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4. MEMBRANE MODEL

1.1. Preprocessing with surface elements

Start Start AxisVM by double-clicking the AxisVM icon in theAxisVM folder, found on the Desktop, or in the Start, Programs

Menu.

New Create a new model with the New Icon. In the dialog windowthat pops up, replace the Model Filename with Membrane 1.

Select the Design Code. ClickOk.

Objective The objective of the analysis is to determine the internal forces

and reinforcements of the following wall structure.

Assume the wall thickness is 200 mm, the concrete is of C20/25,

and the reinforcement is B500A computed according toEurocode-2.

The first step is to create the geometry of structure.

CoordinateSystem

In the lower left corner of the graphics area is, in blue color, thecoordinate system beginning point marked with a blue X. The

coordinate system view can be changed from the Icons Menu

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with the Views Icon. Move the cursor over that icon and thefollowing icon bar is displayed:

The vertical upward direction is taken as the positive Z direction.It has relevance for the direction of gravitational force.

If the view is not already in Z-X plane, switch to it.

Geometry If not already selected, activate the Geometry tab, under whichthe Geometry Toolbar is displayed.

Quad/Triangle

Division

The geometry of the wall is created with the Quad/Triangle

Division Icon. Hold down the left mouse button to display thesub-menu. Clickon the first Icon on the left and the following

dialog window is displayed:

To create the upper part enter N1=20, N2=8.

Close the dialog window with Ok. Now you have to specify the

corners of the Quad. They can be specified graphically or byentering the coordinates. Lets enter them with coordinates :To enter the first corner, Type in the following sequence of keys

:

X=0 Y=0 Z=3, Enter

Specify the relative coordinates of the next corners in a similar

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way. Type in the following sequence of keys :

X=12 Y=0 Z=0, EnterX=0 Y=0 Z=3, Enter

X=-12 Y=0 Z=0, Enter

Exit from drawing quads by pressing Esc.The following Drawing is displayed:

Quad/Triangle

Division

The pillars are created in a similar way. Clickthe

Quad/Triangle Divison Icon. Enter the following values:N1=3, N2=6

Close the dialog window with Ok. Now you have to specify the

corners of the Quad.

Type in the following sequence of keys :

X=0 Y=0 Z=-6, Enter

X=1 Y=0 Z=0, EnterX=0.8 Y=0 Z=3, Enter

X=-1.8 Y=0 Z=0, Enter

Exit from drawing quads by pressing Esc.

The following drawing is displayed:

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Mirror Create the other pillar by mirroring the first one with respect tothe center of structure (X=6). Click the Mirror Icon.

The Selection Icon Bar is displayed:

Select with a selection window all nodes of the pillar.

The selected elements will be highlighted.

Finish the selection with Okand the following dialog windowwill be displayed:

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Set Mirror: Copy, Nodes to connect: None, Copy: All. Now

you have to specify the mirror plane. First select the middlepoint ofthe bottom line of the upper part, then select any point

vertically above it.

The following drawing is displayed:

The geometry of the wall has been successfully created.

Zoom Let's zoom to the structure. Move the cursor over the ZoomIcon on the Icons Menu. The Zoom Icon Bar pops up.

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Fit in Window Clickthe Fit In Window Icon.

GeometryCheck

In the top icon bar, Click the Geometry Check Icon to checkfor possible duplicate entries. In the dialog window displayed thetolerance for merging the nodes can be specified. If the distance

between two nodes is less than the value you enter theyrespective nodes will be merged. Enter .001.

ClickOKand a check summary is displayed when completed.

Elements The next step is to create the finite elements. Activate the

Elements tab.

Surface

Elements

Click the Surface Elements Icon. After selecting All elements

the following dialog window is displayed:

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Set the type of the element to Membrane(plane stress).

Material

Library Import

Click the Material Library Import Icon. The following dialog

window is displayed:

Select C25/30 from the Materials list, then accept it with Ok.

Thickness Enter(type) in the Thickness edit box 200 [mm], then close the

dialog window with Ok.The surface elements have been created.

Display

Options

To view the local coordinate system of the surface elements

clickon the Display Options Icon on the Icons Menu in the leftside. The following dialog window is displayed:

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Check the Surface box in the Local Systems panel.

