Transmissio Tower Structure

8/3/2019 Transmissio Tower Structure

1/36

Structural #1: Analysis of a power transmission towerIntroduction: In this example you will learn to use the 2-D Truss element in ANSYS.Physical Problem: A power transmission tower is a common example of a structure that is madeup of only truss members. These towers are actually 3-D structures, but for the sake of simplicity we willtake a cross-sectional face of the tower. The tower is mainly subjected to loading in the vertical directiondue to the weight of the cables. Also it is subjected to forces due to wind. In this example we will

consider only loading due to the weight of the cables, which is in the vertical direction.Problem Description:

The tower is made up of trusses. You may recall that a truss is a structural element that experiencesloading only in the axial direction.Units: Use S.I. units ONLYGeometry: the cross sections of each of the truss members is 6.25e-3 sq. meter.Material: Assume the structure is made of steel with modulus of elasticity E=200 GPa.Boundary conditions: The tower is constrained along X and Y directions at the bottom left corner, andalong Y direction at the bottom right corner.Loading: The tower is loaded at the top. The load is in horizontal direction only, and its magnitude is5000 N.Objective:To determine deflection at each joint.

To determine stress in each member.To determine reaction forces at the base.

You are required to hand in print outs for the above.Figure:

The five trusses at the top are each 3m in length.


2/36

IMPORTANT: Convert all dimensions and forces into SI units.

STARTING ANSYSClick on ANSYS 6.1 in the programs menu.Select Interactive.The following menu that comes up. Enter the working directory. All your files will be stored in this

directory. Also enter 64 for Total Workspace and 32 for Database. Give your file a jobname.Click on Run.


3/36

MODELING THE STRUCTURE

Go to the ANSYS Utility MenuClickWorkplane>WP SettingsThe following window comes up


4/36

Check the Cartesian and Grid Only buttonsEnter the values shown in the figure above.Go to the ANSYS Main Menu


5/36

ClickPreprocessor>-Modeling->Create>Keypoints>On Working PlaneThe following window comes up

Now we will pick the end points of the trusses.Select the keypoints on the workplane grid. Your points should look like this.If you cannot see the complete workplane then go to Utility Menu>PlotCntrls>Pan ZoomRotate and zoom out to see the entire workplane


6/36

Now create lines connecting the keypointsClick on Preprocessor>-Modeling->Create>-Lines->Lines>Straight LineCreate lines by picking keypoints to make the figure shown below


7/36

MATERIAL PROPERTIES

Go to the ANSYS Main MenuClickPreprocessor>Material Props>Material Models.In the window that comes up which is shown below, for Material Model 1,chooseStructural>Linear>Elastic>Isotropic.


8/36

Enter 1 for the Material Property Number and click OK. The following window comes up.

Fill in 2e11 for the Young's modulus and 0.3 for minor Poisson's Ratio. ClickOK.Now the material 1 has the properties defined in the above table. We will use this material for thetransmission tower.

ELEMENT PROPERTIESSELECTING ELEMENT TYPE:ClickPreprocessor>Element Type>Add/Edit/Delete...In the 'Element Types' window that opens click on Add... The following window opens.


9/36

Type 1 in the Element type reference numberClick on Structural Link and select 2D spar. Click OK. Close the 'Element types' window.So now we have selected Element type 1 to be a structural Link- 2D spar element. The trusses will bemodeled as elements of type 1, i.e. structural link element. This finishes the selection of element type.Now we need to define the cross sectional area for this element.Go to Preprocessor>Real ConstantsIn the "Real Constants" dialog box that comes up click on AddIn the "Element Type for Real Constants" that comes up click OK. The following window comes up.

Type 6.25e-3 for cross sectional area and click on OK.We have now defined the cross sectional area of the link element.

MESHING:DIVIDING THE TOWER INTO ELEMENTS:Go to Preprocessor>Meshing>Size Cntrls>ManualSize>Lines>All Lines.In the menu that comes up type 1 in the field for 'Number of element divisions'. This divides each ofthe lines in your figure into 1 element.


10/36

Click on OK. Now when you mesh the figure ANSYS will automatically divide each line into 1 element.Now go to Preprocessor>-Meshing->Mesh>linesSelect all the lines and click on OK in the "Mesh Lines" dialog box.Now each line is a truss element (Element 1).

