www.oasys-software.com gsa training general concepts

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www.oasys- software.com GSA Training General concepts

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Page 1: Www.oasys-software.com GSA Training General concepts

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GSA Training

General concepts

Page 2: Www.oasys-software.com GSA Training General concepts

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Axis set definitions

x

y

z z

θ

r

r

z

θ φ

Cartesian Cylindrical Spherical

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Beam element axes: non-vertical

X

x

Z

Y

z' z

y

1

2

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Beam element axes: vertical

X

x Z

Y

y' z y

1

2

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Beam element orientation: default

Orientation angle = 0°

No orientation node

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Beam element orientation: by angle

Orientation angle = 90°

No orientation node

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Beam element orientation: by node

Orientation angle = 0°

Orientation node

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Beam element orientation:by node & angle

Orientation angle = 90°

Orientation node

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Plate/Shell Element Axes: Normal

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Plate/Shell Element Axes: Local Axes

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Plate/Shell Element Axes: Global AxesNon-vertical

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Plate/Shell Element Axes: Global AxesVertical

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2D elements

Line

arP

arab

oli

cQuad Tri

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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]

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OK: GSA automatically removes rotational freedom

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

Element releases

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Element offsets:Beam between columns

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Element offsets:Edge beam

Note:

• Element offsets are specified in global directions.

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

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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,…)

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Simple constraints

•Restraints• ui = 0

•Settlements• ui = settlement

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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

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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

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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

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Grid load – one way spanning

span direction

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Grid load – multi way spanning

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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

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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

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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