opensees and lpile

1

Chapter 1

ANALYSIS OF LATERALLY LOADED SINGLE PILES USING

OPENSEES AND LPILE

1.1 Introduction

In this study, the response of laterally loaded piles obtained from the software LPILE

is compared with results obtained using the finite element platform OpenSees. Detail

information on the properties of the pile and soil condition are described. Section analysis

is performed and the effect of boundary conditions at the pile tip is investigated. Finally

results obtained from OpenSees are explained. The objective of this study is to evaluate the

capability of OpenSees to reproduce the results obtained using LPILE. Details on LPILE

software and analysis were provided by the University of Texas team.

1.2 Test Models

1.2.1 PILE

In this study, three single piles with different lengths and embedded into two different soil

types (loose sand and medium sand) are considered. The pile embedment length is 12 ft

and the pile lengths above the ground surface are 0ft, 3ft, and 6ft, respectively. The applied

deflections at the top of pile heads are 4.8 inch, 5.7 inch, and 7.0 inch for the piles embedded

in loose sand and 3.6 inch, 5.2 inch, and 6.2 inch for the piles embedded in medium sand. A

pile test model and its geometry are shown in Figure 1.1. Table 1.1 and 1.2 summarize the

displacements used in this study. These values are selected to reproduce the LPILE cases.

Figure 1.2 shows a deformed pile mesh obtained from OpenSees. The pile is meshed

to have elements with 0.5 ft of length. Every pile element node below the ground surface

is connected to a p-y spring. The p-y spring nodes that are not connected to the pile are

constrained in displacement.

2

Figure 1.1: Test models (piles embedded in loose sand)

Figure 1.2: OpenSees finite element mesh (deformed)

3

Table 1.1: Applied displacements at the top of the pile in LPILE - ultimate load analysis

length of pile head 0ft head 3ft head 6ft head

loose soil 4.8 inch 5.7 inch 7.0 inch

medium soil 3.6 inch 5.2 inch 6.2 inch

Table 1.2: Applied displacements at the top of the pile in LPILE - cracking, linear, andyielding condition (medium soil)

length of pile head 3ft head 6ft head

cracking 0.20 inch 0.2 inch

linear 0.76 inch 1.0 inch

yielding 1.50 inch 2.1 inch

A cross-section configuration of the reinforced concrete pile is illustrated in Figure 1.3.

The pile diameter is 12 inches and its area 113 in2. The cross section moment of inertia

is 1.111 in4. Sixteen #3 reinforced bars are used as longitudinal reinforcement and the

thickness of the concrete cover is set to 1 inch. In LPILE the concrete compressive strength

is 4 ksi and the yield stress of the steel bar is 60 ksi. The initial modulus of the steel is 29,000

ksi. In LPILE, the ultimate moment capacity and nonlinear bending stiffness is calculated

internally based on the cross-section properties. The lateral load analysis is performed using

the nonlinear flexural stiffness computed in the previous step.

In OpenSees the pile is modeled using nonlinear beam column elements with a reinforced

concrete fiber section. The section consists of three parts: a) core concrete, b) cover con-

crete, and c) reinforcing steel. The concrete and steel material properties used in OpenSees

are summarized in Table 1.3. The core and cover concrete are meshed using 12 and 4 seg-

ments in the radial direction respectively and the section is subdivided into 16 fibers in the

circumferential direction as shown in 1.3. Stress-strain curves for the concrete and steel

fibers are plotted in Figure 1.4.

4

−8 −6 −4 −2 0 2 4 6 8

−6

−4

−2

0

2

4

6

Figure 1.3: Discretized section of pile in OpenSees

1.2.2 Soil and p-y Curves

In this study, uniform loose and medium soil conditions are considered. For the loose sand,

the unit weight, γ, is 90 pcf, and the friction angle, φ, is 30o. For the medium sand, γ is 90

pcf and φ is 36o.

LPILE uses 25 pci and 90 pci for the soil subgrade reaction modulus of both loose and

medium sands and follows the extended hyperbolic criteria for the construction of the p-y

curves. The ultimate resistance (pult) for sand is obtained using Reese’s criteria.

