乾點式超音波儀量測混凝土表面之波速特性

NCU Institutional Repository > 工學院 > 土木工程研究所 > 博碩士論文 > Item 987654321/75235

請使用永久網址來引用或連結此文件: http://ir.lib.ncu.edu.tw/handle/987654321/75235

題名:	乾點式超音波儀量測混凝土表面之波速特性
作者:	黃彥儒;Huang, Yan-ru
貢獻者:	土木工程學系
關鍵詞:	超音波波速;表面裂縫
日期:	2017-10-25
上傳時間:	2018-01-16 10:12:38 (UTC+8)
出版者:	國立中央大學
摘要:	乾點式超音波儀可用於檢測現地混凝土劣化程度，多數現地檢測數據顯示，波速直方圖常有雙峰的現象。第一個峰值約略出現在波速 3600 m/s~4500 m/s 之間，第二個峰值則約略在波速2200 m/s~2600 m/s 之間。波速直方圖為何會有雙峰現象？其微觀機制為何？尚未見有文獻進行探討。為探究波速直方圖之雙峰現象，本文中進行一系列的物理模型試驗，透過試驗觀察及理論分析，以建構波速模擬模式。在物理模型試驗方面，採用壓克力版及混凝土版，以鋸片製作具有不同裂縫深度之模型，移動探頭與裂縫間之相對位置，進行不同點位之外視波速量測。量測結果顯示，當探頭遠離裂縫時，外視波速量測值略小於理論值；但當探頭靠近裂縫時，外視波速量測值急遽下降，遠小於理論值。波速急遽下降的量測區域，隨著裂縫深度的加深而擴大。其原因為當探頭過於靠近裂縫時，裂縫可能變成波傳遞的障礙，使得量測外視波速出現異常低，甚至無法量測的情形。從壓克力版與混凝土版之量測波速，經正規化後，兩者相當吻合，顯示波速下降的現象與材料之關連性不大。當探頭過於接近裂縫，出現異常低波速量測值的區域，本文定義為盲區，盲區之量測正規化波速約為0.48～0.49。本文使用之探頭距離為15 公分，當裂縫深度在4.5 公分以內，盲區範圍約略與裂縫深度相當，當裂縫深度大於6 公分，壓克力版及混凝土版全區均為盲區。當探頭接近裂縫時，裂縫形成波傳障礙，使得波傳遞的路徑增加，由物理模型試驗的結果，可求得不同量測點位之距離差值（ΔL）。物理模型的試驗結果顯示，壓克力版與混凝土版之距離差值與量測點位的關係頗為接近，似乎與材料的關連性不大，而是探頭位置與裂縫距離間之函數。由物理模型試驗所求的距離差值（ΔL）固然可以考慮探頭靠近鋸片製作人工裂縫的盲區效應，但現地裂縫寬度遠小於人工裂縫寬度，且不若人工裂縫完全分離，如採用模型試驗所得之距離差值（ΔL），恐有過度考慮盲區之效應。從現地超波速的量測數據顯示，探頭跨越裂縫是導致外視波速下降的主因，但是部分跨裂縫的外視波速並無明顯下降，其可能原因為裂縫屬淺層裂縫或癒合裂縫。故現地調查所得之裂縫密度亦應予以折減。為了考量盲區效應及裂縫密度之折減，本文引入盲區折減因子（α）及裂縫密度折減因子（β）。模擬以網格法量測現地混凝土超音波速，需要完整混凝土之波速、裂縫密度、裂縫深度，這些數據可從現地調查獲得。乾點式超音波探頭距離固定為15 公分，裂隙密度乘以裂縫密度折減因子（β），利用柏松分配方程式，可求得隨機放置探頭之波傳路徑。若探頭位於 ii 盲區內，則總路徑長為波傳路徑與距離差值乘以盲區折減因子（α）之和。若探頭位於非盲區，則總路徑即為波傳路徑。總路徑長除以探頭距離（15 公分）乘以完整材料波速即為外視波速，重複以上的程序，可求得外視波速直方圖及累積機率密度函數。本文提出之α及β 折減因子具有其物理意義，但目前尚欠缺具體而有效的量測方法，本文根據現地波速量測數據以擬合度最佳化求得α及β兩個折減因子。從本文建構之模擬結果與現地波速累積曲線比較，兩者吻合度尚佳。本文提出之模式可合理地模擬波速直方圖的雙峰現象，並解釋此一現象之機制。關鍵字：超音波波速、表面裂縫;A dry-point ultrasonic instrument can be used to detect the degree of deterioration in concrete. Most data shows that wave velocity histograms are often a bimodal distribution. The first peak will appear at a velocity of 3,600 m/s to 4,500 m/s, with the second peak at about 2,000 m/s to 2,600 m/s. Literatures, however, haven’t investigated how wave velocity histograms appear or what their micro-mechanisms are. In order to explore the bimodal distribution of wave velocity histograms, a series of physical model tests were carried out in this paper. Through experimental observation and theoretical analysis, a wave velocity simulation model was constructed. In the physical models test, a series of acrylic and concrete model with different depths of fracture created by saw blade. Apparent wave velocities of various locations were measured by moving the position of the probe. The measurement results showed that when the probe was far from the cracks, the wave velocity value was slightly lower than the theoretical value. When the probe was near the crack, however, the wave velocity value dropped sharply and was much lower than the theoretical value. The rapidly decreasing area continued to expand in conjunction with the increasing depth of the iv cracks. The reason for this was that when the probe was too close to the cracks, the wave velocity was unusually low or unable to be measured. After regularization of the measured acrylic and concrete wave velocities, the two were found to be quite consistent. This showed that the phenomenon of wave velocity decline and material were unrelated. When the probe was too close to the crack, there was an area of abnormally low velocity