ENERGY DISSIPATING MODES AND DESIGN RECOMMENDATION OF H-SHAPED STEEL BAFFLES SUBJECTED TO BOULDER IMPACT

Flexible barriers are one of the most effective protective structures, which have been widely used for the mitigation of rockfalls. As the only compression members in a flexible barrier system, steel posts maintain the integrity of the interception structure to keep the function of the system. Due to the random trajectories of rockfalls, steel posts may be impacted by boulders directly. The impact scenario may result in the failure of the post and even the collapse of the system. In this paper, firstly, steel baffles were proposed to be an additional structural countermeasure to avoid the direct impact of posts. Secondly, numerical method was adopted to study the structural behaviour of steel baffles under direct boulder impact. Then, an available published experimental test of H-shaped steel beams under drop weight impact loading by others was back analyzed to calibrate the finite element model. Finally, numerical simulations were carried out to investigate the energy dissipating modes and energy dissipating efficiency of the H-shaped steel baffles. The simulation results show that there are three typical energy dissipating modes of H-shaped baffles subjected to boulder impact, namely flexural, local compression buckling and shear buckling. Local compression buckling is the most efficient energy dissipating mode. The thickness of the web of an H-shaped baffle is suggested to be 4 mm and 6 mm for the rated dissipating energy of 50 kJ and 100 kJ, respectively.

Recyclability and Redesign Challenges in Multilayer Flexible Food Packaging—A Review

Multilayer flexible food packaging is under pressure to redesign for recyclability. Most multilayer films are not sorted and recycled with the currently available infrastructure, which is based on mechanical recycling in most countries. Up to now, multilayer flexible food packaging was highly customizable. Diverse polymers and non-polymeric layers allowed a long product shelf-life and an optimized material efficiency. The need for more recyclable solutions asks for a reduction in the choice of material. Prospectively, there is a strong tendency that multilayer flexible barrier packaging should be based on polyolefins and a few recyclable barrier layers, such as aluminium oxide (AlOx) and silicon oxide (SiOx). The use of ethylene vinyl alcohol (EVOH) and metallization could be more restricted in the future, as popular Design for Recycling Guidelines have recently reduced the maximum tolerable content of barrier materials in polyolefin packaging. The substitution of non-recyclable flexible barrier packaging is challenging because only a limited number of barriers are available. In the worst case, the restriction on material choice could result in a higher environmental burden through a shortened food shelf-life and increased packaging weights.

The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m³ and 6 m³ were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

Investigations of the Rockfall Impacts on the Flexible Protective Barriers under Seismic Loading

Rockfall triggered by earthquakes can cause severe infrastructure losses and even fatalities. The flexible protective barrier is an efficient rockfall protection system that has been widely used against rockfall. This studyproposed a novel approach to simulate a field test of rockfall impacting the flexible barrier, and the simulation results showed an excellent match with the field test results. Based on this approach, the seismic loading was applied to the numerical model, and four types of seismic loading were adopted, e.g., non-seismic, x-directional seismic, y-directional seismic, and z-directional seismic. This study aims at investigating the dynamic behavior of the flexible protective barrier under different seismic loading during the rockfall impact process. The following findings can be obtained from the simulation results. First of all, the seismic loading can increase the maximum elongation and decrease the final elongation of the flexible protective barrier comparing to non-seismic loading. