Analisis Pengaruh Parameter Geometri dan Isian Beton Bertulang terhadap Perilaku Spun Pile di Bawah Beban Aksial dan Siklik

Muh. Ricki Saprollah, Ir. Ali Awaludin, S.T., M.Eng., Ph.D., IPU.,ACPE. ; Angga Fajar Setiawan S.T., M.Eng., Ph.D

2025 | Tesis | S2 Teknik Sipil

Spun pile prategang merupakan salah satu jenis pondasi yang banyak digunakan karena kemampuannya dalam menahan beban aksial serta efisiensi dalam proses fabrikasi dan instalasi. Namun demikian, kajian mengenai interaksi antarparameter desain, seperti diameter penampang, rasio tulangan longitudinal, mutu beton isian, dan rasio strand prategang, terhadap respons lateral spun pile masih bersifat terbatas, terfragmentasi, dan kurang terintegrasi secara sistematis. Selain itu, belum adanya pendekatan holistik yang mempertimbangkan variasi desain serta kondisi pembebanan kompleks turut menciptakan celah pengetahuan yang signifikan dalam memahami perilaku nonlinier spun pile di bawah pengaruh beban aksial dan siklik.

Penelitian ini melakukan pemodelan numerik terhadap 60 model spun pile prategang menggunakan OpenSees untuk mengevaluasi respons struktur akibat variasi geometri dan pembebanan. Parameter yang divariasikan meliputi rasio strand prategang, diameter penampang, mutu isian beton, rasio tulangan isian serta rasio beban aksial sebesar 8?n 16%. Pemodelan dilakukan secara tiga dimensi menggunakan pendekatan fiber section yang memperhitungkan nonlinier material dan nonlinear geometri akibat deformasi besar serta efek P-Delta. Sistem tumpuan mengikuti konfigurasi pin–rol, dan pembebanan siklik diinput sebagai gaya terpusat dengan time series linear dan path, berdasarkan protokol ACI 374.1-05. Distribusi plastisitas dimodelkan menggunakan elemen force-based beam-column dengan integrasi Gauss-Lobatto.

Hasil simulasi menunjukkan bahwa peningkatan diameter spun pile memberikan dampak paling signifikan terhadap performa struktur, dengan kenaikan kapasitas momen dan geser lebih dari 200%, energi disipasi lebih dari 500%, serta peningkatan daktilitas hingga 40% pada model dengan beton isian, meskipun tipe hollow justru mengalami penurunan daktilitas. Gabungan mutu beton isian dan rasio tulangan isian yang lebih tinggi turut meningkatkan daktilitas hingga 30?n energi disipasi hingga 50%, meskipun pengaruh mutu beton terhadap kapasitas momen dan daktilitas relatif kecil. Peningkatan rasio strand prategang juga berdampak positif terhadap kapasitas momen (10–20%), daktilitas (5–15%), dan energi disipasi (hingga 10%), terutama pada pile berdiameter besar dan beban aksial rendah. Model numerik yang dikembangkan dengan STKO OpenSees menunjukkan akurasi baik dalam memprediksi respons spun pile, dengan bentuk kurva histeresis yang sebanding dengan data eksperimen, sehingga valid digunakan untuk mengevaluasi dan mengoptimalkan desain spun pile tahan gempa.

Prestressed spun piles are widely used as foundation elements due to their high axial load-bearing capacity as well as their efficiency in fabrication and installation. However, investigations on the interaction among design parameters—such as cross-sectional diameter, longitudinal reinforcement ratio, infill concrete strength, and prestressing strand ratio—on the lateral response of spun piles remain limited, fragmented, and insufficiently integrated in a systematic manner. Moreover, the absence of a holistic approach that accounts for design variations and complex loading conditions has created a significant knowledge gap in understanding the nonlinear behavior of spun piles under combined axial and cyclic loads.

This study conducts numerical modeling of 60 prestressed spun pile models using OpenSees to evaluate structural responses under variations in geometry and loading. The investigated parameters include prestressing strand ratio, cross-sectional diameter, infill concrete strength, infill reinforcement ratio, and axial load ratios of 8% and 16%. The three-dimensional modeling adopts the fiber section approach, considering both material and geometric nonlinearities due to large deformations and P-Delta effects. The boundary condition is modeled as a pin–roller support, while cyclic loading is applied as a concentrated lateral force using linear time-series and path-dependent inputs, based on the ACI 374.1-05 protocol. Plasticity distribution is captured through force-based beam–column elements with Gauss–Lobatto integration.

The simulation results indicate that increasing the spun pile diameter provides the most significant improvement in structural performance, with moment and shear capacities increasing by more than 200%, energy dissipation by over 500%, and ductility by up to 40% in infilled models, while hollow sections exhibited reduced ductility. A combination of higher infill concrete strength and infill reinforcement ratio further enhanced ductility by up to 30% and energy dissipation by up to 50%, although the effect of concrete strength on moment capacity and ductility was relatively minor. Increasing the prestressing strand ratio also improved moment capacity (10–20%), ductility (5–15%), and energy dissipation (up to 10%), particularly in larger-diameter piles under lower axial loads. The developed numerical model using STKO–OpenSees demonstrated good accuracy in predicting spun pile responses, with hysteresis curves comparable to experimental data, thereby validating its applicability for evaluating and optimizing seismic-resistant spun pile designs.

Kata Kunci : Spun pile, Fiber section, Perilaku nonlinier, Siklik, OpenSees