BONDEK II COMPOSITE SLABS
BONDEK II profiled steel sheeting is delivered in strapped bundles.
If not required for immediate use, sheets or bundles should be neatly stacked clear of the ground. When stacked they should be on a slight slope to allow drainage of water, should wetting occur prior to use.
The sheets or bundles should not be left exposed in the open for extended periods. If unavoidable, then they should be protected from rain and moisture with waterproof covers.
Depending upon the span of the BONDEK II composite slab temporary lines of support (or propping) located between the slabs supports may be required. This support will need to be kept in place during the laying of the BONDEK II sheeting, the concrete placement and until the concrete has achieved sufficient strength to support the loads. Detailed information on span of BONDEK II sheets between lines of support may be obtained from Lysaght publication BDII-1.
BONDEK II sheeting is normally placed directly upon prepared propping and the propping shall support the BONDEK II sheeting across its full width.
Propping generally consists of substantial timber or steel bearers (minimum bearer width of 100mm is required) supported by vertical props installed to prevent settlement during the placement and curing of concrete.
Notwithstanding the requirement for minimum bearing, where the underside of the BONDEK II sheeting is featured as the finished ceiling, the use of wide form ply strips attached to the bearers will minimise bearer marks. The width of the form ply strips will depend upon the slab depth, sheeting thickness and spans. Form ply strips of 300mm width have been successfully used.
Propping is designed to support construction loads and the mass of wet concrete. For the design of propping refer to Lysaght publication BDII-1.
Cutting of BONDEK II sheets is sometimes necessary to trim sheet sides or to cut sheet ends around projections such as columns and stairways. BONDEK II sheets may be readily cut using a power saw fitted with an abrasive disc or metal cutting blade.
For cutting it is suggested that the sheeting be initially laid "ribs down" and cut through the pans and part through the ribs. The sheeting could then be turned over and the cutting of the ribs completed.
BONDEK II profiled steel sheeting must be laid with the sheeting ribs aligned in the direction of the spans.
Where BONDEK II sheets are laid to form a continuous platform the following details must be observed
The slab supports must be prepared for bearing and slip joints as required (refer to Installation – Placement of Slip Joints).
BONDEK II sheets must continue over each slab span without any intermediate splicing or jointing.
BONDEK II sheets must be laid end to end and the joint generally centralised at the slab supports. Where jointing material is required the sheets may be butted against the jointing material.
BONDEK II sheets must be supported across the full width at the slab support lines and the temporary support lines (propping).
The end and edges of the BONDEK II sheets must be provided with a suitable edge treatment in exposed applications to prevent entry of moisture.
A minimum bearing is required for supports to carry the wet concrete and construction loads. The minimum bearing is 50mm for ends of BONDEK II sheets and 100mm for intermediate supports over which the sheeting is continuous.
The BONDEK II sheeting must be assembled with the side lap ribs interlocking. Interlocking can be achieved by two methods as described below. However, either method may be used in most situations. Variations to these methods may be acceptable.
One method of achieving the interlocking is to progressively lay the BONDEK II sheets parallel with the previous sheet. The female lap rib is placed overlapping the male lap rib of the previous sheet and interlocking is achieved by applying foot pressure, or light kick, to the female lap rib to clip onto, and interlock with , the male lap rib. Interlocking should be done progressively as each sheet is laid down (see Figure 11A).
An alternative method requires the female lap rib to be placed down at an angle to overlap the male lap rib of the previous sheet. The angled sheet is then simply lowered down through an arc to rest adjacent to the previous sheet (see Figure 11B).
The lap ribs should thus be properly interlocked. Where this does not occur due to some damage or distortion from site handling or construction practices then it is recommended that sufficient side lap fasteners be used to pull the laps tightly together.
Side lap joints may require fastening (refer to Installation – Fastening Side Lap Joints).
BONDEK II sheeting, when laid, provides a stable working platform. Where additional securing is required to prevent movement from construction activities and from wind, this may be achieved by use of weights or by use of fastening techniques.
Where the BONDEK II sheeting needs to be fastened to the propping, such as in masonry framework or at cantilever ends, the sheeting may be fastened from underneath using BONWEDGE and BON-NUT suspension systems.
