The availability of Hanson Design Software provides greater flexibility in the application of hollowcore flooring. The selection of software menu items Design or Analysis gives the designer the opportunity to quickly size a hollowcore floor plank for a particular load case.
The plank span length is the primary consideration. For a framed structure the most economical grid is to maiximise the span of the hollowcore plank and minimise the span of the support beams with a minimum number of load paths.
Hollowcore floor planks are best suited as simply supported one way spanning slabs, where lateral restraint of the building is provided by shear walls.
Alternatively, connections between vertical elements and hollowcore flooring can be designed to resist moments. Also, multi-span hollowcore flooring structures can be designed to promote continuity.
manufacture
Hollowcore planks are cast by a self propelled machine on 170m long line steel form casting beds. Earth moist concrete is intensely compacted around core formers and prestress tendons. The tendons are anchored to bulkheads at each end of the form.
floor depth
The load span chart 1.1.6 below can be used for a preliminary selection of a floor plank. A nominal concrete topping of 60mm has been used for all planks except for the 300 plank that has a 75mm topping.
plank width
It is preferable that the floor plan dimensions suit a 1200mm module width. Non modular dimensions can be accomodated with longitudinally cut planks or wet-cast planks.
plank length
The planks are cut to the length required for their location in the floor plan. The ends can be cut to an angle to suit skewed layouts.
connections
The Hanson Detailing Manual covers typical connection details between hollowcore floor planks and supporting beams or walls. The connection details at a support must not only transfer load but also contribute to the monolithic behaviour of the entire structure.
camber and topping
Hollowcore floor planks are cambered because of the upward bending induced by the prestressing. This camber should be allowed for in detailing the planks. A site cast topping unifies the planks into a monolithic floor, takes out differential levels between planks and provides a uniform working surface.
Fire resistance level
The FRL is normally varied by changing the cover to the strands and generally adding topping to the floor. This is effective up to a fire resistance period of 180 minutes. Flexural continuity at one end of a span of imposed loads substantially increases the fire resistance period for structural adequacy or enables a reduction in cover.
loads
The Loads Menu in the design software provides options for input of distributed and point permanent or imposed loads. Advice on point and line loads is also contained in the software and the Precast Handbook.
bearing support
Typical connection and support details are shown in the Hanson Detailing Manual. The design software default bearing length value of 75mm is normal and 60mm is the recommended minimum. The designer must specify the required length, taking into account such factors as the loading, supporting materials, manufacturing tolerances, placement tolerances and any support rotation.
vibration
AS3600 does not prescribe any design criteria for the control of vibration. The Precast Handbook provides further reading on this topic. Hanson's Design Software calculates the fundamental frequency of the plank. A reported value below 3 cycles per second should be investigated further since this is the resonance band for noraml foot traffic.
FIGURE 1 - Plank Indentification
FIGURE 2 - Standard Section Details
FIGURE 3 - Fire Resistance Levels(FRL) and required cover
Hollowcore Flooring, load Span chart 1.1.6, composite structural topping
detailed design
Deatiled design for any floor plank situation should be prepared by the Structural Engineer responsible for the structure as a whole. For the range of Hanson services, including design, costing, detailing, manufacture and erection, contact Hanson.
Specification
A specification is available(see Other Data) as a guide to preparing a general project specification or as a stand-alone specification.
Simply email Hanson for a free copy of the software.