INISTRS

Bulk Data Entry Defines initial stress values and settings for elements in nonlinear analysis.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
INISTRS	`ID`	`ETYPE`	`CIDA`

The following continuation line(s) are optional when ETYPE = SHELL. They can be used to define the sections where initial stress values are applied and they need to be given before the continuation lines starting with EORS.

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
	`SECT`	`NSEC`	`SEC1`	`SEC2`	`SEC3`	etc.

The following continuation lines are used to define initial stress values for an element or a set of elements. They are mandatory and can be repeated as required.

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
	`EORS`	`EID`/`ESETID`	`CIDB`
	`VALUE`	`STRS1`	`STRS2`	`STRS3`	etc.

When ETYPE = SHELL and the SECT line is given, each VALUE line defines initial stress for a shell section; and so, for any shell element (with EID) or shell element set (with ESETID), the number of VALUE lines must be NSEC.

Example 1

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
INISTRS	7
	`ELEM`	1001
	`VALUE`	3.5e4	-1.5e3	0.0	3.0e3	0.0	2.0e3
	`ESET`	200
	`VALUE`	3.0e4	-1.5e3	0.0	3.0e3	0.0	2.0e3

Example 2

(1)	(2)	(3)	(4)	(5)
INISTRS	8	SHELL	-1
	`SECT`	2
	`ELEM`	101
	`VALUE`	3.5e4	0.0	0.0
	`VALUE`	-3.5e4	0.0	0.0
	`ELEM`	102
	`VALUE`	3.0e4	0.0	0.0
	`VALUE`	-3.0e4	0.0	0.0

Definitions

Field	Contents	SI Unit Example
`ID`	Unique identification number. No default (Integer > 0)
`ETYPE`	Element type which initial stress is applied. Blank (Default) The initial stress is applied for a collection of solid and/or shell elements. SHELL Applying initial stress for a collection of shell elements specifically.
`CIDA`	Coordinate system identification number, or stress components flag. Blank (Default) The initial stress components are defined in material coordinate system for solids and in element coordinate system for shells. -2 Material coordinate system -1 Element coordinate system 0 Basic coordinate system Integer > 0: user-defined (prescribed) coordinate system.
`SECT`	Keyword indicating the start of continuation line(s) for the shell sections.
`NSEC`	Number of shell sections where initial stress is applied for shell elements. No default (2 ≤ Integer ≤ 6)
`SEC(i)`	Through-thickness position for the shell sections. `SEC(i)` must be either all blank or all non-blank, i.e., the number of `SEC(i)` must be either `NSEC` or zero; and `SEC(i)` must be given in ascending order if all non-blank. Blank implies that the sections are located uniformly through the shell thickness, starting at the bottom surface and ending at the top surface. A Real value is the multiplier to shell thickness to get the location. -0.5 means the bottom surface of the shell element and 0.5 means the top surface. The through-thickness positive direction, pointing from the bottom surface to the top surface, is determined by the right-hand rule and the order in which the grid points are listed on the connection entry. It is same as the convention for `Z1`/`Z2` of PSHELL. <Blank, or -0.5 ≤ Real ≤ 0.5> Default = Blank
`EORS`	Flag indicating an element, or element SET is selected in the following field. ELEM (Default) Element is selected ESET Element SET is selected
`EID`/`ESETID`	Identification number of the element or element SET to which the stress values apply. No default (Integer > 0)
`CIDB`	Coordinate system identification number or stress components flag. Blank (Default) Implies that `CIDA` is used; -2, -1 or Integer ≥ 0 suppresses `CIDA`. -2 Initial stress components are defined in material coordinate system -1 Element coordinate system 0 Basic coordinate system Integer > 0: user-defined (prescribed) coordinate system.
`VALUE`	Keyword indicating the start of a continuation line for the stress components.
`STRS(i)`	Stress components 4 No default (Real)

Comments

INISTRS and ISTSADD should not have the same ID.
The INISTRS Bulk Data Entry is selected by the Subcase Information command INISTRS.
Initial stress is supported for solid elements (CHEXA, CPENTA, CPYRA and CTETRA) and shell elements (CQUAD4, CTRIA3, CQUAD8 and CTRIA6), only.
Initial stress is currently not supported for:
- solid elements with hyperelastic material in LGDISP analysis
- solid elements with user-defined material in LGDISP analysis
For initial stress of solid elements, 6 stress components are needed for each VALUE line and they are:

STRS1

$σ$ _xx

STRS2

$σ$ _yy

STRS3

$σ$ _zz

STRS4

$σ$ _xy

STRS5

$σ$ _yz

STRS6

$σ$ _zx

Where, x, y and z are the axes in the coordinate system selected via CIDA and CIDB.
For initial stress in element or material coordinate system of shell elements, 3 stress components are needed for each VALUE line and they are:

STRS1

$σ_{11}$

STRS2

$σ_{22}$

STRS3

$σ_{12}$

Where, 1 and 2 are the first two local directions in the element or material coordinate system.

For initial stress in the basic or a prescribed coordinate system of shell elements, 6 stress components are needed for each VALUE line and they are:

STRS1

$σ$ _xx

STRS2

$σ$ _yy

STRS3

$σ$ _zz

STRS4

$σ$ _xy

STRS5

$σ$ _yz

STRS6

$σ$ _zx

Where, x, y and z are the axes in the basic or prescribed coordinate system.