This section describes some of the main modelling features of SPACE GASS. For a more general overview of the features and capabilities of the program, refer to Technical Overview.

Input Methods
SPACE GASS offers a number of data entry methods, including graphical input, datasheet input, sructure wizard input and text file input. All methods operate on a common database and can be used together during the input or editing of a job. In fact, it is uncommon for a single method to be used exclusively during the input of a job.

• Graphical Input
  One of the great advantages of inputting a structure graphically is that you can see exactly what is happening at all times. If you make a mistake, the mistake becomes immediately obvious and you can correct it straight away.
  
  Graphical input offers a full set of graphics commands that enable virtually all parts of the structural, loading and design data to be input or edited graphically. The list of graphics commands includes draw, move, rotate, copy, mirror, erase, stretch, subdivide, intersect, connect, merge, renumber, attributes, restrain, section, material, constrain, load, area load, moving load, combine, mass, steel member, steel connect, show, label, annotate, redraw, zoom, pan, viewpoint, filter, query, grid, snap, ortho, attach, plane, coordinates and scale.
  
  
  
  
• Datasheet Input
  An enhanced form of spreadsheet input, called datasheet input, is available for all types of data. While offering all of the advantages of spreadsheet input such as a tabular display and row or column editing, the datasheet view window allows you see all of the data in a row, even if the row is wider than your screen. Special buttons for generation and other data specific items such as section property shape input or material library input make datasheet input indispensable.
  
  
  
  Highlight multiple rows in a datasheet and then edit them all simultaneously by typing into just one field.
  
  
  
  
• Structure Wizard
  The Structure Wizard provides a very fast means of inputting data into SPACE GASS for standard structures such as continuous beams, beams on elastic foundation, trusses, portal frames, rectangular frames, 3D multi-storey frames, circular frames, etc. After selecting the structure type, you are required to answer some basic questions relating to the frame geometry, supports, loads, etc. The complete structural model is then generated automatically for you. You can then modify or add to the model as required.
  
  
  
  
  
  
• Text file input
  SPACE GASS normally stores the data for each job in a compressed binary file, however it can also import from and export to standard text files. This facility is extremely useful for transferring data between SPACE GASS and other programs such as pre-processor data generators or post-processor design or drafting programs. It is also useful for those of you who still prefer to type your data into a text file rather than using the model generation facilities within SPACE GASS.

Static Analysis
SPACE GASS uses a classic stiffness matrix method of analysis combined with a wavefront matrix solver in its static analysis module. The wavefront analysis method is the latest technology in matrix solution techniques which offers high capacity, high speed and low sensitivity to badly numbered structures. Both linear and non-linear modes are included as standard features. Non-linear mode offers both of the P-delta effects together with axial shortening. You have full control of convergence criteria, load stepping, cable damping and wavefront optimization. All calculations are to 64 bit double precision for maximum accuracy.

Dynamic Frequency Analysis
The SPACE GASS dynamic frequency analysis module calculates the natural frequencies, periods and mode shapes of 2D or 3D structures. Automatic structure self mass calculation is available, together with analysis of multiple load cases, and graphical mode shape animation.

Dynamic Response Analysis
Taking dynamic analysis a step further, SPACE GASS also offers an earthquake response spectrum analysis module. This module takes the results of a dynamic frequency analysis and combines them with earthquake response spectra to calculate displacements, forces, moments and reactions. The results from a response spectrum analysis can be printed, displayed graphically or used in the various design modules in similar fashion to static analysis results. In addition, combination load cases can contain both static and spectral load cases.

Features include a graphical spectral curve editor, the ability to selectively choose the mode shapes to be included in each spectral load case, analysis of multiple spectral load cases, optional automatic scaling of base shear, signing of the results to match the predominant mode shape or a user selected mode shape, calculation of all mass participation factors, and the choice of SRSS or CQC mode combination methods.

