AU596293B2 - Roof truss - Google Patents

Description

Isl*~~sriii)~ 'i I"Crrrr grlpt~LC~i~l&Ti~~ U- L-~ll'~ This document contains the 1 amendments made under Secltion 49 and is correct for printing COMMONWEALTH OF AUSTRALIA The Patents Act 1952-1969 Name of Applicant(s): A.J. S.M. O'LEARY PTY. LTD.

Address of Applicant(s): 16 Milner Place, Thornlands, Queensland, 4164 t#0 a t a Ct Cl, cC

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''cc Address for Service: G.R. CULLEN COMPANY, Patent Trade Mark Attorneys, Dalgety House, 79 Eagle Street, Brisbane, Qld. 4000, Australia.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: ROOF TRUSS The following statement is a full description of the invention including the best method of performing it known to us:

A

2 THIS INVENTION relates to a roof construction incorporating a truss, as well as a method of constructing a roof using the truss. In particular, the invention is directed to a roof construction having a hanging and strutting truss system.

In roof constructions, long rafters are supported between their ends by underpurlins which extend transversely under the rafters. These underpurlins, in turn, are i a °supported by struts. The struts may be angled and/or oo 10 V-shaped (as shown in Fig. 1) or vertical (as shown in Fig.

0 The V-shaped struts shown in Fig. 1 are supported by a load bearing structure, for example the top plate of a wall frame. The vertical struts shown in Fig. 2, on the other hand, are supported by n hanging beam which itself is C c 15 supported at its ends by load bearing structures, for example I ce wall frames. The erection of the hanging beams, struts and ccc0

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underpurlins is both time-consuming and laborious.

Furthermore, as each item must be cut to size, there is a substantial degree of wastage due to unusable offcuts.

In ceiling constructions, long ceiling joists must also be supported between their ends. If a column-free area is required, the ceiling joist must be supported by an overhead structure. A common form of joist support is a hangi ig beam which extends above and transverse to the ceiling joists. The joists are then suspended from the hanging beam as shown in Fig. 2. If the hanging beam is used also as a strutting beam, it is required to be greater than a prescribed minimum strength and hence greater than a r 3 prescribed minimum size. To minimize the size of the beam required to meet prescribed minimum strength ratings, the beams are often of composite laminated construction. However such composite laminate-beams are expensive.

Furthermore, although underpurlins may provide the necessary upward support for rafters, they provide limited downward force on the rafters to resist wind induced uplift on the roof.

0 0 0V 0 0 It is an object of the present invention to 0oo 10 overcome, or substantially ameliorate the above described ooo0 o c, disadvantages of prior art roof and ceiling constructions by Sproviding a roof construction having a truss member for simultaneously supporting rafters and ceiling joists.

a cc It is a further object of the invention to provide a cc 15 roof construction having a truss member which also secures the roof rafters against wind induced uplift.

In one broad form, the present invention provides a roof construction comprising a truss member having a pair of O C spaced-apart chords joined by web members angled thereto, 20 said truss member being supported at its ends by load bearing structures, a plurality of rafters supported between their ends on the upper chord of said truss, and a plurality of ceiling joists suspended from the bottom chord of said truss.

Preferably the rafters are tied down or otherwise secured to the truss so as to resist uplift on the roof.

Typically, the truss is a metal truss having angle-section metal chords and webs. In the preferred embodiment, the chords hav7e a Z-shaped cross section and the k m i I -i I I webs are of channel cross-section.

The truss not only provides vertical support but also stabilises the roof structure in the horizontal plane.

Each truss member of the present invention replaces an underpurlin, a hanging beam, and a plurality of struts.

Furthermore, the truss can be prefabricated in a factory and placed in position when and where required. Advantageously, S00 the truss is made from lightweight metal sections to enable 00 0 0 it to be lifted manually onto the load bearing structures.