measurement, which this paper defines as the “blind zone.” The normalized wave velocity was about 0.48 ~ 0.49. In this paper, the distance of the probe was 15 cm. When the crack depth was within 4.5 cm, the zone was about the same as the depth of the crack. When it was more than 6 cm, they were all in the blind zone. When the probe was close to the crack, the wave was harder to transmit and therefore may have caused the wave path to increase. The distance difference (ΔL) of the different measurement points may be obtained from the results of the physical model test. The physical model of the test results showed that they were close, which appears to indicate that it was not related to the material, but rather the probe position and fracture distance. The distance difference from the physical model test may take into v account the blind effect, but the in-situ width of the crack was much smaller than the artificial width. Furthermore, if the artificial cracks were not completely separated and ΔL was used, there is the possibility of excessive consideration of the effects of the blind zone. The measured data from the wave velocity showed that the probe across the cracks was the main cause of the decrease in wave velocity, but there was no significant decrease in the wave velocity of the cross-cracks. A possible reason was that the cracks were shallow or healing. The crack density obtained from the current survey should also be reduced. In order to consider the reduction of the blind zone effect and fracture density, this paper introduces the dead zone reduction factor (α) and fracture density reduction factor (β). In order to simulate the grid method to measure the wave velocity of concrete, the data for intact concrete wave velocity, crack density, and crack depth can be obtained from a local survey. The distance from the dry-point ultrasonic probe was fixed to 15 cm and the crack density was multiplied by the crack density reduction factor (β). Using the Poisson distribution equation, the wave path of the probe can be obtained randomly. If the probe is in the blind zone, the total path length is the sum vi of the wave propagation path and the distance difference multiplied by the blind zone reduction factor (α). If the probe is in a non-blind zone, the total path is the wave path. The total path length divided by the probe distance (15 cm) and multiplied by the complete material wave velocity gives the apparent wave velocity. Repeat this procedure, and the apparent wave velocity histogram and cumulative probability mass function may be obtained. The α and β reduction factors proposed in this paper have their physical meaning, but there is still no specific or effective measurement method. According to the current wave velocity measurement data, the α and β reduction factors will be found. From the simulation results constructed in this paper and the wave velocity accumulation curve of the current measurement, numerical solutions showed a good agreement with the experiments. The model proposed in this paper can reasonably simulate the bimodal phenomenon of the wave velocity histogram and explain its mechanism. Keywords：P-wave velocity、Surface crack
顯示於類別:	[土木工程研究所] 博碩士論文

文件中的檔案:

檔案	描述	大小	格式	瀏覽次數
index.html		0Kb	HTML	432	檢視/開啟

在NCUIR中所有的資料項目都受到原著作權保護.

社群 sharing

資料載入中.....