Structure Type

 

 

 

Enter the type of and the basic data for structural analysis.

 

 

 

From the Main Menu select Model > Structure Type.

 

Select Configuration > Structure Type from the Menu tab of the Tree Menu.

 

 

 

Structure Type dialog box

 

 Structure Type

 

Select an option as to whether the analysis is to be carried out in 3-D or 2-D.

 

3-D: 3-D structural analysis

 

X-Z Plane: 2-D analysis in GCS X-Z plane

 

Y-Z Plane: 2-D analysis in GCS Y-Z plane

 

X-Y Plane: 2-D analysis in GCS X-Y plane

 

Constraint RZ: 3-D analysis constraining rotational degree-of-freedom about GCS Z-axis

 

Note Usage of Structure Type option
 

6 degrees-of-freedom are considered by default for each node when constraints are not defined by the user.

 

Use the function to exclude unnecessary degrees-of-freedom to ensure the efficiency of the analysis. Quite often, only 2-D behaviors or behaviors with a particular degree-of-freedom constrained are of interest.

 

3 - D
6 degrees-of-freedom per node applicable for a general 3-D structural analysis.

 

X - Z Plane
2-D structural analysis on the GCS X-Z plane. (The Y-direction displacements and the rotations about the X and Z-axes are automatically constrained.)

 

Y - Z Plane
2-D structural analysis on the GCS Y-Z plane. (The X-direction displacements and the rotations about the Y and Z-axes are automatically constrained.)

 

X - Y Plane
2-D structural analysis on the GCS X-Y plane. (The Z-direction displacements and the rotations about the X and Y-axes are automatically constrained.)

 

Constraint RZ
Special 3-D analysis constraining the rotation(torsion) about the vertical GCS axis (GCS Z-axis). The analysis may be applied to a preliminary design of a structure, such as to analyze a lateral shear force distribution for each story.

 

 Mass Control Parameter

 

Define mass type as Lumped Mass or Consistent Mass.

The user can consider whether to convert the model self-weight into lumped/consistent masses for dynamic analysis using the Convert Self-weight into Masses option.

 

Lumped Mass : Convert into lumped masses.

 

The total mass of an element is directly distributed to the nodal points of an element. In general, only the diagonal terms of the lumped mass matrix are considered for mass calculations. Off-diagonal terms are zero.

 

Consider Off-diagonal Masses : When this option is checked on, all terms including off-diagonal terms in the lumped mass matrix are considered for mass calculations. The accuracy of results increases with a full lumped mass matrix, but the analysis time may increase. When ‘Consider Off-diagonal Masses’ option is checked off, the matrix is considered as a vector.

 

When a section offset is considered, a node will be generated at the offset location and the loads, boundary conditions, masses, etc. to be applied to the node will be entered to the node at the offset location. However, structural characteristics related to elements (e.g., element stiffness, loads to be applied to the elements, masses converted from self-weight of elements, etc.) have to be entered at the centroid of a section. If this option is checked, masses converted from self-weight of elements are entered at the centroid of a section. Nodal mass and nodal load, which is entered at the node and has no relation to elements, will be entered at the offset node.

Revision of Gen 2011

Note 1 Off-diagonal Masses can be reflected in the time history analysis.

 

Note 2 When ‘Mass Offset’ is used, only Lanczos method will be supported for the Eigenvalue analysis.

 

Note 3 When ‘Mass Offset’ is used, the Section Offset of a beam element will be taken into account. ‘Mass Offset’ will be effective only in beam elements.

 

Consistent Mass : Convert into distributed masses.

 

Consistent Mass is calculated with the shape function used to derive the stiffness matrix. Off-diagonal mass terms are considered and, unlike the lumped mass, the inertia coupling effect is considered. Therefore, results using the consistent mass  is more accurate than the lumped mass, however it takes more time for numerical computation.

Consistent masses can be applied only when the "Lanczos" option is selected in the Eigenvalue Analysis Control.

Revision of Gen 2011

Note 1 Consistent Mass can be reflected in the time history analysis.

 

Note 2 When ‘Consistent Mass’ is used, only Lanczos method will be supported for the Eigenvalue analysis.  

 

Convert Self-weight into Masses

 

Convert to X, Y, Z: Convert the self-weight into lumped masses in the GCS X, Y, Z-directions

 

Convert to X, Y: Convert the self-weight into lumped masses in the GCS X, Y-directions

 

Convert to Z: Convert the self-weight into lumped masses in the GCS Z-direction

 

Note Usage of Convert Self-weight into Masses
 

The masses of the elements included in the model can be automatically converted into lumped masses in MIDAS/Gen for dynamic analysis or computation of statically equivalent seismic loads. When dynamic analysis is performed with "no not convert" option checked, mass effect cannot be reflected in the analysis.

 

If 'Convert to X, Y, Z' is selected, the mass, which is the weight divided by the acceleration of gravity, is automatically considered in the GCS X, Y, Z-directions. The weight itself is automatically obtained by multiplying the volumetric weight (density) entered in Model > Properties >Material by the volume of the element.

 

If 'Convert to X, Y' is selected, the calculated mass is automatically considered in the GCS X, Y-directions.

 

If 'Convert to Z' is selected, the calculated mass is automatically considered in the GCS Z-direction.

 

In most cases of building structures, lateral behaviors are more important than vertical behaviors. Thus, the vertical components of masses are commonly neglected. The condition of 'Convert to X, Y' saves analysis time and lessens the burden of computer memory capacities.

 

Where structures are analyzed considering only the vertical component of the seismic data or dynamic analyses are required to evaluate machine vibrations on floor slabs and other vertical vibrations, 'Convert to Z' may be more appropriate. The notion is identically applied when masses are generated by "Nodal Masses" or "Load to Masses".

 

For line elements (truss element, tension element, compression element, beam element), each element mass is divided by two and distributed to both ends as lumped masses.

 

For plane elements (plane stress element, plate element) and solid elements, each element mass is divided by the number of nodal corners and lumped to each node as lumped masses.

 

Self weight cannot be converted into mass in Load to Mass. It must be converted in Structure Type.

 

 Gravity acceleration

 

Enter the acceleration of gravity considering the unit system in use.

 

Initial Temperature

 

Enter the initial temperature required for a thermal stress analysis.(Refer to Load > System Temperature or Nodal Temperature)

 

 Align Top of Beam Section with Floor (X-Y Plane) for Panel Zone Effect/Display

 

Align the tops of line elements in the GCS X-Y plane such that their top elevations line up at the floor level (nodal positions of columns) when reflecting rigid offsets or displaying the elements in the Model Window. (Refer to "Rigid Offset Distance")

 

Note
In order to see Panel Zone Effect applied, "Auto Calculate Panel Zone Offset Distances" should be defined first in Model > Boundaries > Panel Zone Effect.

 

 Align Top of Slab (Plate) Section with Floor (X-Y Plane) for Display

 

Align the tops of plate elements in the GCS X-Y plane such that their top elevations line up at the floor level (nodal positions of columns) when displaying the elements in the Model Window.

 

Note

When the alignment options are not selected, the centerlines of the line and plate elements are shown to be connected to the column nodes.