0000ooooo00 0 0 ooo000 10 Preferably, the ceiling joists are suspended from 0000 O T the lower chord of the truss by angle section straps, the 0 t C lower portion of one flange of the strap being fastened to the ceiling joist and the upper portion of the other flange being fastened to the lower chord of the truss.

Alternatively, the joists can be supported from the truss by hooked hanging straps, or any other suitable means.

The top and bottom chords are normally parallel.

However, they may also be angled to fit into confined areas C C Sat the lower ends of rafters.

According to another aspect of the present invention, there is provided a method of roof construction comprising the steps of; providing a truss member as described above and i supporting said truss member at its ends on load bearing structures, erecting the rafters of the roof, said rafters being supported intermediate their ends by the top chord of the truss and suspending a. plurality of joists from the bottom truss chord, said joists being spaced apart along the length of the bottom truss chord, Preferably the rafters are tied down or otherwise secured to the top truss chord to resist uplift on the roof.

Use of a prefabricated truss eliminates the need for cutting and erecting hanging beams, struts and underpurlins, thereby shortening erection time and reducing erection o 00 Go o 0 costs.

C 0 a 0 Caa 10 In order that the invention may be more fully understood and put into practice, a preferred embodiment C thereof will now be described with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of part of a prior art roof construction, Fig. 2 is a perspective view of part of another prior art roof construction, Fig. 3 is a side elevational view of a roof construction using a truss member according to the preferred embodiment of the present invention, Fig. 4 is an end elevational view of the truss member of Fig. 3, Fig. 5 illustrates the connection of the truss chord to a rafter, and Fig. 6 illustrates the connection of a ceiling joist to the bottom chord of the truss.

As shown in Figs. 3 and 4, the truss 10 used in the preferred embodiment comprises an upper chord (or truss il C- beam) 11 and a, lower chord (or tie-beam) 12 spaced apart by angled webs (or braces) 13. The illustrated truss configuration, is a standard truss configuration, and any other suitable truss configuration can be used. In the illustrated embodiment, the truss 10 has a standard truss end at one end and a tapered hip end 14 at the opposite end to suit the roof line. For a gable end however, a standard truss end 14' would be used instead of the tapered end.

Ga 0 0 SThe length and configuration, and load and tied-down aooao a a a a o °oc 10 ratings of the truss 10 can be predetermined from the «construction plans, and the truss prefabricated on the ground ready for installation. Typically, the truss is constructed from lightweight angle-section steel members. In the preferred embodiment, the truss chords are Z section members, while C section channel members are used for the webs 13.

The resulting truss is strong yet lightweight, and can be lifted by a single operator.

In constructing the roof, the truss 10 is first mounted on load bearing structures A, B such as walls or wall 20 frames, or pillars. The rafters 16 are then erected, the rafters being supported between their ends by the truss chord 11. The rafters are also tied down to the truss to resist T uplift forces induced in the roof. One or more collar ties can be strung between trusses supporting rafters on opposite sides of the roof to stabilise them. Erection ties 17 can also be used to support the truss 10 in an upright configuration during erection., The fixing of the rafters 16 to the upper truss 2 f~ chord n1 is shown in more detail in. Fig. 5. A, plurality' of short angle section members 23 are fixed to the upper chord 11 along the length. thereof, at the locations of the rafters 16. Each angle section, 23 is fastened to the upper chord 11 by two self tapping sorews at the points 24 as illustrated.

greater number of screws can be used to achieve higher tie-down. rating). A minimum of three holes 25 are provided 0 C! 0in the upper portion of the angle section 23 which projects 0 0 C0 0000 above the truss chord 11. The angle section 23 is then 000000 0 0 00 10 fastened to a respective rafter 16 by flat headed nails or 000G g 0 0:other suitable fasteners through the holes 25. Preferably, an angle or wedge member 26 is factory fitted to the top of the chord 11 so that the rafter 16 is supported on a surface which is flush therewith.

