HOME OF GANG-NAIL BUILDING SYSTEMS To find out more about MiTek’s products & systems, call your local state office or visit our web site: www.mitek.com.au VIC (03) 8795 8888 NSW (02) 9609 8700 QLD (07) 3268 1666 SA (08) 8234 1326 WA (08) 9411 2845 NZ (09) 274 7109 MALAYSIA (603) 3176 7473 GUIDELINES FOR THE DESIGN FIXING & BRACING OF Posi-STRUT FLOOR & ROOF TRUSS SYSTEMS GUIDELINES FOR THE DESIGN FIXING & BRACING OF Posi-STRUT FLOOR & ROOF TRUSS SYSTEMS
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GUIDELINES FOR THE DESIGN FIXING & BRACING …lodac.biz/pdf/posistrut.pdfINTRODUCTION Posi-STRUT® range of products are parallel chord trusses using timber chords “on flat” and
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H O M E O F G A N G - N A I L B U I L D I N G S Y S T E M S
To find out more about MiTek’s products & systems, call your local state office or visit our web site: www.mitek.com.auVIC (03) 8795 8888 NSW (02) 9609 8700 QLD (07) 3268 1666 SA (08) 8234 1326 WA (08) 9411 2845 NZ (09) 274 7109 MALAYSIA (603) 3176 7473
GUIDELINES FOR THE DESIGNFIXING & BRACING OF Posi-STRUTFLOOR & ROOFTRUSS SYSTEMS
GUIDELINES FOR THE DESIGNFIXING & BRACING OF Posi-STRUTFLOOR & ROOFTRUSS SYSTEMS
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TABLE OF CONTENTSPosi-STRUT® Floor Truss System
Introduction
Advantages
Definitions
Floor Stiffness
Floor Loading
Span Charts for Bottom Chord Support
Span Charts for Top Chord Support
Supporting Structure
Handling and Storage
Set Out and Placement
Trimming On Site
Supporting External Walls
Supported Non-Load Bearing Walls
Support Details
Fixing and Connections
Strongbacks
Stair Openings
Cantilevers
Bracing
Mechanical Services
Posi-STRUT® Roof Rafter & Purlin System
Introduction
Definition
Roof Loading/Camber
Set Out
Sizes
Hold Down Details
Bracing
Span Charts
Speedbrace Fixing
3
3
3
3
3
4
4
5
5
5
5
6
8
8
9
10
12
14
15
16
17
17
17
17
17
17
18
19
22
Posi-TRUSS
Posi-JOIST
Posi-PLUS
INTRODUCTIONPosi-STRUT® range of products are parallel chordtrusses using timber chords “on flat” and the uniquePosi-STRUT® metal webs.
Posi-TRUSS is a made to order parallel chorded trusscommonly used as long span floor joists. They providean economical and high quality floor structure which iseasily assembled and provides excellent access forplumbing, electrical services and air conditioning ducts.Posi-TRUSS may also be used for long span rafters orpurlins to carry tile or steel deck roofing.
As Posi-TRUSSES are designed and manufactured toorder for specific projects, they can incorporate internalbeams and special support conditions.
Posi-JOIST® and Posi-PLUS® trusses incorporate special trimmable ends and are available ex stock. Posi-JOIST® and Posi-PLUS® are designed specificallyfor use as floor joists in domestic type structures andshould not be used for other applications without advicefrom a qualified engineer.
The Posi-STRUT® range of products are available innominal 200, 250, 300 and 400mm depth. Actual overalltruss depth depends on timber sizes used for the chords,and is provided in the design tables enclosed. Posi-STRUTS® make more efficient use of timber thanconventional joists, as they have timber concentrated atthe top and bottom of the truss where it works most efficiently. This concept is similar to that of steel univer-sal beams, where the majority of steel is located in theflanges. The efficient use of timber, combined with thestrength of the Posi-STRUT® webs, make the Posi-STRUT® range of products very lightweight, yetstrong structural members.
ADVANTAGESPosi-STRUTS® offer the following advantages over solidjoists:
• Plumbing, electrical conduit and other services can berun between chords and webs.
• No drilling or notching required to accommodate services.
• Additional width available for fixing flooring.
• Ceiling material can be fixed directly to the trussbottom chords.
• Larger clear spans.
• Internal load bearing walls, piers or stumps andbearers can be reduced or eliminated.
• Shrinkage problems sometimes encountered withunseasoned solid timber are reduced or eliminated.
• Lightweight and easy to handle.
• Posi-JOIST® and Posi-PLUS® trusses may betrimmed to length on site.
• Optional top chord support reduces on-site labour.
• With Posi-Purlins, roof and ceiling can be fixed direct.
• Top chord hanging.
3
Posi-STRUT® Floor SystemDEFINITIONSLoadbearing Partition Walls - walls which carry roofand/or upper floor loads in addition to their own selfweight and wall lining.
Non-Load bearing Partition Walls - walls whichimpart self weight only to supporting structure.
Platform Flooring - flooring fitted continuously fromexternal wall to external wall prior to the installation ofinternal partition walls.
Fitted Flooring - flooring fitted for each room after internal walls have been installed.
Strongbacks - bracing members running at right anglesto Posi-STRUTS® which provide load sharing betweenadjacent members.
LSD - Limit State Design.
FLOOR STIFFNESSThe dynamic response of floor systems to foot traffic andother moving loads is dependant on many factors suchas the floor plan of supported walls, applied load, furniturelayout, etc. The comfort and expectations of occupantsalso varies widely and is very personal.
Posi-STRUTS® have been designed so that the maximum span recommended in Tables 1 to 4 conformsto the vibration standard set out in AS1684.1-1999,Residential Timber-Framed Construction, Part 1 - designcriteria.
When selecting a Posi-STRUT® for your applicationconsideration should be given to the springiness of thefloor. Generally the floor stiffness provided by the Tables meets the expectations of most occupants.Where Posi-STRUTS® are near their maximum span forlarge open areas like rumpus rooms and family rooms, orwhere additional floor stiffness is required the maximumspans given in Tables 1 to 6 should be reduced.