Buckling Analysis
This module enables SPACE GASS to perform a buckling analysis (also known as elastic critical load analysis or stability analysis) on any 2D or 3D structure to determine its member effective lengths and its buckling load factor (the amount by which the applied loads must be factored to reach the buckling load) for each load case. The buckling mode shapes can be shown graphically.

Calculation of the buckling modes and associated load factors is achieved by a continuous (as opposed to linear) eigenvalue method which means that the solution is exact and does not rely on subdivision of members to achieve accurate results.

Effective lengths can be transferred automatically into the member design modules.

Wavefront Analysis Optimizer
For each type of analysis, the wavefront optimizer can drastically reduce the analysis time and keep the program’s memory and disk space requirements to a minimum. Time and space savings of up to 100 fold can be achieved with this module. It offers you the freedom to number your structure logically, rather than having to comply with an optimal analysis numbering sequence.

Steel Member Design
The SPACE GASS steel member design module allows you to design or check selected steel members or an entire steel structure for compliance with a steel structures code. Options include grouping of analysis members, top flange loading, intermediate flange restraints, eccentric end connections, support for most section types, strength and slenderness checks, multiple load cases, analysis-design iterations, and full integration with analysis. Versions of this module are available for a number of international steel structures codes including AISC-LRFD, AISC-ASD, EUROCODE, AS4100, AS1250, AS3990, NZS3404, BS5950 and SABS0162.

Get an instant idea of the parts of your model that have failed the code check by turning on a color-coded design results display.

Steel Connection Design
The SPACE GASS steel connection design module offers full connection design to AS4100 for a wide variety of connection types in any general shaped structure. Options include alignment control, size limit control, design of bolts, welds, plates, cleats and stiffeners, editable bolt, weld and plate libraries, multiple connections, multiple load cases, and full integration with analysis. Fully detailed and annotated drawings of each connection can be produced, viewed and printed from SPACE GASS.

Concrete Column Design
The SPACE GASS concrete column design module allows you to design or check selected concrete columns at the click of a button. The module is fully integrated into SPACE GASS (as well as being available in stand-alone form) allowing the easy transfer of loads, properties and member geometry. The module has the ability to perform section and member checks for columns to AS3600 with code checking capabilities for more codes to follow. It can work in check or design modes and can consider many different shapes, circular and rectangular voids, moment magnification (slenderness effects), compression and tension, multiple reinforcement curves, dual consideration of biaxial moments, and many more features while being very easy to use and configure.

Steelwork Drafting and CAD Interface
A CAD interface module is provided for two-way DXF transfers of drawing data between SPACE GASS and CAD programs such as AutoCAD and MicroStation. You can use it to export plans, elevations, cross sections, member schedules, and connection drawings to your CAD program. Alternatively, it enables you to import into SPACE GASS the basic frame geometry from a CAD drawing.

Units
Mixed units can now be used and you can specify different units for different parts of the input or output data. For example, you could specify lengths in feet, section properties in inches, moments in Kip-feet and stresses in Psi. Alternatively, you could have lengths in m, section properties in mm, strengths in MPa, moments in kNm and translations in cm. You can even mix imperial and metric units.

Libraries
Libraries of standard sections, materials, bolts, plates, welds, reinforcing bars, spectral curves and vehicles are supplied with SPACE GASS. Simply navigate through the editor's library tree to access and retrieve the required data quickly and easily. You can also create custom libraries, edit them and drag data from one library to another.

Renumbering
When inputting or editing a structure, you can opt for full numbering control, or you can allow the program to automatically number the structure for you.

In addition, you can use the built-in renumbering facility to renumber your nodes and members to any desired scheme. You can renumber individual nodes or members, or you can window a group of nodes or members and then nominate a starting number, numbering increment, and numbering direction. SPACE GASS automatically adjusts restraints, constraints, loads, and design parameters to allow for the new numbering sequence.

Filters
You can limit what you see graphically by defining filters that can then be selected from the main toolbar.

Multiple Viewports
SPACE GASS allows you to display up to four different viewports (windows) on the screen at one time. Each viewport is independant of the others so you can show different subsets of the structure, diagrams, restraints, 3D section geometry, etc in each. This feature makes it very easy to interprete and work on small and large models alike.

