If i model my project and add slab,what will be the difference if i dont generate plate mesh, after adding slab i add load and run analysis without generating mesh.
In Ram Concept? The program will always generate the mesh before you run the calculations. If there is a minor error in the first mesh generation, you may choose to skip re-meshing it again the next time. It's a best practice to regenerate the mesh after the design strips are modeled so that the mesh aligns with the strips as best possible.
Not in RAM, i ask in Staad Pro Connect Edition,for a person who has model and add slab without generating mesh,what will be the effect of load distribution on beams
First, some theoretical background.
1) In practice, a concrete slab and a beam are continuously connected throughout their common edge, which means, the deflect in unison along that common edge, and, loads are transferred from the slab to the beam at every point along the common edge.
2) During stiffness and load calculations, generally, line entities like beams, columns and braces are handled using the theory meant for line members, while 2 dimensional entities like slabs and walls are handled using the finite element method.
Now the answer to your question:
In the analysis method that uses the line entities and finite elements, there is no means by which the continuous connection (monolithicity) between the slab and a beam can be modeled exactly. Instead, the analysis model is constructed in such a way that the beam and slab are connected at a number of discrete points. This is what is attained by meshing the slab, and dividing the beam into a number of segments. Hence the use of terms like coarse mesh or dense mesh. Coarse mesh means the number of discrete points of connectivity is few, dense means many.
Those points of connectivity are the sole locations through which a load transfer occurs between the slab and the beam. If you do not mesh the slab, the connectivity present only at the points where the beams and the slab are connected to columns. Thus, any load acting on the slab will bypass the beam and go directly in the column if you don't mesh the slab. It will not reflect the monolithic nature of the connection between them.
Needless to say, a dense mesh is a better representation of the monolithic connection compared to a coarse mesh.
@kris sathia - I have also few questions ?
My question is in the context of designing G+2 RCC structure.
1. what is the difference between plate load and the floor load ? Should I apply floor load or plate load after generating mesh to the plate ?
2. Should I apply self weight to the slab (25 x D) KN/M^2 also under dead load of plate pressure / floor load category to the slab also even after giving dead weight (-1) to the whole structure ?
Your question:
Answer:
By plate load, we assume you are referring to the "ELEMENT LOAD" command.
If you have included the slab in the model as a plate element mesh, then, any pressure load or concentrated load acting on the slab should be applied on the model using the ELEMENT LOAD command. Thus, an ELEMENT LOAD can be applied only if there are plate elements.
If you do not use a plate element mesh, but instead, use an alternative method to model the slab like a rigid diaphragm, or the master-slave command, then, the FLOOR LOAD command is a tool to apply the pressure load acting on the slab. The XRANGE, YRANGE and ZRANGE options of that command help the program in identifying the location on the structure where the pressure load acts.
If the slab is included in the model through a finite element mesh, and if the density of concrete has been specified for those elements, the selfweight command will instruct the program to calculate the dead weight of those elements too in addition to those of the line members. In such cases, you should not apply the (25 x D) KN/M^2 as a separate pressure load (assuming that you meant that 25 kN/m3 is the density of concrete and D is the thickness of the slab).
But if you are using the rigid diaphragm or master-slave methods, then you need to use the FLOOR LOAD command to consider the slab weight.
Kris Sathia
I am clear in doubt no 2 which were asked in above tread. However, I am still having doubt in point no 1. Also, I would like to add few more questions. Please help me to clear it.
Doubt 1
In continuation of Doubt 1, Can we add load on plate under (Plate Load - Pressure on Full Plate) after meshing to a plate and without meshing ?
Also, Please help me to know, Is there any tutorial link to use ( Element Load, Master Slave command) or rigid diaphragm to model slab ?
Doubt 3 -
If I am applying a Live load of -10 KN/M2 in GY direction on a plate (casted by plate element cursor), I am not able to see the post processing result. However, If I am using only the dead load(-1) to the whole structure, I am able to see the post processing result (Includes BM, SF, stress diag . etc). Please help me to know what is the reason and how to rectify it.
P.S - I have set scale value as well and turn on all stress icon also.
Doubt 4-
In continuation of Doubt no 3 , If I am applying a Live load on Plate (by Plate Load - Pressure on Full Plate) without meshing , I am also not able to see any value ("0" value is showing) under LIVE LOAD in post processing mode (Also SF, BM diag is not visible).
Doubt 5-
In Output file - concrete design, Stadd is not showing slab design details.
I have also attached project file along with this list of doubt.3632.Structure1.std
The expression "Pressure on full plate" is to be interpreted as pressure on the full area of the element or elements that the load is applied on. Thus, it acts on the full area of all the elements that are mentioned in the element list. So, for example,
1 TO 49 PR GY -2.5
means 2.5 units of pressure acting on the full area of each of the elements 1 to 49.
If you do not mesh the slab and define it as a single element and apply the pressure on it, the load will act on the full area of the slab.
For answering the rest of your questions, I will defer to some of the others.
Please see the screenshot below - the plate load is applied and you can switch the diagram onscreen as shown:
The batch mode element design is available in the Output file - see the screenshot below:
AndrejLogunov
Please address the following query
paresh said:Doubt 4- In continuation of Doubt no 3 , If I am applying a Live load on Plate (by Plate Load - Pressure on Full Plate) without meshing , I am also not able to see any value ("0" value is showing) under LIVE LOAD in post processing mode (Also SF, BM diag is not visible)
In continuation of Doubt no 3 , If I am applying a Live load on Plate (by Plate Load - Pressure on Full Plate) without meshing , I am also not able to see any value ("0" value is showing) under LIVE LOAD in post processing mode (Also SF, BM diag is not visible)
My doubt is - " If I am applying a Live Load on plate element, I am not able to see any BM due to LL on plate and any changes in Beam BM. Please help me to know why is it so ? and what is the possible reason behind this ?
In continuation of above, I have one more question -
How to design reinforcement of slab if we meshed a plate into 'n' no of plates ? Because in this case, every small plate have different value of BM and stresses. Same is the case for beam.
In practical case, slab and beam can't be design for 'n' no of small small elements.
I have also attached modified staad file after meshin
g.2625.Structure1.std
If you do not mesh the slab, any load acting on the slab will bypass the beams and go directly into the column. So, the slab load will not induce any bending in the beams. That slab load will not induce any bending in the slab either. In the stiffness method, the pressure is converted to concentrated forces and concentrated moments at the 4 corners of the slab. For an unmeshed slab, the 4 corners coincide with the top nodes of the columns. So, the entire slab load goes directly as point forces and moments on the columns.
Regarding viewing the applied loads - see below: