Posi-Joist Home  |  Span Checker  |  CPD Course  |  Technical Info

 Span Checker Banner

SIZE INFORMATION

The six different Posi-Strut web sizes when combined with two 47mm deep chords result in the following six standard joists depths:

PS8    202mm
PS9    225mm
PS10  253mm
PS12  304mm
PS14  373mm
PS16  421mm

Beyond the standard sizes it is possible to achieve a variety of custom depths by rotating the timber orientation of the Posi-Joist or Posi-Rafter through 90 degrees to be on edge.  By combining different timber sections on the top and bottom chord and selecting from the six available Posi-Strut web sizes the possibilities are endless.

The table below illustrates the maximum duct sizes that each of the standard Posi-Joist depths can accommodate.  

Size Information
Site Handling

Storage on site should be for a limited period of time prior to erection of the Posi-Joists. Posi-Joists should either be stored vertically or on the flat. If stored vertically there should be intermediate bearers at node points not within the bay of a joist, as shown below. If stored in a flat position, sufficient bearings should be provided to prevent excessive lateral bending. 

Stacking on Site

It is recommend that completed Posi-Joists be strapped together and wrapped in a waterproof protective covering to protect them from short term exposure to inclement weather. Special precautions should be taken when stacking top chord supported floor cassettes to prevent the stack lozenging in storage. Additional bracing to the ends of the stack should be fixed to stop lateral movement. Care should be taken when handling the Posi-Joists to avoid bending, twisting or dropping. When loading / offloading with a crane, slings should always be attached to the timber chords or the cassette lifting points, and not to the metal webs to avoid buckling. Slings should be attached at panel points closest to the quarter points of the PosiJoists as shown in the diagram.  

Lifting Posi-Joist1

 

Install Guidance

Posi-Joists are generally placed perpendicular to the load bearing supporting walls and should be located so that the distance between them does not exceed the design spacing - always consult the PosiJoist™ layout drawing and proceed with erection of the floors as follows:-

1 - Plan the erection sequence and place the PosiJoists close to where they are required, only distribute a sufficient number of joists around the building which an be erected in a reasonable period of time. Posi-Joists should be protected from inclement weather.

2 - Before lifting the Posi-Joists to scaffold level do make sure the correct end of the joist is at the appropriate support as the end details may be different. Also be aware of any internal supports which are being used and that the special internal bearing detail for the joist is in the correct position.

3 - If the Posi-Joists are supported over more than two supports make sure all the supports are the same level and when the joists are lifted into place they rest on all of the supports.

4 - If the Posi-Joists are supported on masonry hangers, make sure they are the ones specified and are firmly anchored in place and that the masonry is cured in line with hanger requirements. Joists should have a full bearing with no more than a 5mm gap between the end of the joist and the face of the hanger. Masonry hangers with a cavity return and integral strap provide lateral restraint to wall heads.

5 - Make sure the Posi-Joists are erected the correct way around, the joists will normally be marked "TOP" and the first metal web will normally start at the top of the Posi-Joist.

6 - The Posi-Joists are positioned to coincide with the deck joints, the first of which is normally 1210mm away from the wall face in masonry construction or 1200mm from the cavity face in Timber Frame construction when the deck extends to the cavity face; when the joists are spaced at 400 or 600mm centres.  There is normally a 10mm perimeter gap between the face of the deck and the face of the wall in masonry construction to allow for potential expansion of the deck. The board material is normally 1200 x 2400mm, the long dimension spanning at 90° to the joist span. The remaining joists are normally spaced on a grid of 400, or 600mm centres, on occasion at 480mm centres.

7 - When the deck is set out from the face of the wall it is normal to have the first joist edge 50mm from the face of the wall where in Timber Frame construction with the deck set out from the cavity face it is normal to not have a joist close to a wall, the deck and plasterboard being supported on a timber ledger nailed to the frame.  Carefully follow the layout drawing and the wall/joist interface details provided by the Building Designer, in particular in Timber Frame where the joist centres and the stud centres may have to line through.

8 - The penultimate Posi-Joist in the run is set out on the standard module and the last joist is positioned similar to the first in the run.

9 - Posi-Joist stair trimmer joists and trimmers will be required around stair openings which may be on the main joist grid or usually off the grid. Set these joists out strictly in accordance with the architectural and Posi-Joist™ layout drawing and fix the trimmer joist to the stair trimmer and the trimmed joists to the trimmer joist with the metal hangers specified making sure that any 2 ply joists are adequately connected together as detailed.

10 - To temporary brace and space the Posi-Joists which have been laid in position fix a piece of 22 x 97 bracing to the top of the joists at their ends and mid span or around 2.4m centres on spans longer than 4.8m.

11 - Install the strongback bracing as detailed, the strongback is always installed on edge not on flat and must be fixed  to the integral strongback blocks or noggin pieces nailed to the face of the joist. The strongback must be fixed tight to the underside of the top chord.  On all top supported Posi-Joist floors with installed strongbacks it will not normally be necessary to use any temporary diagonal bracing. On bottom supported wide flange chords (72mm or wider) once the strongback and rim boards are fixed in place no temporary diagonal bracing is normally required.  On bottom supported narrow chords (35 - 47mm) then temporary diagonal bracing is required as well as the strongback and rimboard bracing.

12 - When all the Posi-Joists have been positioned and fixed in place, the partition noggins, perimeter noggins, rim boards, when required can be installed, and in the case of masonry construction the steel lateral restraint straps should be fixed in place at no greater than 2m centres and should extend over 3 joists.

13 - The floor carcass is now ready to receive the decking material and acoustic material where required.

14 - The maximum load of sheet materials temporary stored on the Posi-Joists is 250kg/m2 and should not be greater than 300mm deep. This equates to 16 sheets of 18mm chipboard, 13 sheets of 22mm chipboard or 20 sheets of 15mm plasterboard. Where the sheets are stacked by hand they should span lengthways across the joists, (Fig 1 below), when lifted mechanically they should be seated on 5 bearers the width of which are 600mm longer than the width of the board. (Figs 2 & 3 below)

 

Installation of Posi-Joist