Full 3D Geometry View
One of the most useful visual checks of your structural model is the full 3D geometry view, showing the full 3D geometry of the structure from any viewpoint with all member flanges, webs and plates clearly visible. The 3D geometry is fully rendered and has hidden lines removed, resulting in quite realistic views of the structure. You can use it to verify that members are orientated as you intended, you can check for clashing of members, and you can show architects and other non-engineers how the structure will look in real life.

Tension-only and Compression-only Members
Structures such as trusses, towers or braced frames, usually contain ties or braces which are unable to resist compression. For these situations, SPACE GASS offers a tension-only facility which allows you to accurately model the non-linear behaviour of these members. During the analysis phase, any tension-only members which go into compression are disabled for the next analysis iteration. Any disabled tension-only members which subsequently revert back to tension are re-enabled and the process continues until full convergence is achieved.

Conversely, for situations such as where a member bears on another but where there are no bolts or welds to prevent lift-off, a compression-only facility provides the solution. It operates in similar but reverse fashion to the tension-only facility.

Master-Slave Constraints
When modelling a structure, it is often useful to be able to connect nodes together with direct links rather than with members. For example, in order to model the diaphragm action of a rigid floor slab, you could join the perimeter nodes together with a grid of floor slab members or, better still, you could use the master-slave constraints facility to nominate one of the nodes as the master and the other perimeter nodes as in-plane slaves of the master.

The degree of constraint between a slave node and its master can be varied from just one to all six degrees of freedom. Constraints do not suffer from the ill-conditioning problems that rigid members sometimes have.

Catenary Cable Element
The analysis of cable members requires special treatment because of their pure axial capacity, large deflections, and highly non-linear behaviour. The SPACE GASS catenary cable element module uses a large deflection catenary stiffness matrix to accurately model cable behaviour in structures such as guyed masts or cable nets. In addition to being able to apply node loads, thermal loads and uniformly distributed loads to cable members, you can also nominate an actual cable length and an initial pre-tension.

Elastic Supports
In addition to rigid, sliding and pinned supports, SPACE GASS can model translational and rotational spring supports. The six degrees of freedom of a support node can have any combination of fixed, released, deleted or spring restraints applied.

Semi-Rigid Joints
The connection of SPACE GASS members to their end nodes can be modelled as rigid, pinned, sliding or semi-rigid. The six degrees of freedom of a member end connection can be specified as any combination of fixed, released or semi-rigid.

Member Offsets
The member offsets feature lets you offset a member's end nodes away from the physical end of the member. The offset can be in any direction and does not have to be aligned with the member's longitudinal axis. A rigid link is assumed to exist between the end of the member and its offset end node.

This feature is extremely useful for modelling situations where the longitudinal axes of two members to be connected do not meet at a point. For example, if two beams of different depths are to be connected end-to-end so that their top flanges line up, a member offset can be used to model the step where the beams meet. Similarly, the offsets which occur in trusses when the web brace members meet at some distance from the chord's longitudinal axis can be easily accomodated with member offsets.

Loads
Being able to accurately reflect real life loading conditions in the structural model is crucial to obtaining accurate results from a structural analysis program.

• General
  The types of loads that SPACE GASS can model are: node loads (forces and moments), prescribed node displacements (translations and rotations), member concentrated loads (forces and moments), member distributed forces (uniform, triangular and trapezoidal), member distributed moments (uniform, triangular and trapezoidal), thermal loads, prestress loads and self weight. All member loads (where appropriate) can be applied in either member or structure axes. Loads of different types can co-exist in primary load cases, which in turn can be combined and factored to form combination load cases.
  
  
• Area loads
  You can define one or more areas by making a selection of members graphically. Area loads are then calculated and applied to the members.
  
  
  
  
• Moving loads
  A moving load generator lets you specify moving load scenarios, each of which can contain one or more vehicles with multiple wheels travelling along paths that consist of straight and/or curved segments. You can also specify the speed, initial delay, time interval and load factor for each vehicle. Libraries of standard vehicles are supplied and you can create your own custom vehicles and libraries.
  
