plate Vs surface model? dear seniors i had to model slab having more than 4 nodes.we have only four noded plate to model slab.In that what to do?Shall we model slab using surface model?What is the difference between plate and surface model? Thanks in advance -You need to mesh the slab into a number of plates. Along the left side of the STAAD.Pro screen, look for the Geometry page. Under that, there is a Parametric models page through which you can generate a mesh for a slab defined through any number of nodes. Study the description of this feature in the online help (Help-ContentsGUI Manual). In the Getting Started manual, take a look at Tutorial 3. It too shows various ways to mesh simple slabs. In cases like this, you are taking upon yourself the responsibility of meshing the slab into plate elements. If you want to avoid the chore of meshing the slab on your own, surfaces is an option. Surfaces are objects where the meshing is done by the program behind the scenes and you hence have to deal with a limited number of entities on the screen, thus making the model smaller. Surfaces are especially useful if you are modeling a designing concrete shear walls. However, in complex structural arrangements, this "behind the scenes" meshing may not always be free of modeling errors. You may run into poor conectivities between the slab entities and the beam entities and fixing them won't be easy. Also, if the parameters for defining the surface are not provided correctly, you can end up with a very dense plate element mesh with very small sized elements which will make the resulting analytical model very large.
So, stick to meshing the slab on your own until you are comfortable using STAAD. -According to me the basic difference between plate and surface is that Plate behaves like a membrane and takes the command to resist out of plane shear and bending moment as in case of floor slab. The inplane bending moment and shear force, the magnitude of which is quite small for plate, is left to be resisted by the frame The surface takes the command to resist inplane shear and bending moment as in case of shear wall. Surface is a part of the moment resiting frame and helps the frame in resisting moment due to lateral load while plate helps the frame very little in resisting the moment due to lateral load that too throgh Master Slave command only. Surface does the above action automatically as a family member of the frame. Plate behaves as a guest member. I also suppose the surface has to be checked against out of plane buckling whereas it is not done for the plate. Anybody who finds contradictions in the above clarification and can explain the difference between plate and surface in a more refined and explicit way, is requested to post his views because many users, as per my study, are not able to differentiate explicitly between plate and surface.
Application of plate and surface.........in Staad pro Hey, I am kind of a new in staad. Would anybody plz tell me the difference between plate and surface in staad pro. When i should use plate and when surface? Load application upon these????????? Please help me to remove my confusion........
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 modeled using STAAD's SURFACE entity. When you use surfaces in your model, the resulting mesh of finite elements is not easily apparent. In fact, the only place in the program where you get a good view of the meshed state of the surface is in the post-processing mode in the node displacement page. The inability to view the meshed state of the surface makes it very difficult to see the flaws in the modeling. In your structure for example, there may be members which are sharing space with the surface. Unless those members get meshed automatically along with the surface, and more importantly, unless the surface and member meshing is done in such a manner than all the resulting pieces are connected to each other properly, there is no assurance that the members and surface will be able to transfer loads to each other. The inability to see their meshed condition makes it difficult to see if the meshing is done properly. Replacing the surface with quadrilateral elements, and meshing those element is a way to get around the problem. 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. Dear NIHESH.N,
I understand from your reply that, add surface can be use only for shear wall and Generate surface meshing / quadrilateral meshing can be use only for slab to create perimeter for assigning floor area load. Please advise me if it is correct? I have used both methods to create a perimeter of slab to assign floor area load by using staad pro V8i / concrete design and got following results.
1. When I Used add surface button to create a perimeter of slab during modelling, my analysis was successfully completed but design of slab did not gave me any results/ did not designed.
2. When I have used Generate surface meshing / Quadrilateral meshing to create a perimeter of slab,my analysis and design of slab has been done successfully, but my actual size of external beams which was 4 m in length during modelling has also converted to 4 Nos. of individual beam segments (plate sizes) (m1, m2, m3, m4) instead of one 4 m long physical member element (m1).Please advise me How I can convert these 4 segments back into one 4 meter long element.
