阮家榮是澳門大學科技學院土木及環境工程系教授兼教務長。2002年，他以兩年七 個月時間獲得加州理工學院土木工程學博士學位。地震工程學之父G.W. Housner教 授的第三代弟子。2010年，他成為澳大首位35歲前獲晉升為正教授的學者。 Prof Kelvin Yuen is the registrar and professor of civil and environmental engineering at the University of Macau. In 2002, he received his PhD in civil engineering from the California Institute of Technology (Caltech) after a study period of two years and seven months. He is an academic great-grandchild of Prof George W Housner, known as the father of earthquake engineering. In 2010, he became the first UM staff member to be promoted to the rank of full professor before the age of 35. 結構健康監測分為兩大類：靜態監測和動態監測。靜 態監測通常是測量建築結構（例如橋）不同位置的應 變，然後據此判斷其與正常熱膨脹之間的差值是否在 可接受範圍之內。但是靜態監測的問題在於應變直接 取決於施加於建築上的外力或激勵。因此，應變的值 可能只能反應負載情況的變化，而非建築物的健康狀 況。而且，應變測量值也只反映局部行為。 動態監測 動態監測的理念類似於中醫的把脈，不過難度卻大 很多。動態監測不是評估建築物的振幅是否太大， 而是確定振動的時頻性質。例如，敲擊一隻杯子會 產生某個聲頻，這個聲頻並不會隨敲擊力度的改變 而改變。但是，如果杯子上有道裂縫，那麼音頻就 會改變。而且裂縫的位置、長度和深度都會對聲頻 造成不同的影響。但是，結構健康監測的問題比這 個要複雜的多，因為動態負載（地面運動、風負 載、海浪、交通引起的負載）是隨機的，通常無法 完全測量。此外，土木工程的規模很大，尤其是那 些需要接受健康監測的建築物。 在動態結構健康監測系統中，感應器（通常是加速 儀）是安裝在建築物不同位置的。由於典型結構的 重要頻段介乎0.1Hz和20Hz之間，取樣頻率必須為 100Hz或以上，才能對結構反應有足夠的描述。也就 是每個位置每秒鐘要測量最少100次。 另一個困難在於需要確定的未知參數的數量非常大， 因為土木工程（例如橋）是由很多組件構成的。我們 必須要有同樣多甚至更多的方程式才能確定這些未知 參數。在結構健康監測的問題上，這類方程式是從建 築物的感應器上獲得的。在這個情況下，我們可能需 要數量龐大的感應器，但是這樣會造成高昂的成本和 極大的運算量。 ! ere are two major approaches of SHM: static and dynamic. For static approaches, usually the strains of di" erent locations of a structure (especially bridge) will be measured and they will be judged on whether or not they are unacceptably large compared with the normal thermal expansion. However, a major problem of this approach is that strains depend directly on the force or excitation exhibited to the structure. ! erefore, the values of strains may re$ ect only the change of loading conditions instead of the health status of the structure. Furthermore, the strain measurements are also localised quantities. Dynamic Monitoring For the dynamic approach, the idea is similar to pulse checking but substantially more di& cult. Instead of evaluating if the vibration magnitude of the structure is too large, this approach attempts to investigate the time-frequency content of the response. For instance, if one clicks a cup, a speci# c sound frequency will be generated and this frequency is insensitive to how hard the cup was hit. However, if the cup is cracked, the sound frequency will change. In particular, the location, and the length and depth of the crack, will result in di" erent change of such frequency. Nevertheless, the problem in structural health monitoring is far more complicated because the dynamic loadings (ground motion, wind loads, sea wave, tra& c induced loads, and so on) are random and usually cannot be measured. Furthermore, the scale of civil engineering structures is huge, especially for those necessary for the structural health monitoring scheme. In the dynamic structural health monitoring system, sensors (usually accelerometers) are mounted at different locations on the underlying structure. Since the important frequency band of typical structures is from 0.1 Hz to 20 Hz, the sampling frequency will have to be 100 Hz or above in order to have sufficient description of the response, ie to measure 100 times or more within one second at each location. Another difficulty lies with the large number of unknown parameters to be identified, since there are numerous components in civil engineering structures (such as, say, a bridge). We know that we need to have at least the same number of equations to solve the unknowns. In our problem of structural health monitoring, such equations are obtained from sensors located on the structures. In this case, we may need a huge number of sensors but this induces both cost and computational burdens. 53 umagazine issue 16
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