Determination of concrete fracture toughness from modal dynamic response of notched beams

Modal dynamic analysis is proposed to evaluate concrete fracture toughness from notched-through beam tests. The dimensionless function of dependence of frequencies on geometry, which leads to identifying the variation of a natural frequency as a function of crack depth, is first determined for the ( https://www.w3.org/1998/Math/MathML" display="inline"> 150 × 150 × 500 ) mm notched-through specimen. A modal/fracture mechanics approach is used to model the frequency reduction arising from the cohesive interface of the propagating fictitious crack. Therefore, an effective crack length is determined. The computationally obtained length is used to calculate the concrete fracture toughness. The method is applied to test results of high strength concrete. Within the experimental program, the beams are evaluated twice with regards to their frequency responses, before and after an imposed crack. The results proved to be compatible with fracture toughness values obtained from other existing methods. This fact demonstrates that toughness and damage evolution can be conveniently predicted from peak load and dynamic modal responses, within a simple procedure.