EVALUASI PENGUJIAN VIBRASI STRUKTUR (STUDI KASUS : DERMAGA DONGGALA)

Devlin Tedy, Wiryanto Dewobroto
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Abstract

Setiap struktur memiliki perilaku dinamik berupa frekuensi alami yang dapat dicari dengan uji vibrasi di lapangan secara empiris dan analisis numerik. Frekuensi alami terdiri dari massa, kekakuan, dan arah (mode shape). Parameter-parameter tersebut menghasilkan banyak variasi model struktur. Model yang paling tepat dengan kondisi lapangan dapat dicari dengan bantuan hasil uji vibrasi yang berfungsi sebagai kalibrator. Dalam mencari frekuensi alami melalui uji vibrasi sangat tergantung pada teknologi seperti tipe sensor dan cara penempatannya yang digunakan untuk merekam getaran yang diberikan. Tipe sensor terdiri dari berbagai macam seperti uniaxial, biaxial, dan triaxial. Pada kasus uji vibrasi struktur dermaga Donggala menggunakan 6 buah sensor accelerometer uniaxial. Sensor dipasang dalam 3 tempat berbeda masing-masing tempat dalam arah lateral dan vertikal. Hasil pengujian dari pihak surveyor didalam mengevaluasi hasilnya hanya rata-rata tanpa memperhitungkan pengaruh arah. Hal ini yang akan dievaluasi pada penelitian ini. Evaluasi yang akan dilakukan adalah membandingkan hasil pengujian vibrasi dengan analisis numerik. Dari berbagai model analisis numerik dapat diketahui bahwa meskipun nilai frekuensi alaminya bervariasi tetapi masih didalam batas nilai tertentu. Dengan melihat apakah arah penempatan sensor dan arah tumbukan kapal, maka dapat diprediksi perilaku dinamik dermaga apakah translasi atau rotasi yang terjadi. Dengan demikian evaluasi yang digunakan oleh surveyor dengan melakukan rata-rata  tanpa melihat arah adalah tidak tepat. Oleh sebab itu akan dilakukan evaluasi ulang mempelajari arah pemberian gaya, arah pemasangan dan penempatan sensor accelerometer serta perlu melakukan pengelompokan hasil pengujian vibrasi berdasarkan arah sensor. Setelah mempelajari model numerik dari dermaga dapat diketahui bahwa model numerik yang bertranslasi mempunyai kesesuaian dengan data tumbukan pada salah satu titik sensor yang dipasang. Pemodelan numerik yang mendekati nilai ini adalah sesuai dengan data perencanaan sebelumnya. Dari penelitian ini dapat diketahui bahwa pemahaman pengujian vibrasi perlu dilakukan pengelompokan sesuai arah penempatan sensor dan tidak dapat dilakukan rata-rata.

 

Each structure has dynamic behavior in the form of natural frequencies that can be searched by vibration testing in the field empirically and numerical analysis. Natural frequency consists of mass, stiffness, and direction (shape mode). These parameters produce many variations of the structural model. The most appropriate model with field conditions can be sought with the help of vibration test results that function as a calibrator. In searching for natural frequencies through vibration testing it is very dependent on technology such as the type of sensor and the way it is used to record the vibrations given. Sensor types consist of various types such as uniaxial, biaxial, and triaxial. In the case of vibration test the Donggala pier structure uses 6 uniaxial accelerometer sensors. Sensors are installed in 3 different places each in lateral and vertical directions. Test results from the surveyor in evaluating the results are only average without taking into account the influence of direction. This will be evaluated in this study. The evaluation will be done is to compare the results of vibration testing with numerical analysis. From various numerical analysis models, it can be seen that although the natural frequency values vary, they are still within certain limits. By looking at the direction of the placement of the sensor and the direction of the collision of the ship, it can be predicted the dynamic behavior of the pier whether translation or rotation is happening. Thus the evaluation used by the surveyors by averaging without looking at directions is incorrect. Therefore a re-evaluation will be conducted to study the direction of the force, the direction of the placement and placement of the accelerometer sensor and the need to group the results of vibration testing based on the sensor direction. After studying the numerical model from the dock, it can be seen that the numerical model that translates has conformity to the collision data at one of the installed sensor points. Numerical modeling which is close to this value is in accordance with previous planning data. From this research it can be seen that the understanding of vibration testing needs to be grouped according to the direction of the sensor placement and cannot be carried out on average.

Keywords

pengujian vibrasi; analisis numerik; frekuensi alami

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