| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 101 === This thesis aims to make use of the dispersion characteristics of surface wave (R-wave) to detect the depth of deteriorated concrete layer. First, the results obtained from numerical simulation of stress wave propagation in fire-damaged concrete were used to establish the interpretation criteria for identification of surface wave (R-wave) arrival. According to the dispersion characteristics of the surface wave (R-wave), there are two possible wave propagation paths : (1) when the stress wave length (l) introduced by impact is smaller than the thickness of the fire-damaged layer (D), the wave energy will be directly transmitted from the deteriorated layer; (2)when the stress wave length (l) introduced by impact is greater than the thickness of the fire-damaged layer (D), the wave energy will be directly transmitted from deteriorated layer or it may be from the the lower layer which is not deteriorated. Therefore, the parameters considered in numerical studies include the fire-damaged layer thickness (D), the wave velocity of fire-damaged layer, the contact time of impact, the distance between the receiver and the impact point (H) to establish the relationship among the wave velocity , wavelength and wave travel distance. The established relationship can be used to evaluate the fire-damaged depth. Subsequently, experimental studies were carried out to verify the numerical results.
Numerical results show that to measure the R-wave velocity of the deteriorated concrete layer, a very small contact time of the impact or a close distance between the receiver and the impact source (H) (preferably less than 15 cm) can be used to get the signals transmitted directly from the deteriorated concrete layer. To measure the signals from the lower layer without deterioration, both the receiver-impact distance and the contact time of impact must be long enough. Finally, experiment on two fire-damaged concrete specimens was performed and the established equation of the H/D and R-wave velocity was adopted to detect the depth of the deteriorated concrete layer and the extent of fire damage.
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