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Chapter11 Push-Over Analysis 1

11. Push-over analysis

Applicable CivilFEM Product: All CivilFEM Products

Level of Difficulty: Moderate

Interactive Time Required: 90 minutes

Discipline: Structural Steel

Analysis Type: Push Over

Element Type Used: Shell 181 and Surf 154

Active Code: Eurocodes 3 and 8

Units System: N, m, s

CivilFEM Features Demonstrated: Units selection, code selection, material definition, shell definition, push-over analysis.

Problem Description

Given

The problem consists of an analysis of push over applied to a tank which contains water.

Geometry: Height= 25 m

Diameter= 12 m


Push-Over pressures Water pressures

P_BOT= gh

Material: Fe 360

Element type: Shell 181

Surf 154

Pressures: Push-Over Pressures: Gradient pressure with slope= 40

Watt: Gradient pressure with slope= P_BOT/ H_CYL

(H_CYL= 25 m)

Approach and Assumptions

This is a push-over analysis with 3D elastic elements and elastic material properties. Model geometry is defined with nodes and elements.

Summary of Steps

Preprocessing

1. Preprocessing

2. Specify title

3. Set code

4. Set units


5. Define parameters

6. Define materials

7. Define element type

8. Define Shell properties

9. Define Geometry

10. Save the database

Solution

11. Apply displacement constrain

12. Error! No se encuentra el origen de la referencia.s

13. Push-Over Analysis

Interactive Step-by-Step Solution

1. Preprocessing

A typical CivilFEM analysis begins with providing data such as the units system, active code, materials, element types, section and model geometry definition.

2. Specify title

Although this step is not required for a CivilFEM analysis, we recommend that you make it part of all your analysis.

Utility Menu: File Change title

Enter the title: Push-over analysis.

OK to define the title and close the dialog box.

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3. Set code

In CivilFEM you can choose between different codes for checking and designing. CivilFEM allows you to uphold different active codes simultaneously, one for concrete calculations another one for steel calculations and a third one for seismic design. In this example the active codes are the Eurocodes, which is the default option.

Main Menu: CivilFEM Civil Setup

Select Civil Setup

OK to set active code and close the code dialog box

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4. Set units

In CivilFEM you must define a unit system. CivilFEM will need such a system to perform calculations according to Code. You should maintain it during the entire design. In this analysis, we will select the International System units, that is, meters, seconds and Newtons.

Main Menu: CivilFEM Civil Setup

Choose Units Library

OK to accept units and close the units dialog box

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5. Define parameters:

D_CYL= 12 Diameter

H_CYL= 25 High

H_WAT= H_CYL

TH_BOT= 10E-3

TH_TOP= 35E-3

P_TOP= 0

P_BOT= 1000*9.8*H_WAT

SLOPE = (P_TOP - P_BOT)/H_CYL

V2= V2= PII*(H_WAT-TH_BOT)*(D_CYL**2-(D_CYL-TH_TOP)**2)/4

Mw = 2175613.

6. Define materials

Material properties definition is performed with the CivilFEM ~CFMP command. This command automatically defines the ANSYS material properties (density, Youngs modulus, Poissons ratio and thermal expansion coefficient) and the CivilFEM material properties necessary for code checking. In this case we will select Fe 430 steel.

The CivilFEM ~CFMP command allows us to define stress-strain diagrams, to define safety coefficients, to control the linear or non-linear behavior of the material and to select the activation time of the material.

Main Menu: CivilFEM Civil Preprocessor Materials

Pick new to define a new material

Choose Fe 360 Steel and all the material properties corresponding to Fe430 steel are automatically calculated according to Eurocode 3 (active code)

The Add button must be clicked 2 times to define the materials:

1. Fe 360 for the bottom of the tank.

2. Fe 360 material which density is going to be modified to bear the weight of the water in mind.

Density= 7850+(Mw/V2)

Mw= mass of water.

V2= volume of water.

V2= PII*(H_WAT-TH_BOT)*((D_CIL-TH_WALL)**2)/4

3. Material 3 with void density for SURF 154 element. Command MP

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Modify for material 2.