3. What is requirement for division of plate elements? It should divide equally divide into four parts?
Hello Fiaz, Surfaces are one of the many ways that we have available to generate a finite element mesh. Surfaces are convenient, because they allow us to define only the perimeter of the mesh, and then the program handles the submeshing automatically (with parameter input from the user). Surfaces MUST be used for creating a mesh that will represent a shear wall that will be designed by the program. However, surfaces are also valid ways of creating meshes
that will behaves as floors, roofs, wingwalls, box culverts, or any other "surface-type" structure. The Generate Surface Meshing tool is another of the many available meshing tools. It will create a mesh of plates, and is useful for any "surface-type" structure EXCEPT for a wall that will be designed from the Shearwall tab. (Again, these MUST be modeled as Surfaces.) Though I have never tried it, I believe what you are saying that modeling with Surfaces is not conducive to obtaining floor designs. That's because the meshing is done internally, so we don't have access to the plate numbers to be able to specify a concrete design. The effective way to obtain floor designs is to use any of the other meshing methods that result in plates. The fact that the external beams are broken into individual beam segments is a typical program behavior when meshes are placed on existing beams. Although this behavior can be turned off, doing so will make it such that the mesh will not be connected to or supported by the beams. So in reality, you don't want to undo that. What you DO want to do is learn how to use the RC Design module to obtain designs for Physical Members as opposed to using the "batch" mode of design and obtaining 4 different designs for the four segments. (Check the available codes in the RC Designer to be sure your code is supported before you go too far learning how to use the module. If it applies to you, I would encourage you to consider taking our 4-hour online course on Reinforced Concrete Design in STAAD.Pro. The RC Designer is one of the topics in that course.) Plate mesh density is more of an art than a science. There are no hard and fast rules. The general concept is that you need to make the mesh fine enough to give adequate results, but no finer. The art is in determining that density. I recommend trying a density and observing the value of a critical parameter of interest (such as moment at a key location, or deflection at an important node). Then vary the mesh density and note the variation in the value of that critical parameter of interest. You have identified convergence when the value of that critical parameter of interest does not change significantly with subsequent changes in the mesh density. (For some other impportant guidelines on mesh quality and element shape, I can recommend another one of our 4hour online courses that covers model generation and finite element modeling.)
Regards, Chris
Dear Mr. Chris Conrad, Thank you for your detailed explanation. Please advise me how I can turn off the function so that during slab meshing, mesh will not connect / support on existing beams.Please also send me a link for an online course on Reinforced Concrete Design in STAAD.Pro. Regards, Fiaz
Hello Fiaz, To turn alter the automatic behavior of splitting existing members and inserting new nodes when a mesh is placed on them, click View > Options in the Menu Bar. In the Options dialog, choose the Tolerance item. Deselect the checkbox next to "Split member if...." Now, if a mesh is placed on top of an existing member, the existing member will not be subdivided by the mesh nodes. Be aware that this also means that the existing members will not be connected to the mesh, nor will they receive load from nor contribute stiffness to the mesh, except at any locations where the nodes of the existing members happen to coordinate precisely with the nodes of the mesh. Here is a link to the Concrete Design courses:
http://lms.bentley.com/us/desktopmodules/SearchResults.aspx?catId=0&tabindex=3&ta bid=16&description=CRS-STR-STAAD-Reinf-Concrete-Analysis-DesignCRS&count=9&cat1=2&cat2=3&cat3=4&cat4=5&cat5=6&cat6=7&cat7=8&cat8=9&cat9 =213&SortItems=Title%20DESC,StartDateNoTime%20ASC It appears that there are no more open enrollment offerings for that class for the remainder of the calendar year. As I look at the schedule, the next scheduled occurrence of that class is Friday, April 2, 2010. If you are a Bentley LEARN subscriber, you have access to an OnDemand recording of this class. If you are not a Bentley LEARN subscriber, we might be able to add a new open enrollment course offering. Regardless of your Bentley LEARN status, we could also offer custom training as well. Regards, Chris