OpenSees uses the pySimple1 material implemented by Boulanger to define the p-y

springs. It requires three material parameters: a) contributory ultimate resistance of p-y

spring (pult), b) displacement at which 50% of pult is mobilized (y50), and c) drag resistance

ratio within a gap (Cd). The ultimate resistance (pult) for sand is obtained following

Reese’s criteria using a tcl script. The pult value requires information on friction angle,

5

0 0.002 0.004 0.006 0.008 0.01 0.0120

1

2

3

4

5

strain

stre

ss (

ksi)

0 0.01 0.02 0.03 0.040

10

20

30

40

50

60

70

strain

stre

ss (

ksi)

Figure 1.4: Stress vs. strain curves of fibers in section (a) cover concrete (b) steel bar

unit weight, depth, and pile diameter and is factored by charts that have been developed

from experimental field tests. The value of y50 is assumed to vary along the length of the

pile. For clays, y50 is suggested to be equal to 2.5 × εc × diameter, based on Skempton’s

load-settlement concepts. εc represents the strain that occurs at one-half of the maximum

stress on a laboratory stress-strain curve. It can be obtained from a laboratory test or may

be assumed between 0.005 and 0.02. For sands, it is not easy to determine the appropriate

values of y50 in a consistent way. In this study, a y50 equal to 0.02 to 0.006 ft. is chosen

for loose and medium sand respectively. The value of Cd is set to 0.3 for all p-y materials.

Table 1.4 summarizes the soil parameters used to define p-y curves in LPILE and

OpenSees. Figures 1.5 and 1.6 present p-y curves as obtained from LPILE and OpenSees.

1.3 Effect of Boundary Conditions and Axial Force

1.3.1 Effect of Boundary Conditions on Moment-Curvature Curves

Moment-curvature curves generated using OpenSees are presented in Figures 1.7 - 1.9 and

are compared with those obtained using LPILE. Moment-curvature curves depend on axial

force, which in turn is related to the boundary conditions at the top and tip of the pile and

along the pile length. When the longitudinal displacement of the pile is constrained, the

peak value of the bending moment becomes greater than that obtained from an analysis

6

0 0.2 0.4 0.6 0.8 1−100

0

100

200

300

400

500

600

y (in)

p (lb

/ele

men

t)

Figure 1.5: p-y curves obtained using LPILE and OpenSees - Loose Sand (blue line (LPILE)is plotted at every foot depth, and red one (OpenSees) at every half foot)

0 0.2 0.4 0.6 0.8 1−100

0

100

200

300

400

500

600

y (in)

p (lb

/ele

men

t)

Figure 1.6: p-y curves obtained using LPILE and OpenSees - Medium Sand (blue line(LPILE) is plotted at every foot depth, and red one (OpenSees) at every half foot)

7

Table 1.3: Pile section properties used in LPILE and OpenSees

LPILE OpenSees

- core concrete

compressive strength = 4 ksi compressive strength = 6 ksi

strain at compressive strength = 0.004

crushing strength = 5.0 ksi

strain at crushing strength = 0.014

concrete

- cover concrete

compressive strength = 5 ksi

strain at compressive strength = 0.002

crushing strength = 0.0 ksi

strain at crushing strength = 0.006

steel bar yield strength = 60 ksi yield strength = 60 ksi

initial modulus = 29,000 ksi initial modulus = 29,000 ksi

hardening ratio = 0.01

that does not have the constraint. Figure 1.7 illustrates the effect of different boundary

conditions on pile response. For the case shown in Figure 1.7 the maximum resultant

axial force obtained by restricting the axial movement goes up to 225 kips. Figure 1.8

compares moment-curvature curves obtained by applying different axial forces. It is shown

that the moment-curvature curve obtained from LPILE is similar to the curve obtained

from OpenSees with no longitudinal constraint and no axial force.

Figure 1.9 illustrates moment-curvature curves obtained from an OpenSees section anal-

ysis using the same properties used in LPILE for both core and cover concrete. The figure

shows a flat residual moment after a peak value that is slightly lower than LPILE’s. Even

though the use of the same properties for core and cover concrete gives slight better results,

the properties presented in Table 1.3 are used in this study as realistic parameters for a

8

Table 1.4: The parameters to define the p-y curve in LPILE and OpenSees

soil type Loose Medium Loose Medium

(LPILE) (LPILE) (OpenSees) (OpenSees)

friction angle (degree) 30 36 30 36

unit weight 90 pcf 90 pcf 90 pcf 90 pcf

p-y parameters k = 25 pci k = 90 pci y50 = 0.02 ft y50 = 0.006 ft

Cd = 0.3 Cd = 0.3

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0140

2

4

6

8

10x 10

5

curvature (radian/inch)

mom

ent (

lb−

in)

OpenSeesLPILE

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0140

2

4

6

8

10x 10

5


mom

ent (

lb−

in)

OpenSeesLPILE

Figure 1.7: Moment-curvature curve obtained from section analysis - (a) constrained (b)free in longitudinal direction

reinforced concrete model.

