A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
galvanizing as they are prone to corrosion and they are normally the
cheapest choice for normal containment level of vehicles.
The initial material and setup cost of aluminum parapet is high. They are
free of the problem of corrosion and the design of aluminum parapets does
not require surface protection. However, owing to their high material price,
care should be taken on the design to prevent stolen of parts of parapet.
Moreover, aluminum parapet is lighter than steel and has weight savings
over steel parapets.
16. When should engineers consider using truss with K-bracing?
In the arrangement of triangulated framework in truss structures, it is more
economical to design longer members as ties while shorter ones as struts
(e.g. Pratt truss). As such, the tension forces are taken up by longer steel
members whose load carrying capacities are unrelated to their lengths.
However, the compression forces are reacted by shorter members which
possess higher buckling capabilities than longer steel members [34].
For heavy loads on a truss structure, the depth of the truss is intentionally
made larger so as to increase the bending resistance and to reduce
deflection. With the increase in length of the vertical struts, buckling may
occur under vertical loads. Therefore, K-truss is designed in such as way
that the vertical struts are supported by compression diagonals.
17. What are the characteristics of Vierendeel girder? (T1)
The Vierendeel girder design is sometimes adopted in the design of
footbridges. In traditional truss design, triangular shape of truss is normally
used because the shape cannot be changed without altering the length of
its members. By applying loads only to the joints of trusses, the members
of truss are only subjected to a uniform tensile or compressive stress
across their cross sections because their lines of action pass through a
common hinged joint.
The Vierendeel truss/girder is characterized by having only vertical
members between the top and bottom chords and is a statically
indeterminate structure. Hence, bending, shear and axial capacity of these
members contribute to the resistance to external loads. The use of this
girder enables the footbridge to span larger distances and present an
attractive outlook. However, it suffers from the drawback that the
distribution of stresses is more complicated than normal truss structures
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