Caution should be taken when using penetration fasteners such as screws and nails to secure the sheeting to the propping. Penetration fasteners installed from underneath into the BONDEK II sheeting will result in protruding fasteners. Penetration fasteners installed from above the BONDEK II sheeting into the propping will result in protruding fasteners when the propping is removed. In both situations, the removal of the propping bearers may be problematic resulting in damage to the BONDEK II sheeting.
Installing on Steel Frames
BONDEK II profiled steel sheeting may be installed directly upon the erected structural steelwork.
The sheeting may be secured to the structural steel slab supports where required using spot welds or fasteners such as drive nails and self-drilling tapping screws.
Where a movement joint is detailed at a slab support, the sheeting must not be continuous over this support. The end of one sheet may be secured to the support, the end of the abutting sheet must not be secured to allow for movement of the composite slab to take place
The locations of the securing points (fasteners and spot welds) are to be in the flat areas of the pans adjacent to the ribs or between the flutes. The frequency of securing points to provide uplift resistance or lateral restraint will be dependent upon wind or seismic load conditions and accepted building practice. For information on the frequency, type and size of securing systems advice should be obtained from a practising structural engineer.
One securing system which has been successfully utilised is described below. However, the frequency of the securing points may need to be altered to suit the condition on the project:
Securing points adjacent to every rib at the end of sheets and adjacent to the female rib of the side lap at each intermediate slab support over which the sheeting is continuous (see Figure 12).
Secure BONDEK II with drive nails, self-drilling tapping screws or spot welds.
Drive nails should be powder-activated steel nails 4mm nominal diameter, suitable for structural steel of 4mm or greater flange thickness.
Self-drilling, tapping screws should be no. 12-24 x 38mm hex head, suitable for structural steel up to 12mm flange thickness: for structural steel greater than 12mm flange thickness, then pre-drilling will be necessary with the use No 12-24 x 16 hex head thread forming screws.
Spot welds should be 12mm diameter, made with 3.25mm diameter cellulose, iron powder AC/DC high penetration electrodes. When welding, suitable safety precautions should be taken regarding fumes given off during welding of zinc coated products. Surfaces to be welded must be free of loose material and foreign matter. Where the BONDEK II soffit or the structural steelwork has a pre-painted surface, securing methods other than welding may be more appropriate.
In projects of composite beam construction the BONDEK II sheeting mast be fastened in accordance with Clause 9.2 "Composite Beams with Slabs Incorporating Profiled Steel Sheets" of AS 2327. This provision will require a securing point in each pan at each compositely designed steel beam.
In some projects of composite beam construction where stud welding through the sheet has been specified, the stud welding has been considered to be a suitable securing method for the sheeting, however some preliminary fixing by one of the methods mentioned above is necessary to secure the sheeting prior to the commencement of stud welding.
Where through deck stud welding is to be used, it shall comply with the requirements of AS 1554, Part 2 and AS 2327, Part 1. The relevant construction requirements are summarised below:
Zinc coating on sheeting of Z200, Z275 or Z350 complies with Clause 2.5 "Stud Welding Through Steel Sheet" of AS 1554, Part 2.
Sheeting base metal thickness up to 1.0mm complies with Clause 2.5 "Stud Welding Through Steel Sheet" of AS 1554, Part 2.
Mating surfaces of steel beam and sheeting to be cleaned of scale, rust and moisture prior to welding to comply with workmanship requirements of AS 1554, Part 2 and AS 2327, Part 1.
Mating surfaces of steel beam flange and sheeting to be free from paint to comply with Clause 9.2 "Composite Beams with Slabs Incorporating Profiled Steel Sheeting" of AS 2327, Part 1. For pre-painted BONDEK II sheets special welding procedures may be necessary.
Stud welding must be between pan flutes for sheets transverse to beams to ensure there is no gap between mating surfaces. This is a requirement of Clause 9.2 "composite Beams with Slabs Incorporating Profiled Steel Sheeting" of As 2327, Part 1 and Section 4.5.2 (e) "Design Advice Not Contained in the SAA Composite Construction Code" of AISC "Composite Beam Design and Safe Load Tables"
Installation of Masonry
BONDEK II profiled steel sheeting must not be installed directly upon masonry supports. A slip joint must be provided between the surfaces.
