以藍姆波群波速之頻散曲線偵測混凝土品質與混凝土內部缺陷

The preliminary study of using the dispersive velocities of Lame waves to detect the quality of concrete plate and interior defect of concrete.

陳維珺(Wei-Chun Chen)

指導教授 ： 鄭家齊

朝陽科技大學/理工學院/營建工程系/碩士(2015年)

摘要

研究中主要以混凝土板表面經敲擊後激發出板波的傳遞特性，檢測混凝土板結構中是否有缺陷問題。將針對混凝土板結構，以一個敲擊源及一個接收器的配置進行實驗，以短時傅立葉轉換以及再分配時頻譜求得頻散曲線。
利用有限元素模擬可感測敲擊源與接收器擷取接收間距的反應位移波形，得到數值解之波慢-頻率圖，與Disperse程式得到之理論解進行比較分析。研究中以數值模擬之無缺陷及內含缺陷(蜂窩、空洞)、實驗之無缺陷板、混凝土板內含缺陷(自製蜂窩、保麗龍塊、壓克力板、預力套管) ，進行分析比較。
實驗結果得知，當敲擊源從缺陷正上方敲擊時，或測線經過空隙區域，且敲接距離是0.5 m時，發現波長在缺陷上層混凝土厚度約2倍的地方時，波速會開始下降，敲接距離1.0 m和1.5 m波速降低則不明顯；缺陷為蜂窩時，無論敲接距離是0.5 m、1.0 m或1.5 m，在測線經過蜂窩區域皆有波速降低的現象。
數值模擬顯示，無缺陷例在距離近接收到的S_0對稱模態較明顯，隨著距離拉長S_0對稱模態會逐漸消失，A_0反對稱模態會越顯著，可得連續訊號的最小距離至少為敲接收距離的8倍。缺陷例結果得知最佳敲接距離為1.0 m，於波長-波速圖可見缺陷影響波速變化，而缺陷上方混凝土薄層的撓曲振動反應在敲接距離大時較為明顯。

關鍵字

混凝土 ； 缺陷

並列摘要

The purpose of this research is on detecting flaw inside concrete slab structure using the characteristics of Lamb waves generated by an impacting force applying on the surface. The experiments were conducted by one excitation source and one receiver configuration. The dispersion curves of the test results were obtained by short-time Fourier transform spectrum and amplitude reassigned method.

The dynamic FEM is used for modeling concrete slab containing hole or honeycombs. The slowness dispersion diagrams for the responses obtaining from different source and the receiver distances were compared with the theoretical solution obtained by DISPERSE. The concrete slab containing defects (Honeycomb, Styrofoam blocks, acrylic panels, empty tube) were cast for conducting the experiments and the test results were analyzed and compared to the numerical ones.

When the impactor-receiver distance is 0.5 m and hitting directly above the defect or the defect located beneath the survey line, the velocity will begin to decline at the wavelength about 2 times the thickness of concrete above the defect. For the impactor-receiver distance is 1.0 m and 1.5 m, the lower in velocity is not obvious. For a honeycomb under the survey line, regardless impactor-receiver distance, 0.5 m, 1.0 m or 1.5 m, the reduction of wavespeed for various wavelength were found.

Numerical simulations show that for no defect cases the S_0 symmetrical mode is obvious for shorter impactor-receiver distance. As the distance stretched, S_0 symmetric modes will gradually disappear and A_0 anti-symmetric modes will be more significant. The better A0 signal can be achieved at a minimum distance 8 times the slab thickness. Result of defect cases show that the best distance of 1.0 m. The wavelength - velocity figures show the defects can affect the changes of velocity w.r.t. wavelength and the consistent flexural vibration of the thin layer of the concrete above the hole is more significant for the cases with larger impact-receiver distance.

並列關鍵字

defect ； concrete

參考文獻

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