Influence of reinforcement type on the creep of compressed reinforced concrete members

The relevance of this work stems from the absence, in current regulatory documents (SP 63.13330.2018), of methods for accounting for the restraining effect of reinforcement on concrete creep. This omission can lead to a significant overestimation of design deformations and an inadequate assessment of structural stiffness under long-term loading.

A series of 62 specimens of six types was manufactured and tested: control concrete prisms, prisms with internal bar reinforcement, and steel-concrete prisms with external steel plate reinforcement. The latter were produced in three configurations, differing in the length of the tie rods and the presence of transverse ties, as well as steel-concrete web-type specimens. The testing program included both short-term tests until failure and long-term tests under two stress levels (0.3 and 0.5 of the ultimate load) under uniaxial and biaxial compression. It was recorded that, for the same reinforcement ratio, the creep deformations of specimens with internal bar reinforcement were, on average, 20% higher than those of specimens with external plate reinforcement at a stress level of 0.3. When the stress level was increased to 0.5, this difference grew to 25%. Under biaxial compression of the web-type specimens, longitudinal creep strains decreased by 25% compared to the uniaxial compression regime, demonstrating an additional reserve in the deformability of structures operating within closed contours. The obtained data indicate that neglecting the restraining effect of reinforcement in design codes can lead to an overestimation of creep coefficients by a factor of 1.5 to 2 for reinforced concrete elements, and by up to a factor of 3 for steelconcrete composite structures under biaxial compression. The study substantiates the necessity of a differentiated approach to accounting for the influence of reinforcement, depending not only on its ratio but also on its type (bar vs. plate), bar diameter, and the stress-strain state of the element. Directions for improving the current regulatory framework are proposed.

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