An experimental study of the Tension Stiffening effect on the structural stiffness of Reinforced Concrete Cantilevered Balcony Structures using resonant frequency measurement approach

The designs of most reinforced concrete structures are based on the Limit State Design Theory, while the Tensile Capacity of Concrete (TCC) is normally not considered. However, the TCC continues to contribute to structural stiffness over the entire pre-cracking and post-cracking stage, and this effect is known as Tension Stiffening. This paper reports an experimental approach to investigating the TCC effect on the structural stiffness of Reinforced Concrete Cantilevered Balcony Structures (RCCBS) by measuring the resonant frequency. A series of coordinated experimental programmes was carried out using three RCCBS models, each differing from the other in terms of scales, structural characteristics and loading conditions, and the corresponding changes of resonant frequency and tensile stress of concrete at different degrees of damage (by cutting of the tensile steel reinforcement bars) were investigated. A set of empirical relationships was established between the resonant frequency and the tensile stress of concrete as well as the damage, and the results revealed that the sensitivity of resonant frequency varies with the TCC effect. An alternative expression of the TCC effect, called the Normalized Stress Value of Concrete in Tension, is proposed to differentiate between higher/lower ranges of the TCC effect on the structural stiffness of RCCBS.

Research highlights
► We investigate Tension Stiffening (TCC) effect on RC balcony structures.
► Resonant frequency shows bilinear relationship to damage due to TCC effect.
► High TCC effect decreases sensitivity of resonant frequency method to detect damage.
► NSVcon(T) can differentiate high/low TCC effects on structural stiffness.