Several mesh control parameters are defined to control quality of the mesh generated for diaphragms. They are briefly explained below.

Refer to Semirigid Floor Diaphragms for further information.

• Diaphragm Boundary: It determines the extension of meshed area of the diaphragm. If Use Slab Edges for Exterior Boundary is chosen, the program uses slab edges as an exterior boundary of the meshed diaphragm. Note that the area between the most exterior beams and slab edges are also meshed. If Use Beams for Exterior Boundary is chosen, the program uses the most exterior beams as exterior boundary of the meshed diaphragm. It should be known that there should be a closed beam loop constructed with exterior beams. Otherwise, the program fails to mesh in the absence of a closed boundary if this option is chosen, and then it automatically switches to the other option.
• Diaphragm Mass: It determines how diaphragm mass should be processed in analysis. If Use Calculated is chosen, the program applies all surface, line, and points mass loads (as well as deck mass) directly to meshed diaphragms (member masses for beams, columns and walls are directly applied to these members). In contrast to rigid diaphragm analogy where diaphragm mass is lumped at diaphragm mass center, this procedure considers a spatial mass distribution over diaphragms. If Uniformly Distribute Total Mass Over Diaphragm is chosen, the total mass calculated for the diaphragm is distributed to diaphragm shell elements based on shell’s effective areas. This method can be used if a truly uniform mass distribution over the diaphragm exists.

Mesh Controls: These are the same mesh control parameters given in Criteria – General dialog.

• Max. Distance between Nodes on Mesh Line: it allows the user define the maximum distance between nodes on wall edges and nodes on semirigid diaphragm edges. Note that the program may generate additional nodes closer than user entered value, but it is never allowed to be larger than that value. The user can generate coarse or fine mesh by setting Max. Distance between Nodes on Mesh Line. Usually, a coarse mesh gives conservative results since the walls and diaphragms are stiffer. A finer mesh leads to more flexible walls and diaphragms, which leads better results but it may significantly increase analysis time. A good balance should be provided before starting analysis.
• Hard Node Density Factor: This factor is used to determine mesh density around hard nodes which are always located inside semirigid diaphragms. A hard node is defined as a node where a column or a wall is attached. For most cases, a value of 1.0 is a good estimation to obtain relatively good mesh density around hard nodes.
• Merge Node Tolerance: Once meshing process for walls and semirigid diaphragms is completed, the program generates a finite element model for analysis, which is basically composed of nodes and elements (columns, beams, braces and shells in walls and meshed diaphragms). During this process, it is possible that several nodes are very close. To have a good (and valid) analytical model, these nodes are merged to a single node and elements connected to this node are adjusted accordingly. The Merge Node Tolerance is used in such a way that if distance between any 2 (or more) nodes are found to be smaller than the Merge Node Tolerance, then they are treated as a single node (i.e., these close nodes are merged together).
• the Geometry Tolerance is mostly used in geometry calculation as a threshold tolerance value. This should not be confused with a merge (close) node tolerance. Examples are as follows: it is used as a tolerance to check a node is on a line or to check a point is inside a polygon, etc…