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What is a surface element? When should I use Surface element


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What is a surface element? When should I use Surface elements?

Answer :

In STAAD, a surface entity is an object that represents a collection of elements. When the program goes through the analysis phase, it subdivides the surface into a number of elements by itself. This process is called meshing or mesh generation. But during the modeling phase, the user does not see any of those elements which keeps the model small and easy to manage. An entire wall is hence represented by just a few "Surface" entities, instead of hundreds of plate elements.

The advantage of using surfaces is that the minute details involved in the process of converting a physical object like a wall or slab into the mathematical model which consists of plate elements is something that the user doesn't have to bother with. However, in many situations, not knowing these details can lead to errors, some of which are impossible to detect because the underlying elements cannot be seen graphically. Also, not knowing how many elements will be generated during the meshing process can lead to unwanted consequences such as a massive increase in the size of the model, to a point where the program simply cannot handle such a massive volume of data. Consequently, we recommend that surfaces be not used as much as possible.

There is however one situation where the user has no choice but to use surfaces. That is when he/she wants to perform reinforced concrete design of a shearwall per the ACI, British or Indian codes. STAAD can perform a shearwall design if and only if that wall is modelled using STAAD's SURFACE entity.

So when you wish to model a floor slab, roof or a wall that does not need to be designed as a shear wall, we recommend that you use plate elements. In our view, the only drawback of using plates is that you need several of them to model a wall or a slab, and that increases the size of the input data. But at least you can detect and remove every error in the model, and know exactly how many elements and nodes there are in that model

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