CQUAD4

Bulk Data Entry

CQUAD4 – Quadrilateral Element Connection

Description

Defines a quadrilateral plate element (QUAD4) of the structural model.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
CQUAD4	EID	PID	G1	G2	G3	G4	Theta or MCID	ZOFFS
			T1	T2	T3	T4

Example

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
CQUAD4	111	203	31	74	75	32

Field	Contents
EID	Unique element identification number. No default (Integer > 0)
PID	Identification number of a PSHELL or PCOMP property entry. Default = EID (Integer > 0)
G1,G2,G3,G4	Grid point identification numbers of connection points. No default (Integers > 0, all unique)
Theta	Material orientation angle. Default = 0.0 (Real)
MCID	Material coordinate system identification number. The x-axis of this coordinate system is projected onto the element to define the x-axis of the material coordinate system. If MCID = 0, it specifies the basic coordinate system. MCID must be an integer > 0. If blank, Theta = 0.0 is used, unless the material referenced by the element is isotropic (MAT1) – then MCID = 0 is used. See comments 4 and 5. Default is Theta = 0.0 (Integer >0)
ZOFFS	Offset from the plane defined by element grid points to the shell reference plane. See comment 9. No default (Real)
Ti	Thickness of the element at the grid points. Overrides the thickness specified on the PSHELL entry. The default for $image\t2-t4.gif$ (Real > 0.0 or blank)

Comments

Element identification numbers must be unique with respect to all other element identification numbers.
Grid points G1 through G4 must be ordered consecutively around the perimeter of the element.
All of the interior angles must be less than 180°.
The x-axis of the element coordinate is aligned with side 1-2 of the shell element.
Stresses are always output in the material coordinate system. For isotropic elements (elements referencing MAT1) with blank Theta/MCID, the material coordinate system is aligned with the x-axis of the basic coordinate system (or the y-axis if the element is in the YZ plane) i.e. MCID = 0. For anisotropic elements with blank Theta/MCID, THETA = 0.0 is used, and the material coordinate system is aligned with the element coordinate system.

$image\cquad4_1.gif$
Orientation when Theta (real value) is entered in 8th field

$image\cquad4_2.gif$
Orientation when MCID (integer value) is entered in 8th field

If Ti is applied, the average of all four thicknesses is used as the element thickness.
Size optimization of the property referenced by PID is not possible if Ti values are defined here. If the property referenced by PID is selected as a region for free-size optimization, then any Ti values defined here are ignored.
If Ti is present, the PID cannot reference PCOMP data.
Shell elements can be offset from the plane defined by element nodes by means of ZOFFS. In this case all other information, such as material matrices or fiber locations for the calculation of stresses, are given relative to the offset reference plane. Similarly, shell results, such as shell element forces, are output on the offset reference plane.

A positive value of ZOFFS implies that the shell reference plane is offset a distance of ZOFFS along the positive z-axis of the element coordinate system. Note that when ZOFFS is used, both MID1 and MID2 must be specified on the PSHELL entry referenced by this element (otherwise, singular matrices would result).

In OptiStruct, offset is applied to all element matrices (stiffness, mass, and geometric stiffness), and to respective element loads (such as gravity). Hence, ZOFFS can be used in all types of analysis and optimization in OptiStruct. Note, however, that for first order shell elements (CQUAD4 and CTRIA3), the offset operation does not correct for secondary effects, such as change of shell area when offset is applied on curved surfaces. Hence, the value of ZOFFS should be kept within a reasonable percentage (10-15 percent) of the local radius of curvature.

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