session 1. soil-structure interaction for piled-raft...

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Session 1.

Soil-Structure Interaction for Piled-Raft Foundation

MIDAS Geotechnical Know-how Sharing Series

JaeSeok Yang Principal Geotechnical Engineer, MIDAS IT



01 Introduction

02 SSI by Substructure Method

03 SSI by Direct Method

04 Case Study

GTS NX

3

Soil Structure Interaction

Schematic Diagram of Ground Response Analysis

GTS NX

4

Substructure Method Direct Method

Soil Structure Interaction for a Bridge



01 Introduction



04 Case Study

GTS NX

6

Soil Modeling for Structural Design

GTS NX

7

Determination of Soil Springs

GTS NX

8

Foundation Response

GTS NX

9

Foundation Response - Rigid Raft

GTS NX

10

Foundation Response - Flexible Raft

GTS NX

11

Foundation Response

GTS NX

12

Determination of Modulus of Subgrade Reaction

GTS NX

13

Determination of Modulus of Subgrade Reaction

GTS NX

14

The soil-structure interaction is reflected with soil spring data.

• The soil spring data may be applied to the substructure-only model with the super-

structure load applied.

• The soil spring data may be applied to the entire structure model with both the super

and substructure.

Substructure (Indirect) Method



01 Introduction



04 Case Study

GTS NX

16

Bearing Behavior of a Piled Raft

GTS NX

17

Requirements of a Numerical Model for Piled Raft

GTS NX

18

Work Flow of Pile Modeling

GTS NX

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Iterative Process General Steps

GTS NX

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Pile Modeling in GTS NX

GTS NX

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Solid Element Model

GTS NX

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Solid Element Model

GTS NX

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Beam-Solid Connectivity Model

GTS NX

24

Beam-Solid Connectivity Model

GTS NX

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Line-to-Solid Interface Model

GTS NX

26

Line-to-Solid Interface Model

GTS NX

27

Point-to-Solid Interface Model

GTS NX

28


GTS NX

29


GTS NX

30

Line-to-Solid Interface Elements

GTS NX

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Pile Element Parameters

GTS NX

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Pile Element Parameters

GTS NX

33

Verification

GTS NX

34

Verification

GTS NX

35

Interaction between MIDAS Programs

GTS NX

36


GTS NX

37


GTS NX

38


GTS NX

39


GTS NX

40


GTS NX

41


GTS NX

42




01 Introduction



04 Case Study

GTS NX

44

1

2

3

1 Geometry created by the structural team is replicated in Autodesk Revit

2 Converted to a structural model in Midas GEN

3 Imported and analyzed with the ground in Midas GTX NX.

Introduction

The focus of the case study will be a soil structure interaction analysis of a 55 story (168 m) building, in a layered soil down to 50 meters.

Due to the geotechnical condition and the size of the building, a SSI was necessary, providing prevision of settlements, and how those influence the behavior of the structure.

The presentation is mainly focused in the attempt of unifying different platforms and briefly describing the used process.

GTS NX

45

The building comprises 55 story, resulting in 168 m high, being inside the top 25 tallest buildings in Brazil. Designed in full reinforced concrete structure Area of each story: 440 m² Total of 18 columns A total dead load of 300,000 kN

168 m

Building Details

GTS NX

46

• Piled raft foundation • 106 piles • CFA – Continuous Flight Auger - Piles • 100 cm diameter (piles) • 30 m long (piles) • 680 m² (raft)

168 m

Building Details

GTS NX

47

0 5 10 15 0 1 1

Clay

Silty Sand

Fz

Sand

Silty Clay

Silty Clay

Clayey Silt

Sand

0 1000 2000

0

5

10

15

20

25

30

35

40

45

50

0 20 40

Dep

th (

m)

• Sedimentary deposit

• Excess of porewater pressure

• Low capacity profile

• Layered soil alternating sand and clay

SPT N (Blows/30 cm)

CPT qt (MPa)

U0, U2

(kPa)

5 SPT – 50 meters deep

4 CPTu – 43 meters deep Site Investigation

Soil Characterization

GTS NX

48

• Static load tests • Prior to the foundation construction • 3 CFA Piles (diameter of 80, 100 and 120 cm) • Maximum load of 9 MN • Results used to calibrate GTS NX model Load Test

30 m

100 cm

LOAD (kN)

Sett

lem

ent

(mm

)

Theoretical prediction

Pile Load Testing Program

GTS NX

49

Hydraulic Jack

Reaction Piles

Reaction Beam Load Cell

Pile Load Testing Program

GTS NX

50

• Geometry created by the structural team is replicated in Autodesk Revit, including:

• Materials; • Sections; • Properties; • Analytical model; • Loads.

• Using the Revit-Midas/GEN link, the model can be updated between the platforms.

Structural Model – Autodesk Revit

GTS NX

51

• Revit’s model was imported in Midas GEN:

• Imported data: • Materials; • Sections; • Properties; • Loads.

• Input in GEN: • Story information; • Initial boundary condition; • Wind loads;

• Using the export option, a Midas MXT file was created to make the link with Midas GTS NX.

Structural Model – midas Gen

GTS NX

52

• Soil layers • Failure Criteria / Constitutive models

• Mohr-Coulomb for sands • Modified Cam-clay for clays

• Piled Raft model • Concrete elastic properties • 3.5 m thick raft – as a solid element • 106 piles – as beam elements

50

m

100m 100m

Geotechnical Model – midas GTS NX

GTS NX

53

• Pile Model Type – Line-to-Solid Interface Model

Model = Soil (solid) + Pile (line)

+ Interface (line-to-solid)


GTS NX

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• Pile load test calibration • Reproduce the geometry of the pile load test; • Define different load steps to read the settlements; • Class C prediction • Compare to the pile load test Load x Settlement

curve

0

20

40

60

80

100

120

0 2500 5000 7500 10000

PCE

Décourt hyperbolic

FEM Model

LOAD (kN)

Sett

lem

ent

(mm

)


GTS NX

55

+ +

• Full Model • Soil + Piled-Raft + Structure

• Advantages: • More accurate values of differential settlements, due to

the rigidity/stiffness of the superstructure; • Evaluation of wind load cases directly;

GEN


GTS NX

56

• Settlements • Total settlement; • Differential settlement Analysis; • Angular distortion Analysis.

Results

GTS NX

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• Pile Loads • Distribution of load along the pile.

• Pile Springs

Results

GTS NX

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• Pile bending moments • Distribution of bending moments along the pile.

Results

GTS NX

59

• Successful interaction between platforms

Revit + Midas GEN + Midas GTS NX

• Key results (GTS NX):

• Settlements from the piled raft foundation;

• Distribution of bending moment in piles;

• Springs can be exported, being different for each pile;

• Area springs can be exported, simulating the contact of the raft with the soil.

• Working in the same platform reduces the number of iterations between the structural and geotechnical teams.

• Midas offers two powerful platforms – for structural and geotechnical engineering – that are evolving to work together, in a full model, taking SSI to another level.

Conclusions

GTS NX

60

Q & A

session 1. soil-structure interaction for piled-raft...

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