Products: ABAQUS/Standard ABAQUS/Explicit ABAQUS/CAE
A nonstructural mass:
is a contribution to the model mass from features that have negligible structural stiffness (such as paint on sheet metal panels in a car);
can be used to bring the net mass of one or more components in the model up to a known value;
can be positive to add mass to the model and negative to remove mass from the model, with the corresponding increase or decrease in the element stable time increment in an ABAQUS/Explicit analysis;
can be specified in the form of a total mass of the nonstructural features to be distributed over one or more components in the model;
can be specified in the form of an increase in density over the smeared region;
can be specified in the form of mass per unit area to be applied over a smeared region consisting of shells, membranes, and/or surface elements; and
can be specified in the form of mass per unit length to be applied over a smeared region consisting of beam and/or truss elements.
The mass contribution from nonstructural features can be included in the model even if the features themselves are omitted. The nonstructural mass is smeared over an element set that is typically adjacent to the nonstructural feature. This element set can contain solid, shell, membrane, surface, beam, or truss elements. The nonstructural mass can be specified in the following forms:
a total mass value,
a mass per unit volume,
a mass per unit area (for element sets that contain conventional shell, membrane, and/or surface elements), or
a mass per unit length (for element sets that contain beam and/or truss elements).
A “structural” mass is defined as the sum of all the mass contributions to an element outside of the nonstructural features. This may include the mass due to any material definitions associated with the element; any “mass per unit area” given on the section definition for shell, membrane, and surface elements; mass from any rebars included in shell, membrane, and surface elements; and any additional inertia given on the section definition of beam elements. A nonstructural mass contribution to an element is ignored if that element has no structural mass.
A given element in the model can have contributions from multiple nonstructural mass specifications. The nonstructural mass in a given element will participate in any mass proportional distributed loads, such as gravity loading, defined on that element. When a nonstructural mass is added to a shell or beam element with active rotational degrees of freedom, the nonstructural contribution affects both the element mass and the element rotary inertia. The element stable time increment increases with a positive nonstructural mass and decreases with a negative nonstructural mass. In general, it is easier to use a nonstructural mass definition to bring an additional mass into the model than to do the same with a group of point masses. It is also more beneficial in an ABAQUS/Explicit analysis due to a possibly higher time increment.
The nonstructural feature is assumed to have no damping associated with it. Any mass proportional damping specified as part of the material definition (see “Material damping,” Section 20.1.1) will be applied only to the mass contribution from that material to the element.
To define a nonstructural mass contribution to the model mass, you must first identify the region over which the contribution must be added. You then specify the value of the nonstructural mass using the appropriate units and, if the total mass from the nonstructural features is known, determine how the nonstructural mass is distributed over the region.
| Input File Usage: | *NONSTRUCTURAL MASS, ELSET=element_set_name |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
The nonstructural mass can be specified in different types of units, depending on the types of elements contained in the specified region.
A total nonstructural mass with units of “mass” can be spread over a region containing solid, shell, membrane, beam, and/or truss elements.
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=TOTAL MASS total mass of the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
A nonstructural mass with units of “mass per unit volume” can be spread over a region containing solid, shell, membrane, beam, and/or truss elements.
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=MASS PER VOLUME added density due to the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
A nonstructural mass with units of “mass per unit area” can be spread over a region containing conventional shells, membranes, and/or surface elements.
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=MASS PER AREA added mass per unit area due to the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
A nonstructural mass with units of “mass per unit length” can be spread over a region containing beam and/or truss elements.
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=MASS PER LENGTH added mass per unit length due to the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
There are two methods available for distributing the nonstructural mass over the region when the total mass from the nonstructural features is known.
If you do not want to change the center of mass for the region, distribute the nonstructural mass in proportion to the element structural mass. This method results in a uniform scaling of the structural density of the region. ABAQUS uses mass proportional distribution by default.
The element structural mass in shell, membrane, and surface elements includes any mass contribution from rebar provided that the rebar are defined as a rebar layer (see “Defining reinforcement,” Section 2.2.3).
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=TOTAL MASS, DISTRIBUTION=MASS PROPORTIONAL total mass of the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
Alternatively, you can distribute the nonstructural mass in proportion to the element volume in the initial configuration. This method results in a uniform value added to the underlying structural density over the region. Therefore, the center of mass for the region may be altered if the region has nonuniform structural density.
| Input File Usage: | *NONSTRUCTURAL MASS, UNITS=TOTAL MASS, DISTRIBUTION=VOLUME PROPORTIONAL total mass of the nonstructural feature |
| ABAQUS/CAE Usage: | Property or Interaction module: Special |
