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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