C 15 Battens 18 are then fastened transversely across the rafters 16 and a roof 19 erected on the battens according to known construction methods, The bottom chord 12 supports a plurality of ceiling joists 15 which are spaced along the length of the bottom chord 12 and orientated transversely thereto. The connection between the ceiling joists 15 and the bottom chord 12 is shown in more detail in Fig. 6. Each ceiling joist is suspended from the bottom chord 12 by a ceiling tie 28 which typically is a length of angle section metal. The bottom portion of the ceiling tie 28 is connected to a respective joist 15 by fasteners 29 through one flange, while the upper portion of the ceiling tie 28 is connected to the bottom. chord, 1.2 by fasteners .27 -through the other flangsa.

8 In an alternative construction each ceiling joist is suspended from the bottom chord. 12 of the truss 10 by a hanging strap. The hanging strap comprises a, lower flat portion. 27 having a, plurality of holes 29 to enable the strap to be nailed or fastened to the face of the joist. The upper portion of the hanging strap is twisted and bent to form a hook which is hooked over a flange on the bottom chord. The ceiling joists are set in line under the truss 0 0 0 000 0 10 and then fixed to the chord 11 using the hooked straps.

G 0 I 0e 10 At the tapered end of the truss 14, a trimmer joist 22 can be used to span the end region (Fig. 3).

Using the abovedescribed construction, large column-free areas can be provided in dwellings without the expense of prior art constructions as the expensive hanging and strutting beams required previously can now be replaced by lightweight one-piece trusses.

The foregoing describes only one embodiment of the present invention, and modifications which are obvious -to those skilled in the art can be made thereto without departing from the scope of the invention as claimed in the following claims. For example, although the truss member is preferably made of metal angle sections, the truss can 4l alternatively be made from timber components.

Claims (7)

1. A roof construction comprising a truss member having a pair of spaced-apart chords joined by web members angled thereto, said truss member being supported at its ends by load bearing structures, a plurality of rafters supported between, their ends on the upper chord of said truss, and a plurality of ceiling joists suspended from the bottom chord of said truss. c o c

2. A roof construction as claimed in Claim 1, wherein c o ,ac said rafters are secured to the truss to resist uplift forces P 00 induced on the roof.

3. A. roof construction as claimed in Claim 1 or 2, wherein the truss is a metal truss, said chords having a 2= shaped cross-section and said webs being of channel cross- section.

4. A. roof construction as claimed in any preceding claim, wherein said ceiling joists are suspended from the lower chord of the truss by angle section metal straps, the lower portion of one flange of each strap being fastened to a respective ceiling joist and the upper portion, of the other flange of each strap being fastened to the bottom chord of said, truss.

A roof construction as claimed in any preceding claim, wherein said rafters are connected to the top chord of said truss by angle section metal members, the lower portion of one flange of the, metal members being fastened to the top chord of said truss and the upper portion of the other flange of the metal :members being fastened to respective rafters.

6, A method, Of roof construction, comprising the steps of providing a, truss member having a. pair of spaced-apart chords joined, by 'web ,members angled, thereto 1 and suppor.-ting said 'truss member at its ends on load bearing structures, erecting the rafters of -the r~oof 1 said rafters being supported intermediate their: enids by 'the 'top chordC of the trus s 1 a nd, suspending a, plurality of joists from the bottom chord a0 of the truss, said 3,4 t being spaced-apart along the length of 'the bottom, chord.,

7. method as claimed in, Claim 6, further comprising v the step of securing said rafters to the top chord of tho a 'truss to resist uplift forces induced on the rnof. A. trzuss when used in the roof construction of Claim A, roof construction substantially as b,.ereknbefora described with r~eference to Figs. 3 'to 6 of -the accompanying drawings. A method. of roof constr:uction substantially as hereinbefore, described. 'with, reference 'to Figs. 3 to 5 of the accompanying drawings. <~DATE D thi s 13th day of2 April, 988. S. M. 0O'LEARY PTY. LTD. 'By 'their Patent Attorneys G 0 CULLJEN' CO.