Product: ABAQUS/Standard
User subroutine UTRACLOAD:
can be used to define the variation of the distributed traction load magnitude as a function of position, time, element number, load integration point number, etc.;
if needed, can be used to define the initial loading direction for the distributed traction load as a function of position, element number, load integration point number, etc.;
will be called at each load integration point for each element-based, edge-based, or surface-based nonuniform distributed traction load definition during stress analysis;
cannot be used in mode-based procedures to describe the time variation of the load; and
ignores any amplitude references that may appear with the associated step definition or nonuniform distributed traction load definition.
SUBROUTINE UTRACLOAD(ALPHA,T_USER,KSTEP,KINC,TIME,NOEL,NPT,
1 COORDS,DIRCOS,JLTYP,SNAME)
C
INCLUDE 'ABA_PARAM.INC'
C
DIMENSION T_USER(3), TIME(2), COORDS(3), DIRCOS(3,3)
CHARACTER*80 SNAME
user coding to define ALPHA and T_USER
RETURN
ENDALPHA
Magnitude of the distributed traction load. Units are FL–2 for surface loads, FL–1 for edge loads, and F for edge moments. ALPHA is passed into the routine as the magnitude of the load specified as part of the element-based or surface-based distributed load definition. If the magnitude is not defined, ALPHA is passed in as zero. For a static analysis that uses the modified Riks method (“Unstable collapse and postbuckling analysis,” Section 6.2.4 of the ABAQUS Analysis User's Manual) ALPHA must be defined as a function of the load proportionality factor, 
. The distributed load magnitude is not available for output purposes.
T_USER
Loading direction of the distributed traction load. T_USER is passed into the routine as the load direction specified as part of the element-based or surface-based distributed load definition. The vector T_USER passed out of the subroutine is used as the initial loading direction 
discussed in “Distributed loads,” Section 27.4.3 of the ABAQUS Analysis User's Manual. The direction of T_USER as defined by the subroutine should not change during a step. If it does, convergence difficulties might arise. Load directions are needed only for a nonuniform general surface traction, shear surface traction, and general edge traction. If a direction is defined for the nonuniform normal edge traction, shear edge traction, transverse edge traction, or edge moment, it will be ignored. See “Distributed loads,” Section 27.4.3 of the ABAQUS Analysis User's Manual, for details.
KSTEP
Step number.
KINC
Increment number.
TIME(1)
Current value of step time or current value of the load proportionality factor, , in a Riks step.
TIME(2)
Current value of total time.
NOEL
User-defined element number.
NPT
Load integration point number within the element or on the element's surface, depending on the load type.
COORDS
An array containing the coordinates of the load integration point. These are the current coordinates if geometric nonlinearity is accounted for during the step (see “Procedures: overview,” Section 6.1.1 of the ABAQUS Analysis User's Manual); otherwise, the array contains the original coordinates of the point.
DIRCOS
Orientation of the face or edge. For three-dimensional facets the first and second columns are the normalized local directions in the plane of the surface, and the third column is the normal to the face. For solid elements the normal points inward, which is the negative of what is defined in “Conventions,” Section 1.2.2 of the ABAQUS Analysis User's Manual; for shell elements the normal definition is consistent with the convention. For two-dimensional facets the first column is the normalized tangent, the second column is the facet normal, and the third column is not used. For three-dimensional shell edges the first column is the tangent to the shell edge (shear direction), the second column is the in-plane normal (normal direction), and the third column is the normal to the plane of the shell (transverse direction).
JLTYP
Identifies the load type for which this call to UTRACLOAD is being made. The load type may be an element-based surface load, an edge-based load, or a surface-based load. This variable identifies the element face or edge for which this call to UTRACLOAD is being made. This information is useful when several different nonuniform distributed loads are being imposed on an element at the same time. See Part VI, “Elements,” of the ABAQUS Analysis User's Manual for element face and edge identification. The load labels are shown in Table 1–2. For surface- or edge-based loading (TRSHRNU, TRVECNU, EDLDNU, EDNORNU, EDSHRNU, EDTRANU, EDMOMNU), j in the load type identifies the face or edge of the element underlying the surface.
Table 1–2 JLTYP values for surface traction and edge load labels.
| Load Label | JLTYP | Load Label | JLTYP | Load Label | JLTYP | ||
|---|---|---|---|---|---|---|---|
| TRSHRNU | 510+j | EDLDNU | 540+j | EDTRANU | 570+j | ||
| TRSHR1NU | 511 | EDLD1NU | 543 | EDTRANU | 573 | ||
| TRSHR2NU | 512 | EDLD2NU | 544 | EDTRANU | 574 | ||
| TRSHR3NU | 513 | EDLD3NU | 545 | EDTRANU | 575 | ||
| TRSHR4NU | 514 | EDLD4NU | 546 | EDTRANU | 576 | ||
| TRSHR5NU | 515 | EDNORNU | 550+j | EDMOMNU | 580+j | ||
| TRSHR6NU | 516 | EDNOR1NU | 553 | EDMOM1NU | 583 | ||
| TRVECNU | 520+j | EDNOR2NU | 554 | EDMOM2NU | 584 | ||
| TRVEC1NU | 521 | EDNOR3NU | 555 | EDMOM3NU | 585 | ||
| TRVEC2NU | 522 | EDNOR4NU | 556 | EDMOM4NU | 586 | ||
| TRVEC3NU | 523 | EDSHRNU | 560+j | ||||
| TRVEC4NU | 524 | EDSHRNU | 563 | ||||
| TRVEC5NU | 525 | EDSHRNU | 564 | ||||
| TRVEC6NU | 526 | EDSHRNU | 565 | ||||
| EDSHRNU | 566 |
SNAME
Surface name for a surface-based load definition. For an element-based or edge-based load the surface name is passed in as blank.