Accept the change with Ok.

If the Mesh, Node, Surface Center is switched on among the

Graphics Symbols, it is visible that the program uses 9-nodemembrane elements. These 9 nodes are the corners, middpoints

and center point of surface element. If you move the cursor onthe surface center symbol (a filled square), a hint window is

displayed with the property of the surface element: its tag,material, thickness, mass and references, as shown in the next

drawing:

The red line shows the x axis of the local coordinate system, theyellow one the y axis and the green one the z axis.

Line Support To create the supports click on the Line Support Icon and

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select the bottom lines of the pillars with a selection box.

Finish the selection with Ok. The following dialog window is

displayed:

To create a pinned support use the following settings:

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Nodal DOF Click the Nodal DOF Icon, select all nodes with the Allcommand and accept the selection. In the dialog window scroll

to Membrane inPlane X-Z and apply it.

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1.2. Preprocessing with domains

Start Start AxisVM by double-clicking the AxisVM icon in theAxisVM folder, found on the Deskto, or in the Start, ProgramsMenu.

New Create a new model with the New Icon. In the dialog window

that pops up, replace the Model Filename with Membrane-2.

Objective The objective of the analysis is to determine the internal forcesand reinforcements of the following wall structure:

Assume that the wall thickness is 200 mm, the concrete is ofC25/30, and the reinforcement is B500A, computed according toEurocode-2.

The first step is to create the geometry of structure.

Coordinate

System

In the lower left corner of the graphics area is the global

coordinate system symbol. The positive direction is marked by

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the corresponding capital letter (X, Y, Z). The default coordinatesystem of a new model is the X-Z coordinate system. It is

important to note that unless changed the gravity acts along the Z direction.

In a new model, the global coordinate default location of thecursor is the bottom left corner of the graphic area, and is presetto X=0, Y=0, Z=0.

The location of the cursor is defined as a relative coordinate.

You can change to the relative coordinate values by pressing thed labeled button on the left of the Coordinate Window. (Hint:

In the right column of the coordinate window you can specifypoints in cylindrical or spherical coordinate systems). The origin

of the relative coordinate system is marked by a thick blue X.

Geometry If not already selected, activate the Geometry tab. TheGeometry Toolbar is displayed:

Line Press down the left mouse button while the mouse is on the LineIcon. (Note: Icons default display is to the last icon selection)

The following icon sub-menu is displayed:

Note: When the a line type is chosen, the Relative coordinate

system automatically changes to the local system (d prefix)

Polygon Select the Polygon icon, which is the second from left. Whenthe Polygon is chosen, the Relative coordinate system

automatically changes to the local system (d prefix)

The polygon coordinates for the frame model can be drawn withthe mouse, or by typing in their numerical values.

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Set the first point (node) of the polygon by typing in theseentries:

X=0 Y=0 Z=3Finish specifying the first line point by pressing Enter.

To enter the remaining nodes of the polygon membrane model,enter the following sequence of values:X=1 Y=0 Z=0, Enter

X=0.8 Y=0 Z=3, EnterX=8.4 Y=0 Z=0, Enter

X=0.8 Y=0 Z=-3, EnterX=1 Y=0 Z=0, Enter

X=0 Y=0 Z=6, EnterX=-12 Y=0 Z=0, Enter

X=0 Y=0 Z=-6, Enter

Exit from the command by clicking Esc twice.

Translate Click the Translate Icon. Select the top horizontal line and

finish the selection with Ok. Choose Incremental from theMethod panel, N=1, Nodes to Connect: None, then close the

dialog window with Ok. Now you must specify the translationvector. Click any empty place in the Graphics Area, then type

in the following sequence:X=0 Y=0 Z= -0.75, Enter

The following drawing results:

Elements The next step is to create the finite elements. Click the

Elements tab.

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Domain Click the Domain Icon, then selectAll. Accept the selectionwith Okand the following dialog window is displayed:

Set the type of the element to Membrane (plane stress).

MaterialLibrary Import

Click the Material Library Import Icon and the followingdialog window is displayed:

Thickness Enter(Type in) 200 [mm] as the thickness of wall

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,

then close the dialog window with Ok.

