Integrated Solver Optimized for the next generation 64-bit platform

Finite Element Solutions for Geotechnical Engineering

Seismic Response Spectrum Analysis for 2D

Abutment

Tutorial 28: Updated by Angel Francisco Martinez

GTS NX

2

1. Plane strain elements are used to model both the ground conditions and Abutment.

2. Pile elements are modeled as beam elements and embedded in Embankment, Clay and Soft Rock layers.

3. Model the load in surrounding ground generated by earthquake and evaluate dynamic behavior and vibration effect of ground and abutment.

4. Check the eigenvalue of ground through Eigenvalue analysis, Analyze ground dynamic behavior affected by earthquake.

5. Starting Files Required: GTS NX 2D Tutorials 28_start.gtb

Objectives

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Step 01 File > Open

1. Main Menu >

File>Open 2. Double click GTS NX

2D Tutorial 28_start.gtb.

3. Main Menu > Analysis > Setting > Unit System> tonf>m>s

4. Click [OK].

Procedure

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ID Name Type

Modulus of Elasticity(E) [tonf/m2]

Poissons Ratio()

Unit Weight(Y) [tonf/m3]

Unit Weight (Saturated) [tonf/m3]

Cohesion (c)

[tonf/m2]

Friction Angle [] K0

1 Embankment Mohr

Coulomb 4,000 0.35 1.8 1.85 1.5 25 1

2 Clay Mohr

Coulomb 850 0.3 1.7 1.7 5 20 1

3 Weathered

Rock Mohr

Coulomb 15000 0.35 2 2 20 32.5 1

4 Soft Rock Mohr

Coulomb 30,000 0.27 2.4 2.4 45 35 1

5 Hard Rock Mohr

Coulomb 300,000 0.2 2.5 2.5 170 38 1

6 Abutment Mohr

Coulomb 232,000 0.19 2.5 2.5 300 36 1

7 Pile Elastic 21,000,000 0.3 7.8 - - - -

Materials

Step 02: Mesh> Material

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ID Name Type Subtype

1 Embankment 2D Plane Strain

2 Clay 2D Plane Strain

3 Weathered

Rock 2D

Plane Strain

4 Soft Rock 2D Plane Strain

5 Hard Rock 2D Plane Strain

6 Abutment 2D Plane Strain

7 Pile 1D Beam

Properties

Step 03: Mesh>

Property

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Step 03 Mesh > Property

1. Main Menu Model >

Property 2. Click on [Create] >Select

[2D]. 3. ID 1, Name Embankment. 4. Element Type > [Plane

Strain] 5. Material > Click

[Create]>Select Isotropic. 6. ID 1, Name Embankment,

Model Type [Mohr Coulomb].

7. Enter the material properties as shown.

8. Click [OK]. 9. Click [Apply]. 10. Similarly create the

Properties for all the soil layers Weathered Rock, Clay, Soft Rock, Hard Rock and Abutment.

Procedure 2

4

5

5 6

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Step 03 Mesh > Property

1. Main Menu Model >

Property 2. Click on [Add] > Select

[1D]. 3. ID 7, Name Pile. 4. Element Type > [Beam]. 5. Material > Click [Add]. 6. ID 7, Name Steel, Model

Type [Elastic]. 7. Enter the properties as

shown. 8. Click [OK]. 9. Property > Click [Add]. 10. ID 1, Name Pile, Type

[Beam]. 11. Click-on Sectional Library 12. Select [Pipe], D > Enter

0.508m, tw > enter 0.012m.

13. Click [OK], Click [OK].

Procedure 2

5

6

11 12

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Step 04 Mesh > 2D Mesh

1. Main Menu > Mesh >

Generate> 2D> Auto Area 2. Select Object Edges >

Select the edges as shown.

3. Mesh Size > Element Size 1,

4. Property > Select Embankment Name > Embankment.

5. Click [Advanced Option]. 6. Type [Triangle], Check-off

[Register Each Area Independently].Click [OK].

7. Click [Apply]. 8. Similarly create the mesh

sets for Clay, Weathered Rock, Soft Rock, Hard Rock & Abutment.

Procedure 2

5

1

3

6

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Step 05 Mesh >

Element>Extract

1. Main Menu >

Mesh > Element >Extract Element

2. From Geometry > Select [Edge].

3. Select the 20 edges of the Pile as shown.

4. Property ID > 7 : Pile .

5. Mesh Set > Enter name Piles.

6. Click [OK]

Procedure

2

4

1

3

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Step 06 Mesh >Element

> Parameter

1. Works Tree > Mesh > Mesh

set > Pile. Right Click to invoke Context Menu > Display > Element Csys.

