다층 시멘트 모르타르 슬래브 구조에 적용한 표면파기법에 관한 연구

Abstract

The spectral analysis of surface waves (SASW) method, a non-destructive testing method, has mainly been developed and used for many years in the fields of geotechnical engineering and highway engineering such as for examining the material properties of pavement systems, soil media, etc., under an infinite half space condition. Extensive research in this area has been focused on understanding the applicability and limitations of the SASW method in recent decades. There are not many research cases for non destructive testing in a new building construction and in the inspection of an existing building structures. This study will apply the SASW NDT to the single and multi-layer cement morlar slab specimens to examine the behavior of surface waves as an early age stage of many structural member inspections. The SASW method consists of examination is subject to an impact using, for example, a 12-mm steel ball, to generate surface wave energy at various frequencies. Two vertical accelerometer receivers are used to detect the energy transmitted though the testing media. Recording signals in digitized form using a data acquisition system and processing them, surface wave velocity can be obtained by constructing a dispersion curve. With the dispersion curve, the shear wave velocity can be plotted using forward modeling, which can be related to the various material properties. This paper presents the relationship of the theoretical and experimental compact dispersion curves when the SASW method is applied to multi-layer thin cement mortar slab systems with a finite thickness. The test results of surface wave velocity obtained from the experimental compact dispersion curve due to different boundary conditions and reflections from the boundaries. An experimental study was conducted to examine if the dispersive characteristics of Rayleigh wave exist in the multi-layer cement martal slab systems. This study result can be utilized in examining structural elements of general concrete structures and be applied in the integrity analysis of concrete structures with a finite thickness.