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Steel Designers' Manual - 6th Edition (2003)
Fig. 2.21 Composite truss
Vierendeel panel
much greater, as is the cost of fireproofing the truss members. For maximum
economy, trusses should be fabricated from T-sections and angles using simple
welded lap joints. The openings between the diagonal members should be designed
to accept service ducts, and if a larger opening is required a Vierendeel panel can
be incorporated at the centre of the span. Because a greater depth is required for
floor trusses, the integration of the services is always within the structural zone (Fig.
2.21).
Stub girder construction
Anatomy of structure 65
Stub girders were developed in North America in the 1970s as an alternative form
of construction for intermediate range spans of between 10 and 14 m. They have not
been used significantly in the UK. Figure 2.22 shows a typical stub girder with a
bottom chord consisting of a compact universal column section which supports the
secondary beams at approximately 3-metre centres. Between the secondary beams
a steel stub is welded on to the bottom chord to provide additional continuity and
to support the floor slab. The whole system acts as a composite Vierendeel truss. A
disadvantage of stub girders is that the construction needs to be propped while the
concrete is poured and develops strength. Arguably, a deep universal beam with
large openings provides a more cost-effective alternative to the stub girder because
of the latter’s high fabrication content.
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