2. As can be seen the Element Csys are not aligned in the same direction. This will result in wrong display of results.

3. Main Menu > Mesh > Element > Change Element Parameter.

4. In Selection filter select [1D]>> Change Cys.

5. Base Element select any element whose Z axis is parallel to Global X-axis

6. Select the Pile mesh set from the works tree.

7. Click [OK].

Procedure

4

1 3

5

2

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Step 07 Mesh >Element >

Create Surface Spring

1. Main Menu >Mesh >

Element > Other> Surface Spring

2. Change units to Kgf and cm

3. Object Type > Select [Element-Edge], Element Width > Enter 100 cm.

4. Select the edges of the left end of Embankment 2.

5. Select [Point Spring], Kx > Enter 2.1984.

6. Mesh Set>Embankment Springs Left.

7. Click [Apply]. 8. Select element edge on

the right side of Embankment 2.

9. Kx = 5.6673. 10. Click [Apply].

Procedure

3

5

1

4

6

8

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Step 08 Mesh >Element >

Create Surface Spring

1. Using the same

method define the springs on the edges of each layer.

2. The value of subgrade modulus for each layer and each edge is shown in the adjoining table.

3. For the Hard Rock layer in addition to the spring on the left and right edges, springs are also assigned at the bottom edge as Ky = 91.5910

Procedure 2

1

3

Layer Left Right Bottom

Embankment 2.1984 5.6673 -

Clay 0.7164 0.7164 -

Weathered Rock 15.5995 15.5995 -

Soft Rock 21.2965 17.8252 -

Hard Rock 215.6363 312.347 91.591

Subgrade Modulus (kgf/cm3)

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Step 09 Analysis > General

1. Main Menu >

Analysis > General

2. Name Eigen Value, Analysis Type > Select [Eigenvalue].

3. Click-on Analysis Control [ ].

4. Number of Frequencies 5.

5. Click [OK], Click [OK].

Procedure

2

4

3

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Step 10 Analysis > Perform

1. Main Menu > Analysis >

Perform 2. Check on EigenValue. 3. Click [OK]. 4. All the messages during the

analysis will be shown in the Output Window. Especially, one needs to be very cautious about warning messages, because these messages indicate that the analysis results may not be correct. The model is automatically saved before the analysis. The result is saved as binary file(*.TA*) in the same folder as the model. The detail analysis information is also saved in a text file(*.OUT).

Procedure

2

1

3

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Step 11 Results >

Vibration Mode

1. Main Menu >

Result > Vibration Mode Shape

2. Check the periods of 1st and 3rd modes where mass participation is the largest.

3. Keep the record of periods of 1.081346 sec and 0.56453 sec.

Procedure

2

1

3

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Step 12 Dynamic Analysis > Response Spectrum

1. Return to the Pre Mode 2. Main Menu > Dynamic

Anlysis> Load > Response Spectrum

3. Click the boton next to Spectrum function

4. Add Response Spectrum Functions

5. Click [Design Spectrum].

6. Design Spectrum [UBC 1997], Seismic coefficient Calculation Option > Automatic. Soil Profile Type (S) > Sb. Seismic Zone Factor > Zone 1 (0.07). Max Period > Enter 6 secs.

7. Click [OK].

Procedure 2

1 3

4

6

5

7

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Step 12 Dynamic Analysis > Response Spectrum

1. Click OK 2. Click Close 3. Direction: X 4. Select Function

Name UBC97.

5. Click Add 6. Click OK

Procedure

2

1

3

4

5

6

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Step 13 Analysis > General

1. Main Menu > Analysis

> General 2. Title Response

Spectrum. 3. Solution Type:

Response Spectrum 4. Activate All Sets 5. Click-on Analysis

Control [ ]. 6. Eigen Vectors >Number

of Frequencies: 5 7. Click [OK] Button 8. Drag and drop the Load

Set, 1st Degree, from Set Tree into Activated.

9. Click [OK] Button.

Procedure 2

3

4

5

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Step 14 Analysis Control

1. In General tab>Eigen

Vectors >Number of Frequencies: 5

2. Click on the Dynamic tab

3. Check on Correction by Damping Ratio and click on [ ] .

4. Select Mass and Stiffness Proportional

5. Select Calculate from Modal Damping, and Select Period [sec]

6. Enter the periods for 1st and 3rd modes from previous eigenvalue analysis.

7. Enter 0.05 in Damping Ratio for both Mode 1 and 2

8. Click [OK] Button.

Procedure

4

5

1 2

6

7

8

3

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Step 15 Analysis > Perform

1. Main Menu > Analysis >

Perform 2. Check on Response

Spectrum only. 3. Click [OK]. 4. All the messages during the

analysis will be shown in the Output Window. Especially, one needs to be very cautious about warning messages, because these messages indicate that the analysis results may not be correct. The model is automatically saved before the analysis. The result is saved as binary file(*.TA*) in the same folder as the model. The detail analysis information is also saved in a text file(*.OUT).

Procedure 2

3

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Step 16 Results >

Displacements

1. Post Works Tree >

Response Spectrum> Modal Combination> Displacement > TX

Procedure

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Step 16 Results > Beam Element Force

1. Post Works Tree >

Response Spectrum> Modal Combination> Beam Force Element> Axial Force

Procedure