Kajian Analitik dan Eksperimental Frekuensi Sistem Struktur Braced Monopod Anjungan Lepas Pantai

Abstrak. Anjungan lepas pantai (offshore platform) dengan sistem struktur braced monopod menerima beban layan dan beban lingkungan gelombang, arus, angin, dan gempa. Beban gelombang merupakan beban lingkungan yang berpengaruh pada anjungan lepas pantai (offshore platform). Oleh karena itu, perlu dievaluasi sensitivitas tanggap anjungan lepas pantai (offshore platform) tersebut pada tingkat kenyamanan layan sistem struktur. Dilakukan kajian eksperimental di laboratorium pada sistem struktur portal ruang tiga kaki satu lantai dengan pembebanan impact (impulse) untuk melihat pengaruh peredam eksternal (Tuned Mass Damper (TMD) spons dan kabel peredam dashpot) dalam mereduksi tanggap (perpindahan dan percepatan), frekuensi natural, dan damping ratio sistem struktur. Hasil eksperimen menunjukkan redaman eksternal (TMD spons dan kabel peredam dashpot) cukup efektif meningkatkan nilai damping ratio, mereduksi tanggap struktur (perpindahan dan percepatan), namun kurang efektif mereduksi frekuensi alami struktur. Frekuensi yang relatif sama dibandingkan terhadap frekuensi sistem tanpa redaman eksternal memperlihatkan tidak signifikan tambahan kekakuan sistem oleh peredam eksternal. Abstract. Braced monopod offshore structures are usually subjected to service and environmental loads such as current, wind, and earthquake. Wave is the environmental load that has dominant effect to offshore structures. Therefore, evaluation of responsivness of offshore structures must be done in level of comfort serviceability. Experimental study has been done in laboratory to 3D model of one story frame structure with three legs. The dynamic external load was impact load to observe effect of external damper (tuned mass damper (TMD)-sponge and dashpot cable damper) to obtain responses (displacement and acceleration), natural frequencies, and damping ratios of structural system. Experimental results showed that external damper (tuned mass damper (TMD)-sponge and dashpot zable damper) are quite effective to increase damping ratio and to reduce responses (displacement/acceleration) of structures. They were less effective to reduce natural frequencies of the structures. The frequency from experimental study of which structure without external damper compared to structure with external damper added, are not significant in differences; showed that added stiffness on structures by external damper is insignificance