![](bg5.png)
Figure 11: The additional plastic hinge makes the structure
unstable, and it collapses.
To determine that location approximately,
additional nodes are added on the member, as shown
in Figure 10. It must be pointed out that there are
many ways to identify the location and magnitude of
the maximum bending moment (or axial force or
shear force) on a member, and the introduction of
additional nodes is only one of them. It is assumed
that a plastic hinge is formed at the location of the
maximum moment. When the user applies a full
hinge at that location, iSA immediately shows that
the structure is kinematically unstable, as shown in
Figure 11. By repeating this exercise with suitable
guidance from the teaching staff, students will be
able to build up a sense of progressive collapse of
structural systems.
4 CONCLUSIONS
The notion of having an adequate ‘safety factor’ in
itself is not enough. Indeed, it could even give us a
false sense of security. We need to emphasise to our
students the importance of understanding physical,
holistic structural behaviour such as the equilibrium
of whole structures, the effects of compatibility, the
effects of a lack of fit, etc. We need to equip our
students with the fundamental and essential skills
they need to be able to check and verify computer-
generated results manually. We need to adopt easy-
to-use structural analysis software that can provide
and stimulate rapid experimental learning through
the investigation of ‘what if?’ scenarios, that can be
used to check computer-generated results to reflect
on ‘whether it really makes physical sense’, and that
can also be used as a creative design tool. We need
to revise our curricula to phase out or reduce the use
of old-fashioned manual calculation techniques and,
instead, increase our emphasis on practical aspects
and on a physical/holistic understanding of structural
behaviour.
To prevent a catastrophic collapse, such as that
which occurred on 9/11, we need to understand how
a structure will behave and respond under all
possible loadings, including that from a terrorist
attack. Therefore, we should design every structure
so that:
1. It will not fail catastrophically if a part or parts
of the structure are damaged or destroyed;
2. It will be able to re-distribute the load when
parts of the structure have failed; and
3. It will have a high degree of redundancy and be
able to provide alternative load paths to avoid
sudden collapse.
iSA, a user-friendly 2D structural analysis
program with an easy-to-use GUI, has been
described here. This software is a handy tool for
instructor teaching and student learning in structural
analysis (e.g., the matrix stiffness method, second-
order analysis, dynamic modal analysis, plastic
analysis, stability analysis, moving load analysis,
etc.). As the analysis results are presented instantly,
this is an efficient and rapid self-learning tool with
which students can build up their confidence,
engineering sense and understanding of structural
behaviour.
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