Positioning

Elements that have position attributes (for example SCTN’s) can be re-positioned in a variety of ways. The two main methods are position Explicitly and position Relatively.

4.1.1 Explicitly (AT)

Positioning explicitly allows the user to position elements at specific co-ordinates with respect to the WORLD or other design elements. Selecting Position > Explicitly (AT)… from the main menu will display the Positioning Control toolbar and the Explicit Position form. By default the Start position of the current element is displayed showing East/West, North/South and Up/Down co-ordinates with respect to the world. The Datum options list allows the user to specify the point on the element to which the position co-ordinates will apply. The user may specify Start, End, Centre or Designate Position.

Depending on the option specified, applying modified co-ordinates will have the following effect on the element:

Start - Relocates the start position of the element to the specified

co-ordinates, leaving its end position unchanged.

End – Relocates the end position of the element to the specified

co-ordinates, leaving its start position unchanged.

Centre – Relocates the entire element, locating its centre at

specified co-ordinates and modifying the start and end positions.

Designate Position – used in conjunction with the Positioning Control toolbar, the user can specify a point

on the element for re-positioning. The entire element is relocated, or re-orientated, with the Designated

Position at the specified co-ordinates and the start and end positions modified.

On opening the Explicit Position form a ‘bounding box’ is displayed around the element together with an axes aid, showing the cardinal directions, and a label showing the Start position.

Changing the Datum re-displays the axes aid and label to the specified position.

the position data. The bounding box will adjust to show the new position and clicking the Apply button on the form will re-position the element.

To define a position by reference to existing design items, use the Positioning Control toolbar and the cursor to identify the required positions by picking them in the graphical view. If required, use the Lock check boxes to fix the current co-ordinate along any axis.

To position another section, use the Select menu options on the form to change the focus of the form. Use the CE or Owner option if the required item is selected in the design explorer, or use the Pick or Pick

Owner option and then select the required item with the cursor when prompted. The form will display the

current position and the user can then change any part of this by entering new values.

4.1.2 Relatively (BY)

Positioning relatively allows the user to position elements by a specified distance, along one or more axes, from its current position. The directions can be with respect to the world or other design elements. Selecting Position > Relatively (BY) from the main menu displays the Positioning Control toolbar and the Position By form.

The form allows the user to specify a distance along a single axis or varying distances along any combination of the three axes. By default the axes directions are with respect to the world although any valid design element may be used. An axes aid is displayed at the start position of the current element.

Entering distances against any of the axes will display a New

Position label at the entered distance(s) from the current

position, thus enabling the user to see if the new location for the element is correct.

Clicking the Apply button on the form moves the entire element to its new location.

The Positioning Control toolbar and the cursor can also be used to define distances graphically. Having picked two points the distances will be entered against the relevant axes on the form. If required, use the Lock check boxes to fix the current co-ordinate along any axis.

An alternative method of re-positioning the start or end of a SCTN element is to use Extend Through or Extend By functions.

4.1.3 Extend Through

Extend Through allows the user to specify a plane, position and orientation to extend either end of the

section to. The section will only extend along its Z axis, i.e. its extrusion direction, as the plane is infinite in its planar dimensions. In PDMS a plane’s direction is defined by the direction of a vector normal (i.e. perpendicular in all directions) to the plane. The position of the plane is defined by the start position of that vector. Selecting Position > Extend > Through… displays the Extend Section – Relative form.

The End of Section list allows the user to specify which end of the section will be extended (or trimmed) to the plane. Four choices are available to the user.

Nearest end – This is the default setting. The end of the

section nearest to the plane will be repositioned.

Start – The start position of the section will be moved. End – The end position of the section will be moved. Pick – On clicking Apply the user will be prompted to pick which end of the beam is to be re-positioned.

When the Extend Section - Relative form is displayed, a label is placed at each end of the section to identify which end is the Start and which is the End.

The user can define the plane position explicitly by entering co-ordinates in the Plane Direction East/West, North/South and Up/Down

textboxes, or by using the Cursor and

Intersection options from the forms menu and

graphically selecting the position.

The Plane Direction is set by default to Up, however any direction can be entered to orientate the plane.