  Wheel loads are automatically distributed to the adjacent members as member and/or node loads. After the analysis, influence lines can be generated.
  
  
  
  
  
  
• Combinations
  Combination load cases can be defined using primary load cases or other combination load cases.
  
  
  
  
• Load case management
  Manage your load cases by copying, deleting or renumbering entire load cases in a single operation.
  
  

Shape Builder
The SPACE GASS shape builder is a graphical tool that calculates section properties for any shaped cross section. You can use it to build up a cross section from multiple sub-shapes, each of which can be independently positioned, orientated and dimensioned as required. The final shape can then be used in the analysis and design parts of the program.

The shape builder graphics window shows the cross section and its section properties changing dynamically as you manipulate it. Sub-shapes can be read from a SPACE GASS section library, input by typing in boundary coordinates, or obtained by selecting and dimensioning a standard shape.

Query Options
There are a number of methods at your disposal for querying the structural model or the analysis results. By simply clicking on a member or a node you can open an information window that gives a full set of information about the selected item. The entire structural model can also be labelled and colour coded in various ways to show more information at a glance.

When querying analysis results, you can move a crosshair along any member and obtain a dynamic display of the deflections, forces and moments at the crosshair location. Alternatively, you can click on a member to open a scrollable results window which gives details of the deflections, forces and moments along the member for all load cases.

Cleanup
Remove annoying analysis error messages at the click of a button using the "Clean-up" feature. The clean-up removes items such as restraints, constraints, offsets and loads that are not connected to any nodes or members. It can also be used to remove unused sections or materials, or merge nodes that are very close together.

Saved Views
You can save up to 100 different views of your model, each with its own set of scales, viewpoint, filtering, superimposed diagrams, etc. Saved views can be quickly recalled and displayed using the toolbar combo box.

Enveloping
You can create an envelope of selected load cases for any diagram types by clicking on the envelope button.

Individual load cases


Envelope of load cases

Tapered Members
Quickly generate tapered members with or without haunches using the taper feature.

Program Output
All analysis and design results are presented in a clear and concise report form for direct insertion into a set of computations. The report viewer lets you see any of the input or output data in an easy-to-use scrollable form. The report viewer also includes a tree structure on the left-hand side that allows you to see exactly what is included and then quickly navigate to any part of the data. You have full control over numeric formatting, margins, fonts, columns per page, etc.

SPACE GASS also lets you produce loading diagrams, deformed shapes, bending moment diagrams, shear force diagrams, axial force diagrams and mode shapes on the screen or printer. Multiple load cases and diagram types can be superimposed together if desired.

Text and graphical output can be directed to PDF, HTML, TXT or BMP files without you having to re-configure your printer or report settings.



The following display shows a PDF file produced by SPACE GASS and viewed in Adobe Acrobat Reader. Note that bookmarks for easy navigation are included in the PDF file. The PDF format in particular offers a very convenient means of generating a report that can be distributed to others for viewing or printing.

Merging Jobs
Other jobs can be opened and merged with the current job. You can control the numbering and the insertion point of the job being merged.

Interfacing with MS-Access, MS-Excel and MS-Word
Data can be imported from or exported to MS-Excel, MS-Access and MS-Word.

Running Other Programs from SPACE GASS
An external macro such as another program, batch file or MS-Excel/Access macro can be run from within SPACE GASS.

Running SPACE GASS from Other Programs
SPACE GASS can be controlled externally from another program or batch file using a script file.

Context Sensitive Help and On-line Manual
The SPACE GASS user manual is a comprehensive 600+ page document which is supplied in PDF format that you can view or print, and as an on-line help document. It contains full instructions for operating the program together with numerous worked examples, hints, tips and techniques.

When accessed from the help menu it becomes a fully cross referenced on-line manual that you can browse through or search. In addition, it forms the programs's context sensitive help system that is activated whenever you request help from within the program.