KAJIAN RESPON JEMBATAN DI ACEH UTARA TERHADAP GEMPA BERDASARKAN DATA MIKROTREMOR

Abstract

The parameters of the bridge's resistance to dynamic loads, such as natural frequency and damping ratio, were determined by theoretical and experimental modal analysis. Microtremor measurements were performed on two types of bridges: steel truss bridges and reinforced concrete bridges. The goal is to establish the value of the bridge's dynamic characteristics as well as the bridge's feasibility based on SNI 2833-2008's natural vibration period limit. The natural frequency of the dynamic test is used to compare natural frequencies to theoretical frequencies to determine the condition of the integrity and level of stiffness of the structure or structural elements. The HVSR (Horizontal to Vertical Spectral Ratio) approach is used to analyze microtremor data on the ground, while FSR (Floor Spectral Ratio) and RDM (Random Decrement Method) analysis is used to analyze microtremor data on bridges. According to the findings of the first case study, the natural frequency of the soil is 1.25–1.35 Hz. The steel truss bridge's natural frequency value from the FSR is 0.81–3.29 Hz, while the RDM values are 1.12–3.46 Hz, indicating that the frequency produced is less stable on the NS component. The damping ratio is 2.02–4.97% in this case. The same analysis was carried out on a different type of bridge in the second case study, with a natural ground frequency of 1.11 - 1.47 Hz. The reinforced concrete bridge's natural frequency value from the FSR is 2.21 - 3.62 Hz, and the RDM results are 2.30 - 3.62 Hz. In each component, the frequency found tends to be stable. The damping ratio result is 2.05 - 4.81%. The period of the experimental results shows identical results to the period of the theoretical calculation results, with the average experimental result period being 7.24% greater than the period of the theoretical calculation results. According to the experimental data, the bridge damping ratio is around 3.16% . This result is in accordance with the literature, which is around 2-5%.