Supervisors Checklist - What to Look for - July 2012 Relevant to SA

TRUSS INSTALLATIONTRUSS INSTALLATIONThings to look out for on site

TRUSS INSTALLATIONTRUSS INSTALLATIONThings to look out for on site .......

An item by item guideline to Site Supervisor’s checklist, as required by Regulation 74, Development Regulations 2008, South Australia

ByBy

Afzal LaphirAfzal LaphirEngineering ManagerEngineering Manager

Timber roof truss erection, fixing and bracingPart 2 – Site Supervisor’s Checklist

Specimen Truss LayoutSpecimen Truss Layout


Item 1 Item 1 –– Hip end framingHip end framingLoose timber or jack trusses


Item 2 Item 2 –– Location of special loadsLocation of special loadsSolar heating, air con. HWS, other

Location of Special Loads should beshown on the layout.

In the example on the right trusses NG2In the example on the right, trusses NG2,M6 and NG1 have been designed tosupport the solar tank/panels on the topchord

And trusses NG1, NG2 , PCG1 andPCG2 are designed to carry an a/c unit onthe bottom chord.


Item 3 Item 3 –– bottom chord clear of nonbottom chord clear of non--loadbearingloadbearing wallswallsAS4440 ref: clause 2.2.2

Non-loadbearing walls, as designated, shall not carry any truss loading and shall not be packed totouch the underside of trusses.

Note: One way to ensure a gap is maintained between the underside of trusses and top of nonNote: One way to ensure a gap is maintained between the underside of trusses and top of non-loadbearing wall is to set these walls at a lower level than the loadbearing walls. Therecommended difference in level is the ceiling batten depth (if any) plus minimum 10mm.

Note: Trusses are built with cambers toallow for the initial deflection at the take-up of load and some creep as the timbersettles.

Thus, packing to the underside of a trussover a non-loadbearing wall may stopthese deflections and in turn support thetruss in an incorrect positiontruss in an incorrect position

A truss carrying a large load (eg: girdertrusses) may require more camber thana standard truss.


Item 4 Item 4 –– Internal support/tieInternal support/tie--downdown

Roof trusses that are internally supported would typically have aRoof trusses that are internally supported would typically have aSupport Here label (as shown) attached to the bottom chord at theinternal support location

INTERNAL SUPPORT

Internal supports are typicallyshown on the layout like this


Item 5 Item 5 –– Fixing to top of bracing wallsFixing to top of bracing wallsNon-loadbearing bracing walls require special fixings

A pair of timber blocks or a pair of Pryda ShearConnectors (PSC) may be used to transfer racking loadsfrom the ceiling diaphragm to non-load bearing bracingwalls.

Note: It is the responsibility of thewall frame supplier to provideinformation on fixing to top of non-loadbearing bracing walls.

T bl 8 22 f AS1684 2 2010 id dditi l d t il f

Note: Pryda Hitch Brackets are not shown for clarity.These are required at max. 1800mm c/c (see Item 6)

Table 8.22 of AS1684.2:2010 provide additional details forwalls parallel and perpendicular to truss bottom chords.Some bracing walls with high capacities may requiremultiple pairs of these shear connectors. Read Pryda’sI t ll ti G id f P f b i t d ll d P dInstallation Guide for Pre-fabricated walls and PrydaBracing for further details.


It 5 It 5 Fi i t t f b i llFi i t t f b i ll

Pryda Shear Connectors (PSC) are used toPSC are fixed to top of bracing walls andcan be used as a direct substitute for a

Item 5 Item 5 –– Fixing to top of bracing wallsFixing to top of bracing wallsuse Pryda Shear Connectors (PSC)

Pryda Shear Connectors (PSC) are used totransfer racking loads from the ceiling diaphragm tonon-load bearing bracing walls.

PSC are always used in pairs

can be used as a direct substitute for apair of nail fixed timber blocks asspecified AS1684.

These straps allow vertical movement ofPSC are always used in pairs These straps allow vertical movement oftrusses (to release creep deflection) andensures that truss camber dissipation isuninhibited by over-driven nails

3 NAILS3 NAILS

4 OR 5 NAILS

TRUSS PERPENDICULAR TO WALLTRUSS PERPENDICULAR TO WALL TRUSS PARALLEL TO WALLTRUSS PARALLEL TO WALL


It 6 It 6 Fi i t Fi i t l db il db i llllItem 6 Item 6 –– Fixing to nonFixing to non--loadbearingloadbearing wallswallsUse of Pryda Hitch brackets to provide lateral restraint

Points to check: Nail near top of slot Don’t drive nail homeDon t drive nail home Allow trusses to deflect Fixed at not more than 1800mm c/c

Incorrect installation could cause bending and bucklingcause bending and buckling of hitch bracket


Item 7 Item 7 –– Truss locations/orientationsTruss locations/orientationsItem 7 Item 7 –– Truss locations/orientationsTruss locations/orientationsTruss spacings, spans, truncated girder stations

Obtain these information from the Truss Layout and fromtruss detail sheets (if required).