Write +(Mw)/V2 for density.

Choose bi-linear for type of Analysis Diagram. (It is necessary that the type of graph is changed of linearly to bilinear for the type of analysis that is going to be realized).

Choose Biso for plasticity key.

Ok

Modify material 1. Choose bi-linear for type or Analysis Diagram and Biso for plasticity key for the material

Ok.

Write MP,DENS,3,0

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7. Define element type

Checking and designing according to codes is only performed on CivilFEM supported element types, although you can use any ANSYS element to define your model, only the CivilFEM supported elements will be checked according to codes. In the element type menu you can see the CivilFEM supported beam elements.

We will use Shell 181 and Surf 154

Main Menu: CivilFEM Civil Preprocess Element Types Other

ElementsAdd/ Edit/ Delete.

Add.

Choose Shell181 and Apply.

Choose Surface Effect 154 and Ok.

Click on Options for Surf 154.

Choose exclude for midside nodes and Full Area w/tan for Pres vector orientation.

Ok.

Close.

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8. Define Shell Properties

Main Menu: CivilFEM Civil Preprocess Shell Vertex

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Choose Steel.

Write TH_BOT for thickness.

Choose material 1

Ok.

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Main Menu: CivilFEM Civil Preprocess Shell Vertex

Choose Steel.

Write TH_TOP for thickness.

Choose material 2

Ok.

Exit.

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Main Menu: CivilFEM Civil Preprocess Beam & Shell Properties.

CivilFEM command ~BMSHPRO will be used to define ANSYS real constants.

Choose New Shell.

Choose SHELL 181 for Ename

Choose vertex 1

Apply.

Choose vertex 2

Ok.

Exit.

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9. Define real constant for surf element

Main Menu: Preprocessor Real Constants Add/Edit/Delete.

Add.

Choose Surf 154 and Ok.

Write 0 for Added mass/unit area.

Ok.

Close.

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Or:

Write R, 3,0.

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10. Define Geometry

Main Menu: Preprocessor ModelingCreateVolumesCylinder Hollow Cylinder.

Write D_CYL/2 for Rad-1 and H_CYL for Depth.

Ok.

Main Menu: Preprocessor ModelingDeleteVolumes Only.

Pick All.

Ok.

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Utility Menu: Select Entities

Choose Areas By Location.

Choose Z coordinates.

Write H_CYL for Min,Max.

Ok.

Main Menu: Preprocessor ModelingDeleteAreas Only.

Pick All.

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Ok.

Utility Menu: Select Everything

Main Menu: Preprocessor Numering CtrlsCompress Numbers.

Choose Areas.

Ok.


Choose Areas By Num Pick.

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Ok.

Write 2, 3.

Ok.

Utility Menu: Select Comp/ AssemblyCreate Component

Write Walls for component name.

Choose Areas.

Ok.

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Choose Areas By Num Pick.

Ok.

Write 1

Ok.

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Write Bottom for component name.

Choose Areas.

Ok.


( A regular mesh is obtained after the lines are concatenated).


Select Lines by Location with z=0. (From full)

Ok.

. Utility Menu: Select Entities

Select Lines by Location with y=0, 6. (Reselect)

Ok.

MainMenu:PreprocessorMeshingMeshAreasMapped

ConcatenateLines

Pick All.

Ok.

Commands:

LSEL,S,LOC,Z,0 (Select lines, from full, by location, z= 0)

LPLOT ( Plot lines)

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LSEL,R,LOC,Y,0,6 (Select lines, reselect, by location, Y=6)

LPLOT

LCCAT,ALL ( Concatenate lines)

ALLSEL


Concatenate the next lines in the same way.

Comands:

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LSEL,S,LOC,Z,0

LPLOT

LSEL,R,LOC,Y,0,-6

LPLOT

LCCAT,ALL

ALLSEL

LSEL,S,LOC,Z,25

LPLOT

LSEL,R,LOC,Y,0,6

LPLOT

LCCAT,ALL

ALLSEL

LSEL,S,LOC,Z,25

LPLOT

LSEL,R,LOC,Y,0,-6

LPLOT

LCCAT,ALL

ALLSEL


Utility Menu: Select Comp/AssemblySelec Comp/Assembly

Choose by component name.