FLOOR LOADINGPosi-STRUTS® have been designed for the following Deadand Live Loads.
Dead Loads - are due to the mass of the structure andpermanent fixtures. An allowance has been made inthese designs for the following permanent loads:
Flooring - 22 mm Particle board flooring or equivalent plywood.
Ceiling - 13 mm plasterboard direct or 10 mm plasterboard on battens.
Floor covering - normal floor covering loads e.g.carpets or vinyl tiles. If, clay or heavy ceramic tilesare to be used, on large areas (i.e. greater than 3 square metres), further professional advice shouldbe sought before commencing construction.
Live Loads - are temporary loads due to furniture orpeople which may vary over time.
Posi-STRUT® floor systems in this manual have beendesigned for 1.5 kPa which is suitable for domestic flooronly. For commercial or public buildings seek advicefrom your Posi-STRUT® supplier.
Note: The Posi-STRUT® span chart tables attached, arenot designed to support load bearing walls. All roof loadsto be supported by external wall only. For Posi-STRUTS®
that must support load bearing walls, contact your nearest MiTek office.
4
SPAN CHARTS FOR TOP CHORD SUPPORT FLOOR TRUSSESNote:1. All charts designed using LSD method.2. Minimum Joint Group JD5.3. Spans have been produced for 45mm wide top chord bearings.
Maximum Spans for 35 mm thick timber
*Important Note: For spans in the range of 1100 to 2600, top chords may require to be a minimum grade of F11 or MGP12 to conform to AS1170.1-1997.#Important Note: For spans in the range of 1100 to 2600, top chords may require to be a minimum grade of F8 or MGP12 to conform to AS1170.1-1997.
Posi-STRUT®
Size
TimberSize
(mm x mm)
OverallDepth(mm)
PSW3520
PSW3525
PSW3530
35 x 7035 x 90
35 x 7035 x 90
35 x 7035 x 90
197197
248248
302302
-1000
-3200#
-3300#
38004000
40004900
40005100
38004300
47005000
50005600
44004600
51005400
57006000
F5 F8 F11 F17-
4000
-4600#
-5200#
MGP1042004600
49005300
55005900
MGP1245004800
52005500
58006100
MGP15--
--
-1100
3000*3600
3000*3900
3000*3900
36003900
37004600
37004800
39003900
47004900
52005600
F5 F8 F11 F17--
-3500#
-3900#
MGP1038003900
45004800
51005400
MGP1239003900
48005100
53005700
MGP15
Timber Grade450 mm Posi-STRUT® Centres 600 mm Posi-STRUT® Centres
Table 3. Maximum Spans for Domestic Floor Loads - Live Load 1.5 kPa
Maximum Spans for 45 mm thick timber
*Important Note: For spans in the range of 1100 to 2600, top chords may require to be a minimum grade of F8 or MGP12 to conform to AS1170.1-1997.
Posi-STRUT®
Size
TimberSize
(mm x mm)
OverallDepth(mm)
PSW4525
PSW4530
PSW4540
45 x 7045 x 90
45 x 7045 x 90
45 x 7045 x 90
248248
302302
412412
43004700
49005300
4800*6300
47005100
53005700
63006700
49005300
55005900
65007000
53005600
59006300
60007500
F5 F8 F11 F1745005100
51005800
61006900
MGP1052005500
58006200
69007300
MGP1254005700
61006500
72007700
MGP153700*4200
4200*4700
-5500
43004700
49005200
57006100
45004800
50005400
59006400
49005200
55005600
65006900
F5 F8 F11 F1739004500
45005000
54005900
MGP1048005000
53005700
63006700
MGP1250005200
56005600
66006900
MGP15
Timber Grade450 mm Posi-STRUT® Centres 600 mm Posi-STRUT® Centres
Table 4. Maximum Spans for Domestic Floor Loads - Live Load 1.5 kPa
SPAN CHARTS FOR BOTTOM CHORD SUPPORT FLOOR TRUSSESNote:1. All charts designed using LSD method.2. Minimum Joint Group JD5.
Maximum Spans for 35 mm thick timber
*Important Note: For spans in the range of 1100 to 2600, top chords may require to be a minimum grade of F8 or MGP12 to conform to AS1170.1-1997.
Maximum Spans for 45 mm thick timber
Posi-STRUT®
Size
TimberSize
(mm x mm)
OverallDepth(mm)
PSW4525
PSW4530
PSW4540
Posi-JOIST®
Size
PJ25-70PJ25-90
PJ30-70PJ30-90
PJ40-70PJ40-90
45 x 7045 x 90
45 x 7045 x 90
45 x 7045 x 90
248248
302302
412412
44004900
49005500
59006500
49005200
55005800
65006900
51005400
57006000
67007200
54005800
61006500
72007700
F5 F8 F11 F1746005200
52005800
62007100
MGP1053005600
60006300
71007500
MGP1255005900
62006600
74007900
MGP1538004300
43004800
52005600
44004800
51005400
61006400
46005000
53005600
63006700
50005400
57006000
67007200
F5 F8 F11 F1740004500
45005100
55006100
MGP1049005200
55005900
66007000
MGP1251005500
58006100
68007300
MGP15
Timber Grade450 mm Posi-STRUT® Centres 600 mm Posi-STRUT® Centres
Table 2. Maximum Spans for Domestic Floor Loads - Live Load 1.5 kPa
Posi-STRUT®
Size
TimberSize
(mm x mm)
OverallDepth(mm)
PSW3520
PSW3525
PSW3530
35 x 7035 x 90
35 x 7035 x 90
35 x 7035 x 90
197197
248248
302302
11003800
2900*4500
3700*5000
38004200
46005000
53005600
40004400
49005200
54005800
44004800
52005500
58006200
F5 F8 F11 F173600*4100
4200*4600
4600*5300
MGP1043004600
51005400
57006100
MGP1246004900
53005700
59006300
MGP15-
3300
11003900
11004400
34003800
42004600
48005200
37004000
44004800
50005400
40004300
48005100
54005800
F5 F8 F11 F173100*3400
3400*4100
4100*4500
MGP1038004200
47005000
53005600
MGP1241004300
49005200
55005900
MGP15
Timber Grade450 mm Posi-STRUT® Centres 600 mm Posi-STRUT® Centres
Table 1. Maximum Spans for Domestic Floor Loads - Live Load 1.5 kPa
5
SUPPORTING STRUCTUREThe supporting structure should be checked to ensurethat beams, walls and footings are capable of supportingall loads from floors and/or roof.
