC-2-1 PHC-2 soil surface 18 theoretic crack strain value mm 5mm 8mm 1mm 15mm strain 1-6 Tensile strain m depth 3.7m depth 5m depth 1.4m depth Displacement load (mm) Compressive strain m depth.7m depth 5m depth 1.4m depth Displacement load (mm) Embedded depth (m) PHC-4 theoretic crack strain value PHC-4 PHC-4 21 soil surface mm 5mm 8mm 1mm 15mm strain 1-6 Tensile strain m depth.7m depth 3 5m depth 1.4m depth Displacement load (mm) Compressive strain m depth.7m depth 5m depth 1.4m depth Displacement load (mm)

18 Earth Pressure (kpa) Embedded Depth (m) 3. ing Results Pile soil pressure Displacement Loads (mm) PHC-2 PHC-2 Earth Surface T1 T2 T3 T4 T5 T Earth Pressure (kpa) 2mm 5mm 8mm 1mm 15mm Earth Pressure (kpa) Embedded Depth (m) Displacement Loads (mm) PHC-4 T1 T2 T3 T4 T5 T Earth Pressure (kpa) PHC-4 2mm 5mm 8mm 1mm 15mm

19 4. Calculation on pile-soil interaction 4.1 Soil pressure calculate API P u min ( C z / d C 1 2, ) z C z s 3 s Reese LFP P u z tan sin tan z A sz[ Ks (1 tan tan a) D tan( ) cos a tan( ) D K s z D tan (tan sin tan a) K a ] P Broms 3 u s p K Dz Guo 2 2n n P u ssrk pd ( z a) m P u m z y z

20 4. Calculation on pile-soil interaction Embedded Depth (m) API 1993 Reese Broms Guo Earth Pressure (kpa) Embedded Depth (m) API 1993 Reese Broms Guo Soil pressure Embedded Depth (m) API 1993 Reese Broms Guo Earth Pressure (kpa) Embedded Depth (m) API 1993 Reese Broms Guo Soil pressure

21 4. Calculation on pile-soil interaction Earth Pressure (kpa) API 1993 Reese Broms Guo 'm' method PHC-1 PHC-2 PHC-3 Earth Pressure (kpa) API 1993 Reese Broms Guo 'm' method PHC-1 PHC-2 PHC Displacement (mm) Deep in.175m Displacement (mm) Deep in.875m Earth Pressure (kpa) API 1993 Reese Broms Guo 'm' method PHC-1 PHC-2 PHC-3 P u z tan sin tan z Asz[ Ks (1 tan tan a) D tan( ) cos a tan( ) D z Ks tan (tan sin tan a) Ka] D S K D ( z a ) 2 2n n s r p min (C1 z C 2 D) sz, C3 sz Displacement (mm) Deep in 1.25m

22 4. Calculation on pile-soil interaction 4.2 Bending moment M Strain EI D Bending moment of pile When the pile is elastic M EI D 2 2 EId y / d z Get displacement by quadratic integral of bending curvature Embedded depth (m) soil surface Bending moment (kn m) PHC-2 2mm 5mm 8mm 1mm 15mm 2mm 25mm Embedded depth (m) soil surface Bending moment (kn m) PHC-4 2mm 5mm 8mm 1mm 15mm 2mm 25mm

23 4. Calculation on pile-soil interaction Displacement comparisons Piles 2mm Displacement load -1 - Strain transfer -2 m ing p-y - PHC-4 Piles Strain m p-y 5mm Displacement load Piles Piles Strain m p-y 1mm Displacement load Strain m p-y 2mm Displacement load

24 4. Calculation on pile-soil interaction Embedded Depth (m) 4.2 New displacement method Earth Surface Equation (7) Value Displacement (mm) (a)1mm Displacement load PHC-4 Embedded Depth (m) Earth Surface Equation (7) Value Displacement (mm) (b)15mm Displacement load Embedded Depth (m) Earth Surface Equation (7) Value Embedded Depth (m) Earth Surface Equation (7) Value Displacement (mm) Displacement (mm) (c)2mm Displacement load (d)3mm Displacement load

25 4. Calculation on pile-soil interaction 4.3 Simple calculation on pile-soil interaction F T i 6 i1 i T i P Zb i F P i b (.9 y n ) 1.25 D i yu ym y k P=Pm(y/ym) 1 n Pm Pu P k b /6 3b /8 y p i p ( p p y 1/ n i p ( ) m ym u k p k m h y k ) y ( p y y u z D m m y u p u y m )

26 4. Calculation on pile-soil interaction 4.4 Results comparisons Force (kn) simple calculation method 'p-y' curves method 'm' method Displacement (mm) (a)phc-1 Force (kn) simple calculation method 'p-y' curves method 'm' method Displacement (mm) (b)phc Force (kn) 5 simple calculation method 'p-y' curves method 'm' method Displacement (mm) (c)phc-3 Force (kn) 1 5 simple calculation method 'p-y' curves method 'm' method Displacement (mm) (d)phc-4

27 4. Calculation on pile-soil interaction Buried Depth (m) Calculation Buried Depth(m) 1 2 Calculation Displacement (mm) (a) 1mm Displacement Loading Fan(214) Displacement(mm) (b) 25mm Displacement Loading Buried Depth(m) Calculation Displacement(mm) (c) 4mm Displacement Loading Buried Depth(m) Calculation Displacement(mm) (d) 55mm Displacement Loading

28 4. Calculation on pile-soil interaction Burial Depth (m) Calculation 3. bending moment (kn m) (a) 5mm Displacement load Burial Depth (m) Fan(214) Calculation 3. bending moment (kn m) (b) 1mm Displacement Load 15 1 Force (kn) 5 simple calculation method 'p-y' curves method 'm' method Displacement (mm)

29 5. Conclusion Maximal bending moment locates at 5.D to 6.D embedded depth, concrete of pile cracks around this area primarily. Degree of prestress and reinforcement ratio has a significant influence on failure mode of PHC piles. There are four stages for PHC piles: (1) elastic stage when the displacement of pile head below 8mm~1mm. (2) Concrete of tensile zone cracked, which means soil-pile system become elastic-plastic. (3) Reaching 4mm displacement load, concrete of compressive zone are out of work, stiffness of pile decreases gradually. After that, soil-pile separation has a significant influence. (4) failure stage: lateral bearing capacity drops dramatically. The test indicate that the distribution law of soil pressure is that with the change of pile depth, the side earth pressure of pile increased first and then decreased, and reversed in a certain depth.

30 5. Conclusion PHC piles performs a good plastic property and deformation ability considering soil-pile interaction, which is a suitable type used in IJB. With the increase of displacement loads, the pressure of shallow soil grows faster and its maximum is close to the limit passive earth pressure, while that of the deep soil is relatively slow or even increase reversely. It can be seen that the transformation method and the 'm' method to calculate the horizontal deformation of pile are not accurate for nonlinear elastic and larger deformation. Although the 'p-y' curves method takes the non-linear effects of soil into account, there still exists a large error in calculating the large deformation value. The horizontal displacement calculation method of pile-soil interaction that obtained by tests can calculate precisely and accurately the pile displacement.

31 THE 3 RD INTERNATIONAL JOINTLESS BRIDGES WORKSHOP Thanks for your attention!