BOUNDARY CONDITIONS AND CONSTRAINTSAPPLYING BOUNDARY CONDITIONS

The tower is constrained in the X and Y directions at the bottom left corner and in the Y direction at

the bottom right corner.Go to Main Menu. Click on Preprocessor>Loads>Define

Loads>Apply>Structural>Displacement>On KeypointsSelect the keypoint on which you want to apply displacement constraints. The following windowcomes up.


11/36

Select UX and UY for the bottom left corner and UY for the bottom right corner and click OK. Thedefault displacement value is taken to be zero.APPLYING FORCESGo to Main Menu.Click on Preprocessor>Loads>Define Loads>Apply>Structural>Forces/Moment>On Nodes.Select the top node.Click on OK in the 'Apply F/M on Nodes' window. The following window will appear.

Select FX and enter 5000 as the Force/Moment value.Click on OK.The figure on the ANSYS Graphics window will look like the following.


12/36

Now the Modeling of the problem is done.

SOLUTIONGo to ANSYS Main Menu>Solution>-Analysis Type->New Analysis.Select static and click on OK.Go to Solution>-Solve->Current LS.Wait for ANSYS to solve the problem.Click on OK and close the 'Information' window.

POST-PROCESSINGListing the results.Go to ANSYS Main Menu.Click on General Postproc>List Results>Nodal Solution. The following window will come up.


13/36

Select DOF solution and All U's. Click on OK. The nodal displacements will be listed as follows.

Similarly you can list the stresses for each element by clicking Gen Postprcessing>ListResults>Element Solution.Now select LineElem Results. The following table will be listed.


14/36

MODIFICATION

You can also plot the displacements and stress.Go to General Postproc>Plot Results>-Contour Plot->Element Solution. The followingwindow will come up.

Select a stress to be plotted and click OK. The output will be like this.


15/36

http://www.andrew.cmu.edu/course/24-ansys/htm/s1_tower.htm

Structural #2: Analysis 2-D Beam structureIntroduction: In this example you will learn to use the 2-D Beam element in ANSYS.Physical Problem: Structural analysis of the frame shown below.Problem Description:

The structure is made up of beams. You may recall that a beam is a structural element whose length isvery large compared to the other two dimensions.Units: Use S.I. units ONLYGeometry: The members have a annular cross-section. The cross sections (A) of each of the trussmembers is 5.5e-3 sq meter. The polar radius of gyration (R) is 5.5e-2 meter. (hint: Use the values ofA and R to find Izz then find the value of the outer diameter (The beam height))Material: Assume the structure is made of steel with modulus of elasticity E=210 GPa.Boundary conditions: All the DOFs are constrained at the bottom end, i.e. the bottom end is a built-inend.Loading: The structure is loaded at the ends of the two arms. The load is in the negative Y direction.The load value is 5000 N each.Objective:

To determine deflections at the points of application of load.To determine the maximum stress in the structure.Also determine the maximum possible load the frame can take. Look up for the value of yield stress

for steel. Assume a factor of safety of 1.25.
http://www.andrew.cmu.edu/course/24-ansys/htm/s1_tower.htmhttp://www.andrew.cmu.edu/course/24-ansys/htm/s1_tower.htmhttp://www.andrew.cmu.edu/course/24-ansys/htm/s1_tower.htm


16/36


IMPORTANT: Convert all dimensions and forces into SI units.STARTING ANSYS

Click on ANSYS 6.1 in the programs menu.Select Interactive.The following menu that comes up. Enter the working directory. All your files will be stored in thisdirectory. Also enter 64 for Total Workspace and 32 for Database.Click on Run.

MODELING THE STRUCTUREGo to the ANSYS Utility MenuClickWorkplane>WP Settings

The following window comes up


17/36

Check the Cartesian and Grid Only buttonsEnter the values shown in the above.Go to the ANSYS Main MenuClickPreprocessor>Modeling>Create>Keypoints>On Working PlaneThe following window comes up


18/36

Now we will pick the end points of the trusses.

5 meters is now 1 X 5 units, since each cell in the grid is 1 unit across, 5 meters is 5 cells wide.Using this conversion select the keypoints on the workplane grid. Your points should look like this.


19/36

If you cannot see the complete workplane then go to Utility Menu>PlotCntrls>Pan ZoomRotateand zoom out to see the entire workplane.Now create lines connecting the keypoints

Click on Preprocessor>Modeling>Create>Lines>Lines>Straight LineCreate lines by picking keypoints to make the figure shown below.


20/36

MATERIAL PROPERTIESGo to the ANSYS Main MenuClick Preprocessor>Material Props>Material Models. In the window that comes upchooseStructural>Linear>Elastic>Isotropic. The following window will appear.