As Posi-STRUTS® allow the use of large open areas withfewer bracing walls, the stability of the structure should bechecked in all cases.
1. Solid Brick Construction
Lateral stability and strength of supporting walls shouldbe checked in accordance with Masonry Code AS3700-1998.
2. Timber Framed Construction
The strength and bracing of timber framed walls supporting Posi-STRUTS® should be checked using SAATimber Framing Code AS1684-1999 or be designedusing AS1720.1-1997.
3. Elevated Building
For traditional elevated buildings where a central row ofpiers is to be removed, additional bracing may berequired to provide stability to the building. This may beprovided by designing ground level shear walls at eachend of the building, or by using braced partition wallslocated centrally. If in doubt, consult MiTek Australia Ltd.
In all of the above cases the stability of the structure reliesto some extent on the bracing provided by the panel flooring. For this reason it is important that floor trussesbe fixed securely to supporting walls.
All cross walls and end walls should be securely fastened to the outer supporting walls. For timber framedwalls use a 50 x 100 mm Strapnail at each intersection.For masonry construction, a continuous timber top plateshould be installed and joined to each intersecting topplate at cross walls using 50 x 100 mm Strapnails.
HANDLING AND STORAGEAll Posi-STRUT® components should be strapped andstacked vertically with the bottom chord clear of theground, supported on bearers located directly underweb points. Posi-STRUTS® may be stacked on top ofeach other with bearers aligned as closely as possible to web panel points.
Posi-STRUTS® should not be left exposed to weather forextended periods of time without adequate protection. Ifcovered, ensure adequate air circulation around the trusses.
Typical stacking of Posi-STRUTS®
Care should be taken when handling the Posi-STRUT® toavoid bending, twisting or dropping. Slings should alwaysbe attached to the timber chords, and not to the metalwebs to avoid buckling.
When lifting Posi-STRUTS® with a crane, slings shouldbe attached at panel points closest to the truss quarterpoints. See diagram.
SET OUT AND PLACEMENTPosi-STRUTS® are generally placed perpendicular toload bearing supporting walls and should be located sothat distance between them does not exceed thedesigned spacing.
Care should be taken to place the Posi-STRUTS® theright way up. Unless marked otherwise Posi-STRUTS®
are always manufactured so that Posi-Web starts at thetop chord at each support point. There are occasionswhere it is necessary to design and manufacture Posi-STRUTS® with the first web starting at bottom chordlevel. In this case trusses will be marked “THIS WAY UP”.
Right way up Wrong way up
TRIMMING ON SITE Only Posi-PLUS and Posi-JOIST members can betrimmed to length on site. Posi-TRUSSES are required tobe manufactured to the required span for each project. Ifadjustments to span are required for Posi-TRUSSES youshould consult with your supplier.
Bearers as close aspossible to web points.
Bearers directly under web points.
Bearers as close aspossible to web points.
Bearers directly under web points.
60° or lessUse fabric sling. Do notuse chains or wire ropewhich may damage webs.
60° or lessUse fabric sling. Do notuse chains or wire ropewhich may damage webs.
6
Trimming limitations for Posi-JOIST®
Posi-JOISTS® within the limits specified below may betrimmed each end by up to 335 mm for PJ20, PJ25 andPJ30 and up to 430 mm for PJ40. Posi-JOISTS®
should only be cut at locations between verticalwebs. The following procedure will allow trimming ofPosi-JOISTS® to match your exact span.
• Where a supporting wall is to provide support to two abutting Posi-JOISTS®, position Posi-JOISTS® first so that there is equal bearing for each Posi-JOIST®. Alsoensure that there is a vertical member located over thesupporting wall.
• Check opposite support to ensure that a vertical timberweb is also located over the support (allowable misplacement 5mm). Adjust location of truss until it is possible to trim without cutting through verticals.
• Use the first Posi-JOIST® as template for remainingtrusses.
Note: Do not cut through vertical webs. It should only be necessary to cut at a position between verticalmembers.
Trimming limitations for Posi-PLUS®
Posi-PLUS® members may be trimmed at either end towithin a minimum distance of 90 mm from the Posi-STRUT® web.
SUPPORTING EXTERNAL WALLSCASE 1. Upper Storey of 2 Storey - for the upperstorey of two storey construction, where the lower studw a l lprovides continuous support, and where wall plates andlintels have been sized in accordance with AS1684 lowerstorey load bearing walls, standard Posi-STRUTS® maybe used to support upper walls where the effective lengthof roof supported does not exceed that given in Table 5.
below.
Note: The above table has been determined for sheetroof at 900mm centres and tiled roof at 600mm centreswith maximum 25° roof pitch.
Where effective length of roof supported is greater thanthose in Table 5, F-Frame as specified below, solid bearer or standard Posi-STRUT® with timber verticalsinserted under studs may be used.
Table 5. Maximum Effective Length of Roof (EL)Supported by Standard Posi-STRUT® Trusses
Posi-STRUT® or Sheet Roof Tile Roof Posi-JOIST® Size (mm) (mm)
PSW3520 5,050 3,950
PSW3525 5,550 4,350
PSW3530 6,750 5,300
PSW4525 8,150 6,100
PSW4530 9,000 6,750
PSW4540 7,450 5,600
F-Frame for EL < 3600mm
F-Frame for EL > 3600mm
Where there are larger openings in the upper storey wallwhich cause a concentrated load on the Posi-STRUT® orF-Frame, a suitable timber vertical member should beinserted between the top and bottom chord under thepoint load to transfer it down to the wall below.
