DEFLECT: A Computer Aided Learning Package For Teaching Structural Design- Phase Two

C. MacCallum and R. Hanna

The Mackintosh School of Architecture, Glasgow School of Art, 167 Renfrew Street, Glasgow, G3 6RQ, Scotland, UK.

 

Abstract

This paper reports on Phase Two of a SHEFC funded project jointly carried out by the Department of Civil, Structural and Environmental Engineering, University of Paisley, the Mackintosh School of Architecture, and Lamp Software. The project aims to build a computer-assisted learning package on the response of structures to load. The software will be used as an interactive teaching tool for both architectural and engineering students.

The package has four levels: Beginners (Level 1), Intermediate (Level 2) and Advanced (Levels 3 and 4). The first two levels have been completed after continuous feedback from both institutions. Level 1 is geared towards architectural and engineering students to help them understand structural behaviour of building components, such as deflection. Level 2 is a graphical editor that enables students to draw precisely the structure of their designs, investigate the deflection of structural members and identify areas of tension and compression. Levels 3 and 4 are a design tool which is aimed at architectural and civil engineering students where they can design and analyse realistic structures by choosing structural members from a library, and specify materials and multiple loads.

Phase One of DEFLECT was presented in the 14th ECAADE conference , which was held at the University of Lund, Sweden. In Phase Two, the range of structural examples was expanded to include typological classics. This was accompanied by additional teaching and learning material. The package was enlarged to include bending moment and shear force diagrams, tapered and curved members, and additional materials such as glass.

 

Introduction: Structures in the Architectural Curriculum

In the course of more experience of architectural teaching and examining than one cares to admit, it has been both interesting and rather depressing to note how many architecture students, even in their final year, have clearly not understood basic structural concepts, or how structures work. There appears, in particular, to be widespread difficulty in grasping whether something is in tension or compression, and the suggestion that diagonals in a truss may need to change direction in mid-span can be met with astonishment, aesthetic objections, embarrassment, or even tears. Given the desirability of a productive fusion of structure and concept, the major importance of structure as one of the factors the designer can exploit, this seems strange, but it is demonstrably the case.

Clearly, whatever knowledge "traditional" teaching methods may have imparted, they have too frequently failed to produce understanding. The use of simple models which demonstrate basic structural concepts with materials like thread, or balsa wood, or paper, are immensely useful. These studies tend to be done in the early years, and the general relevance of their lessons may not always be understood, but for whatever reasons - and many are possible - it is sadly clear from annual degree shows, not to mention the professional press, that the lessons do not always stick.

It is response to this interesting if rather exasperating state of affairs that the DEFLECT project was conceived. As with other interactive, computer aided learning packages, it allows students to proceed at their own pace, whether motivated by a curiosity about what happens if one "does things" to a structure - loads it, pushes it, or changes the material of which it is made, or by "the need to know".

Discussions with engineering colleagues revealed, interestingly, that the problem was by no means confined to architects, and it was felt that such a package would benefit engineering as well as architectural education. Initial student trials have been encouraging, but we shall have to await future degree shows for a fuller story.

 

The Modelling And Illustration Of Structural Behaviour

The graphic communication of structural theory has grown greatly in complexity since Leonardo da Vinci’s masterly illustrated studies on Equilibrium, and Galileo’s analysis of Force and Moment Equilibrium in a cantilevered.[1] In nineteenth century France, where the theory and application of iron construction was evolving rapidly, and heated debate raged about the relationship between structure and architecture, the graphic communication of structural ideas was particularly sophisticated, but the advent of computerised calculation and graphics in our time has transformed the field. Not since the invention of children’s building blocks has there been quite such a powerfully responsive educational tool for examining the consequences of one’s structural decisions as that offered by CAL.

Despite the very limited number of mainly computerised structural design tools that aid design, an attempt is made here to review them. For example, the 'Pin, Rigid, Plastic and Grid', programme developed by Gardner[2] at Kingston University is a useful programme, but it has not been designed as a tool for teaching and/or learning structures. The programme is written for the DOS rather than the WINDOWS operating system and this limits the possibilities of 'dynamic linking' to and 'object embedding' from other WINDOWS applications such as spreadsheets, word-processing and databases.

