Attachment 4 - Site Investigation and Slab Report

Dowel bars are cast into the concrete on one side       10        ARTICULATED WALLING – KEY POINTS
of the joint with the other end allowed to slide/       ■    Reactive soils swell and shrink with moisture
move by wrapping and greasing this half of the               variation causing a doming or dishing of footing
bar, coating it with an approved bond-breaking               systems and possible distortion of both external
compound or providing an appropriate sleeve within           and internal walls of domestic-scale buildings.
which the bar can slide. The sliding ends of dowel      ■    Articulation greatly limits cracking or distortion
bars should have purpose-made plastic caps at the            of walling and jamming of windows and doors
ends or plugs of polystyrene equal to the joint width        caused by foundation movement.
taped at the end to enable the articulation joint to    ■    Articulated walling reduces the size and
close. Articulation joints bridged by dowels should          cost of footings for buildings on reactive-soil
be finished with a filler strip and sealant where            sites. These benefits are most significant for
they are visible Figure 35. Note that the steel bars         masonry‑walled buildings.
crossing the joint should be suitably protected from    ■    Although articulation is most effective
corrosion. Typically, galvanised bars are used. In           for masonry walling, it is also a benefit for
coastal locations the use of stainless steel dowel           frameclad-walls.
bars may be required.                                   ■    Articulation increases the allowable deflection
    As bond beams will typically have either 12-mm           for the footings thus giving the engineer more
or 16-mm-diameter dowel bars (ie bond beams are              latitude to design a more economical footing.
typically reinforced with N12 and N16 bars), a length   ■    Articulation joints should be positioned and
of 600 mm should be sufficient for dowel bars.               detailed with care to allow the building fabric to
    Joints in bond beams must be considered in the           flex in harmony with the footing movement.
design of the structural system. They should be         ■    Wallheight should be minimised in order to
located at returns/intersecting walls such that the          limit the extent of movement that must be
joint in the bond beam does not result in instability        accommodated in an articulation joint.
of the wall or limit the ability of the bond beam       ■    Bond beams should be carefully detailed where
to transfer horizontal loads to lateral supports             crossed by articulation joints.
Figure 17. In order to transfer wind uplift loads, a    ■    Arches in buildings on reactive-soil sites will
vertically reinforced and grouted core should be             require additional precautions as outlined in
provided on both sides of the joint, similar to the          Section 8.
requirement for window and door openings.               ■    The addition of appropriate bed-joint
    Above window and door openings. Bond beams               reinforcement may significantly strengthen
above openings act as lintels to support the loads           a wall, reduces cracking and permits
above.                                                       more‑economical footings to be used.
    Joints should be designed, located and detailed
in such a way that the effectiveness of the bond        11     REFERENCES
beam to support loads is not affected. However,         1 AS 2870 Residential slabs and footings –
articulation joints should be moved away from the          Construction Standards Australia, 1996.
sides of openings to allow continuity of the bond       2 Building Code of Australia, Volume 2, Housing
beams and comply with AS 3700 requirements. The            Provisions Australian Building Codes Board,
reinforced bond beams will mean that there is less         2007.
risk of cracking at openings than would otherwise       3 Foundation Maintenance and Footing
be the case.                                               Performance: A Homeowner’s Guide, CSIRO
    Alternatively, if joints away from window and          Publishing Building technology File 18, 2003.
door openings are not acceptable, then more rigid          Available for purchase at www.publish.csiro.au.
footings should be provided.                            4 Government Guide to Standards and Tolerances
                                                           Victorian Building Commission, Office of Fair
                                                           Trading NSW, Tasmanian Government and ACT,
                                                           2007
                                                        5 Special Provisions for the Design of Residential
                                                           Slabs and Footings for South Australian
                                                           Conditions The Footings Group, The Institution of
                                                           Engineers Australia, Adelaide, 1 March 1994.
                                                        6 AS 4773 Masonry in small buildings, Part 1 –
                                                           Design, and Part 2 – Construction, (to be
                                                           published).




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