Note: 1. Posi-STRUT® chords and F-Frame chords maybe considered to act in conjunction with wallplates to form a double plate or ribbon plate.
2. Where openings are positioned in end walls, lintels are to be sized in accordance withAS1684.
Vertical webs to suitstud spacing
Posi-STRUT® braces at2400mm maximum centres
Chord size and grade are similar tostandard Posi-STRUT® trusses
Vertical webs at600mm centres
Posi-STRUT® braces at2400mm maximum centres
70 x 45 MGP10 fixed to 90 x 35 MGP10 (min.) wall plateswith 2/3.75mm diameter x 75mm long nails @ 600mm centres
90mm minimum clearance
Lintel to AS1684
Lower storey wall
Studs carryingconcentrated loads
Opening
Upper storey wall
Timber verticals to be placed under studs where effective length of roof supported by upper storey wall is greater than specified in Table 7.
CASE 3. Building with Hip Ends - Both of the abovetwo cases apply, provided the truncated girder truss station does not exceed the effective length of roof supported specified in Table 5.
End wall - Building with Hip End Upper Storey of 2storey
EL = Truncated Girder Truss Station + 2 x Overhang
CASE 4. End Walls for Single Storey Buildings withHip Roof - As for case 2 except EL = Truncated GirderStation.
End wall - Building with Hip End Single Storey
EL = Truncated Girder Truss Station + 2 x Overhang
CASE 5. End Walls for Buildings with Gable Roof -Similar to that of building with Hip End, except the effective length of roof supported is as follows:
EL = 2 x Verge Overhang + Truss Spacing
WARNINGWhere stair wells or other voids are located adjacentexternal walls, the stability of the external wall should bechecked by a structural engineer.
Generally, F-frames may beused to support upper walls oftwo storey construction at endwalls where floor and ceilingacts as a diaphragm to restrainthe external wall against lateralloads.
However, F-frames should notbe used whenever supportingexternal walls that have anopening for a void area or staircase as shown. In thesecases, the external walls arerequired to be designed by astructural engineer.
CASE 2. Single Storey - for a single storey constructionwhere continuous support for the end F-Frame is notavailable, frames using Posi-JOIST® detail may beused provided the roof load (EL) does not exceed thatspecified in Table 6, and that pier spacing does notexceed 1200 centres.
Where the effective length of roof supported exceedsthat specified in Table 6, use either solid timber or laminated ConstructaBEAMS to support end wall androof loads. Bearer sizes to be taken from AS1684-1999, relevant State Timber Framing Code or refer Gang-NailSpan Charts for laminated ConstructaBEAMS orAutoBEAM.
End wall - Single Storey
EL = 2 x Overhang + Truss Span
Posi-JOIST END 25 (PJE25)
Table 6. Effective Length of Roof Supported. (EL)
Posi-JOIST®
End SizeSheet Roof
(mm)Tiled Roof
(mm)
PJE25
PJE30
PJE40
7200
7200
7200
3600
3600
3600Common Posi-STRUT®Lower storey wall
Overhang
StrongbackF-Frame or standard Posi-STRUT®
Truncatedgirder truss
Truncated girder station
CommonPosi-STRUT®
Solid timber or laminated ConstructaBEAMbearer supported by brick piers
Overhang
StrongbackTrip-L-Grip both sides
Truncatedgirder truss
Truncated girder station
CommonPosi-STRUT®
Solid timber or laminated ConstructaBEAM bearer supported by brick piers Overhang
Truss Span
Overhang
1200 max. 1200 max. 1200 max.
50 62
(Typical)
1200 max. 1200 max. 1200 max.
50 20
(Typical)
1200 max. 1200 max. 1200 max.
50 62
(Typical)
Upperstorey
Opening
Lowerstorey
Floor
Internalwall
Do not useF-frame,solid beareror standardPosi-STRUT
8
Posi-STRUT® Top Chord Support
The maximum span of top chord supported Posi-STRUTS®
may be increased to the maximum span of the bottomchord trusses, if the end vertical web is fastened to thesupporting beam with Gang-Nail Trip-L-Grips or if one ofthe following details are used:
1. Double end vertical web - see Figure ‘X’.
2. Timber End Block - see Figure ‘Y’.
Figure ‘X’
Timber End Block for Top Chord SupportedPosi-STRUTS®
Support width 35 mm - 60 mm
Support width 60 mm - 90 mm
Support width greater than 90 mm
Figure ‘Y’
SUPPORTING NON-LOAD BEARING WALLSWalls Perpendicular to Posi-STRUTS®
Walls placed perpendicular to the Posi-STRUTS® requireno additional support.
Walls Parallel to Posi-STRUTS®
a) Platform Flooring
Walls placed parallel to the Posi-STRUTS® do notrequire additional support where a platform floor is to beused and the flooring material is capable of supportingwalls. However, for braced walls, noggings are requiredat 1200 mm centres (to be located at truss web points) totransfer bracing forces into the adjacent Posi-STRUTS®.
b) Fitted Flooring
Where flooring is fitted to each room after internal wallshave been constructed, an additional truss is requiredbelow the wall to provide support to both the wall andflooring.
Braced Wall Support
Fitted Flooring
Double trusses used under non-load bearing internalpartition walls should be located such that the partition isbearing equally on both trusses. Flooring and strong-backs should be fixed to both trusses.
SUPPORT DETAILSPosi-STRUT® Bottom Chord Support
Posi-STRUTS® may be supported on their bottom chordas shown
Non-load bearingpartition wall
2 skew nailsto top chordat each end
90 x 35 (F5)nogging at
1200mm max.centres under partition wall
Platform flooring
Non-load bearingpartition wall
Double trusscentred underpartition wall
Fitted flooring
Concealed beam
Waling plate or lintel
Load bearing wall
Trip-L-Grip
GN 75 x 100
Timber block nailed to end web
Truss to be supportedon bottom chord
Load bearing or non-load bearing stud wall
External brickwork
Gang-Nail Joist Hanger
Load bearing wall
Waling plate or lintel
GQ - 75 x 100
Support width
Support width
Support width
GQ - 75 x 100
GQ - 75 x 125
Table. Recommended Timber Blocking Sizes
Posi-STRUT Depth 200 250 300 400
Strongback Size 90 x 35 120 x 35 140 x 35 190 x 35
9
Posi-JOIST® Bottom Chord Support
Posi-JOISTS® should only be supported on their bottomchord as shown.