The CADS programme[3], on the other hand, is very professional in its outlook and has an attractive user interface, and it can analyse three dimensional as well as two dimensional structures. Its usage in architectural education and practice is, however, hindered by its complexity and incompatibility with the design process.

The QSE Space for Windows programme[4] , which has over 2500 users world wide, is a powerful structural analysis software designed by engineers for engineers. This package can generate very quickly 2D and 3D frames and use any material, e.g. steel, concrete, timber. It can also draw tapered and curved members, and display bending moment, shear force, stress and axial diagrams for individual elements and full structural members.

An interactive programme for structural simulation and design, CASDET (Computer Aided Structural Design Education Tool), aimed at educating architects and civil engineers, has been cited in the literature. Developed by Piccolotto and Rio[5] on an HP workstation, it can be ported to a PC running Windows NT, and consists of an interface and five modules (tools). The Graphic tool is a graphic editor that allows students to draw structural members, import and edit pictures. The Structures tool enables the creation and analysis of complex structures and change the properties of structural members. The Mathematical tool enables mathematical operations to be performed. The CAI-tool provides teachers with standard methods on how to create computer based exercises on structures. The Video-tool is for animation and visualisation, and can present laboratory experiments on members and show photorealistic images of existing buildings and structures. The 3-D tool, the most advanced module, allows the creation of 3-D objects and the exploration of the behaviour of skeletal structures in space.

 

The DEFLECT Programme

The uses of computers in education have increased greatly since the 1960s. Their role has been categorised under three headings.[6]

a) As a 'supercalculator' for performing complicated and time consuming calculations

b) As a teaching tool for computer programming

c) As an aid to the interactive teaching/learning process: in this computers have made a major contribution to education. In computer aided learning (CAL) the computer can be used in two modes: as a 'substitute tutor' and as a 'simulated laboratory'. In the first mode the student participates in an interactive dialogue with the computer, i.e. direct instructional device. In the second mode, the student performs experiments on a model programmed into the computer. This mode allows students to study the response of the system following changes to important variables. The DEFLECT programme for structural design and analysis falls under the second mode of CAL.

The aim of DEFLECT is to create an interactive environment for learning and teaching structures to students of Architecture and Civil Engineering. It will enhance students' understanding of how structures respond to and behave under load. It will also enable students to investigate the effects of changing materials, section sizes, and overall geometry, on the deflection of the structural form. The programme has a graphical user interface with one right hand menu leading to sub-menus, an on-line help file on how to operate the software, and a second help file (What is) which explains basic structural concepts in a simple manner. The programme consists of four levels (Fig. 1).

Fig.1 Levels of the DEFLECT Programme

 

Level 1 (Example Structures)- effects of a single load on pre-defined structures:

As a 'learning resource', this level allows students to examine the behaviour of pre-defined structures under load, and to explore the effects of changing key variables, i.e. loads, joints and supports, on the deflection of the structural form. Members which are in tension and compression can be identified easily.

This level has six screens of pre-set structures (Fig. 2-a and b), including typological classics.

Fig.2a. Screens of pre-defined structures in Level 1

 

Fig. 2b. Individual structures under deflection in Level 1

 

Level 2 (Draw Your Own Structure)- effects of a single load on user-defined structures:

The facilities provided by this level can be used as a learning and teaching resource, where students can be asked to investigate a structural design problem and arrive at a solution.

A graphical interface permits students to draw their own structures and investigate structural deflection under load. The effects of changing key parameters on deflection can also be studied. Applying different joints, supports and loads to structural members will produce various types of 'mechanisms' that the software can identify as 'stable' or 'unstable'. Areas of tension and compression within a structural member are very well highlighted using a colour scheme. While the positioning of 'point' load is confined to the quarter point, mid span and the end point of a structural member, the 'uniformly distributed load' is automatically adjusted over the full length of the member.

Drawing aids such as Grid and Snap can be displayed on and off, and their value can be changed. Dynamic animation of loaded structures is also possible, and two magnification options (zoom in/zoom out) are available. Figure 3 shows some features of this level.

This level also has a facility to display shear, bending moment and reaction diagrams.

Fig. 3 Level 2 allows students to draw their own designs and examine their deflection under load.

 

Level 3 (Real Loads)- Effects of loads on user defined structures with variable properties:

At this level, students can give real dimensions to structural members and specify cross sectional properties. The type of joint between complete members is automatically determined by the software according to common practice in real life situations. Tapered members can be drawn and their shape can be changed easily.