Double Click Isotropic. The following window comes up.


21/36

Fill in 2.1e11 for the Young's modulus and 0.3 for Poisson's Ratio. Click OKNow the material 1 has the properties defined in the above table. We will use this material for thestructure.

ELEMENT PROPERTIES:SELECTING ELEMENT TYPE:

ClickPreprocessor>Element Type>Add/Edit/Delete... In the 'Element Types' window that opens

click on Add... The following window opens.

Type 1 in the Element type reference number.Click on Structural Beam and select 2D elastic. Click OK. Close the 'Element types' window.So now we have selected Element type 1 to be a structural Beam- 2D elastic element. The trusses willbe modeled as elements of type 1, i.e. structural beam element. This finishes the selection of elementtype.Now we need to define the cross sectional area, the second moment of inertia etc. for this element.Go to Preprocessor>Real Constants.


22/36

In the "Real Constants" dialog box that comes up click on AddIn the "Element Type for Real Constants" that comes up click OK. The following window comes up

Type in 5.5e-3 for cross sectional area, calculate Izz from the value of the cross-sectional area andpolar radius of gyration and enter it. Also calculate and enter the height and click on OK. The height ofthe beam is required to calculate the maximum stress, which will be at the top surface of the beam.We have now defined the geometric properties of the beam element.

MESHING:DIVIDING THE STRUCTURE INTO ELEMENTS:

Go to Preprocessor>Meshing>Size Controls>Manual Size>Lines>All Lines. In the menu that

comes up type 1 in the field for 'Number of element divisions'.


23/36

Click on OK.Now go to Preprocessor>Meshing>Mesh>LinesSelect all the lines and click on OK in the "Mesh Lines" dialog box.Now each line is a truss element (Element 1).

BOUNDARY CONDITIONS AND CONSTRAINTS:APPLYING BOUNDARY CONDITIONS

The tower is constrained in the DOFs at the bottom node.Go to Main MenuClick on Preprocessor>Loads>Define

Loads>Apply>Structural>Displacement>OnKeypoints.Select the keypoint on which you want to apply displacement constraints. The following window comes

up.

Select All DOF and click OK.APPLYING FORCES

Go to Main MenuClick on Preprocessor>Loads>Define Loads>Apply>Forces/Moment>On Nodes.Select the top right node and the top left node.Click on OK in the 'Apply F/M on Nodes' window. The following window will appear.Enter the value of the force.


24/36

The figure looks like this now.

Now the Modeling of the problem is doneSOLUTION:Go to ANSYS Main Menu>Solution>Analysis Type>New Analysis.Select static and click on OK.Go to Solution>Solve>Current LSWait for ANSYS to solve the problem.Click on OK and close the 'Information' windowPOST-PROCESSING:


25/36

Listing the resultsGo to ANSYS Main MenuClick on General Postprocessing>List Results>Nodal Solution. The following window will come up.


Similarly you can list the stresses for each element by clicking Gen Postprocessing>ListResults>Element Solution. Now select LineElem Results. The following table will be listed.


26/36

MODIFICATIONS:You can also plot the displacements and stress.Go to General Postprocessing>Plot Results>Contour Plot>Element Solution. The followingwindow will come up.



27/36

Structural #4: Analysis of a 3-D truss structureIntroduction: In this example you will learn to use the 3-D Truss element in ANSYS.Physical Problem: Analysis of the 3D truss structure shown in the figure below.Problem Description:

The tower is made up of trusses. You may recall that a truss is a structural element that experiencesloading only in the axial direction.Units: Use S.I. units ONLYGeometry: the cross sections of each of the truss members is 1.56e-3 sq meter.Material: Assume the structure is made of aluminum with modulus of elasticity E=75 GPa.Boundary conditions: The structure is constrained in the X, Y and Z directions at the bottom threecorners.Loading: The tower is loaded at the top tip. The load is in the YZ plane and makes an angle of 75 withthe negative Y axis direction. The load value is 2500 N.Objective:

To determine deflection at each joint.To determine stress in each member.To determine reaction forces at the base.Give three examples where similar 3D trusses are used in practice. Model one of them (with reasonable

assumptions of dimensions, material properties and loading) using ANSYS. You don't have to solve it.You can do so to check whether your assumptions were reasonable!!



28/36

IMPORTANT: Convert all dimensions and forces into SI units.

STARTING ANSYSClick on ANSYS 6.1 in the programs menu.Select Interactive.The following menu that comes up. Enter the working directory. All your files will be stored in thisdirectory. Also enter 64 for Total Workspace and 32 for Database. Give your file an appropriate job

name.Click on Run.


