Attachment 4 - Site Investigation and Slab Report

                   barrier systems within the masonry walling or            requiring minor repair work such as repointing.
                   cavity. For situations where the damp-proof course       Note that these fine cracks usually occur in the
                   is more than say 400 mm above the footing or the         mortar joints where they often go unnoticed.
                   risk of cracking in this area must be minimised, it      Damage in categories 3 and 4 will generally
                   is recommended that the articulation joint should        require more substantial repairs.
                   extend down to the footing and allowance be made             Thus while articulation allows a more flexible
                   for movement in any built-in components such as          and therefore economical footing system for a
                   termite barriers.                                        particular walling type and soil reactivity, the
                       Ideally, the wall layout for the building should     expected performance levels of the standard
                   follow a basically straight grid pattern so the          designs having articulated walling follows the same
                   beams of a raft slab can follow the wall pattern         philosophy outlined above regarding acceptable
                   economically and simplify the division of the wall       crack widths, ie the majority of articulated walls
                   into independent panels by articulation joints.          on footing systems complying with AS 2870 will
                       The roof construction (framed, trussed or            perform satisfactorily, some will display fine cracks
                   beam‑and-rafter) should include adequate bracing         and a few will have noticeable cracking.
                   to prevent spreading of the roof framing and hence           Articulation may therefore be used in two ways
                   the tops of walls being pushed out which could           for any given walling type: it may be used to reduce
                   cause cracking of internal walls that are located        the required footing size, or, by maintaining the
                   adjacent to the eaves.                                   footing size required for the non-articulated case,
                                                                            to further reduce the risk of walls cracking and
                   4        FOOTINGS FOR ARTICULATED WALLS                  windows and doors jamming. The latter approach is
                   One of the benefits of articulated walling is the        recommended for walls containing arches, and for
                   reduction in the size and ultimate cost of footings      buildings with rendered or painted finishes where
                   required for a building with masonry walls on            any cracking that may occur is more noticeable.
                   reactive soils. Because an articulated structure has         If one of the standard footing designs in AS 2870
                   sufficient flexibility to move in harmony with the       (which ensure compatibility between footing design
                   footings without developing unacceptable cracks,         and tolerable movement for the type of walling
                   the footing can be designed to be less rigid than        system) is not used, the designer should consider
                   would be required for a non-articulated masonry          the following points when determining the allowable
                   superstructure.                                          deflection of the footings:
                       Regarding the ‘acceptability’ of cracking,           ■ Materials and construction of internal and
                   AS 2870 includes guidance on this by classifying the         external walls
                   damage that may occur to walls. Adoption of the          ■ Surface finish of internal and external walls
                   deemed-to-comply or standard footing designs in          ■ The number of articulation joints and their
                   AS 2870 should ensure that the majority of damage            location
                   to walls falls into damage category 0 (either no         ■ Length and plan arrangement of walls
                   cracking or hairline cracks less than about 0.1 mm       ■ The inclusion of damage-prone elements such
                   in width), some may fall into category 1 (fine cracks        as masonry arches.
                   less than about 1 mm in width which do not need
                   repair) and a few may fall into category 2 (noticeable       Suggested maximum limits for the deflection
                   cracks less than about 5 mm in width that can be         for the design of footings and rafts for various types
                   easily filled). Damage categories 3 and 4 include        of construction given in AS 2870 are reproduced in
                   cracking from 5 mm to 15 mm and 15 to 25 mm              Table 1. The limit adopted for a particular design
                   respectively with doors and windows jamming and,         will depend on the form of construction and take
                   in the worst cases, possibly distorting. Damage          account of factors such as the distance between
                   within these categories seldom occurs, and when          articulation joints, number of storeys, first-floor
                   it does, is usually the result of some specific site     construction materials, wall surface finish, and
                   problem. The range of categories acknowledges            whether or not the masonry is reinforced. The
                   that standard footing designs on typical sites of a      design limit for deflection should be nominated
                   particular soil classification (Class A, S, M and H)     by an experienced engineer. Note that for
                   will generally perform satisfactorily, but that soil     non‑articulated, full-masonry construction, a
                   conditions are variable. Thus, in some instances the     deflection of the footing of around 5 mm over a
                   soil and therefore footing movements will be greater.    10-m span may cause cracking.
                       The Guide to Standards and Tolerances4                   Should more than one form of construction be
                   produced by various State Government Authorities,        used in a building, it is possible to design footings
                   refers to a category 2 crack as being a defect           with different limits of deflection in separate parts


Page 4 Articulated Walling