Experimental analysis of stress block parameters for normal and high-strength concrete and possible influence on strong-column-weak-beam philosophy

A comprehensive experimental investigation is carried out to establish concrete stress–strain models for normal and high-strength concrete through uniaxial unconfined compression tests on concrete cubes with target characteristic compressive strengths ranging from 30 to 90 MPa at increments of 10 MPa. The primary aim is to develop strength-specific stress block parameters for structural design applications. Mix design of concrete is carried out conforming to the Indian Standard for each concrete grade, with 30 specimens cast for bulk testing and subsequent analytical investigation. A procedure is proposed to construct a parabolic-rectangular design stress–strain relation (stress-block) from the ensemble of bulk testing conditioned to the same target characteristic strength. The strain at peak stress is proposed as a function of the characteristic strength, whereas the ultimate strain is observed to be nearly independent of it. Stress-block parameters (shape and centroid factors) for the design of beams and columns are developed conforming to the proposed stress–strain relation, which is contingent on the characteristic strength. Further, the influence on the associated moment of resistance of beams and axial force-bending moment interaction of columns is investigated. The flexural strength of the (under-reinforced) beam remains unaffected by the proposed modification, as validated using a 3-point flexure test. However, in columns under axial load, the use of strength-independent stress-block parameters leads to an underestimation of flexural strength, and the extent of underestimation increases with the grade of concrete. Additionally, the modulus of elasticity shows a linear relationship with strength, given a lower bound threshold is considered.