NSMASS
NSMASS, Elem,
Action, UNIT,
VAL, DISTRB
Applies nonstructural mass to selected elements.
ElemElement on which to apply nonstructural mass. If ALL, the command applies nonstructural mass to all selected elements (ESEL). A component name is also valid.
ActionCommand action requested:
ADD – Add nonstructural mass to the specified element or elements. DEL – Delete all previously defined nonstructural mass from selected element(s). LIST – List the input value of nonstructural mass. If multiple NSMASS commands are issued, this option lists the total accumulated nonstructural mass. 
The following options apply only when
Action= ADD:UNITUnit of the input value of nonstructural mass:
0 – Total Mass (default). 1 – Mass per unit volume. 2 – Mass per unit area. 3 – Mass per unit length. VALInput value of the nonstructural mass. A positive value increases (accumulates) the total nonstructural mass. A negative value reduces the total nonstructural mass.
DISTRBNonstructural mass distribution method. Valid only when
UNIT= 0.0 – Mass proportional distribution (default). 1 – Volume proportional distribution. 2 – Area proportional distribution. 3 – Length proportional distribution.
Notes
NSMASS supports current-technology structural elements only:
Table 203: Supported Elements
| Category | Element Types |
|---|---|
| 2D/3D Structural Solid | PLANE182, PLANE183, SOLID185, SOLID186, SOLID187, SOLSH190, SOLID285 |
| 2D/3D Structural Shell | SHELL208, SHELL209, SHELL181, SHELL281 |
| 2D/3D Surface Effect | SURF153, SURF154, SURF156 |
| 2D/3D Structural Link, Beam, Pipe, and Elbow | LINK180, CABLE280, BEAM188, BEAM189, PIPE288, PIPE289, ELBOW290 |
| 2D/3D Gasket | INTER192, INTER193, INTER194, INTER195 |
Applying Nonstructural Mass
NSMASS offers two methods for nonstructural mass application:
For consecutive accumulation or reduction of total nonstructural mass to the same
elements, you can issue multiple NSMASS commands, each specifying a
different unit (UNIT) or distribution method
(DISTRB).
Use care when selecting the unit and distribution method to ensure compatibility with the selected elements.
Distribution of Total Nonstructural Mass (UNIT =
0)
Specify UNIT = 0 to distribute the total nonstructural mass
over all selected elements proportionally to the mass, volume, area, or length
(DISTRB = 0, 1, 2, or 3, respectively):
Table 204: Supported Total Mass Distribution Methods
DISTRB | Applicable Element Types |
|---|---|
| 0, 1 | Supports all element types listed in Table 203: Supported Elements with the exception of SURF156. |
| 2 | Supports these structural shell and surface-effect elements: SHELL208, SHELL209, SHELL181, SHELL281, SURF153, and SURF154. |
| 3 | Supports structural link, beam, pipe, and elbow elements, and the SURF156 structural surface line-load-effect element. |
Direct Input of Nonstructural Mass Density (UNIT = 1, 2,
or 3)
The nonstructural mass is applied directly to the selected element in one form of mass
densities: mass per unit volume (UNIT = 1), mass per unit area
(UNIT = 2), or mass per unit length
(UNIT = 3):
Table 205: Supported Units for Direct Input of Mass Density
DISTRB | Applicable Element Types |
|---|---|
| 1 | Supports all element types listed in Table 203: Supported Elements with the exception of SURF156. |
| 2 | Supports these structural shell and surface-effect elements: SHELL208, SHELL209, SHELL181, SHELL281, SURF153, and SURF154. |
| 3 | Supports structural link, beam, pipe, and elbow elements, and the SURF156 structural surface line-load-effect element. |
Nonstructural Mass Behavior: Saturated Mass vs. Attached Mass
NSMASS accounts for two behaviors of the nonstructural mass:
The nonstructural mass is applied uniformly to the entire volume of the element (that is, the saturated nonstructural mass).
Example: The moisture content in a structure can be simulated with the saturated nonstructural mass.
This behavior of the nonstructural mass can be defined via a mass- or volume-proportional distribution of total nonstructural mass (
DISTRB= 0 or 1), or direct input of mass density (UNIT= 1).The nonstructural mass is attached to the element at the location where element nodes are defined (that is, at the attached nonstructural mass).
Example: The thin exterior insulation on a pipe can be simulated with the attached nonstructural mass.
This behavior of the nonstructural mass can be defined via area or length proportional distribution of total nonstructural mass (
DISTRB= 2 or 3), or via direct input of mass density (UNIT= 2 or 3).The attached nonstructural mass is assumed to have a negligible thickness or cross-sectional area. Therefore, for structural elements with rotational degrees of freedom, element rotational inertia is not affected by the attached nonstructural mass. To properly account for the attached nonstructural mass on these elements, position the element nodes (SECOFFSET) at the locations where the nonstructural mass is applied (for example, at the top surface of a shell element).
Assumptions and Limitations
Elements with inhomogeneous materials (such as a structural shell with a composite section) are not supported for mass proportional distribution (
DISTRIB= 0).Elements with a TAPER, GENB, COMB, or GENS section type are not supported.
The element volume, area, or length used for total nonstructural mass distribution (
DISTRIB= 0, 1, 2, or 3 respectively) are calculated using the undeformed element geometry.The element mass used for total nonstructural mass distribution (
DISTRB= 0) is calculated using undeformed element geometry and mass density at the reference temperature. The program excludes elements with zero or unspecified density from the distribution and issues a warning message for the excluded elements.NSMASS does not account for subsequent modifications made to the selected elements. Issue NSMASS only after defining the selected elements.