Trusses: Introduction, Types, Hazards in Firefighting, and References

This report provides a comprehensive overview of trusses, essential structural elements in construction. It begins with an introduction to trusses, defining their purpose and importance in building design. The report then delves into the different types of trusses, distinguishing between floor trusses (including HY Joists, Pryda Longreach Truss Joists, and Posi Strut Truss Joists) and roof trusses (such as King Post trusses, Pratt trusses, and Queen Post trusses). Each type is described in detail, highlighting their structural characteristics and applications. A significant portion of the report addresses the hazards posed by trusses during firefighting operations, emphasizing the void spaces that can accelerate fire spread and weaken structural integrity. The report concludes by summarizing the key takeaways and providing references for further study. This report is designed to help students understand the design, functionality and the risks associated with trusses.

TRUSSES
1. Introduction
2. Types of Trusses
3. Floor Trusses
4. Roof Trusses
5. Hazards posed by trusses during firefighting
6. Conclusion
7. References

Introduction
 A truss is defined as beams or any elements put together to
form a rigid structure.
 In engineering terms a truss is known as a structure made
of two force members that are joined together to form a
assemblage that behaves as one.
 Usually trusses are comprised of triangular units that are
made up of a straight elements that have their endings
connected at joints called nodes (Corbett, 2009).
 Tensile and compressional forces acts on the nodes of the
trusses.
 Main reasons why trusses are used include; they are more
lightweight, trusses reduce deflection, and can support
more load compared to single members.

Types of Floor
Trusses
 Storey houses or houses with
suspended floors require floor
trusses-
floor trusses
are also known as joists.
 A joist is defined as a structure
constructed horizontally to support
a floor that spans an open area
such as a basement, crawl place,
etc.
 There are three main joists;
1. HY Joists
2. Pryda Longreach Truss Joists
3. Posi Strut Truss Joists

Types of Floor Trusses
(Cont.) HY Joist
 These types of joists are the
most preferred as they use
less timber to cover a larger
span.
 This type is formed by
joining solid timber franges
to a group of joined plywood.
 End-blocking as shown in
this image ensures that
joints do not topple over.

Types of Floor Trusses (Cont.)
Pryda Longreach Truss Joists
 This type of trusses use metals to
make diagonal webs instead of
timber. This lowers both cost and
total weight (Pearson South Africa,
2009).
 They are mostly used for floors that
need shallower trusses and are
more spacious to allow for services.
 The webs are put depending on the
design of the timber and whole floor
outlook.

Types of Roof
Trusses
 A roof truss is defined as a structural
design on the roof of building that is made
of straight elements pieced together to
form triangles for the aim of supporting or
carrying the load.
 A roof truss is a structural design that is
made up of straight structural elements
such as timber joined together forming
triangles. The straight members have their
ends bonded at nodes.
 The major types of roof trusses are;
1. King post trusses
2. Pratt roof trusses
3. Queen Post trusses
4. Howe trusses

Types of Roof Trusses
(Cont.)
King Post trusses
 In this type of truss, purlins are usually
supported by the principal rafter.
 The common rafters are closed spaced
and are supported by the purlin.
 The struts are used to prevent the
sagging of principal rafters.
 In this type, the spacing of the truss is
within a, maximum of 3 meters from
center to center and the spans varies
between 5 and 8 meters.
 The king post truss type is mostly
preferred in cases where the roof is very
expansive and need to be beautified.

Types of Roof Trusses
(Cont.)
Pratt truss
 This is a type of roof truss that uses
vertical web elements.
 The design uses vertical elements
for tension and diagonal elements
for compression (Dunn, 2010).
 The vertical (web) elements take
tensile forces while diagonal embers
(angled braces) take compressional
forces acting on the truss.
 This type is very efficient as diagonal
members shoulder gravitational
forces.

Hazards posed by trusses during
firefighting
 Trusses are designed and manufactured in such way
that they have void spaces. These spaces are helpful
when doing wiring and HVAC. These open spaces, in
times of fires, can allow continuous spread of fires and
superheated smoke. The fires can weaken the truss
and the floor being supported. The hazard of collapse
is created when firefighters start working on top or
below spaces trying to put out fires (Huth, 2009).
 Therefore the fire service and firefighters need to be
careful on the whole building as the fires have
weakened the structural stability of the building or
structure and thus need to put out fires while being
very careful to possibility of structural failure,
increase of fires than normal and many more risks.

References
Corbett, G. (2009). Fire Engineering's Handbook for
Firefighter I and II. Tulsa: Fire Engineering Books.
Dunn, V. (2010). Collapse of Burning Buildings, 2nd
Edition: A Guide to Fireground Safety. Tulsa: PennWell
Books.
Huth, M. W. (2009). Understanding Construction
Drawings. New York: Cengage Learning.
Pearson South Africa. (2009). FCS Construction
Carpentry and Roof Work L2. Cape Town: Pearson South
Africa.