1.3.2 Effect of Boundary Conditions on Bending Moment and Shear Force

While LPILE uses the precalculated ultimate bending moment and the variation of flexural

stiffness based on the section analysis, OpenSees uses a fiber section. Therefore, during the

analysis the moment-curvature curve can be affected by the local boundary conditions and

in turn affect the bending moments and shear forces that are developed along the pile.

In an analysis where the top and bottom of the pile are constrained vertically, the pile

section develops a large internal axial force. This force causes the peak value of the bending

9

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0140

1

2

3

4

5

6x 10

5


mom

ent (

lb−

in)

OpenSees (compression − 10 kip)OpenSees (no axial force)OpenSees (tension − 10 kip)LPILE

Figure 1.8: Moment-curvature curve obtained from section analysis - free in longitudinaldirection and different axial forces

0 0.005 0.01 0.0150

1

2

3

4

5x 10

5


mom

ent (

lb−

in)

OpenSeesLPILE

Figure 1.9: Moment-curvature curve obtained from section analysis - free in longitudinaldirection and using the same concrete properties as in LPILE

10

−1000 0 1000 2000 3000 4000−150

−100

−50

0(a)

pult and pressure (lb/in)

dept

h (in

ch)

soil capacity − LPILEsoil capacity − OpenSeessoil pressure − LPILEsoil pressure − OpenSees

−1000 0 1000 2000 3000 4000−150

−100

−50

0(b)


dept

h (in

ch)


Figure 1.10: Soil pressure (a)pile tip free in vertical direction (b)pile tip constrained invertical direction (3ft pile head - medium sand)

moment, generated due to a lateral load, to be higher than that obtained from a section

analysis without any axial force, as shown Figure 1.13 (b). For the 3ft head pile embedded

in medium sand, about 150 kips of axial force is developed along the pile depth when the

pile is laterally loaded and the tip is constrained in the vertical direction. Figures 1.10

- 1.13 demonstrate the difference in pile displacement, and internal force due to different

boundary conditions.

To reproduce LPILE results, the ultimate strength of t-z spring and q-z springs (that

provide the vertical skin friction resistance and the pile tip resistance) are set to a small

value and the pile is free to move in vertical direction.

11

0 2 4 6 8 10−150

−100

−50

0

50

100(a)

disp (in)

dept

h (in

)

OpenSeesLPILE

0 2 4 6 8 10−150

−100

−50

0

50

100(b)

disp (in)de

pth

(in)

OpenSeesLPILE

Figure 1.11: Pile displacement (a)pile tip free in vertical direction (b)pile tip constrainedin vertical direction (3ft pile head - medium sand)

−20 0 20−150

−100

−50

0

50(a) Shear Force Diagram

Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50Moment Diagram

M (kip−inch)

dept

h (in

ch)

OpenSeesLPILE

OpenSeesLPILE

−50 0 50−150

−100

−50

0

50(b) Shear Force Diagram

Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50Moment Diagram

M (kip−inch)

dept

h (in

ch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.12: Pile force (a)pile tip free in vertical direction (b)pile tip constrained in verticaldirection (3ft pile head - medium sand)

12

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0140

1

2

3

4

5

6

7

8

9x 10

5 (a)

curvature

mom

ent (

lb−

in)

ele61ele41ele40ele39ele38secAnalysis

0 0.002 0.004 0.006 0.008 0.01 0.012 0.0140

1

2

3

4

5

6

7

8

9x 10

5 (b)

curvature

mom

ent (

lb−

in)

ele61ele41ele40ele39ele38secAnalysis

Figure 1.13: Moment-curvature curves (a)pile tip free in vertical direction (b)pile tip con-strained in vertical direction (3ft pile head - medium sand)

1.4 Comparison of results from LPILE and OpenSees - Loose Sand

Plots of soil pressure, displacement, and internal force (shear force and bending moment)

in the pile as calculated by OpenSees for a loose sand condition are compared with results

obtained from LPILE. The plots are shown in Figures 1.20 - 1.16. OpenSees shows good

agreement with LPILE’s output. Envelopes of soil pressure, pile displacement, and pile

force for different pile head lengths are shown in Figures 1.23 - 1.26.

