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Concrete In Australia : March 2013
16 Concrete in Australia Vol 39 No 1 NEWS tested during the costing and tendering period. Formwork costs at the time were high and the reduction in formwork materials had to be weighed against an e cient structural oor system that minimised material quantities. Flat plate oor systems had many positive construction bene ts, including e cient installation of building services and minimum formwork requirements. However, for long span oor areas with heavy loading, the structurally e cient banded slab system provided material savings. Post-tensioning was introduced in the bands to further reduce the band depths, to control de ections and further reduce slab depths. During nal design, a banded slab system was adopted for the oors of the clinical levels, including a combination of post-tensioning in the bands and conventional reinforcement in the slabs, as the most appropriate for future exibility. On the ward oors, two-way, post-tensioned at slab was adopted and over-depth sections were provided in discrete areas, to allow for future wet area set downs. Another consideration was where specialist treatment areas in oncology, radiography and nuclear medicine use medical equipment that delivers targeted levels of radiation to the patient. Scattered radiation must be attenuated by appropriate shielding that is incorporated within the walls, oors and roof elements of the radiation treatment areas. Typically, radiation attenuation performance is directly related to the material density and thickness of the element through which the radiation is passing. Concrete s density and ease of placement makes it ideal as a shielding material. Wall and roof depths can be large, particularly around the linear accelerators, where the radiation levels are highest. In the oncology bunkers, the roof of the bunkers also form the oor to the accommodation level above and planning constraints meant that only a limited zone was available to form the bunker roof. ere was no restriction on space for the wall elements and normal weight concrete with a minimum density of 2350kg/m3 was used. Walls 2.2m thick were required in the primary barrier zone adjacent to the linear accelerators and an equivalent depth of normal weight concrete was required for the roof. An overall zone of only 1360mm was available at the roof level which was inadequate using normal weight concrete alone and an alternative construction had to be developed. e solution was to use a hybrid construction, comprising four sheets of 100mm thick steel plate and a 960mm depth of heavy weight concrete, with a minimum dry density of 3500kg/m3. To achieve the heavier density, local aggregates had to be sourced. Barytes and magnetite, available in the north of the state, were investigated. Magnetite was chosen based on easier availability and cost. e reinforcement design in the bunker elements was based on controlling crack widths arising from restrained shrinkage and early age thermal stresses. A maximum crack width of 0.2mm was adopted for the reinforcement design, based on limits used in the nuclear industry for containment vessels. e massive elements meant that early age temperature gradients and peak temperatures had to be controlled, and trial mixes to test the thermal characteristics of the concrete during the hydration process, were developed by the contractor. Low heat cement was used to control the peak temperature and thermal blankets used to control thermal gradients. In situ temperature monitoring was undertaken during the The 3D model of the entire Fiona Stanley Hospital.