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A joist area support is a beam or a wall that is on the same floor as the joist area, and which meets the criteria described below: ( Note: In what follows a plane refers to any flat surface, whether or not it is sloped.)
Supports must be continuous members - they cannot be made up of two or more members in series. In this case, the joist area should be split into several areas, each with one of the members forming a support.
The term "joist area" is also applied to CLT floor and roof panels.
For 4-sided areas
Each support for a particular direction must meet or cross both of the parallel edges that define the joist direction. This ensures that all joists are supported by that member.
Joist supports do not have to be perpendicular to the parallel edges; nor do there have to be supports at the ends of the area, so that the area can be cantilevered at one or both ends.
No two supports for one direction can intersect, nor can they meet at the edge of the joist area. This ensures that the edge joists are both properly supported and that at least one of them is the critical joist for the area.
If there are more than two supports for a joist direction, they must all lie in the same three-dimensional plane. If there are three or more potential supports for a direction, and they do not lie in the same plane, that direction is disqualified.
If there are only two supports, they can be in different planes, but such non-planar joist areas are not designed by Sizer (see Out-of-Plane Joist Areas, below).
If a member supports just some of the joists in the area (i.e. it intrudes into the joist area but does not span it and is not parallel to the joists), then that joist direction is disqualified. Such a member must lie in the same three-dimensional plane as the legitimate supports for the area; if it does not, it is ignored.
There cannot be more than 6 supports (beams and walls) in one direction, nor can the supports create more than 6 spans on the joists, including cantilevers. In addition, there cannot be more than a total of 6 beams forming potential supports in both joist directions, or a total of 6 walls. These restrictions were imposed to ensure compatibility with existing Sizer data files. However, they should not be a problem in realistic building situations.
For 3-sided areas
The following rules refer to the two dimensional plan view projection of a joist area in three-dimensional space.
One end of both supports for a particular direction must meet at one vertex of the joist area, and the other ends must meet or cross the edge opposite to that vertex. The joist direction is parallel to this edge. This ensures that the supports fully span the joist area and support all joists running in the joist direction.
One or both supports may meet the opposite edge somewhere in the middle, so that the area is cantilevered on one or both ends of the joists.
You cannot have more than two members supporting the 3-sided joist area in any direction. Multi-span joists have been implemented in SIZER for 4-sided areas only.
Members that form potential supports in one direction cannot intersect members supporting in the other direction, if that intersection is in the interior of the joist area. It is therefore impossible to have a joist area that can be cantilevered in two joist directions.
IMPORTANT: The program does not check to ensure that supports for 3-sided joist areas are at the correct elevation. In other words, supports meeting at a vertex can be separated vertically by two feet, but still form the corner of the joist area. The user must check that the supports have the same elevation at the vertex where they meet, otherwise nonsensical results will occur without any warning. Note that SIZER performs this checking for 4-sided areas only.
Out-of-Plane Joist Areas (4-sided only)
Sizer allows joist areas that are supported by members that do not lie in the same plane, so that the joist area is not a flat surface, as long as there are no more than two supports in either joist direction. Existing files may have such joist areas, and rules for defining beam elevations (see Beam Supports) may cause areas that were in-plane to be out-of-plane. In this case, the user must adjusts the gridpoint elevations of the beam's supports to create a designable joist area.
SIZER does not design out-of-plane joist areas, as it is impossible to determine the correct orthogonal component to the load on such areas.
Loads are transferred from the out-of-plane area to supports below.
Out-of-plane joist areas are not included in the materials list.
We recommend putting all out-of-plane areas in the same group.
Warning messages
A detailed message is supplied giving the exact reason the joist area cannot be created or designed.