13

−1000 0 1000 2000 3000−150

−100

−50

0


dept

h (in

ch)


Figure 1.14: Soil pressure (0ft pile head) - loose sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.15: Pile displacement (0ft pile head) - loose sand

−50 0 50−150

−100

−50

0Shear Force Diagram

Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.16: Pile force (0ft pile head) - loose sand

14

−500 0 500 1000 1500 2000 2500−150

−100

−50

0


dept

h (in

ch)



0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE


−20 0 20−150

−100

−50

0


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE


15

−500 0 500 1000 1500 2000 2500−150

−100

−50

0

50


dept

h (in

ch)



0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE


−10 0 10−150

−100

−50

0

50


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50

100Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE


16

−1000 0 1000 2000 3000−150

−100

−50

0

5012ft embedded − loose sand


dept

h (in

ch)

soft soil capacity − LPILEsoil capacity − OpenSeessoft soil pressure (0ft) − LPILEsoft soil pressure (3ft) − LPILEsoft soil pressure (6ft) − LPILEsoft soil pressure (0ft) − OpenSeessoft soil pressure (3ft) − OpenSeessoft soil pressure (6ft) − OpenSees

Figure 1.23: Envelopes of soil pressure for different pile head lengths - loose sand

−2 0 2 4 6 8−150

−100

−50

0

50


disp (in)

dept

h (in

ch)

soft soil (0ft) − LPILEsoft soil (3ft) − LPILEsoft soil (6ft) − LPILEsoft soil (0ft) − OpenSeessoft soil (3ft) − OpenSeessoft soil (6ft) − OpenSees

Figure 1.24: Envelopes of pile deflection for different pile head lengths - loose sand

17

−30 −20 −10 0 10 20−150

−100

−50

0

50


shear force(kip)

dept

h (in

ch)


Figure 1.25: Envelopes of shear force for different pile head lengths - loose sand

−600 −400 −200 0 200 400 600−150

−100

−50

0

50


moment (kip−in)

dept

h (in

ch)


Figure 1.26: Envelopes of moment of pile for different pile head lengths - loose sand

18

1.5 Comparison of results from LPILE and OpenSees - medium sand

Plots of soil pressure, displacement and internal force (shear force and bending moment) in

the pile as obtained from OpenSees for medium sand condition are compared with results

obtained from LPILE. They are shown in Figures 1.33 - 1.29. OpenSees shows good agree-

ment with LPILE’s output. Envelopes of soil pressure, pile displacement, and pile force for

different pile head lengths are shown in Figures 1.36 - 1.39.

19

−1000 0 1000 2000 3000 4000−150

−100

−50

0


dept

h (in

ch)


Figure 1.27: Soil pressure (0ft pile head) - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.28: Pile displacement (0ft pile head) - medium sand

−50 0 50−150

−100

−50


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.29: Pile force (0ft pile head) - medium sand

20

−1000 0 1000 2000 3000 4000−150

−100

−50

0


dept

h (in

ch)



0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE


−20 0 20−150

−100

−50

0


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50Moment Diagram

M (kip−inch)

dept

h (in

ch)

OpenSeesLPILE

OpenSeesLPILE


21

−1000 0 1000 2000 3000 4000−150

−100

−50

0

50


dept

h (in

ch)



0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE


−20 0 20−150

−100

−50

0

50


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50

100Moment Diagram

M (kip−inch)

dept

h (in

ch)

OpenSeesLPILE

OpenSeesLPILE


22

−1000 0 1000 2000 3000 4000−150

−100

−50

0

5012ft embedded − medium sand


dept

h (in

ch)

medium soil capacity − LPILEsoil capacity − OpenSeesmedium soil pressure (0ft) − LPILEmedium soil pressure (3ft) − LPILEmedium soil pressure (6ft) − LPILEmedium soil pressure (0ft) − OpenSeesmedium soil pressure (3ft) − OpenSeesmedium soil pressure (6ft) − OpenSees

Figure 1.36: Envelopes of soil pressure for different pile head lengths - medium sand

−2 0 2 4 6 8−150

−100

−50

0

50


disp (in)

dept

h (in

ch)

medium soil (0ft) − LPILEmedium soil (3ft) − LPILEmedium soil (6ft) − LPILEmedium soil (0ft) − OpenSeesmedium soil (3ft) − OpenSeesmedium soil (6ft) − OpenSees

Figure 1.37: Envelopes of pile deflection for different pile head lengths - medium sand

23

−30 −20 −10 0 10 20−150

−100

−50

0

50


shear force(lb)

dept

h (in

ch)


Figure 1.38: Envelopes of shear force of pile for different pile head lengths - medium sand

−600 −400 −200 0 200 400 600−150

−100

−50

0

50


moment (kip−in)

dept

h (in

ch)


Figure 1.39: Envelopes of moment of pile for different pile head lengths - medium sand

