Ram Series manual


General properties

These properties define both, the material parameters and the section or shell parameters.

Data->General Properties   

Global and Local axes for beams

The model is created related to a global axes system XYZ that is unique for the entire problem. But every beam must have its own local axes system X'Y'Z' in order to:

1.       Refer section properties like Inertia modulus or thickness and height to this system.

2.       Some of the loads (that have the prefix Local) are related also to this system.

3.       Strength results over the beams are referred to this local axes system.

The main property of this system is that the local X' axe must have the same direction than the beam.

 


The ways for defining local axes systems are:

1.       Default. The program assigns a different local axes system to every beam with the following criteria:

ˇ         X' axe has the direction of the beam.

ˇ         If X' axe has the same direction than global Z axe, Y' axe has the same direction than global X. If not, Y' axe is calculated so as to be horizontal (orthogonal to X' and Z).

ˇ         Z' axe is the cross product of X' axe and Y' axe. It will try to point to the same sense than global Z (dot product of Z and Z' axes will be positive or zero).

Note: The intuitive idea is that vertical beams have the Y' axe in the direction of global X. All the other beams have the Y' axe horizontal and with the Z' axe pointing up.

2.       Automatic. Similar to the previous one but the local axes system is assigned automatically to the beam by GiD. The final orientation can be checked with the Draw Local Axes option in the GiD Conditions window.

3.       Automatic alt. Similar to the previous one but an alternative proposal of local axes is given. Typically, User should assign Automatic local axes and check them, after assigning, with the Draw local axes option. If a different local axes system is desired, normally rotated 90 degrees from the first one, then it is only necessary to assign again the same condition to the entities with the Automatic alt option selected.

4.       User defined. User can created different named local axes systems with the GiD command:

Data->Local axes->Define

and with the different methods that can be chosen there. The names of the defined local axes will be added to the menu where Local axes are chosen.

Note 1: rambshell tries to correct the local axes system if the local X' axe does not point to the direction of the beam. It will fail if local X' axe is orthogonal to the direction of the beam.

Note 2: The final local axes system for every beam can be visualized in the postprocess stage. It is convenient to check the correctness of these systems after calculation is performed.

Global and Local axes for shells

The model is created related to a global axes system XYZ that is unique for the entire problem. But every shell element must have its own local axes system X'Y'Z' in order to:

1.       Refer section properties like orthotropy properties to this system.

2.       Some of the loads (that have the prefix Local) are related also to this system.

3.       Strength results over the shell are referred to this local axes system.

4.       Dimension of steel in shells is based on X' and Y' directions.

The main property of this local axes system is that the local Z' axe must have the same direction than the normal of the element.

 


The ways for defining local axes systems are:

1.       Default. The program assigns a different local axes system to the shell with the following criteria:

ˇ         Be N the unitary normal of the shell element, U the vector (0,1,0) and V the vector (0,0,1). Then:

ˇ         Z' axe has the direction and sense of N.

ˇ         If Nx<1/64 and Ny<1/64, then X' axe will be in the direction of the cross product of U and N (UxN).

ˇ         If not, X' axe will be in the direction of the cross product of V and N (VxN).

ˇ         Y' axe will be the cross product of Z' axe and X' axe.

Note: Intuitively, this local axes system is calculated so as if element is approximately contained in the plane XY, local X' axe will point towards global X axe. If not, this X' axe is obtained as orthogonal to global Z axe and local Z' axe.

2.       Automatic. Similar to the previous one but the local axes system is assigned automatically to the shell by GiD. The final orientation can be checked with the Draw Local Axes option in the GiD Conditions window.

3.       Automatic alt. Similar to the previous one but an alternative proposal of local axes is given. Typically, User should assign Automatic local axes and check them, after assigning, with the Draw local axes option. If a different local axes system is desired, normally rotated 90 degrees from the first one, then it is only necessary to assign again the same condition to the entities with the Automatic alt option selected.

4.       User defined. User can created different named local axes systems with the GiD command:

Data->Local axes->Define

and with the different methods that can be chosen there. The names of the defined local axes will be added to the menu where Local axes are chosen in the conditions window.

Note 1: rambshell tries to correct the local axes system if the local Z' axe does not point to the direction of the normal of the element. It will fail if local Z' axe is orthogonal to the direction of the normal.

Note 2: The final local axes system for every shell element can be visualized in the postprocess stage. It is convenient to check the correctness of these systems after calculation is performed.

Rectangular section

This condition is assigned to beams with its transversal section
rectangular. Properties to enter are:

ˇ         Local axes system. Defined in previous section.

ˇ         Units. Defined in previous section.

ˇ         The Width y is the width of the rectangular section following the Y' direction. Width z is the width in the Z' direction. G is the torsion modulus (8.1e10 N/m2 for steel) and E is the Young modulus (2.1e11 N/m2 for steel).

Note: Remember that for an isotropic material:     (for steel  u=0.3)

ˇ         The Specific Weight (different from density). The weight is considered in the direction of the gravity, which will be defined later. Its default units are N/m3.

Once the values are filled in, the condition must be assigned to the beams.

The conditions that have been assigned and their local axes can be viewed with the Draw button in the conditions window.

Beam Section

The definition of the properties for a general beam section is very similar to that of the rectangular section. Instead of giving the width and height of the section, the area (A), the Torsor modulus (J) and the inertia modulus for the Y' (Inertia y) and Z' axes (Inertia z) of the beam are given. Default units for the area are m2 and for the inertia modulus are m4.

Shell properties

This condition is assigned to the isotropic (homogenous) shell surfaces.

Properties to enter are:

ˇ         Local axes system. Defined in previous section.

ˇ         Units. Defined in previous section.

ˇ         Thickness is the width of the shell in the orthogonal direction to the shell surface.

ˇ         E is the Young modulus (2.1e11 N/m2for steel) and nu is the Poisson coefficient with value 0.3 for steel (it is non-dimensional).

ˇ         The Specific Weight (different from density). The weight is considered in the direction of the gravity, which will be defined later. Its default units are N/m3.

Once the values are filled in, the condition must be assigned to the surfaces that define the shells.

The conditions that have been assigned can be viewed with the Draw button in the conditions window.

Anisotropic shell properties

Properties defined in this condition are similar to that of the shell condition. The difference is that the material is orthotropic. The orthotropy axes are the ones defined in the Local axes field of the condition. The properties to enter are the Young Modulus (Ex, Ey), the Poisson coefficients (nuxy, nuyx) and the Shear modulus (Gxy, Gxz, Gyz). They are all referred to the local axes X' and Y'.

Note: Remember that to maintain the elasticity hypothesis it is necessary to accomplish that:

Exˇ nuxy= Eyˇ nuyx

Default units for E and G are N/m2 and nu is non-dimensional.

Remember that for an isotropic material:

For and orthotropic material:

Solid properties

This condition is assigned to solid volumes.

Properties to enter are:

ˇ         Units. Defined in previous section.

ˇ         E is the Young modulus (2.1e11 N/m2 for steel) and nu is the Poisson coefficient with value 0.3 for steel (it is non-dimensional).

ˇ         The Specific Weight is the self-weight of the solid (different from density). The weight is considered in the direction of the gravity, which will be defined later. Its default units are N/m3.

Once the values are filled in, the condition must be assigned to the volume that defines the solid.

The conditions that have been assigned can be viewed with the Draw button in the conditions window.