Applicability of the regulatory approach for reducing the modulus of elasticity under short-term actions for high-strength concretes

Introduction . According to SP 63.13330.2018, when calculating the second group of limit states for shortterm loads, the modulus of elasticity of concrete is taken with a reduction factor of 0.85. Historically, this factor accounted for inelastic deformations and short-term creep. However, its validity for modern high-strength (B80–B100 and higher) and modified concretes, as well as for steel-concrete composite structures, has not been experimentally confirmed. Aim . An experimental and theoretical assessment of the applicability of the 0.85 factor to the initial modulus of elasticity of high-strength modified concretes under short-term actions on pre-loaded structures. Materials and methods . More than 100 specimens of self-compacting concrete class B90–B100 with a modulus of elasticity of 55 GPa were tested: prisms, cylinders, steel-concrete composite prisms with steel plates, and cores extracted from pre-compressed columns. The following scenarios were implemented: standard tests, increased load holding times, elevated stress levels (up to 80 %), long-term pre-compression (over 3 months) followed by additional loading, and core tests. The modulus of elasticity was determined according to GOST standards and by a developed methodology (between loading stages). Results . The deformation behavior of the concrete under study was almost linear up to failure, with minimal microcracking and creep. The maximum reduction in the modulus of elasticity across all scenarios did not exceed 10 %, and for reference prisms it was no more than 7 %, which is lower than the standard 15 %. The applicability of the findings to steel-concrete composite structures and the feasibility of estimating the modulus of elasticity from core samples were confirmed. Conclusions . For high-strength modified concretes, the application of a reduction factor of 0.9 instead of 0.85 under short-term loads is justified, which allows for a reduction in the design horizontal displacements of high-rise buildings by 5–10 %.