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Home arrow Engineering arrow Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete: Proceedings of the International RILEM Workshop FRC-CREEP 2016

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Mid-term Deflections Under Constant Load

The 0 point of the deflection curves was set after an offset of three minutes. This choice is due to the dispersion of the deflections recorded during the first minutes. This dispersion corresponds to the resetting of the slabs in their frame (after transportation from the punching press to the creep test apparatus), to the fibres distribution or mesh position and to the gradual application of the load as the screw is lowered. The deflection values during the first minutes cannot be analysed in a reliable way because all these parameters have not been investigated yet and because the duration of the load application may vary from one creep device to another. More work is needed on that subject.

Deflection versus time curves for slabs still in the pre-cracking phase

Fig. 2 Deflection versus time curves for slabs still in the pre-cracking phase

Figures 2 and 3 show the deflections of the slabs. They were separated into two sets: slabs still in the pre-cracking phase and slabs which load was reduced because their total deflection exceeded 2 mm (without the 3 min-offset). The first set of slabs (Fig. 2) were reinforced with metal fibres or welded wire mesh, apart from one slab reinforced with synthetic fibres; the second (Fig. 3) were reinforced with synthetic fibres, apart from two slabs—one reinforced with metal fibres and the other with welded wire mesh.

The shape of the curves, showing an inflection point around 120 days, is due to a rapid rise in ambient temperature, linked to repairs carried out on the heating system of the room. The acceleration of the deformations was observed during a rapid transition from 10° to 18 °C (see [2]).

Under their respective load (varying from 1 to 2 as said before), all slabs (except one) had relatively small deflection values (< 3 mm). The exception is a slab reinforced with synthetic fibres, which deflection was exponential and interrupted at around 20 mm when the loading plate came in contact with the loading screw (see Fig. 1).

One type of polymeric fibres provided reinforcement that is clearly superior to that provided by the two other polymeric fibres.

The behaviour of the metal fibres was more homogeneous but the variety of fibres tested is not sufficient to draw a general conclusion.

Deflection versus time curves for slabs under creep load

Fig. 3 Deflection versus time curves for slabs under creep load

The creep deformations of the two slabs reinforced with a welded wire mesh were of the same order as those reinforced with metal fibres; the third slab behaved in a similar manner to the slabs reinforced with synthetic fibres.

 
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