Masonry construction consists of walls made from either fired clay bricks or precast concrete blocks, bound together by mortar. Masonry construction may be reinforced and infilled with concrete or mortar. Lintels in this type of construction are typically made from steel or precast reinforced concrete (see Figure 14). Generally such construction systems are considered to be brittle and are subject to cracking from any imposed horizontal load.
Where precast concrete wall units are used in the same manner as masonry walls, then this section applies to such constructions.
The natural expansion and contraction of concrete slabs may be sufficient to cause such cracking. For this reason it is necessary for a slip joint to be provided between the BONDEK II slabs and its supports. For masonry walls supporting BONDEK II sheeting, the top course of masonry should be constructed level. Where bricks with frogs are used, the top course must be laid with the frogs facing down.
Placement of Slip Joints
Slip joints are required to allow relative movement between the slab and the slab support. Consequently no mechanical connection (such as fasteners) are allowed. This movement is for thermal expansion and contraction, long term shrinkage, creep effects of concrete and slab flexural movements.
Where slip joints are detailed on steel frame construction, the slip joint material may be placed directly on to the cleaned surface of the steel work.
Slip joints are required in masonry construction. Where the top course of masonry is not constructed level, then it must be finished with a level bed of mortar prior to placement of the slip joint to provide an even bearing surface.
The slip joint must be rigid enough to prevent the slab loads depressing it into holes and depressions, thus preventing a mechanical connection. The width of the slip joint should not extend beyond the face of the slab support.
There are various commonly used slip joint materials. Materials which have been used successfully are:
ALCOR: bitumen coated aluminium membrane (or similar).
MALTHOID: bitumen impregnated fibre-reinforced membrane (or similar).
Other materials suitable for this application consist of a non-rotting synthetic carrier impregnated with a neutral synthetic or petroleum based material. Such materials flow under pressure or temperature, however they do not run or solidify and so allow movement to occur. For details of such materials refer to the manufacturers.
Fastening Side Lap Joints
To maintain a stable platform under load, and to minimise concrete seepage during pouring, the side lap joints may require fastening. Fasteners shall be No 10-24 x 16mm self-drilling tapping screws and be located on the side lap rib midway between embossments The frequency of fasteners will depend upon the situation as described below:
The minimum fastener requirement is one fastener at mid-span for support spacing of 2750mm or greater.
To obtain a point load rating of 2.3kN (235kg) the side lap joints will require fastening for support lines spaced over 2000mm. For 1.0 BMT BONDEK II a single fixing at mid-span is required up to a maximum of 3250mm spacing between supports. For 0.75 BMT BONDEK II two fixings at third points are required up to a maximum of 2400mm spacing between supports.
For exposed BONDEK II soffits where good visual quality is required, it may be necessary to provide fasteners as close spacings to ensure a uniform soffit between adjoining sheets, and to further reduce concrete seepage.
In special circumstances where other thicknesses are used, advice on side lap fixing is available from the nearest Lysaght office.
Cutting and Fitting Edge Form
Edge Form is a simple, strong, lightweight, easy to use slab edge form. Edge Form simplifies the installation of most BONDEK II slabs, neatly retaining the concrete. Edge Form is easily fastened to the BONDEK II sheeting and provides a smooth top edge for quick and accurate screeding.
Edge Form is easily spliced and bent to form internal and external corners of any angle and should be fitted and fully fastened as the sheets are installed. There are various methods of forming corners and splices. Some of these methods are shown in Figure 16.
The Edge Form must be fastened to the underside of unsupported panels every 300mm. The top flange of Edge Form must be tied to the ribs every 600mm with builders strapping
No 8-18 x 12mm self-drilling, tapping screws or similar fasteners should be used for all fastening.
The Edge Form zinc coating matches the corrosion protection of BONDEK II sheeting. Where the Edge Form is subjected to a more sever environment then a suitable protection system, as described fro the BONDEK II sheeting in General Data – Corrosion Protection, should be chosen to match.
Seepage of water or fine concrete slurry can be minimised by following accepted construction practices. The following is provided as a guide only.
The gap between abutting BONDEK II sheets may be sealed using a waterproof tape. Alternatively, by sandwiching contraction joint material between the butting ends of sheeting, seepage would be minimised.
BONDEK II sheeting ends which abut Edge Form may be more effectively sealed with waterproof tapes as above, but in any case with the minimum bearing requirement the concrete seepage would be minimised.
