地震超材料為近年在地震工程中所提出的抗震新概念，有別於傳統隔減震設計，其裝設於結構物外部並主要利用局部共振之消能機制，將特定頻率之地震波傳能量衰減以避免結構物受到損壞，而此特定頻率區間稱為帶隙。基於前人研究初步成果，本研究為進一步瞭解樁型地震超材料結構之波傳衰減效益及縮尺效應之影響，首先以數值模型進行單元晶格掃頻分析，並規劃以不同縮尺因子於實驗室進行試驗，最後
以數值分析進行驗證。
樁型地震超材料之單元晶格組成由內而外分別為混凝土圓柱、橡膠及砂土，由前人研究得知橡膠楊氏模數為影響帶隙頻率範圍之主要設計參數，故利用壓縮試驗求得合理之橡膠楊氏模數，再以有限元素分析軟體 COMSOL 針對單元晶格模型所得之頻散曲線獲得其帶隙頻率範圍。試驗利用簡諧波方式輸入面波以預期產生縱波，並利用加速度感測器量測在通過樁型地震超材料結構前後之輸入波及輸出波加速度，為避免試驗中之波傳反射，邊界設置泡棉以模擬低反射邊界，使波傳能量經由泡棉吸收減少反射。將真實試驗量測之輸入波輸入至有限元素分析軟體 COMSOL 之數值模型，在土體呈現線彈性行為的理想假設下，初步驗證數值分析結果的合理性與代表性。
經由試驗結果得知，於距離砂土表面與泡棉較遠點位之量測反應較具可信度，其受干擾程度較其他量測點位為少。除了試驗結果之頻率反應函數，亦藉由時間域之極值與方均根值比較，驗證頻散曲線所呈現之頻率帶隙。由試驗與數值分析結果比較可知，兩者之間有一致之趨勢以及相當的吻合程度。後續研究將進一步改善本試驗規劃不盡完善之處，如油壓致動器動態容量提升、砂土表面沉陷因應對策、以其他較合
適材料取代泡棉模擬低反射邊界、增加加速度與位移量測點位等；此外除了考慮縱波輸入外，亦會進行剪力波與表面波輸入試驗，進一步驗證數值分析結果的合理性與代表性。

Metamaterial structures composed of artificially designed unit cells of diverse geometry, composition, and periodic arrangement often possess counterintuitive properties and exhibit quite different behavior from structures consisting of natural materials. Thus, they are theoretically capable of manipulating wave propagation and energy flow. Since seismic waves usually possess lower frequency content compared with electromagnetic, optical, and acoustic waves, a considerably larger scale is
required for the design of seismic metamaterial structures based on Bragg scattering. Therefore, local resonance that is theoretically attributed to negative effective mass rather than to Bragg scattering might be a more practically feasible method of blocking, deflecting, redirecting, or attenuating seismic waves in earthquake engineering.
In this study, a subwavelength resonant metamaterial consisting of a concrete cylinder coated with rubber and surrounding sand was devised to be periodically arranged in a two-dimensional plane as a pile-type barrier against seismic waves. For feasibility of laboratory testing, seismic metamaterial specimens with assumed dimension scale factors of one-tenth and one-twentieth were designed and fabricated based on their dispersion analysis result. All the materials were assumed to ideally possess nominal, linearly elastic, and continuous properties except that the Young’s modulus of the rubber material was obtained through performing compression tests on a rubber pad specimen. A series of laboratory-scale tests was conducted using a steel container filled with sand embedded with the specimens, on which harmonic plane waves with various excitation frequencies were imposed to generate primary waves. Foam layers were attached to the insides of the steel container in order to reduce the effect of wave reflection during tests as much as possible. Several accelerometers were installed at different plane locations and depths of the sand before and after the wave passed through the seismic metamaterial structures.
By appropriately considering the real material properties as well as appropriate boundaries and supports for numerical simulation, and precluding some unreliable test measurements that may be attributed to non-uniform sinking of sand and uncertainty of foam layers, the experimental transmission spectra and several other author-defined attenuation and response ratios were found to almost coincide with the dispersion analysis result. The attenuation performance in the theoretical omnidirectional frequency band gap presented in the dispersion curve was significantly better than that in other frequency ranges. Within the theoretical omnidirectional frequency band gap, the seismic metamaterial structure, the one-tenth scaled one in particular, performed better than pure sand, as was expected. The time-domain finite element simulation result also showed an acceptable level of agreement with the experimental result. In the future test studies, some imperfections in the methodology should still be further improved, including the dynamic capacity of hydraulic actuators, non-uniform sinking of sand, use of materials that would better lessen the effect of wave reflection, and more distributed measurement points. Furthermore, in addition to primary bulk waves, shear bulk waves and surface waves will be adopted as the experimental excitation waves.

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