- Enter the type of and the basic data for structural analysis.
From main menu, select [Project] Tab > [Settings] Group > [Structure Type]
Fig. Structure Type dialog box
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
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.
6 degrees of freedom per node applicable for a general 3-D structural analysis.
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.)
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.)
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.)
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 mass matrix is constructed by concentrating the total mass of an element at its nodal points, resulting in a diagonal matrix. Since the non-diagonal entries are zero in this case, only the diagonal entries are typically stored and used for analysis. However, considering only the diagonal entries poses a problem in that it cannot perform a complete transformation related to the mass matrix.
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 ’r;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 into 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 the self-weight of elements are entered at the centroid of a section. Nodal mass and nodal load, which are entered at the node and have no relation to elements, will be entered at the offset node.
Off-diagonal Masses can be reflected in the time history analysis.
When ’Mass Offset’ is used, only the Lanczos method will be supported for the Eigenvalue analysis.
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.
Consistence 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 are 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.
Consistent Mass can be reflected in the time history analysis.
When ’Consistent Mass’ is used, only Lanczos method will be supported for the Eigenvalue analysis.
Convert Self-weight into Masses : Specify whether to convert the self-weight of the structure to mass for dynamic analysis.
Convert to X, Y, Z : Convert the self-weight into lumped masses in the GCS X, Y, and 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
The masses of the elements included in the model can be automatically converted into lumped masses or consistence masses in midas Civil for dynamic analysis or computation of statically equivalent seismic loads.
When dynamic analysis is performed with "Do 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.
Consistent Mass can be reflected in the time history analysis.
When 'Consistent Mass’ is used, only the Lanczos method will be supported for the Eigenvalue analysis.
Enter the acceleration of gravity considering the unit system in use.
Enter the initial temperature required for a thermal stress analysis.(Refer to Load > Temperature > System Temperature or Nodal Temperature)
Align Top of Beam Section to Center Line (X-Y Plane) for Display
When representing an element inputted in the model window, align the top of the linear element that is placed in the X-Y plane of the global coordinate system to coincide with the element's center line.
Align Top of Slab(Plate) Section to Center Line (X-Y Plane) for Display
When representing a plate element in the Model Window, align it to the centerline of the plate element in the X-Y plane of the global coordinate system.
When the alignment options are not selected, the centerlines of the line and plate elements are shown to be connected to the column nodes.