In the picture above the plane has been initially positioned using the Cursor > Element option and then moved be entering a new North co-ordinate. The Plane Direction has been set to South; note the plane aid and direction vector displayed to help the user visualise the position and direction of the plane.

Clicking Apply button extends the end of the current element to the plane.

The position of any Secondary Nodes owned by the section is measured from its start position. If the user requires the Secondary Nodes to stay in their original position when the start position of the section is moved, then the Maintain Sections’ Node Positions check box needs to be selected. Otherwise, the

Secondary Nodes will move with the start position, i.e. their Z distance attribute will be maintained. Checking the Cut end(s) to plane check box on the form will orientate the end of the section to the plane direction after it has been extended or trimmed.

4.1.4 Extend By

Extend By allows the user to lengthen or shorten the section by moving its Start or End position through a

specified amount. Selecting Position > Extend > By… from the main menu displays the Extend Section -

Explicit form.

When the form is displayed a label is placed at either end of the section to identify the Start and End locations. The Extend pull-down allows the user to select which end of the section will be extended, the choices being Start,

End or Pick.

If the Pick option is selected the user will be prompted to select the end of the section that will be re-positioned when the Apply button is pressed.

The user can move the end of a section either by Distance or by a Proportion of the sections current length; by selecting the appropriate radio button and entering the desired amount.

Entering a positive value will lengthen the section and entering a negative value will shorten it.

To maintain the position of any Secondary Node owned by the section, click the Maintain Sections’ Node Positions checkbox.

4.1.5 Drag Explicitly

The Drag Explicitly function allows the user to re-position a section, have any attached sections lengths adjust and realign the Secondary Nodes automatically. It is, therefore, equivalent to using three operations, that is Position > Explicitly (AT)…, Connect > Trim to Pline > all attached and Position > Align Secondary Nodes, in one.

Selecting Position > Drag Explicitly… from the main menu displays the Drag Explicitly form and Positioning Control toolbar. The Datum options list enables the user to select the element

Origin or an ID Design point as the point for the dragging

operation; however, the Origin co-ordinates with respect to the World are displayed by default.

Any valid design element may be used to define the axis system for the direction boxes by entering the appropriate element in the wrt box.

The Positioning Control toolbar may be used to determine the new position by graphical pick, as described earlier.

A bounding box and axes aid at the start position are also displayed. Entering new co-ordinates in the axes boxes will move the bounding box to the new location.

After clicking Apply the section is re-positioned and all attached sections trimmed to the new joint positions.

All connected sections will trim to the new position of the owning section, adjusting their length as

necessary. The behaviour of the attached sections depends on whether the joint is dominant or subordinate, as described in Joint Freedom later in this chapter.

4.1.6 Align Secondary Nodes

When a section that owns Secondary Nodes is repositioned or extended, it is possible that the secondary nodes may become misaligned. This can be corrected by selecting Position > Align Secondary Nodes from the main menu.

This function realigns the node(s) with their attached member(s) and may be executed from SCTN, STRU, ZONE or SITE level.

4.1.7 Joint Freedom

Where two sections are connected via a joint, the joint may be defined as either dominant or subordinate. This setting, which is determined by the Jfree attribute of the SJOI, controls how the attached section behaves when the section owning the joint is moved.

If the joint is subordinate, i.e. the attached section is dominant and Jfree is set to false, the attached sections will extend or trim, maintaining their original orientation, to the Pline that they were trimmed to on creation.

If the joint is dominant, i.e. the attached section is subordinate and Jfree is set to true, the attached sections will realign to the new joint position.

The column is the owning section with two beam sections attached.

Joint is Subordinate. Column moved, beams extended to original Plines but maintain original orientation.

Joint is Dominant. Column moved, beams extended and realigned to new joint position and cut planes are automatically re-aligned.

The standard default is for joints to be subordinate. The default setting can be changed by selecting Settings > Tolerances… from the main menu to display the Section Tolerances form.

Joint freedom can be changed after the joint is created by selecting Connect > Joint Subordinate or Connect > Joint Dominant from the main menu. The user will be prompted to select the section ends to apply the chosen setting to.