To ensure correct truss orientation isachieved on site, most truss detailerswould show the truss mark on thewould show the truss mark on thelayout at the same end as the markingon the actual truss on site would be.The installer should check with trussmanufacturer for confirmationmanufacturer for confirmation.

Truss orientation is particularly important fortrusses with internal support and those (eg:girders) that appear to be symmetrical buthaving timber or nailplates that are different atthe corresponding ends.


It 7 It 7 T l ti / i t tiT l ti / i t tiItem 7 Item 7 –– Truss locations/orientationsTruss locations/orientationsExample of how a fabricator would represent a truss where orientation is criticalis critical

Where ends are marked as below (End A & End B), this information isprinted or stamped on the bottom chord of trusses that depends oncorrect orientation on sitecorrect orientation on site.

The layout will also be labeled to show correct orientation.

Note: Fabricators will be providing these markings only on trusses where orientationNote: Fabricators will be providing these markings only on trusses where orientationis critical. Below is a good example of a truss which appears to be symmetrical butthe nailplates aren’t.


Item 8 Item 8 –– Truss bowTruss bowAS4440 ref: Fig 3.2 (L/200 max)

Trusses shall be erected with minimal bow, in the truss and in anychord, with a tolerance not exceeding the lesser of L/50 and 50mm,where L is the length of the member in question (see illustration)g q ( )


Item 9 Item 9 –– Truss plumbTruss plumbAS 4440 ref: Fig 3.3 (H/50 max)

Trusses shall be so erected that nopart of the truss is out of plumb with apart of the truss is out of plumb with atolerance exceeding the lesser ofheight/50 and 50mm


It 10 It 10 S l t ti bS l t ti bItem 10 Item 10 –– Supplementary timberSupplementary timberScabs, noggings etc

Note: Supplementary noggings (min 70x35 F4 onedge) may be supplied to site where plasterboardis fixed directly to bottom chords.

At hip ends, these noggings to be fitted where thebottom chords of the jacks and creepers do notcontinue to run parallel to the main run of trusses

Sometimes scabs, tee-stiffeners or waling plates arerequired as part of the truss, and these are supplied assupplementary timber to site with the truss pack.

continue to run parallel to the main run of trusses.In other areas, supplementary noggings to befitted between trusses where internal walls runparallel to the common trusses

The correct fixing of these members are provided bythe truss manufacturer.

Here is an example of scabs being marked appropriately on thetruss and on the supplementary timber for easy recognition.

MARKING ON TRUSS

MARKING ON SUPPLEMENTARY TIMBER


Item 11 Item 11 –– Truss TieTruss Tie--Down requirementsDown requirementsAs given in the Truss Layout

Information on truss tie-downs is obtained from thetruss layout as shown.

The connector symbols are given alongside theconnector description and fixing details (see below)

Connector Symbolsare shown thus


Item 11 Item 11 –– Truss TieTruss Tie--Down requirementsDown requirementsSome typical tie-down connectors and fixing details

QHS6(wrapped round)

4 nails

2 nails

1/MG 2/MG

4 nails per leg to underside of top plate

4 nails

QHS6(face fixed)

4 or 6 nails per leg to4 or 6 nails per leg to as required


Item 12 Item 12 –– Fixing of multiFixing of multi--ply trussesply trussesAs per Pryda’s specifications

All members (chords and webs) of multi-ply trussesmust be laminated prior to loading. Information onfixing requirement is provided in Pryda’s TechnicalUpdate TU22

Fastener Specification:Double Laminates:2.80 dia x 65 nails for 2/35 thk3.05 dia x 75 nails for 2/45 thk

Triple Laminates:Same nail specification, but fixed from both outer faces


It 13 It 13 T h d b iT h d b iItem 13 Item 13 –– Top chord bracingTop chord bracingLayout of steel cross bracingTop chord bracing as shown on the layout should be maintainedon site. Some girder trusses may require supplementary bracing(see item 26)


Item 14 Item 14 –– steel brace splicesteel brace spliceAS4440 ref: Fig 4.20

Source: AS4440-2004


Item 15 Item 15 –– Steel brace endSteel brace end--fixing at apexfixing at apexAS4440 ref: Fig 4.21