The following drawing results:

It is easy to observe the symbol of the domain - a blue line on theinner contour of the domain. Moving the cursor over it a hint

window is displayed with the properties of the domain:

DomainMeshing

Click the Domain Meshing Icon. Select the domain with theAll command (the asterisk) and finish the selection with Ok. The

following dialog window is displayed:

Type in 0.75 [m] for the average mesh element size. After

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closing this dialog window with Okthe automatic meshgeneration is started. The progress of mesh generation is shown

in a window.

After the mesh generation is completed, the following drawing is

displayed:

If you move the cursor on the surface center symbol (a filledsquare), a hint window is displayed with the property of the

surface element : it's tag, material, thickness, mass andreferences as shown in the next drawing.

Line Support The next step is to specify the supports. Click the Line supportIcon. Select the bottom lines with a selection box.

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Accept the selection with Ok. The following dialog window isdisplayed:

To create pinned support set the dialog window as shownbelow:

Close the dialog window with Ok, and the following drawing is

displayed:

Nodal DOF The next (optional) step is to set the nodal degrees of freedom.Click the Nodal DOF Icon. Select all nodes with the All

command, finish the selection with Ok, and in the dialogwindow select Membrane in plane X-Z.

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Press Okand the load is applied.

The following drawing is displayed:

Static The next step is the analysis and postprocessing. Click theStatic tab.

Linear Static

Analysis

Click the Linear Static Analysis Icon. The model will be saved

with it's current name (which is Membrane 2 in this case).

A Model Save Dialog will appear if you havent alreadyassigned a name for the model. Accept save and a Save dialog

window appears, where you can specify the model filename andpath.

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Calculation During the calculation the following window is visible:

Click the Details button to view the details of calculation:

The topmost label shows the current computation step, and thebar below it shows its progress. The second bar shows the global

progress of computation. The estimated memory requirementshows the estimated virtual memory needed. If the virtual

memory of the computer is set to a lower value than the needed

value, an error message is displayed. When the computation hasfinished, the progress bars will disappear.

Postprocessor Close the window with Ok. By default the postprocessor willstart with the ez displacement, the display mode will be isoline.

You will see the vertical displacements.

DisplayOptions

For a clearer view, switch offthe display of Loads. Click theDisplay Options Icon, and uncheckthe Load box.

Fit in Window Clickon the Fit in Window Icon.

The following drawing results:

Click the Result Component combo box (the one showing

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ez[mm] and select nx from Surface Internal Forces.

Min/Max

Value

To find the location of maximum internal force. Clickthe Min,

Max Value Icon. The following dialog window is displayed:

Here you can select the component you are interested in. Accept

nx by clicking Ok. A dialog window will show the value and

location of the negative maximum.

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ClickOkand another window is displayed showing the location

and value of positive maximum.

The color regions are delimited by the values in the ColorLegend Window. You can change the number of colors by

dragging the handle beside the level number edit box or enteringa new value.

Color Legend

Setup Window

To find the ranges with a normal force larger than -100 kN/m,

Click on the values in the Color Legend Window. In the ColorLegend Setup dialog window check Auto Interpolate, then

click on the bottom value in the left column, and replace 331.62 with -100.

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Close the dialog window with OK, and the new ranges will be

applied.

The following drawing results:

The regions with a normal force greater then -100 are hatched.

Isoline View the internal forces in Isoline display mode. Click theDisplay Mode combo box (the one which displays Isosurface

2D) and select Isoline from the list.

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The isoline drawing is shown below:

View the internal forces of the supports. Select rz from LineSupport Internal Forces in the Result Component combo box.

Result DisplayParameters

Click the Result Display Parameters Icon, and the followingdialog window is displayed. Check the Lines box in the WriteValues To panel and set the Display Mode to Diagram

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Close the dialog window with Okand the values of supportforces is displayed on the screen:

R.C. Design The next step is to calculate the reinforcement. Click the R.C.

Design tab:

Clickon the Reinforcement Parameters Icon, and select all

surface elements with the All command. Complete the selection

with OK, and the following dialog window is displayed:

Close the dialog window with OKand the axb diagram is

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displayed:

The area of reinforcement in the x direction is the sum of the axt

and axb values.