Attachment 4 - Site Investigation and Slab Report

                      The use of full-height door frames provides an           unreinforced masonry arch with the addition
                  opportunity to run electrical cable for light switches       of bed-joint reinforcement intended only to
                  or power points down from the ceiling between the            hold closed any crack(s) that may occur (see
                  wall and frame by increasing the gap between the             Section 9).
                  two. Note that any services installed in the gap must    ■   Locate articulation joints as close as possible
                  not inhibit closing of the joint.                            to the arch (ie at the sides of the buttresses)
                                                                               to limit the differential movement that could
                  7.7      Wall/Ceiling Junctions                              occur across the arch. The minimum width of
                  Masonry interior walls of a building with a framed           each buttress should be sufficient to resist the
                  roof require top plates to support ceiling joists.           horizontal force from the arch and overturning.
                  The ceiling lining is then fixed under the joists and        If detailed calculations are not carried out, the
                  butted to the top plate. The cornice may be timber or        width of the buttress should be no less than the
                  quarter-round plaster and should be fixed through            height of the arch.
                  the ceiling lining to the ceiling joists and/or to the   ■   Provide a steel lintel to support the arch. The
                  top plate, not to the walling. As there may be some          lintel can be curved to suit the shape of the
                  movement between the wall and the ceiling, the               arch with flat sections welded to each end for
                  cornice must be large enough to conceal the top              building into the buttresses. In this case the
                  plate and be free to move independently of the wall          lintel will be designed to carry the entire weight
                  Figure 32.                                                   above the arch and articulation joints may be
                      If a trussed roof is used, there is no need for a        located adjacent to the arch in a similar manner
                  top plate on internal masonry non-load-bearing               to other openings. Although not recommended
                  walls since the ceiling joists (bottom chords of the         aesthetically, articulation joints may be located
                  trusses) should not rest on internal walls.                  at the arch crown.
                      A gap of at least 10 mm (AS 16849) should be left    ■   Ensure that the footings supporting arches are
                  between the bottom chord of the trusses (or ceiling          continuous so as to avoid having the two sides of
                  battens when used) and the top of the wall where a           the arch supported on separate footings.
                  trussed roof is used – after the roofing and ceiling     ■   Provide a stiffer footing system under masonry
                  are fixed. This gap, plus an allowance for movement          walls containing arches. If the differential
                  must be covered with a timber or plaster cornice             movement of footings due to ground movement
                  fixed only to the ceiling, allowing the wall/truss to        is limited to the point where articulated walling
                  move up and down and the wall to move in its own             is not required, the risk of cracking in arches
                  plane without causing cracking Figure 32 (b).                will be significantly reduced. For slab-on-
                                                                               ground footings, only those edge/internal beams
                  8        Masonry Walls with Arches                           supporting masonry with arches will need to be
                  Many different types of arches can be built into             stiffened.
                  masonry walls. Unlike other openings in walls, all       ■   Maintain the area around footings to ensure
                  arched openings require a minimum arch depth                 consistent moisture conditions in the soil
                  (300 mm) or narrow band of masonry above the                 and thus reduce the potential for differential
                  crown. Arches are particularly susceptible to                movements (shrinkage and swelling) of reactive
                  cracking from footing movement. Such cracking                soils. For more information refer to Section 2.
                  occurs because any footing movement will cause
                  a concentration of stresses at the crown or highest      9       REINFORCED MASONRY
                  point in the arched section of masonry. Cracking         While the use of articulation is normally confined
                  could be severe enough to destroy the structural         to unreinforced cavity and veneer construction, it is
                  effectiveness of the arch. Unlike normal openings,       also relevant for reinforced brick masonry.
                  articulation joints can not generally be located             More-flexible footings may be used where
                  adjacent to the arched opening because sufficient        articulated masonry containing correctly detailed
                  masonry must be provided at each side of the             and positioned reinforcement is used. The footings
                  opening to support (ie buttress) the arch. For           should be designed in accordance with engineering
                  these reasons arched openings are generally not          principles, with the additional crack-control
                  recommended for buildings on reactive-soil sites.        provided by the reinforcement in the wall permitting
                      If arches are required, some options which may       a more generous maximum deflection to be adopted
                  be considered include:                                   for the footing design Table 3.
                  ■ Reinforce the arch depth (Figure 33) to ensure             According to AS 4773 articulation joints are
                      structural performance in the event of a             not required for reinforced masonry designed in
                      crack. The arch may still be designed as an          accordance with Part 1 Section 12. For information


Page 20 Articulated Walling