Measurements of intact and cracked concrete structural elements by the SASW method

Abstract

Research was conducted to apply the Spectral-Analysis-of-Surface-Waves (SASW) method to the identification of internal cracking in concrete structural elements such as beams and columns. The SASW method is a nondestructive technique which involves the propagation of surface stress waves along the exposed face of a structural element. By yielding the relationship between wave velocity and wavelength of the surface wave energy, the SASW method provides information about how the stiffness of a material varies with depth. SASW measurements were made on intact and cracked concrete structural elements. Surface waves propagated through cracked concrete at consistently lower velocities. These velocity reductions corresponded to the presence of visibly detectable cracking and, in some cases, occurred in the absence of visible cracking. This result demonstrated the ability of the SASW method to detect otherwise hidden damage. When the cracks were reclosed by the application of a compressive load, the surface waves propagated at velocities comparable to those of uncracked concrete. In addition to performing velocity measurements, material damping measurements were made on intact and cracked concrete structural elements. These measurements revealed that the presence of cracking can be qualitatively assessed through an increase in observed surface wave material damping, with material damping ratios ranging from less than 1% in undamaged concrete to around 3% in damaged concrete