Side laps of BONDEK II sheeting must be fastened as recommended Installation – Fastening Side lap Joints in order to minimise the concrete seepage.
Where there is a sizeable gap between the end of the BONDEK II sheet and adjoining Edge Form or adjoining BONDEK II sheet it may be necessary to provide a support for the overlaying waterproof tapes. BONFILL may be used for this support . Alternatively, the ends of the ribs can be taped off individually.
There are various commonly used waterproof tapes with qualities suitable for the application. Reference to the manufacturer of such tapes should be made for details.
Placement of Fittings
Fittings complying with Clause 14.2 "Embedded Items and Holes in Concrete" of AS 3600 may be used. Such fittings include pipes and conduits with their associated fittings, sleeves, inserts, chairs and other supports, plastic foam strips for plasterboard attachment, contraction joint material and many more.
Longitudinal fittings and full depth vertical fittings must be located in the region bounded by the sheeting ribs and the top-face reinforcement. For singular fittings and where the pipes and conduits are to be placed transverse to the slab span, then it is recommended to locate them at a level between the bottom-face and top-face reinforcement.
To minimise the quantity and size of holing of the BONDEK II sheeting, services and their associated fittings should be supported from the slab soffit by the use of accessories such as BON-NUT, BONWEDGE and Ceiling Suspension Nut.
Placement of Movement Joints
Movement joints allow relative movement between adjoining slabs, and so are accompanied by slip joint material placed under the BONDEK II sheeting.
Movement joints require the installation of jointing material in the vertical plane. The joint material consist of a compressible filler and a sealer in the top section of the joint. These materials will allow expansion and contraction to occur and also provide the necessary water tightness.
Movement joints are contraction joints, control joints (or dummy contraction joints) and expansion joints.
Contraction joints may be positioned traverse to, or parallel with, the span of the BONDEK II composite slab.
Contraction joint material must be placed between the abutting ends of sheeting to ensure separation of sheeting and composite slab. Transverse contraction joints, where detailed, must be located over the slab supports (see Figures 12 and 14). The BONDEK II sheeting and any slab reinforcement must not be continuous through the contraction joints. The contraction joint material may be sandwiched between the abutting BONDEK II sheets.
The location and spacing of the contraction joints is generally detailed by the design engineer, since the joints are a break in the continuity of the slab structure and performance.
Contraction joints are generally located where the stress contractions from shrinkage are expected to occur, such as:
in abrupt changes in cross section
at irregularly-shaped slabs (L T H W); shapes to be divided into rectangular shapes
in long slabs
where slabs behave in different ways
many factors affect the amount of shrinkage and thus the spacing of contraction joints will vary widely. Typical spacings which have been successfully adopted are 15m to 30m (depending upon the climatic conditions).
Expansion joints allow for expansion and contraction and careful consideration by the design engineer is needed for the detailing, location and spacing. Generally, for the location and placement of expansion joints, the aspects covered above for contraction joints apply, however the spacings are generally further apart.
BONDEK II profiled steel sheets act as longitudinal tensile reinforcement as per conventional bar or fabric reinforcement in reinforced concrete slabs. Holing of BONDEK II sheets to accommodate pipes and ducts would reduce the effective area of steel.
Acceptable regions for holing are as follows, however the size and quantity of holing must be on the approval of the design engineer since the extent of holing, and the accompanying reduction in area of concrete, may affect the slab performance
Keep within a length of 0.1 x clear span from an interior support of the slab for slabs designed as a continuous slab.
Holes should be placed in the central pan of any sheet with a minimum edge distance of 15mm from the rib gap.
Holes should be circular with a maximum of 150mm in diameter.
Holes must be cut using a suitable drill or hole saw.
Cutting of BONDEK II sheeting should be carried out after the concrete has cured. This will require accurate location of ducting outlets (eg electrical outlets) during formworking. Small pilot holes drilled through the BONDEK II prior to concrete could be used. The pilot holes should be taped to prevent concrete seepage.
For holes outside the above limitations, advice is available from Lysaght Technical Advisory Service or from a practising structural engineer.
Inspection of the installed sheeting by the relevant site supervisor is recommended at regular intervals of installation to ensure that the sheeting has been installed in accordance with this publication and with accepted building practice.