GSA Training General concepts

Definition of Structural Engineering Structural Engineering is the art of designing structures to withstand loads that we cannot predict using materials whose properties we cannot measure by methods of analysis that we cannot prove and to do so in a manner that ensures that the public and client are ignorant of our shortcomings

Axis set definitions x y z z θ r r z θ φ Cartesian Cylindrical Spherical

Beam element axes: non-vertical

Beam element axes: vertical

Beam element orientation: default Orientation angle = 0° No orientation node

Beam element orientation: by angle Orientation angle = 90° No orientation node

Beam element orientation: by node Orientation angle = 0° Orientation node

Beam element orientation: by node & angle Orientation angle = 90° Orientation node

Plate/Shell Element Axes: Normal

Plate/Shell Element Axes: Local Axes

Plate/Shell Element Axes: Global Axes Non-vertical

Plate/Shell Element Axes: Global Axes Vertical

2D elements Linear Parabolic QuadTri

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. u i = f(u j,u k,…)

Simple constraints Restraints u i = 0 Settlements u i = settlement

Joints Two degrees of freedom in the model are linked in a given direction u si = u mi 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 u sx = u mx - u mθz. x u sy = u my + u mθz. y u sθz = u mθz M = F x Slave F F x Master

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

Error norm The error norm is a measure of the accuracy of the solution Static analysis Solve for uf = K u Calculate residual r = f – K u Solve for ũ r = K ũ Calculate error norme = || ũ || / ||u|| Modal analysis Solve K φ – λ M φ = 0 Calculate error norme = || K φ – λ M φ || / || K φ ||

Cursor modes in Graphic Views RotateZoomVolumeSelectPolylineSculpt Geometry Click -zoom in & pan delete last volume clear & select picked item start or finish line create node if necessary, add node to topology list Drag rotatezoom boxnew inclusive volume clear & select items drag existing vertex drag existing node on grid plane Ctrl+ Click pick object point pan-toggle picked item -as Click but use node as start of next element Ctrl+ Drag Vert.: zoom Horz.: distance -new exclusive volume toggle items-- Shift+ Click reset object point zoom out & pan delete all volumes select picked item - Shift+ Drag pan--select items-- Ctrl+ Shift+ Click re-scale

GSA Views Gateway Object Viewer Table Views Graphic Views Output Views Report Views Chart Views

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 casesAnalysis CasesCombination Cases L1 (e.g. Dead Load)A1 = L1C1 = 1.35A A2 L2 (e.g. Live Load)A2 = L2C2 = 1.35A A3 L3 (e.g. Wind Load)A3 = L3C3 = 1.35A A A3 C4 = C1 or C2 or C3 Non-Linear Analysis Load casesAnalysis CasesCombination Cases L1 (e.g. Dead Load)A1 = 1.35L L2C1 = A1 or A2 or A3 L2 (e.g. Live Load)A2 = 1.35L L3 L3 (e.g. Wind Load)A3 = 1.35L L L3

K.I.S.S. It is easy to make something difficult It is difficult to make something easy “Things should be made as simple as possible, but no simpler” Albert Einstein