Members are of two types: Planar and Linear. A library of cross sectional sizes of members is also supplied. Loads can be specified by the student and applied to structures at specific positions. Animated deflections can be generated with deflection values for each member displayed at mid-span and both ends. The displayed deflection can be exaggerated using the 'Enlarge' command. Shear and bending moment diagrams and values (numeric) are included in this level. Fig. 4 shows some worked examples.

Fig. 4 Level 3 enables the construction of real structures with variable properties

 

Level 4 (Real Materials): Effects of loads on user defined structures using real materials:

In this level, which is a complete analysis tool, the student can apply real materials to structural members, add loads and display shear and bending moment diagrams and computed values. In addition to a library of materials which contains concrete, steel, masonry, timber, glass, and aluminium, it is possible to specify a material which is not in the above list by choosing ‘other’ and typing Young’s Modulus of Elasticity (KN/mm2).

The ability to draw ‘curved’ members besides ‘straight’ and ‘tapered’ members is a useful and interesting feature in this level. The user can also change the shape of curved and tapered members for additional flexibility in object manipulation and editing.

Fig. 5 Level 4 enables the construction of curved structures with real materials

 

Software Evaluation: Student Trials

Before finalisation, the software was appraised twice by students from both institutions and their comments provided useful feedback for improvement. The appraisal was intended to investigate a number of key issues regarding the value of the software as a CAL package for teaching structures, its usefulness, and the ease of use, i.e. interaction with the interface. In Phase One, Questionnaires were administered to six groups from 1st year engineering studies at Paisley University, and to 16 students from the 2nd year at the Mackintosh School of Architecture. Students' knowledge of deflection, tension and compression was assessed before and after using the software, and their attitudes towards the software were measured. Results of assessment from Paisley University confirmed that the programme was a very good teaching tool, particularly when combined with structured exercises. Students also showed a great deal of satisfaction with the software image and ease of use.[7]

Results from the Mackintosh showed that students regarded the software as an extremely useful tool for teaching and learning structures. They found the 'What is' file an excellent learning resource on structures. Twelve out of sixteen students rated all the software attributes as 'good' or 'very good'.

In Phase Two, a similar appraisal procedure was carried out in both institutions where observations and questionnaires were employed for data collection. Informal discussions with staff from Paisley University suggest that DEFLECT was seen by engineering students as a useful teaching tool. However, further investigation of students’ response is currently in progress. Response from the Mackintosh School shows a high rate of satisfaction among the fourteen students who took part in the experiment.

 

Acknowledgement

The development of the programme would not have been possible without the financial support of the Scottish Higher Education Funding Council, and the collaboration of students of Paisley University and the Mackintosh School of Architecture is also gratefully acknowledged.

The programme was devised and developed by the following:

University of Paisley: R. Hardy; D. Wilson; D. Crowther (Phase 1 only)

Mackintosh School of Architecture: Professor C. MacCallum; Dr. R. Hanna; Dr. T. Sharpe (Phase 2 only)

Lamp Software: T. Craddock; N. Dowdy

 

References

1. Sandaker, B. N. and Eggen, P., The Structural Basis of Architecture, Phaidon Press Ltd, London, 1993, p. 33

2. Gardner, M., Structures Software: Pin, Rigid, Plastic and Grid, School of Civil Engineering, Kingston University, Surrey KT1 2EE, 1992

3. Computer and Design Services Ltd, CADS Analyse 3D: Frame Analysis Software for Windows, Dorset, BH18 8AX, 1995.

4. Piccolotto, M. and Rio, O., Structural Design Education With Computers, in Proceedings of ACADIA 95: Computing in Design, University of Washington, Seattle, October, 1995, pp.285-299

5. QSE Space for Windows, Technical Manual, QSE Limited, Cambrian House, Chipping Sodbury, Bristol BS17 6AD, England

6. The Scottish Central Institution Committee for Educational Development, How Computers Can Be Used in Tertiary Education, Robert Gordon Institute of Technology, Aberdeen, 1987, Booklet 9

7. Hardy, B., Wilson, D. and Crowther, D., Evaluation of Student Assessment of Computer Aided Learning Package on Response of Structures to Load, Internal Report, University of Paisley, June 1996.