Orthotropic Layers#
Orthotropic Materials#
An orthotropic material is one that has pronounced differences in physical properties in two or more directions at right angles to each other. The effect of the orthotropicity is to introduce a second critical frequency and between the two critical frequencies the sound transmission loss is reduced compared to a simple isotropic panel. An example of such a material might be hollow core bricks, or steel trapezoidal roof sheets, or a concrete floor with cast in ribs.
INSUL can model both corrugated or trapezoidal (ribbed) materials as well as materials that are not profiled but have different stiffness in the X and Y directions.
The predictions are based on Heckl's (1960) paper "Untersuchungen An Orthotropen Platten".
The INSUL model for these types of panels relies on the Orthotropic Ratio property which describes the ratio of stiffness in the y and x direction (By/Bx), where this ratio should always be greater than 1.
Temporary changes to the Orthotropic Ratio can be made from the Properties window. Permanent changes can be made from the Materials Editor.
Note
Most timber materials in INSUL are now modelled as orthotropic.
Corrugated or Trapezoidal Layers#
Thin materials are often corrugated or ribbed to increase their stiffness and hence ability to span larger distances between supports.
The bending stiffness of these types of materials is different in the direction of the corrugations compared to the direction at right angles to the corrugations. This can dramatically lower their transmission loss by lowering the critical frequency in the direction of the corrugations. Panels which have differing stiffness in each direction are known as orthotropic. Their sound transmission properties are well predicted by theories developed by Heckl (1960) and more recently by Windle and Lam (1994).
To model a corrugated or trapezoidal (ribbed) material use the INSUL Panel tabs to select Single > Panel 1 > Layer 1. Select Profiled Metal from the Category list and chose any material from the Product list. Now click on the material in the INSUL Illustration to open the Properties window. The dimensions of the corrugated or trapezoidal profile are displayed in the Properties window.
The profile dimensions can be changed directly from the Properties window by updating:
- Depth and pitch values for corrugated profiles
- Width, period, valley and height values for trapezoidal profiles
Profile dimensions are stored in INSUL's database and can be accessed via the Materials Editor, where existing profiles can be permanently changed and new profiles can be added.
Sometimes trapezoidal steel sheets are used as permanent formwork to construct concrete floors. There are interesting features in predicting their performance of these Composite Steel Floors.