29/36

MODELING THE STRUCTUREGo to ANSYS Utility Menu. Click on Workplane>Change Active CS to..>Global Cartesian.Go to the ANSYS Main Menu.ClickPreprocessor>Modeling>Create>Keypoints>In active CSThe following window comes up


30/36

Fill in the keypoint number (1,2,3...) and the coordinates. Make sure you get the correct coordinates fromthe figure. Create all the 10 keypoints. Make sure the numbering of your keypoints matches thenumbering of the joints in the figure.If you cannot see the grid then go to Utility Menu>Display Working PlaneIf you cannot see the complete figure then go to Utility Menu>PlotCntrls>Pan Zoom Rotate andzoom out to see the entire figure.Now create lines connecting the keypoints

Click on Preprocessor>Modeling>Create>Lines>Lines>In Active Coord.Pick the endpoints of each element to create the lines. Rotate the figure for more accessible views.

You can use the Utility Menu>PlotCtrls>Pan Zoom Rotate window to rotate the model and see its3D nature.

MATERIAL PROPERTIESGo to the ANSYS Main MenuClickPreprocessor>Material Props>Material Models. In the window that comes up which isshown below, for Material Model 1, chooseStructural>Linear>Elastic>Isotropic.

Double click Isotropic for Material Model 1.


31/36

Fill in 7.5e10 for the Young's modulus and 0.3 for minor Poisson's Ratio. Click OKNow the material 1 has the properties defined in the above table. We will use this material for theelements of the structure.

ELEMENT PROPERTIES:SELECTING ELEMENT TYPE:

ClickPreprocessor>Element Type>Add/Edit/Delete... In the 'Element Types' window thatopens click on Add... The following window opens.

Type 1 in the Element type reference number.Click on Structural Link and select 3D spar. Click OK. Close the 'Element types' window.So now we have selected Element type 1 to be a structural Link- 3D spar (cable) element. The trusseswill be modeled as elements of type 1, i.e. structural link element. This finishes the selection ofelement type.Now we need to define the cross sectional area for this element.Go to Preprocessor>Real Constants.In the "Real Constants" dialog box that comes up click on AddIn the "Element Type for Real Constants" that comes up click OK. The following window comes up.


32/36

Type 1.56e-3 for cross sectional area and click on OK.We have now defined the cross sectional area of the link element.

MESHING:DIVIDING THE TOWER INTO ELEMENTS:Go to Preprocessor>Meshing>Size Controls>Manual Size>Lines>All Lines. In the menu thatcomes up type 1 in the field for 'Number of element divisions'.

Click on OK.Now go to Preprocessor>Meshing>Mesh>Lines.Select all the lines and click on OK in the "Mesh Lines" dialog box.Now each line is a truss element (Element 1).

BOUNDARY CONDITIONS AND CONSTRAINTSAPPLYING BOUNDARY CONDITIONS

The tower is constrained in the X, Y and Z directions at the four bottom corners.Go to Main MenuClick on Preprocessor>Loads>DefineLoads>Apply>Structural>Displacement>On Keypoints


33/36

Select the keypoint on which you want to apply displacement constraints. The following window

comes up.

Select UX, UY, UZ and click OK.APPLYING FORCES

First find the components of the force along the Y and Z directionsGo to Main MenuClick on Preprocessor>Loads>Define Loads>Apply>Structural>Forces/Moment>OnNodes.Select the top node.Click on OK in the 'Apply F/M on Nodes' window. The following window will appear.Enter the value of the Z-component of the force.Repeat the procedure to apply the Y-component of force.

Now the Modeling of the problem is done


34/36

SOLUTIONGo to ANSYS Main Menu>Solution>Analysis Type>New Analysis.Select static and click on OK.Go to Solution>Solve>Current LS.Wait for ANSYS to solve the problem.Click on OK and close the 'Information' window

POST-PROCESSINGListing the resultsGo to ANSYS Main MenuClick on General Postprocessing>List Results>Nodal Solution. The following window will comeup:


Similarly you can list the stresses for each element by clicking General Postprocessing>ListResults>Element Solution. Now select LineElem Results.

MODIFICATIONS:You can also plot the displacements and stress.Go to General Postprocessing>Plot Results>Contour Plot>Element Solution. The followingwindow will come up.


35/36



36/36

Transmissio Tower Structure

Documents

Transcript of Transmissio Tower Structure