Posi-PLUS® Bottom Chord Support
Posi-JOIST® Top Chord Support
Where it is necessary to support Posi-JOISTS® by thetop chord as shown, Trip-L-Grip’s are required to fastenthe truss end vertical web to face of the supporting beam.
FIXING AND CONNECTIONSFixing to External Walls
Each Posi-TRUSS® to be fixed onto the supportingstructure by a minimum of 2 / 3.15 mm diameter x 75 mmlong nails. For wind classification areas higher than N2refer to AS1684 for details.
Posi-STRUT®
Posi-JOIST®
Fixing to Internal Walls
When Posi-STRUTS® are to be fixed to internal wallsplace Posi-STRUTS® side by side and fix as above or butt together using a 50 x 100 mm Strapnail to connectPosi-STRUTS®.
Fixing to Internal Load Bearing Walls
Posi-STRUTS® are generally not designed to supportload bearing internal walls, however where there is asupporting wall directly below, Posi-JOIST® and Posi-PLUS® trusses should be strengthened as illustrated below.
Truss to be supportedon bottom chord
Load bearing or non-load bearing stud wall
External brickwork
Gang-Nail Joist Hanger
Load bearing wall
Waling plate or lintel
Packer block required for Posi-PLUS®
Waling plate or lintel
Load bearing wall
Trip-L-Grip
50 x 100mm Strapnail or4T5 (43 x 120mm) Tylok
90 x 35mm block
2/3.15 dia. x 75mm long nailsto top and bottom chords
Load bearing wall
2/3.15 dia. x 75mm long nailsto top and bottom chords
90 x 35mm block
10
Load Bearing Cantilever
Standard Posi-PLUS® trusses may support an externalload bearing wall on a cantilever provided that the cantilever does not exceed 160mm and maximum standard roof truss span does not exceed 12m for bothsheet and tile roof. Wall cladding of 30kg/m2 maximum isalso allowed for.
Note: The detail above is applicable to Posi-PLUS®
trusses only.
With Posi-TRUSSES® and Posi-JOISTS® special designwill be required which should be discussed with yoursupplier at the time of ordering.
Fixing to Steel Beam
Note:
1. Size of packers and timber fixing plate to suit steelflange width.
2. Timber fixing plate is to be contained within the steelbeam flange so as to restrain any vertical loadsinduced by Posi-STRUT® trusses.
Posi-TRUSS®
Posi-PLUS®
Packers 70 x 35 or 70 x 45mm softwoodfastened securely to steel web
Universal steel beam
Gang-Nail Joist HangerJH70160 for 70mm wide chordJH95150 for 95mm wide chord
Skew nail top flangeto fixing plate
Timber fixing plate between steel beam flangessecurely fixed back to packers
Packer blocks required with Posi-PLUS®
Gang-Nail Joist Hanger
50mm minimum160mm maximum
PP250 or PP300 truss
Notched Posi-PLUS® to Steel Beam
STRONGBACKSStrongbacks are bracing members running at rightangles to Posi-STRUTS®. Strongbacks significantlydampen vibrations and increase the stiffness of the floorsystem. The performance of the floor depends verymuch on the proper installation of strongbacks.Strongbacks to be supported off end walls and any internal walls to increase floor stiffness. They should beplaced at 2400mm maximum spacing along span of eachtruss.
Strongbacks must be fixed to the central vertical webs oneach Posi-STRUT® with 3/3.15 mm diameter nails andspliced in accordance with details following.
Table 7. Timber Blocking Size Required
Posi-PLUS® Timber Blocking Size
PP 250 deep
PP 300 deep
120 x 35
140 x 35
Timber blocking fitted between each Posi-PLUSand nailed securely to Posi-PLUS timber web.Refer Table 7 for member size
Posi-PLUS Joist
UniversalSteel Beam
15mm maximum notch depth
Timber blocking fitted between each Posi-PLUS and nailed securely to Posi-PLUS timber web.Refer Table 7 for member size
Posi-PLUS Joist
UniversalSteel Beam
Posi-PLUS not to extendmore than D/3 oversteel beam
Provide adequate clearance to ensurePosi-PLUS is only supported onbottom chord
Minimum distance 90mm
D
DO NOT OVERCUT Posi-PLUS CHORD
WRONG WRONG
11
The ends of strongbacks (and wherever internal partitions are crossed) should be anchored to the wall to improve dynamics.
Note:
1. Timber grades for strongback sizes given in the abovetable to be equivalent to or higher than grade used forPosi-STRUT® chord sizes.
2. Alternatively a deeper section strongback of a lowergrade may be used. Reduce by one grade for each25mm increase in depth.
3. Table 8 applies to standard design charts in this document only. Where Posi-STRUT® trusses are custom designed using MiTek2000 software, strong-back sizes specified by MiTek2000 computationsshould be used.
Strongback fixing and splice
Strongback to double truss connection
Table 8. Recommended Strongback Sizes
Posi-STRUTDepth 200 250 300 400
StrongbackSize 90 x 35 120 x 35 140 x 35 190 x 35
3/3.15 dia. nails
Splice plate.Same size andgrade as Strongback
Timber splice plate fixed toStrongback with 5/3.15 dia. nails each side of splice
Timber splice plate
Strongback fixed toPosi-STRUT®vertical web
4/3.15 dia. x 75mm nails to each web
Strongback
Double Posi-STRUT®
Alternative strongback splice
When strongback location changes, the strongback mustrun through to the next Posi-STRUT® and be connectedto the side as per detail following.