Source: AS4440-2004


Item 16 Item 16 –– Steel brace endSteel brace end--fixing at heelfixing at heelAS4440 ref: Figs 4.22 and 4.23

Source: AS4440-2004


Item 17 Item 17 –– Steel brace fixing at Steel brace fixing at heel to girder trussheel to girder trussAS4440 ref: Figs 4.24

Source: AS4440 2004Source: AS4440-2004


Item 18 Item 18 –– Steel brace fixing at cantileversSteel brace fixing at cantileversAS4440 ref: Fig 4.25

Source: AS4440-2004


Item 19 Item 19 –– Top chord restraintsTop chord restraintsAS4440 ref: Fig 4.1 spacing and fixing

Information on type and spacing of top chordrestraints are obtained from the Truss Layout, underTruss Design Criteria as shown


It 19 It 19 T h d t i tT h d t i tItem 19 Item 19 –– Top chord restraintsTop chord restraintsTimber Roof battens should be fixed and spliced adequatelyRoof tile battens should be made continuous at ends

No two splices shall be adjacent on any truss top chord

Continued …..

and spliced in other areas such that no two splices areadjacent and only 1 in 3 battens are spliced on any trusstop chord.

A di l P d f t th t l lt ti fAccordingly Pryda roof trusses assume that only alternative roofbattens are considered effective for top chord restraints (i.erestraint spacing = 700 mm) of trusses supporting concrete tiles.

For sheet steel roofs, every batten is assumed to be effective andytherefore is required to be spliced properly (see below)

Splice joints of timber roof battens supportingsheet steel require special consideration

Read Pryda’s TechnicalUpdate TU12 for furthersheet steel require special consideration,

treated as shown in the details belowUpdate TU12 for furtherdetails on effectiveness ofroof battens


Item 19 Item 19 –– Top chord restraintsTop chord restraints C ti dItem 19 Item 19 –– Top chord restraintsTop chord restraintsTrusses under scotch valleys need additional ties

Continued …..

Top chords of roof trusses that are located underneath scotchvalleys (or similar) must be provided with additional top chordrestraints.

These restraints should be maintained at same spacing as theroof battens

Provide restraints at same spacing as roof p gbattens. (cross bracing not shown for clarity)


Item 19 Item 19 –– Top chord restraintsTop chord restraints C ti dItem 19 Item 19 –– Top chord restraintsTop chord restraintsTop Hat Construction requires special consideration

Continued …..

Truss manufacturers may chose to form a trussin two segments, Top Hat Construction, oftendictated by manufacturing or transportationdictated by manufacturing or transportationrestrictions.

This form of construction requires specialconsideration, especially bracing and lateral, p y grestraints for horizontal top chord of the lowertruss.


Item 20 Item 20 –– Intermediate top chord tiesIntermediate top chord tiesAS4440 ref: Fig 4.2 at valley trusses

Intermediate top chord ties at valleys are only requiredif the valley truss spacing is greater than the designtop chord restraint spacing.

Accordingly, these additional ties will NOT be requiredif the valley truss spacing is maintained as below:

Valley Trusses as top chord restraints

What is the preferred spacing?

For concrete tile roofs 600mm (standard- For concrete tile roofs – 600mm (standard truss spacing)

- For sheet roofs – 900mm or standard roof batten spacing


Item 21 Item 21 –– Fixing of valley trussesFixing of valley trussesAS4440 ref: Fig 5.6


Item 22 Item 22 –– Web Tie/Web braceWeb Tie/Web braceUsing mid height ties, tee-stiffeners or Pryda Web Stiffeners

Web Bracing – using Mid-Height Tie

Mid-height ties are only applicable when a minimum three similarly configured trusses are in a row

Otherwise alternatives like Tee-stiffeners or Pryda Web Stiffeners should be used.

Truss layout should provide information on any web-tie requirement (as shown above)


It 22 It 22 W b Ti /W b bW b Ti /W b bItem 22 Item 22 –– Web Tie/Web braceWeb Tie/Web braceUsing mid height ties

Continued …..

MID-HEIGHT WEB TIE

Minimum 70 x 35 F5 Web Tie fixed with 2/2 8 dia x 65 nails atfixed with 2/2.8 dia x 65 nails at each crossing web

It 22 It 22 W b Ti /W b bW b Ti /W b bItem 22 Item 22 –– Web Tie/Web braceWeb Tie/Web braceUsing Pryda Web Stiffeners or Tee stiffeners PRYDA WEB STIFFENERS

Continued …..

