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Joist Area Definition
A joist area is either a sheathed frame consisting of dimension lumber joists, rafters, headers, rim boards, etc., or a CLT floor or roof panel.
Shape
The projection of the joist areas on the two-dimensional concept mode plan view may be triangular (3-sided) or trapezoidal (4-sided with at least two parallel sides). A quadrilateral without parallel sides will be disqualified
Supports
Joist areas can either be simply supported or cantilevered. Joist areas must have at least two beams or walls supporting the entire width of joist area intersecting its specified joist direction. Refer to Joist Supports. for detailed rules.
Elevation
The joist area can be oriented any way in three-dimensional space.
The elevation of the joist area is determined by the elevation of its supports, therefore a vertex of a joist area can be at a different elevation than the elevation specified for the gridpoint at that vertex.
This occurs, for example, when beams at elevations of 8 feet and 12 feet, separated by 4 feet horizontally, support a sloping roof. If the roof area hangs over the lower beam by a horizontal distance of 1 foot, then the elevation of the edge of the joist area will be 7 feet, regardless of whether you have changed the gridpoint elevations along the gridline defining the joist edge.
Creating a Joist Area
Press the Joist button and click on any four gridpoints. If the area is triangular, the first gridpoint is also the fourth gridpoint. The joist area must be supported by at least two beams and/or walls. The Data Bar permits youto change joist directions when supports in more than one direction exist.
The design properties of each joist area depend upon the currently selected Design Group in the Groups field of the Data Bar.
Overlap
If two joist areas are on the same floor, their projections to the two-dimensional concept mode plan view cannot overlap, even if the joist areas do not overlap in three-dimensional space.
Joist Direction
A Joist Direction is a line between gridpoints that define adjacent vertices of the joist area. Joists are allowed to run parallel to this line.
3-Sided Joist Area
A 3-sided joist area can have either one or three possible directions, depending on whether it has two or three potential supports, as described in Joist Supports.
For two supports, the joists run parallel to the side opposite to the vertex where the supports meet.
In the case of three supports, the joists can run parallel to any of the sides.
4-Sided Joist Area
For 4-sided areas, joists must run in a direction for which there are parallel joist edges.
Thus a parallelogram will have two possible joist directions, and a trapezoid that isn't a parallelogram will have just one. The joist area must also be properly supported along this direction, as described in Joist Supports.
If there are two possible directions Sizer will assume the joists span in the shortest direction. The user can then change the joist direction in the Data Bar.