User and standard FEAP element

[ibry]

Hi everyone,

Recently, I am working on reinforced concrete subjected to dynamic loading. Concrete material is modeled by user element and user macro, whereas reinforcement uses standard FEAP element (truss element). My question is how FEAP distinguishes the user and standard element? Because FEAP still calculates coordinates of truss element by user macro (I don't expect it), eventhough I have used truss element by standard FEAP element. Meanwhile, if I write calculation of coordinates and volume also in the user element file, the running time will be slow. Please give me an advice about that.

Thank you in advance.

[Prof. R.L. Taylor]

I assume your user element is an "elmtnn" where "nn"  = "01" or something.

Feap finds the user element when it looks at the material set associated with an element.  If you want to superpose two types of materials on the same element you can but you want to add a truss for the reinforcement.  Does the truss lie on the edge nodes of the user element or pass through it.  If the former you specify which nodes as a separate element; if the latter you have to program yourself to compute the truss nodes from the concrete element nodes.

When an element is set up the values of the local parameters are preset as XL, UL, etc.  -- no other values such as volume, area are computed -- you have to do it or you can compute and save as  history variables (probably "n3" and "nh3" ones - see the programmer manual).  That way you do not have to compute every tie - but you use memory to store them so there is always a tradeoff on which to do when problems get large.

If this does not answer your question provide more information (and the version of feap you are using).

[ibry]

Thank you for your reply, Prof. Taylor.

I want to use two kinds of material. First, I use user element (and user macro as well) for the concrete and second, I use standard FEAP element for the reinforcement using truss element. Is it possible?
If it is possible, how can I distinguish the concrete and truss element in the user macro file?
Because when I don't expect to calculate the coordinates of the truss, FEAP still calculate them.
So the minimum element size is always zero (since truss element is only 1D).
FEAP version I used is 8.4.

In this case, my user element file works well when I use only one element.
I need to compute the volume element in my approach, so I have to calculate the coordinates first in array mr(np(33)).
However, FEAP calculates the coordinates for truss element as well because I put the calculation in the user macro file.
I just ask how to differentiate the two element in order to avoid the calculation of truss element.
I have used like flag, but it didn't work. Maybe you could give an example to apply this.
Thank you in advance.

[Prof. R.L. Taylor]

You need to have two material sets and two element sets:

one for the concrete where elements are solids (which must be 3-node triangles or 4-node quads in 2-d or 4-node tets or 8-node bricks in 3-d) and

a second for the truss elements where the elements only have two nodes

feap will compute the stiffness and residual for each element and assemble into the global problem for solution.

I do not understand what your umacr is used for.