When analysing a three dimensional frame it is necessary to know the orientation of the structural section used for each member relative to the global coordinate system.  Initially, Multiframe assumes that the web or direction of principal strength of the section is aligned so that the principal direction lies in a vertical plane passing through the member.  In the case of a vertical column, it is assumed that the principal direction passes through the global x axis.  If you wish to have the section oriented at another angle (referred to by some engineers as the beta angle) you can use the Member Orientation… command from the Frame menu.

To change the orientation of a member or members

§    Select the member or members to be specified

§    Choose Member Orientation  from the Frame menu

A dialog box will appear which displays the section's shape.  The view of the section shape in the dialog is the view you would see if your eye was at joint 2 and you were looking down the member towards joint 1.

§    Click and drag on the shape to rotate it to a new orientation or type in a new orientation angle

§    Click OK to set the new orientation

When you set the orientation you are effectively defining the direction of the local y' axis of the member.  The angle you type is the angle between the y' axis and a vertical plane passing through both ends of the member.  As the angle increases the y'-axis will rotate towards the z'-axis.

A number of parametric options are also available for specifying the orientation of members.  Instead of specifying an angle, the user can choose a number of advanced options that define the plane containing either the member’s y-axis or z-axis.  The plane is defined by the local x-axis of a member and either a point in space or a direction.  The orientation point can be defined by its coordinates or by specifying a joint.  Similarly, the direction may be defined as either a vector or by specifying a global axis direction.  Care must be taken to ensure that the point or direction define a valid plane. As such the orientation point should not lie along the line of the x-axis and the orientation direction should not be parallel to the members x-axis.

You can also choose to flip the orientation of the section about its x and/or y axes.

You can display the section axes on the members in the Frame window by using the Symbol command from the Display menu.  You can also show the member axes in this way.