ProtaStructure : Floor Mesh and Analysis - Generate Mesh

Floor Mesh and Analysis - Generate Mesh

The floor mesh is generated in the "FE Floor Analysis" pre-processor, which is accessed by clicking the "Floor Mesh and Analysis" button.

Generate Model

A triangular mesh consisting of DKT plate elements and frame members (if they exist) will be generated generated when the “Generate Model” button is clicked on the toolbar. Beams and walls are modelled as frame members sliced to be compatible with the plate mesh.

The size of triangular plate members generated is determined by a combination of the “Plate Element Size” and the “Mesh Uniformity Factor”. These values should be tailored carefully according to the required mesh density, as the mesh density significantly affects the model size and accuracy of computations.
The generated model will be saved automatically after meshing.

Mesh Density

Mesh density is strongly influenced by the target Plate Element Size that is provided as input before generating the model. Minimum plate sizes will be dictated by p hysical boundaries in the model (e.g. column boundaries) and by seed nodes. Specifying the “Plate Element Size” too small results in an overly fine mesh requiring longer to perform the calculations. Conversely, if the “Plate Element Size” is too large, the mesh will be too crude to produce accurate results. 

ProtaStructure suggests an initial default of 800 mm, and for a simple regular layout such as shown in figure above where the slabs are placed in square with the supporting columns at the corners this default will be very reasonable.  In the figure above, 6 plates segments (which generated with a mesh uniformity of 100%) are produced between column heads.
We recommend that you generally aim for around 6 to 8 plate segments between column heads.

Mesh Uniformity Factor

The mesh generated will be strongly influenced by the "Uniformity Factor" . The "Uniformity Factor" can be modified to adjust the uniformity of the mesh for various floor plans. Acceptable values range from "0" to "100". If "100" is entered the plate element size will generally be similar everywhere in the model. At the other extreme, if "0" is entered, the size of the plate elements will be smaller in relatively smaller slab panels, cantilever slabs and around the slab openings. Lower uniformity will result in smaller and denser mesh sizes around complex area such as column, wall and slab opening position. 
Lower mesh uniformity may be preferable to more accurately capture abrupt change in forces (e.g. moment).
The figure below shows a 9 panels with different size, then meshing with the default  Plate Element Size and keeping the Mesh Uniformity Factor at 100% results in the mesh.

This is not an ideal mesh. There are only 4 segments between columns in some panels (clouded in the figure above). At this point, an ideal balance between Plate Element Size and Mesh Uniformity Factor need to be achieved for more satisfactory solution.

By retaining same Uniform Mesh Factor and reducing the Plate Element Size to achieve the objective of having a minimum of 6 plates between the columns, we must reduce the  Plate Element Size to 500 mm as shown in figure below. This produces a total of about 1800 plates; the top right is now OK but we are generating more plates than required in other panels.

Let's try on another comb i nation,  Plate Element Size of 800 mm and a Uniformity Factor of 50%. The outcome is shown in the figure below and shows that 6 to 8 plate segments are generated between column heads. It has 813 plates rather than 1800 and the amount of mesh generated is clearly more than adequate.

The key objective is to choose an ideal balance of Plate Element Size and Mesh Uniformity Factor to produce minimum number of plates but still sufficient to a accurately replicate the "true" behavior of the slab (so analysis time is minimized). Generally try to achieve 6 to 8 plates between the column heads.

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