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192 Barry’s Advanced Construction of Buildings
Steel loops on end of purlins
fit over 12 studs cast in frame
Purlins sit
into rebate
in frame
Stooled end
of purlin
Precast reinforced
concrete purlin
Rafter of precast
reinforced concrete
portal frame
Figure 4.38 Connection of concrete purlins to concrete portal frame.
Glulam
Glulam is the name that has been adopted for the product of a system of making members
such as beams and roof frames from laminae of natural wood glued together to form longer
lengths and shapes than is possible with natural wood by itself. Glulam is defined as a
structural member made from four or more separate laminations of timber arranged with
the grain parallel to the longitudinal axis of the member: the individual pieces being assembled
with their grain approximately parallel and glued together to form a member which
functions as a single structural unit. The advantage of glulam is that both straight and
curved sections can be built up from short, thin sections of timber glued together in long
sections, up to 50 m, without appreciable loss of the beneficial properties of the natural
wood from which they were cut.
A range of standard glulam straight roof and floor beams are produced in a variety of
sizes up to 20 m long and 4.94 m deep. These beams can be cut, holed and notched in the
same way as the timber from which they were made. A wide range of purpose-made portal
frames, flat pitched and cambered roof beams and arched glulam structures is practical
where the curved forms and natural colour and grain can be displayed and where medium
to wide clear spans are required.
Glulam structural members
Because of the labour costs involved in the fabrication of glulam members, glulam cannot
compete with any of the basic steel frames in initial cost. However, glulam comes into its
own in one-off, purpose-designed, medium-span buildings, where the durability of glulam
and the appearance of natural wood are an intrinsic part of the building design, e.g. in