以藍姆波群波速之頻散曲線偵測混凝土品質與混凝土板後掏空狀況之初步研究

The preliminary study of using the dispersive velocities of lame waves to detect the quality and under neath void of concrete plate

江瑞驥(Ruei-Ji Jiang)

指導教授 ： 鄭家齊

朝陽科技大學/理工學院/營建工程系/碩士(2013年)

摘要

研究中主要以混凝土表面敲擊後激發的板波傳遞特性，來檢測混凝土板結構表面劣化深度及板後掏空的問題。本研究將針對混凝土板狀結構，以一個敲擊源及一個接收器長距離配置的方式檢測，以短時傅力葉轉換以及再分配頻譜求取雷姆波群波波到時間的時頻譜頻散曲線。
利用有限元素模擬可感敲擊並擷取固定間距的反應位移波形，取得數值解之頻率-相位波速頻散曲線圖，再與DISPERSE程式得到之理論解做比較分析。研究中模擬單一混凝土板、兩種雙層複合板(混凝土板+土壤、劣化混凝土層+普通混凝土層) ，做分析比較。數值模擬結果顯示，混凝土板敲擊接觸時間以60μs為最佳選擇，最短可選擇之敲擊接收距離為板厚的10倍。雙層複合板(混凝土板+土壤)數值模擬影像顯示，波長改變處為混凝土板厚。雙層複合板(劣化混凝土層+普通混凝土層)數值模擬影像顯示，在波速上升的轉折點，所對應的波長幾近於上層混凝土板厚度的兩倍。
試體選擇單層混凝土板施做，試驗結果顯示，各儀器設置下在敲擊能量頻率範圍內A0模態波慢與混凝土板實驗結果重合。

關鍵字

蘭姆波 ； 有限元素

並列摘要

This research aims to develop a method to detect depth of surface deterioration and void in substrate of a concrete slab using Lamb waves generated from the objective surface. This method features configuration of one excitation source and one receiver and application of Short Time Fourier Transform (STFT) with its energy density spectrum reassigned in order to obtain dispersion curves of Lamb waves. At first the best contact (impact) duration(of 60μs) and the shortest available propagation distance between a source and receiver were found by comparing the numerical frequency-wave speed relationship calculated from the displacement response, with the theoretical relationship by execution of DISPERSE program. The simulated models include single concrete slabs, double composite panels (concrete slab plus + soil), and two layer composite plate (deteriorated concrete later plus + ordinary concrete slab). This comparison also demonstrates critical consequences including the facts that the change of wave-speed of A0 mode at the wavelengths equal to the thickness of the slab in the case of a plate with soil substrate, and the wavelength corresponding to the point where the group velocity rises is approximately twice as the depth of the upper layer of the slab in the two layer composite board. A sample specimen of single concrete slab is chosen for experiments, and consequently the result shows in a specific range of frequency generated by corresponding excitation instrument, the slowness-frequency relationship translated from the mode A0 in dispersion curves obtained from experiments agrees with the theoretical one.

並列關鍵字

Ansys ； LAMB WAVES

參考文獻

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