Experimental investigation of cracking and deformations of concrete ties reinforced with multiple bars

- Cracking and deformations of concrete ties with multiple bars are investigated.
- A specific equipment for producing and testing such ties was developed.
- Two reinforcement schemes are considered: 4-bars reference and 16-bars alternative.
- The alternative schemes secure indistinguishable deformation behaviour of identical ties.
- The experimental crack spacing is practically independent on the ∅/p ratio.

Interpretation of test results may be inadequate even for simple test layouts. On the one hand, conventional tests, that investigate a concrete prism reinforced with a single bar in the centre, do not allow to account for the effect of variation of the diameter-to-reinforcement ratio (∅/p). This important limitation should be related to the use of simple specimens in constitutive modelling. On the other hand, a tie-test typically provides measurements of average deformations of the internal reinforcing bar and the concrete surface. The experimental evidence, however, often contradicts the general assumption of the equivalence of the mean strains of reinforcement and concrete. The strain difference is closely related to the width of the concrete cover. This paper investigates the effect of distribution of bar reinforcement on deformation and cracking behaviour of tensile elements. Special testing equipment has been developed to investigate ties reinforced with multiple bars. The test program consists of 23 ties. The number and diameter of the bars vary from 4 to 16 and from 5 mm to 14 mm, respectively. Two different covers (30 mm and 50 mm) are considered as well. The deformation analysis is based on measurements of the average reinforcement and concrete surface strains. The development of cracks was investigated using digital image correlation (DIC). The Model Code 2010 and Eurocode 2 predictions are compared with the experimental data. While the Design Codes predict that the maximum crack spacing is dependent on the ∅/p ratio, the test results indicate that the crack distances are actually much less dependent on the reinforcement characteristics.

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