To introduce you to the concepts and techniques you will use in Section Maker, this chapter will describe the creation of a structural section step by step. The section you will draw is shown below.

First, you will draw the section to scale, inside the Shape window. Make sure that your units are set up correctly by using the Units command from the View menu. This example is carried out in American units; you can use other units if you wish.

It is necessary to set up the sizes for drawing in the Shape window.

§    Choose Size… from the View menu.

A dialog box will appear with four fields in it specifying the maximum dimensions of the section.

§    Type 4 for the maximum x coordinate and then press the Tab key to move to the second field

§    Type in -4 for the minimum x coordinate and then use the Tab key to move to the next two fields entering 6 and -6 for the maximum and minimum y coordinates.

§    Click the OK button when you have finished entering the values.

If you make a mistake entering the numbers, you can use the backspace key to delete the character just to the left of the blinking cursor and you can use the Tab key to move from one field to the next.

To create the I-beam that forms the basis of the section, you can use Section Maker's commands for automatically generating a common structural shape.

A note on terminology:

Section Maker uses the term "section" to refer to a structural cross sectional shape and its associated sectional properties that is stored in the Multiframe Sections Library. The term "shape" is used to refer to a geometric shape such as a polygon, circle or rectangle or an assemblage of these shapes. A section is made up of one or more shapes.

§    Choose Place Shape from the Shape menu.

A dialog will appear with a picture of an I shape and fields where you can enter the dimensions of the shape.

§    Choose Steel for the material type

§    Type in 12 for the depth then enter 8 for the width, 0.5 for the flange thickness and 0.25 for the web thickness.

§    Click the OK button

The I shape will be drawn on the screen centred in the Shape window. The I shape is generated as an assembly of three rectangles. The corners of the rectangles will be highlighted with small black boxes (called handles) to indicate that the rectangles are selected.

Note:

The properties for the section are displayed in the Properties window.

To place the channel on the top of the I shape, you can take an existing channel from the Sections Library.

§    Choose Place Section… from the Shape menu

A dialog will appear allowing you to select a section from the Sections Library

§    Click on the C name in the list of groups

The names of the channel sections stored in this group will be displayed in the list on the right.

§    Click on the name C10x20 to select this section

§    Click the OK button

The dimensions of the section will be taken from the library and the section will be drawn in the centre of the Shape window. This C shape will be made up of three rectangles modelling the web and two flanges and two shapes modelling the fillets between the web and flange. The corners of the placed section will be highlighted to indicate that the group of shapes is selected.

Before you can place this C shape on top of the I shape, you need to rotate it by 90 degrees

§    Choose Rotate … from the Geometry menu

A dialog will appear allowing you to enter the number of degrees to rotate the shape. The angle of rotation is measured in degrees with positive being anti-clockwise

§    Type in -90 for the angle of rotation

§    Click the OK button

The C shape will be rotated so that it is oriented ready to move on to the top of the I shape.

You can move shapes in Section Maker by dragging them with the mouse.

To drag the C shape

§    Point anywhere inside the C shape but away from the black boxes, which show that it is selected.

§    Press and hold down the mouse button.

§    Drag the shape until its sits evenly on top of the I shape

§    Release the mouse button.

As you drag the shape it will be redrawn at its new position

At every change that you make to the section, the new section properties will be automatically recalculated and updated in the Properties window.

Now you can draw the additional plate on the bottom flange of the section.

To make it easier for you to draw the frame, you can use Section Maker's Grid option to make drawing automatically align to a grid with regular spacing.

§    Choose Grid… from the View menu.

A dialog box will appear with values for the x (horizontal) and y (vertical) spacing of the grid.

§    Type 0.5 for the x spacing, use the Tab key to move to the y spacing and type 0.5 for it also

§    Click on the Visible check box to display the grid in the window.

§    Click on the Snap check box to make subsequent drawing align with the grid.

This will also turn on the Visible button to make the grid visible in the Shape window.

§    Click on the OK button to confirm your settings.

Now move the pointer inside the Shape window and notice that as you move the mouse, the coordinates of the pointer are shown at the bottom left hand corner of the window. The coordinates are shown in the same units as Deflection in the Units dialog. The coordinates will automatically align to the nearest point on the grid. You can now begin to draw the shape to scale in the Shape window.

§    Click on the Rectangle tool to select it

§    Press the mouse button at the bottom left corner of the I shape

§    Drag down and to the right to draw the bottom plate

§    Release the mouse button when the plate is the correct size, i.e. when the coordinates read x=4, y=-6.5

Notice that the properties for the rectangle displayed in the Data window are negative. This is because as yet no material types have been assigned to that shape. Any shape, which does not have a material type, is assumed to be a hole and is subtracted from the property calculations. Next we will set the material for the rectangle.

In order to compute the deflections in a structure, Multiframe needs to know the Young's Modulus and Shear Modulus for the materials in the section. You can choose what type of material each shape in the section is made of by choosing from the range of materials properties stored in the Sections Library.

The rectangle you have just drawn should be selected. If not, select it by clicking on it.

§    Choose Select Material from the Shape menu

A dialog box will appear with a list of the materials in the library.

§    Click on the name Steel in the list

§    Click the OK button

This will define the bottom plate to take its material properties from those for steel stored in the library. The shapes will be drawn filled with the colour depending on shape type and patterned for their material, solid for steel in this case.

Before you install your section in the Sections Library you will probably want to align the Centroid of its area with the x-y axes so that all properties will be calculated relative to the Centroid.

To align the Centroid of the section with the axes

§    Choose Select -> All from the Select sub-menu under the Edit menu

This will select all the shapes in the section

§    Choose Align To Centroid->Centroid from the Geometry menu

All of the selected shapes in the Shape window will be moved so that their common Centroid is aligned with the x-y axes.

§    Choose Size To Fit from the View menu

This will make the whole section visible in the window.

Once the shapes move, the properties will be automatically recalculated and displayed in the Properties window. You can check that the section is aligned with the axes by verifying that the coordinates of its Centroid (xc, yc) are 0.000,0.000.