Pryda Web Stiffeners (PWS) are specially designed so that they could be installed in the factory and easily stacked and transported without any inconvenience.y

Using PWS also ensures that the site installer (builder) is not relied upon for correct installation, giving peace of mind that the integrity of the truss is maintained.

Timber Tee-stiffeners are used as an alternative to PWS, and normally specified when mid-height ties become inapplicable. TIMBER TEE STIFFENERS


Item 23 Item 23 –– bottom chord restraints and bracingbottom chord restraints and bracingAS4440 ref: fig 4.28

Information on type and spacing of bottom chordrestraints are obtained from the Truss Layout, underTruss Design Criteria as shown

The adequacy of Direct FixedPlasterboard to function as bottomchord restraints is now checked inPryda Build software, and all Pryda rooftrusses are designed accordingly.

For further information, read Pryda’sTechnical Update TU32 or contact apPryda design office


Item 24 Item 24 –– Truss to truss connectionsTruss to truss connectionsFixing to girder trusses

Information on truss to truss connections are alsoobtained from the truss layout.


Item 24 Item 24 –– Truss to truss connectionsTruss to truss connectionsExamples of common truss boots

Continued …..

Fix all screws prior to loading. Use appropriate No. 12 Type 17 screws.

N d l f lti l i t d

COMMON TRUSS BOOTS (fixed with either bolts or No.12 Type 17 screws)Screw Fix Option:

Need longer screws for multi-laminated trusses or a cluster of nails around truss boot if 35mm screws are used.

HEAVY DUTY TRUSS BOOTS (fixed with M16 bolts)

Bolt Fix Option:

Fix all bolts prior to loading. Use standard washers against timber face Use standard washers against timber face.


Item 25 Item 25 –– Girder truss positions Girder truss positions

In the example given here girder truss positions aret e e a p e g e e e g de t uss pos t o s a eshown for the apex girder (SD1), mono girder (MG1)and the truncated girder girder (TGG1).


Item 26 Item 26 –– Girder truss restraints Girder truss restraints Supplementary top chord restraints

I dditi t t d d f b i ti l t t

End Fixing Detail to Truss as per AS4440

In addition to standard roof bracing, sometimes supplementary topchord bracing is required for girder trusses. An example is given here.

Also refer Item 13

End Fixing Detail to Support as per AS4440

SpeedbraceCross Brace


Item 27 Item 27 –– OverhangsOverhangsEaves or verge details, timber or metal fascia

The basic information relating to Fascia and Eave types isobtained from the truss layout, under Truss Design Criteria

Even if metal fascia is used, additionaltimber member is required at hipcorners to support some creepers


Item 28 Item 28 –– Waling plate fixingWaling plate fixingAS4440 ref: Fig 5.5


Item 29 Item 29 –– Connection to timber/steel beamsConnection to timber/steel beamsAS4440 ref: Fig 5.5


Item 30 Item 30 –– GableGable end framingend framingItem 30 Item 30 –– GableGable--end framingend framingAS4440 ref: Clause 6.2

Detailed information on Gable-End framingmay be obtained from Pryda’s Guide toGable-End framing


Item 31 Item 31 –– Truss modifications/defectsTruss modifications/defectsAS4440 ref: Clause 3.9

Under no circumstances shall a truss be modified by cutting, drilling, or byany other method that may interfere with its structural integrity, withoutbeing approvedbeing approved.

Approval must be obtained from the truss fabricator prior to carrying outany modifications to trusses.

Need Approval

Need Approval


Item 32 Item 32 –– Truss site suitabilityTruss site suitabilityCorrosive environmentsRead Pryda’s Technical Update TU 30 for detailed information on corrosion.


Item 33 Item 33 –– Advice on cornice fixingsAdvice on cornice fixingsAS4440 ref: Appendix B3


It 34 It 34 B i WidthB i WidthItem 34 Item 34 –– Bearing WidthsBearing WidthsAS4440 ref: Appendix B

The adequacy of bearing widths for timber trusses are checked byThe adequacy of bearing widths for timber trusses are checked bythe Pryda Build software, and these widths are usually obtainedfrom the Truss Detail Sheets.

Bearing Widths given here


Item 35 Item 35 –– Steel roof battensSteel roof battensMust be legibly and durably marked with the reference AS 1397

Here is an example of a properlymarked steel roof batten withmarked steel roof batten, withreference to AS 1397.

Documents

Supervisors Checklist - What to Look for - July 2012 Relevant to SA