Ok.

Choose Bottom.

Ok.

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Main Menu: Preprocessor MeshingMesh Tool.

Pick on Set button.

Choose Shell 181 , mat 1 and real constant 1.

Ok.

Choose Areas and Free Tri mesh.

Click on Mesh buttom.

Pick All and Ok.

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Ok.

Choose Walls.

Ok.

Main Menu: Preprocessor MeshingMesh Tool.

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Pick on Set button.

Choose Shell 181 , mat 2 and real constant 2.

Ok.

Choose Areas and mapped cuad mesh.

Click on Mesh buttom.

PIck All.

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Select nodes attached to Areas, all.

Ok.

Main Menu: Preprocessor MeshingMesh AttributesDefault Attribs.

Choose Surf 154, material 3 and real constant 3.

Ok.

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Main Menu: Preprocessor ModelingCreateElementsSurf

/ContactSurf to Surf.

Ok.

Pick All.

Ok.

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11. Save the database

Before moving to the next step, we will save all we have done so far. The save operation will save the database to file.db and file.cfdb

Toolbar: CFSAVE

Solution

In this step we will define the analysis type and its options, apply loads and initiate the finite element solution. A new, static analysis is the default option, so we will not need to specify analysis type for this problem. Also, there are no analysis options for this problem.

12. Apply displacement constraints

We will constrain all DOF at the bottom of the tank.




Ok.

Choose Bottom.

Ok.

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Main Menu: Solution Loads Apply Structural Displacement

On Areas

Pick All.

Choose All DOF to be constrained

Ok.

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13. Apply pressure loads

Push Over pressures:


Select Elements By Attributes and Elem type num.

Write 2 for type of element .

Ok.

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Main Menu: Preprocessor Loads Define Loads Settings For

Surface LdGradient

Choose Pressure.

Write 40 for Slope value.

Choose z direction for Slope direction.

Ok.

Main Menu: Preprocessor Loads Define Loads Apply

StructuralPresureOn Elements.

Write ALL.

Ok.

Choose Constant value.

Write 5 for LKEY.

Write 1225.1 for VAL2 .

Write 1278.6 for VAL3.

Write 0 for VAL4.

Ok.

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Main Menu: Preprocessor Load State Write LS File.

Write 1 for the Load Step File.

Ok.

Or: ~CFLSWRT,1

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Surface LdGradien

Choose Pressure.



Ok.

Other pressures:

Bottom pressures


(Select Bottom component)


(Select elements attached to Areas)



Pick All.

Write P_BOT for load pres value.

Ok.

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Walls pressures:


(Select Walls component)


(Select elements attached to Areas)


Surface LdGradien.

Choose Pressure.

Write SLOPE for Slope value.


Ok.

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Pick All.

Write P_TOP for load press value.

Ok.

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Surface LdGradien

Choose Pressure.



Ok.


StructuralInertiaGravityGlobal

Write 9.81 for z component.

Ok.

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14. Push Over Analisys

Main Menu: Seismic Desing Define Spectrum

Write 0.9 for the ground acceleration.

Choose Class A

Choose Elastic.

Choose 1 for Horizontal and Vertical behavior fact.

Choose 210-2 for Damping factor.

Ok.

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Main Menu: Seismic Desing Modal Solution.

Write 50 for Number of modes to be extracted.

Choose Block Lanczos as the Extraction Method.

Ok.

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Main Menu: Seismic Design PushOver Analisys.

Write 163 for Node Number.

Write 1 for Lambda and 50 for SS num.

Choose z for vertical axis.

Push LS File and click on S01 file.

Click on Modal Shape button.

Click on Load Modes button.

Choose the worst direction.

Click on Solve button.

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ESEL,U,TYPE,,2 to view shell elements without the surf elements.

~RETROFT,LAMBDA,1

Push-over analysisProblem DescriptionGivenApproach and AssumptionsSummary of StepsSolution

Interactive Step-by-Step SolutionSolution

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