Calculating the critical value of the natural frequency and deformation modulus of reinforced concrete structures for dynamic monitoring

Introduction . This ongoing study considers the dynamic characteristics of building structures with cracks in concrete when monitoring using vibration diagnostics. Previously developed methods provided an assessment of the reduction in stiffness and natural frequency in structural elements. Critical values of frequency and corresponding deformation modulus were then determined; when reached, further operation of the building would be impossible. An original approach to determining the critical value of the natural frequency and the corresponding deformation modulus of concrete is described. Aim . To determine the critical natural frequency of a building section (floor/wall), beyond which the building can no longer be exploited. Materials and methods. Values of the critical natural frequency and the corresponding value of the deformation modulus of the slab and wall were obtained using examples. The impact of combined boundary conditions, i.e., the combination of hinged supports and rigid fixing, on the natural frequencies of various building structures is examined. Results . The obtained calculation results, with regard to vibration diagnostics, indicate a margin of strength and load-bearing capacity for the slab, while the wall has sufficient strength, albeit with an insignificant margin of load-bearing capacity. Conclusions . Compared to the approach outlined in the EMERCOM methodology, the proposed method is advantageous in calculating the critical value of the natural frequency and the deformation modulus of concrete in building structures.