Connection of strongback to Posi-STRUT® atchange of span
Strongback fixing using Gang-Nail Back Bracebracket
The Back Brace allows the strongback to be fixed at positions other than at timber vertical webs. This enablesthe strongback to be fixed in a continuous line when thereare variations in span.
Note:
1. All screws MiTek 14 gauge x 30mm.
2. Do not over tighten screws.
Trip-L-GripStrongback
70 x 35 (F5) timber blockfixed using 2/3.15 dia. nailsto top and bottom chords
Strongback
2 screws to faceof strongback
1 screw intotop and bottomchord of Posi-STRUT
Strongback
3/3.15 dia. nails
Splice plate asspecified in Table 9
Table 9. Splice Plate Sizes
JointType
GN PlateType & Size
Tylok PlateType & Size
StrongbackSize
90 x 35120 x 35140 x 35190 x 35
SingleSingleDoubleDouble
GE75150GE75150GQ50150GQ63150
6T106T106T58T7
12
STAIR OPENINGSWhere openings are required on the upper floor for stairwells, one or more shorter Posi-STRUTS® may beused and supported on headers fixed to adjacentPosi-STRUTS®.
The header beam maybe supported on double Posi-STRUTS® as shown below. For header beam sizes refer Table 10. The connection of the header to the double Posi-STRUT®
is as shown on page 13.
Note that header beams have been designed to carry Posi-STRUT® floor loads only.
Note:
Posi-JOIST to be supported by fixing end vertical webas specified on page 9.
Posi-PLUS® Header Beam Fixing Detail
Double Posi-JOIST®
Double Posi-STRUT®
Header Beam
Shortened Posi-STRUT®
Refer page 13for fixing details
Shortened Posi-JOIST®
Double Posi-STRUT®each side of stairwell opening
Knee wall
Header Beam
Shortened Posi-STRUT®with extended top chord
End supportingstructure
4/3.15 dia x 75mmlong nails to each web
Double Posi-PLUS®
Double Posi-PLUS®
Header Beam
Refer page 18for fixing details
Shortened Posi-PLUS®
Table 10. Header Beam Sizes to Support Posi-STRUTS® Only
PSW3525 35 x 70 3500 4100 450035 x 90 3800 4500 4500
PSW3530 35 x 70 3800 4600 460035 x 90 4100 4600 4600
PSW4525 45 x 70 3900 4600 490045 x 90 4100 4900 4900
PSW4530 45 x 70 4100 4900 490045 x 90 4600 4900 4900
PSW4540 45 x 70 4800 5300 540045 x 90 5200 5400 5400
Illustrated below are some common types of stairwells(refer to Figures 1 to 3). For each diagram there are certain conditions that need to be observed.
For other types of stairwells, and for dimensions greater than those shown in Figures 1 to 3, contact yourPosi-STRUT® supplier.
Case 1
Figure 1
Case 2
Figure 2
Case 3
Figure 3Note:
1. These double Posi-STRUTS® have been designed to carry header beams which support shorter Posi-STRUTS® only. They will not carry the stairwellitself.
2. Double Posi-STRUTS® have also been designed for 600mm maximum truss centres. Therefore, web layouts of 600mm truss centres should be used.
PSW3525 35 x 70 2800 2900 290035 x 90 2900 2900 2900
PSW3530 35 x 70 2900 3000 300035 x 90 3000 3000 3000
PSW4525 45 x 70 3000 3600 360045 x 90 3400 3600 3600
PSW4530 45 x 70 3200 3600 360045 x 90 3600 3600 3600
PSW4540 45 x 70 3800 4200 4200
Hea
der B
eam
Spa
n(2
700m
m m
ax.)
Shortened Posi-STRUT®
Header Beam
1200mm max.
Posi-STRUT® span
Double Posi-STRUT® as Table 12
Double Posi-STRUT® as Table 12
Load bearing walls
StairOpening
(void)
Header Beam Connection
Where double Posi-STRUTS® are supporting headerbeams, strongbacks are to be fixed to each truss using4/3.15 mm diameter x 75 mm long nails.
2/3.15 dia. x 75mmlong nails
DoublePosi-STRUT®
Trip-L-Grip fixed tomanufacturers specifications
4 layers of 7mm x 600mm longF7 structural plywood todouble Posi-STRUT®
170 x 35mm tightly fitted blocksto be fixed at panel pointseach side of Header Beam
70 x 35mm timber blockfixed back to plywood.Length and nailing patternas per plywood blocking
65 7015
15TypicalNailingPattern
14
CANTILEVERSCantilevered balconies can be formed using solid timbereither fitted into trusses between chords or off to the sideof the truss as shown below. The cantilever beam canbe sized from timber span charts and should extend backinto the building to a distance greater than the balconylength. Balcony cantilevers should be no greater thanone fifth of the floor truss span.
Built in cantilever beam.
Lapped and nailed cantilever beam.
Note:
1. Cantilever beam has been designed to carry balconyload only. Size and grade can be obtained fromAS1684.
2. If cantilever is exposed to weather, place damp proofcourse between joist and Posi-TRUSS®.
SECTION Y-Y
Suitable dry timberpacker fixed with3.15 dia. nail
Concealed beam
Balcony length no greater than S/5
No less than balcony length
Span to first support (S)
3.15 dia. nails @ 225mm centres
Suitable dry timber block
Cantilevered beam
Balcony length no greater than S/5
3/3.15 dia. nails
Span to first support (S)
3/3.15 dia. nails
Tie Trip-L-Grip
Strongback
Suitable dry timber block
Cantilevered beam
Balcony length no greater than S/5
3/3.15 dia. nails
Greater than balcony length
3/3.15 dia. nails
Tie Trip-L-Grip
Strongback
Suitable dry timber block
Cantilevered beam
Balcony length no greater than S/5
3/3.15 dia. nails
Span to first support (S)
3/3.15 dia. nails
Tie Trip-L-Grip
Y
Y
X
X
Suitable dry timber packerTie
Packer block required for Posi-PLUS
Span to first support (S)
Greater than balcony length
Strongback
For cantilever beams built into Posi-STRUT® trussesensure full bearing along top and bottom chord usingsuitable dry timber packers fixed to both truss and beamwith 3.15mm dia. nails at 225mm centres.
