Columns Trusses or Plane Frames Arches Analysis and design software Structural Design spreadsheets Mathematical relationship between SF, BM, slope and deflection

Introduction

A high proportion of the structural engineer's work comprises Structural Analysis.  The application of mathematics to determine forces, stresses and strains in the structures they are called  upon to design.

The accurate and economic design of structures usually requires the use of a variety of formulae and considerable calculation.  For some structures, the mathematics involved may be simple, but for others it can be of an advanced standard involving laborious calculation.  For most complex structures, computer programs are normally used.

The main problems with computer software are the overwhelming amount of information provided in the analysis results and the fact that the programs are only as clever as the software designer and as such may contain serious flaws in the analysis procedure.  It has been suggested that CAD could mean Computer Aided Disaster if the engineer believes everything the computer results tell them.

In saying this, I use 3D analysis software frequently with my students and they get on very well with it.  Within about an hour most of them can enter and analyse beams and portal frames.  The software they use is produced by a company called CADS. It is very user friendly and  has excellent graphic results as well as textual results.  The process of analysis is very straight forward and I would recommend you take a look at it if you are looking for such a piece of software.

has been established for about 30 years and not only do they produce structural analysis software but also structural design and detailing packages which all inter-link.

Clearly the designer must have a sound knowledge of the nature, properties and behaviour of the structural elements and materials to enable accurate interpretation of the computerised results.

Although mathematics is such an important tool, it must be remembered that structural engineering is not an exact science.  Construction materials and human beings do not behave in a perfect manner and in developing mathematical theories for the design of structures, assumptions have to be made which may be very close to the truth for some materials in certain circumstances but which may be wide of the mark in others.

One Professor of Engineering has said "Don't expect the structure to make the same assumptions as you do"  Therefore it is necessary to interpret very carefully the results given by mathematical or computer analysis and to apply to the problem sound common sense, intuition and a 'feel' for the structure.  During the construction of a bridge of novel design, many eminent engineers proved by mathematics that it could not stand up; the bridge is still there.

Laboratory experiments on structural models of proposed important structures are very common and as a result, the values given by mathematics are frequently adjusted on an empirical basis with considerable resulting economy in materials and costs.

Two basic principles apply to all types of structural design:

 The structure must be stable.  (All forces must be in equilibrium.) The stresses caused in the various elements of the structure as a result of the external forces and the consequent reactions from other elements or from the ground, must not exceed the values decided as safe.

Top of the page