24

1.6 Comparison of results from LPILE and OpenSees - cracking, linear, yield-

ing: medium sand

For the cracking, linear, yielding cases, the displacement and internal force (shear force and

bending moment) of the pile embedded in medium sand are compared with results obtained

from LPILE. The plots are shown in Figures 1.49 - 1.48. Overall, OpenSees shows good

agreement with LPILE’s results. However, the soil pressure and internal forces evaluated

in OpenSees are, in some cases, quite different to LPILE’s. The reason for these differences

may be that at a small deformation the p-y curve stiffness in OpenSees, corresponding to

the intermediate parabolic portion of the p-y curve, does not match well to the p-y curves

obtained from LPILE. As shown in Figure 1.5 and 1.6, the soil resistance before the ultimate

resistance (about 0.1 inch to 0.4 inch of y50) from OpenSees does not match well LPILE

results.

25

−1000 0 1000 2000 3000 4000−150

−100

−50

0


dept

h (in

ch)


Figure 1.40: Soil pressure (3ft pile head) : cracking - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.41: Pile displacement (3ft pile head) : cracking - medium sand

−5 0 5−150

−100

−50

0


Fx (kip)

dept

h (in

ch)

−200 0 200−150

−100

−50

0

50Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.42: Pile force (3ft pile head) : cracking - medium sand

26

−1000 0 1000 2000 3000 4000−150

−100

−50

0


dept

h (in

ch)


Figure 1.43: Soil pressure (3ft pile head) : linear - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.44: Pile displacement (3ft pile head) : linear - medium sand

−10 0 10−150

−100

−50

0


Fx (kip)

dept

h (in

ch)

−500 0 500−150

−100

−50

0

50Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.45: Pile force (3ft pile head) : linear - medium sand

27

−1000 0 1000 2000 3000 4000−150

−100

−50

0


dept

h (in

ch)


Figure 1.46: Soil pressure (3ft pile head) : yielding - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.47: Pile displacement (3ft pile head) : yielding - medium sand

−20 0 20−150

−100

−50

0


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.48: Pile force (3ft pile head) : yielding - medium sand

28

−1000 0 1000 2000 3000 4000−150

−100

−50

0

50


dept

h (in

ch)


Figure 1.49: Soil pressure (6ft pile head) : cracking - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.50: Pile displacement (6ft pile head) : cracking - medium sand

−5 0 5−150

−100

−50

0

50


Fx (kip)

dept

h (in

ch)

−200 0 200−150

−100

−50

0

50

100Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.51: Pile force (6ft pile head) : cracking - medium sand

29

−1000 0 1000 2000 3000 4000−150

−100

−50

0

50


dept

h (in

ch)


Figure 1.52: Soil pressure (6ft pile head) : linear - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.53: Pile displacement (6ft pile head) : linear - medium sand

−10 0 10−150

−100

−50

0

50


Fx (kip)

dept

h (in

ch)

−500 0 500−150

−100

−50

0

50

100Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.54: Pile force (6ft pile head) : linear - medium sand

30

−1000 0 1000 2000 3000 4000−150

−100

−50

0

50


dept

h (in

ch)


Figure 1.55: Soil pressure (6ft pile head) : yielding - medium sand

0 2 4 6 8 10−150

−100

−50

0

50

100

disp (in)

dept

h (in

)

OpenSeesLPILE

Figure 1.56: Pile displacement (6ft pile head) : yielding - medium sand

−10 0 10−150

−100

−50

0

50


Fx (kip)

dept

h (in

ch)

−1000 0 1000−150

−100

−50

0

50

100Moment Diagram

M (kip−inch)

OpenSeesLPILE

OpenSeesLPILE

Figure 1.57: Pile force (6ft pile head) : yielding - medium sand

31

1.7 Conclusion and Remarks

Overall, the analysis of laterally loaded pile using OpenSees is in good agreement with

results obtained from LPILE. The maximum moment obtained from OpenSees is at around

5ft of depth below the surface and is a little bit larger than that obtained from LPILE. The

response obtained from OpenSees at very low displacements is different than that obtained

using LPILE. This is due to discrepancies in p-y curves between OpenSees and LPILE. A

robust way to determine y50 should be found, or the current p-y model might need some

modification so that the value of y50 can be defined in a more consistent way.

Pile boundary conditions are important as they affect the behavior of a fiber section.

When the vertical movement of the pile tip (as well as pile top) is restrained, large axial

forces are developed, even though the pile is laterally loaded. Induced axial forces change the

moment-curvature behavior of the pile cross section. This consideration can be significant

in nonlinear analysis of a laterally loaded pile whose tip is embedded in a stiff soil or rock

soil as well as in analysis where the pile is modeled with t-z and q-z springs.

Documents

opensees and lpile