PSI - Issue 81

Mohammad Daffa Noorsyahputra et al. / Procedia Structural Integrity 81 (2026) 84–91

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To reduce invasive aquatic plants, several control measures have been developed, including biological, chemical, physical, and mechanical methods (Uka and Chukwuka, 2007; Khotsa et al., 2025). However, due to its high resilience, water hyacinth remains difficult to eradicate once established (Prabhakaran et al., 2024). Mechanical removal is considered one of the most practical approaches for large-scale management, enabling direct harvesting of biomass using specialized vessels (Odedra et al., 2025; Nalaka et al., 2024). In such systems, the trash box serves as the main storage compartment for harvested water hyacinth and entrained water. The accumulated biomass, with a bulk density of approximately 96 kg/m³, produces significant static loads on the structure, where variations in collected volume directly influence stress and deformation in the trash box (Bhisikar et al., 2025; Davies and Mohammed, 2011). Therefore, this study numerically evaluates the structural response of the trash box under varying operating loads to assess its safety and provide engineering insight for design optimization. 2. Analytical Calculation Before conducting the numerical analysis, a theoretical formulation was developed for describing the pressure acting on the trash box structure. This analytical technique provides initial insight into the load distribution caused by the bulk of water hyacinth enclosed within the box, as well as a foundation for establishing the loading conditions in the numerical model (Jacques, 2020; Lee et al., 2020; Ridwan et al., 2023). The primary load acting on the bottom plate of the trash box is due to the weight of the stored water hyacinth. This material behaves similarly to a bulk fluid with a relatively uniform mass distribution, allowing the pressure on the plate surface to be assumed as uniform. This load is represented as a hydrostatic pressure due to a homogeneous column of material, with vertical pressure primarily determined by the filling height and operating similarly across the plate area. This analytical formulation is based on the hydrostatic pressure principle from fluid statics theory (White, 2011; Çengel and Cimbala, 2006). The pressure ( ) applied to the plate elements in the finite element analysis is defined as shown in Eq. (1). = ℎ (1) In this formulation, represents the volumetric weight of the material, while ℎ represents the height of the material column inside the trash box. The volumetric weight is defined as the product of the bulk density ( ) and gravitational acceleration ( ) , as expressed in Eq. (2). = (2) For the side walls, the lateral pressure generated by the stored water hyacinth is assumed to follow the at-rest earth pressure condition, as the walls are considered rigid with negligible lateral deformation. Under this assumption, the lateral pressure distribution is expressed by Eq. (3) (Thompson, 2025; Ronan, 2019). = 0 ℎ (3) The coefficient of earth pressure ( 0 ) at rest is the ratio of lateral to vertical stress when the wall is motionless and no lateral strain occurs. It can be empirically estimated using Jaky’s formula, as expressed in Eq. (4) (Mesri and Hayat, 1993; Budhu, 2011). 0 = 1 − sin ( ) (4) Where is the internal friction angle of the bulk material. Furthermore, overload conditions are defined as operating scenarios in which lateral or vertical loads exceed design limits due to increased accumulation of water hyacinth. This approach allows the analysis to capture potential extreme loading cases and to evaluate whether the trash box structure maintains adequate strength and stability under maximum load conditions. To evaluate structural safety under loading conditions, the safety factor ( SF ) is defined as the ratio of the material's yield strength to the maximum stress determined by numerical analysis. This can be stated using Eq. (5) (Budynas and Nisbett, 2015). = (5) where is the yield strength of galvanized steel and is the maximum stress for each load case. This definition enables consistent evaluation of structural integrity under both normal and extreme operating loads.