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GSA Essentials


GSA – Using Analytical Software

• Introduction

• Getting Started

• Structural Model Types

• Information Required

• Input Data

• Realistic Input

• Tutorial example


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


GSA - Introduction


GSA - Introduction

What is GSA?

“GSA has developed from a program for the static analysis of three-dimensional structures composed of skeletal elements, to become a complete analysis package with connection to spreadsheet, CAD and design programs.”


GSA - Introduction

What is GSA?

• Written by Oasys for Arup (but also commercially available).

• Based on Stiffness Matrix and Dynamic Relaxation Philosophies

• 3 dimensional - 6 degrees of freedom

• Not material specific


GSA – Getting Started

Graphics WindowGateway

Object Viewer



Notes are very useful for version numbers and memory prompts



Structural Type:

• Space

• Grid

• Plane

• Plane Stress

• Plane Strain

• Axisymmetric


GSA - Structural Model Types

Space

• 6 degrees of freedom:

• x,y,z translation

• xx,yy,zz rotation

• Example: Any structural with 3D load paths and loading (Stadia!)

• Note: Most common

Grid


• z translation

• xx,yy rotation

• Example: Floor plate or Bridge Deck where we are interested in out of plane forces and displacements



Plane Stress


• x,y translation

• zz rotation

• Example: Any 2D analysis such as a frame or support system where we are interested in in plane forces

Plane


• x,z translation

• yy rotation

• Example: This is used for modelling for example a 2D frame.



Axisymmetric


• x,y translation

• no rotation

• Example: A continuous problem with an axis of rotation such as a cylindrical tank or vessel

Plane Strain


• x,y translation

• no rotation

• Example: This is a 2D representation (slice) of a long problem such as a tunnel. The slice is constrained in its section unlike plane stress


GSA – Information Required

Model Structure

GSA MODEL OUTPUTINPUT


GSA – Information Required

Model Structure

GSA MODEL

INPUT

• Geometry

- Nodes

- Elements

• Properties

- Restraints

- Materials

• Loads

- Permanent

- Variable

OUTPUT

• Forces

• Deflections

• Stresses

• Graphics


GSA – Input Data

Sequence

You start to create a model in the following sequence:

• Define the nodes – Nodes are points in space represented by co-ordinates

• Define the elements - Elements are the items that are analysed. Their position in space is determined by the nodes which they are connected to.

• Assign properties – Both nodes and elements have properties.

• Define the loads – Loads can by applied to both nodes and elements


GSA – Input Data

For simple models follow the order on the bottom of the main screen

All menus are duplicated in the Gateway


GSA – Input Data

Method

There are three ways of inputting data into GSA to define the nodes and elements:

• Manually – inserting data in tabulated format


GSA – Input Data


GSA – Input Data

Method



• Sculpting – using the sculpt toolbar you can define the geometry in the graphics window


GSA – Input Data

SCULPT TOOLBAR


GSA – Input Data

Method



• Sculpting – using the sculpt toolbar you can define the geometry in the graphics window

• Copying – alternatively duplicate existing geometry to extend the model


GSA – Input Data


GSA – Input Data

Properties

• Node Properties• Restraints

Free Pin Encastre

Translational: X Y Z

Rotational: XX YY ZZ

Six degrees of freedom:


GSA – Input Data

Properties

• Node Properties• Restraints• Constraint axis

- The default constraint axis for a node is the GLOBAL axis.

- An user defined axis can be created and used to constrain a node so it can have support conditions related to the new axis.

GSA uses the right-hand rule to define axes.


GSA – Input Data

Global Axes

User Axis - created to constrain nodes for section of building that is at an angle on plan


GSA – Input Data

Properties

• Element Properties• Element Type

Main Types:• Beam – bending, torsion and

axial• Bar – axial only• Tie – tension only (non-linear)• Strut – compression only (non-

linear)

Other types:• Links• Mass• 2D (Quad 4, Quad 8, Tri 3 and

Tri 6)• Cable• Spacer

Beam

Bar

Struts


GSA – Input Data

Properties

• Element Properties• Element Type• Section property

- The section property defines the element’s material, cross-section, etc


GSA – Input Data

Properties

• Element Properties• Element Type• Section property• End releases

- End releases define the restraints at the end of the element in term of its local axis

- As with nodes there are six degrees of freedom.

Simply supported connection

Rotation released about the local yy and zz axis of the element (indicated by cross-hairs)


GSA – Input Data - Properties

• Element Properties• Element Type• Section property• End releases• Orientation

• Orientation is used to alter the local axis of an element.

• The element y and z axes are rotated from their default positions about the element x axis by the orientation angle (Beta).

Revised Local Axis

Global axis

Default Local Axis

X

x Z

Y

y' z y

1

2

X

x

Z

Y

z' z

y

1

2


GSA – Input Data

Properties

• Element Properties• Element Type• Section property• End releases• Orientation

- Alternative to Beta angle is to orientate elements to a node

x

z

y ŷ

ŷ

ŷŷ

ŷ

ŷ

ŷ


GSA – Input Data

Loads• Beam Loading

- Beam Load

- Prestress

- Distortion

- Thermal Load


GSA – Input Data

Loads• Beam loading

• Gravity

?


GSA – Input Data

Loads• Beam loading

• Gravity

• Node Loading - Node Loads – Fx, Fy, Fz, Mxx, Myy, Mzz applied at node in node axis directions

- Settlement which is a displacement or rotation applied at node.

Note that a node should be restrained in a direction before a settlement is applied


GSA – Appropriate Modelling

Model Structure

GSA MODEL

RUBBISHOUT

RUBBISH IN



Why did thecolumns crackon site?



If the analysis model doesn’t reflect what’s actually built in terms of DETAILING then it may be meaningless.

Analysis should never be carried out in a vacuum, oblivious to the practicalities of construction, which in themselves may vary from region to region.



Make sure that you design for all the induced forces



• Sleipner A Offshore Platform



Ensure that you model is sufficiently detailed to get accuracy

Make sure that you model is not over-complicated so that mistakes are not missed

i.e. Design your model to give you the required results


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

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