For beams supplied separate to trusses, fix to verticalwebs with a minimum of 3/3.15mm dia. nails and to thefirst strongback with 1 Trip-L-Grip. Provide lateral ties totop edge of beam at 600mm centres fixed to beam with1/3.15mm dia. nail.
15
BRACINGEnd and Internal Support Bracing
Speedbrace bracing at 2400 mm maximum centres alongsupporting walls.
Plywood Panel at 2400 mm maximum centres.
Speedbrace
3/30 x 2.8mmreinforced head nails
3/30 x 2.8mmreinforced head nails
2/30 x 2.8mmreinforced head nails
2/30 x 2.8mmreinforced head nails
Speedbrace
3/30 x 2.8mmreinforced head nails
3/30 x 2.8mmreinforced head nails
2/30 x 2.8mmreinforced head nails
2/30 x 2.8mmreinforced head nails
Speedbrace at 2400mm centresalong supporting wall
3/30 x 2.8mmreinforced head nails
2/30 x 2.8mmreinforced head nails
7mm structural plywood or6.4mm thick CSR masonitebraceboard fixed to top andbottom plates with 3.15 dia. x 50mm long nails @ 75mm maximum centres
Truss height plus height of top and bottom plates
3/3.15 dia. x 75mmlong nails at bothends of plywoodbracing frame toend of floor truss
Standard truss centresplus 35mm web width
Alternative End and Internal Support Bracing
Plywood Bracing Frame at 2400 mm maximumcentres.
Timber Diagonal Bracing at 1800 mm maximum centres.
Posi-PLUS® offcut or seasoned timber blocking at 1800 mm maximum centres.
Truss height
Standard truss centresless truss width
2/3.15 dia. x 75mm long nails to support of floor trusses
7mm structural plywood or 6.4mm thick CSR masonite braceboard fixed to top andbottom plates with 3.15 dia. x 50mm long nails @ 75mm maximum centres
Plywood bracing frame
3/3.15 dia. x 75mm long nails at both ends of plywood frameto vertical web of floor truss
70 x 35 (F5)diagonal brace
3/3.15 dia. x 75mmlong nails typical
3/3.15 dia. x 75mmlong nails typical
Alternative brace to be in opposite direction
70 x 35 (F5)diagonal brace
3/3.15 dia. x 75mmlong nails typical
3/3.15 dia. x 75mmlong nails typical
Posi-PLUS offcut or seasoned timber blocking nailed down to top plate or support
Wall plate/flooring nailed to Posi-PLUS joists,Posi-PLUS offcut or seasoned timber blocking
30 x 2.8mmreinforced head nails@ 100mm centres
100mm
16
A D
W
H
MECHANICAL SERVICESPosi-STRUT® trusses allow mechanical service ductsand plumbing to be easily accommodated. Maximumclearance available for the different Posi-STRUT® depthsis given in Table 13.
Posi-STRUT®
SizeDimension
ADimension
D
PSW3520
PSW3525
PSW3530
PSW4525
PSW4530
PSW4540
127
178
232
158
212
322
120
170
220
150
200
280
280
320
350
310
340
490
200
280
310
260
300
460
120
230
280
200
260
410
50 75 100
Dimension H
Dimension W
125 150 175 200
-
180
240
150
210
370
-
140
210
60
170
330
-
-
170
-
130
300
-
-
130
-
70
250
Table 13. Maximum Mechanical Service Clearances
End and internalsupport bracing at
2400mm maximum spacing
Strongbacks tobe fixed to vertical websat 2400mm maximum centres
17
INTRODUCTIONPosi-STRUT® rafter and purlin details contained in thismanual are only suitable for domestic construction.Although Posi-STRUT® rafters and purlins provide aneconomical solution for many commercial and lightindustrial buildings they need to be specifically designedfor each building. For structures other than domesticbuildings, consult MiTek Australia Ltd. or a licensedGang-Nail fabricator.
DEFINITIONPosi-STRUT® rafters are trusses placed parallel to roof pitch.
Posi-STRUT® purlins are trusses placed perpendicular to roof pitch.
ROOF LOADINGPosi-STRUT® rafters and purlins have been designed toallow for the following dead, live and wind loads.
Dead Loads
Dead loads are due to the weight of the roof structure and permanent fixtures. An allowance hasbeen made for the following permanent loads.
1. Roof and ceiling material
- Terracotta tiles and 13mm plaster battened, maxi-mum load 90kg/m2
- Concrete tiles and 13mm plaster battened, maxi-mum load 80kg/m2
- Steel decking and 13mm plaster battened, maximumload 40kg/m2
2. Self weight of Posi-STRUT® rafters and purlins.
Provision for hot water units and air conditioning unitshave not been considered, Should there be the need for such services then contact MiTek Australia Ltd.engineers for advice.
Live Loads
Live loads are temporary loads due to maintenance ofthe roof structure. These loads are in accordance withAS1170.1-1989.
Wind Loads
The Posi-STRUT® rafters and purlins have beendesigned to conform to AS1170.2-1989 Wind LoadingCode, AS4055-1992 Wind Load for Housing for the maximum design gust wind speed in Table 14.
CAMBERCamber of span/300 or 20mm maximum should be setinto each truss.
SET OUTPosi-STRUT® rafters and purlins have been designed for600, 900, 1200, 1500 and 1800mm centres and in nocase should the design maximum truss centres beexceeded.
Sizes for battens or purlins used in conjunction with Posi-STRUT® rafters to be in accordance with AS1684-1999 ‘Residential Timber-Framed Construction’.
Posi-STRUT® rafters and purlins used in open carports and garages may have higher criteria. In these situations consult MiTek Australia Ltd. engineersfor further advice.
SIZESThe Posi-STRUT® rafters and purlins are available infour nominal sizes 200, 250, 300 and 400mm depths.
