www.oasys-software.com gsa training general concepts

www.oasys-software.com

GSA Training

General concepts


Axis set definitions

x

y

z z

θ

r

r

z

θ φ

Cartesian Cylindrical Spherical


Beam element axes: non-vertical

X

x

Z

Y

z' z

y

1

2


Beam element axes: vertical

X

x Z

Y

y' z y

1

2


Beam element orientation: default

Orientation angle = 0°

No orientation node


Beam element orientation: by angle


No orientation node


Beam element orientation: by node


Orientation node


Beam element orientation:by node & angle


Orientation node


Plate/Shell Element Axes: Normal


Plate/Shell Element Axes: Local Axes


Plate/Shell Element Axes: Global AxesNon-vertical


Plate/Shell Element Axes: Global AxesVertical


2D elements

Line

arP

arab

oli

cQuad Tri


Element Types

•0D• Mass• Ground Spring

•1D• Beam• Bar• Strut• Tie• Spring• Link• Cable• Spacer

•2D• Plane Strain• Plane Stress• Flat Plate• Flat Shell• Fabric• [Curved Shell]


OK: GSA automatically removes rotational freedom

No good: GSA is fooled into allowing nodes to rotate about longitudinal axis

Element releases


Element offsets:Beam between columns


Element offsets:Edge beam

Note:

• Element offsets are specified in global directions.

• Element axes are with respect to the flexible part of the element.


Constraints

•Constraints are where a condition is applied to a degree of freedom in the model:

• Restraints• Settlements• Joints• Rigid constraints

•These constraints can all be represented as constraints equations.

• ui = f(uj,uk,…)


Simple constraints

•Restraints• ui = 0

•Settlements• ui = settlement


Joints

• Two degrees of freedom in the model are linked in a given direction

• usi = umi

• Joints relate the displacement/force at the slave degree of freedom s to the master degree of freedom m.

• Joints are an “artificial” feature and can be misused.

• Joints may not give an equilibrium condition

Master

Slave

F

moment lost

F


Rigid constraints

•Rigid constraints are a set of constraint equations that maintain equilibrium

•For a rigid constraint in the x-y plane the equations are

• usx = umx - umθz . x

• usy = umy + umθz . y

• usθz = umθz

M = F x

Slave

F

F

xMaster


Grid load

•Load applied to a position on a grid plane.

•Load is not applied directly to elements.

•Load is distributed to the elements surrounding the load depending on the span type:

• One way• Two way – for simple load conditions• Multi way – for general load conditions

•Distributed load is in equilibrium with applied load


Grid load – one way spanning

span direction


Grid load – multi way spanning


Lists and Sets

•In graphic view – select elements• Edit | Copy (Ctrl+C) puts element list onto the clipboard• Edit | Paste (Ctrl+V) the list where required

•Or• Edit | Save Selection as List• Saved lists can be used for:

•Load application•Result output•Graphical display


Cases and Combinations

•Load Cases• Loads are assigned to a Load Case• Referenced as L1, etc

•Analysis Cases• Analyse single or multiple load cases for results• Load factors can be applied: 1.35L1+1.5L2• Referenced as A1, etc

•Combination cases• Combine multiple linear analysis cases• Load factors can be applied: 1.35A1+1.5A2• Envelope Analysis and Combination cases


Cases and Combinations

Linear Analysis

Load cases Analysis Cases Combination Cases

L1 (e.g. Dead Load) A1 = L1 C1 = 1.35A1 + 1.5A2

L2 (e.g. Live Load) A2 = L2 C2 = 1.35A1 + 1.5A3

L3 (e.g. Wind Load) A3 = L3 C3 = 1.35A1 + 1.5A2 + 0.75A3

C4 = C1 or C2 or C3

Non-Linear Analysis

Load cases Analysis Cases Combination Cases

L1 (e.g. Dead Load) A1 = 1.35L1 + 1.5L2 C1 = A1 or A2 or A3

L2 (e.g. Live Load) A2 = 1.35L1 + 1.5L3

L3 (e.g. Wind Load) A3 = 1.35L1 + 1.5L2 + 0.75L3

www.oasys-software.com gsa training general concepts

Documents

complateshell element

orientation nodewww

local axes

constraints equations

master degree of freedom

defaultorientation angle

nodeorientation angle

node angleorientation