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5.1  Introduction

main objective for this research was to compare the single circular tube member
and three circular tube member under axial compressive behavior. Therefore, in
order to assess the behaviour of these two type of member, an experimental
investigation will be undertaken in both tension and compression test as both
test provide a simple and effective way to characterize how the material’s
response to the applied loading. In this chapter, the conclusion of the
research will be stated and recommendation to further the research related to
the collapse behaviour of space trusses will be further elaborated.


5.2  Discussion and Conclusion

In this research,
the result of the experimental investigation on the ultimate load of three
circular steel tubes which is subjected to axial compressive load has been
described. From the experimental result, observations indicate that the
presence of three circular steel tube in replace of single steel tube effectively
increasing the truss member ductility and compressive strength.

From all the graph
plotted, it can be summarized that the member consist of the three circular
steel tubes member can sustain higher axial load and displacement compare to
single steel tube member before it fails. The steel tubes tested in tensile
test not only reach the standard of the tensile strength that range between 400
– 550 MPa as provided by ASTM but it also reach steel material percentage
elongation more than 10% as stated by Design of Steel Structures, EN 1993(EC3)
for steel before it fail by fracture. Therefore it can be conclude that the
steel tube used for this study have higher material’s ductility behaviour.

For both specimen
tested in compression, which is single steel tube member (CS1, CS2 and CS3) and
three circular steel tube member (S1, S2 and S3), the failure took place by buckling
on the mid height of the specimen of single steel tube and the outward bulging
at both end of the outer tube for three steel tube specimens due to outward
push of the middle tube. With the existence of the other two other tube (middle
and outer) which can helps in withstanding the increase in load, therefore the
structure can at least give a warning sign before it collapse rather than a sudden
catastrophic failure.

In addition, if a truss
structure is to remain stable after buckling of the most heavily stressed
compression member, the remaining members in the structure must be capable of
absorbing the total energy released from the failed member. If the members
surrounding the failed members are unable to support this sudden increase in
load, progressive buckling and collapse of the structure will ensue. The collapse
mode of the structure will be similar to the failure mode exhibited by the individual
compression members, where the collapse is sudden, showing no ductility in the
load-displacement response (Parke, 1988).


5.3  Recommendation


In this study,
test were restricted with small variation of thickness and diameter of the
steel section where the scope of the study has been discovered. One particular
area that requires in-depth studies is the connection between each tube. Designing
a connection is not a simple task. Shockingly, research has proven that 30% of
structural failures are caused by defective detailed design of the joints
between structural members (Seward,
1998). Normally, connections have high shearing forces that an engineer
must examine when designing the connection. A failure can occur if the structural
engineer underestimates the design force the connection is withstand. Future
study should therefore include the follow-up work to investigate the different
type of connection between this three tube as the way on how this these three
steel tube is being connected will effect on the load transfer pattern.

On the other hand,
for further research, the steel tubes subjected to different types of loading
application e.g eccentric and cyclic loading, will enlarge the potential
applications of these space truss structural elements. It has been shown by
previous researcher that the structural behavior of the composite column can be
greatly influenced by how the load is applied to the section of the steel.

trusses are reticulated three-dimensional frameworks, constructed from an
assembly of discrete elements, possessing high strength to weight ratios, which
are frequently used to cover large, column-free areas (Makowski, 1987). In
construction, their use is not only restricted to roof structures. Therefore,
new formulation of the steel member contribution factor might be necessary and
thus further research is recommended.