As all Posi-STRUT® rafters and purlins are made toorder, they are produced in the exact length required forthe job.
HOLD DOWN DETAILSFixing types for various spans, spacing and roof coveringare given in Table 15.
For more accurate assessment of hold down require-ments on specific projects, refer to MiTek Australia Ltd.engineers.
Details for fixing wall plates to foundations to be by others. The supporting structure must also be designedby others to resist all vertical and horizontal loadings.
Support web withsquare cut timberblock nailed tosupport
END AND INTERNAL SUPPORTBRACINGAt external and internal supports, Posi-STRUT® rafters andpurlins should be braced back to the top plate with the following:
1. Timber Diagonal Bracing (TDB) at 1200mm centresrecommended for PS30 and PS40
2. Plywood Bracing Frame (PBF) at 2400mm centres.
3. Gang-Nail Speedbrace (GSB) at 2400mm centres.
7mm structural plywood or6.4mm thick CSR masonitebraceboard fixed to top andbottom plates with 3.15 dia. x 50mm long nails @ 75mm maximum centres
Truss height plus height of top and bottom plates
3/3.15 dia. x 75mmlong nails at bothends of plywoodbracing frame toend of floor truss
For top chord supported Posi-STRUT® trusses end panelbracing may be omitted if end web is fastened to end wall atbottom chord level.
HERRINGBONE BRACINGUse of Gang-Nail Bracing Strap to connect the top chord ofone Posi-STRUT® to the bottom chord of the adjacent Posi-STRUT®. This type of bracing is to run continuouslythrough the Posi-STRUT® trusses. Refer to detail below.
Herringbone bracing to be at least 3000mm maximum centres. For spans less than 3000mm herringbone bracingis not required.
For PS40 Posi-STRUT® trusses herringbone bracingshould be spaced at 1800mm maximum centres.
PERMANENT BRACINGThese recommendations provide for:
a) Wind Classification areas N4 and C1.
b) Walls being stable in their own right.
c) Roof spans as per Tables 16 to 20.
d) Maximum truss centres - 1200mm for tiled and1800mm for sheet roof.
LATERAL RESTRAINTTop Chord
For roofing battens or roofing purlins use sizes asrequired by AS1684 National Timber Framing Code, at900mm maximum centres.
Bottom Chord
For ceiling battens or ceiling joists use sizes as requiredby AS1684 Residential Timber-Framed Construction at900mm maximum centres.
For suspended ceilings or where ceiling battens do not provide restraint to bottom chords, eg. metal furring channels clipped to trusses, bottom chord tiesmay be required. Use 50 x 25 (F5) ties for trusses up toand including 900mm centres, and 70 x 35 (F5) ties fortrusses at up to 1800mm centres. Fix ties to each trusswith one 3.75mm diameter nail. Splice by lapping overadjacent trusses.
MAXIMUM SPAN CHARTSNote:1. All charts designed using LSD design method.2. Minimum Joint Group JD5.
b) Roof length ‘L’ is 1 to 1.5 times the truss span ‘S’
c) Roof length ‘L’ is long compared to the truss span ‘S’
SPEEDBRACE FIXINGROOF BRACING - Posi-STRUT Rafters -Trusses are placed parallel to roof pitch.
Top Chord Bracing
The top chord bracing shall be arranged according to thefollowing roof lengths using single Speedbrace:
Note:
The following bracing details are designed for the stabilityof Posi-STRUT® truss only. The stability of supportingand end walls should be checked by others.
a) Roof length ‘L’ is less than truss span ‘S’
Where the roof length ‘L’ is very short compared to thespan ‘S’ such that it would result in a brace anglegreater than 45°, a diagonal bracing arrangement isrequired as given below. Bracing bays should bespaced across the roof such that the angle is alwaysbetween 30° and 45°.
Posi-STRUT Rafters
Speedbrace End Fixingrefer detail on page 24
Ceiling battensat 600mmmaximum centres
Roofing battens or purlinsat 900mm maximum centres
Speedbrace
Speedbrace Splicerefer detail on page 24
End bracing required
Between 30° and 45°
Fall
L
S
BRBRBR
L
S
BRBRBRBRBRBR
L
S
BRBRBRBRBRBR
BRBRBR BRBRBR
BRBRBRBRBRBRBRBRBR
Support
Fall
Support
Fall
Support
Fall
30° - 45°
30° - 45°
30° - 45°
23
b) Roof length ‘L’ is 1 to 1.5 times the truss span ‘S’
ROOF BRACING - Posi-STRUT Purlins -Trusses are placed perpendicular to roof pitch.
Top Chord Bracing
The top chord bracing shall be arranged according to thefollowing roof lengths using single Speedbrace:
Note:
The following bracing details are designed for the stabilityof Posi-STRUT® truss only. The stability of supportingand end walls should be checked by others.
a) Roof length ‘L’ is less than truss span ‘S’
Where the roof length ‘L’ is very short compared to thespan ‘S’ such that it would result in a brace anglegreater than 45°, a diagonal bracing arrangement isrequired as given below. Bracing bays should bespaced across the roof such that the angle is alwaysbetween 30° and 45°.
For Posi-STRUT purlins with span greater than 4000mm,double Speedbrace shall be used.
Posi-STRUT Purlinsat 1800mm maximum centres
Top chord tiesat 900mm maximum centres
Wall
Speedbrace
Between 30° and 45°
Fall
S
L
BRBRBR
BRBR
Support
Fall
30° - 45°
BRBRBR
BRBR
S
L
Support
Fall
30° - 45°
BRBRBR BRBR
24
Typical End Fixing Detail
Typical Splice Detail
Three nails through common holes in overlapped ends
Top chord
2 nails intotop chord
Speedbrace
2 nails intotop chord
Bend brace over end truss top chord and fix with three nails to the face of the top chord
End bracingrequired
c) Roof length ‘L’ is long compared to the truss span ‘S’
S
LSupport
Fall
30° - 45°
BRBRBR BRBR
BRBRBRBRBRBR
MiTek Australia Ltd. ABN 98 004 564 587 GN007-12/02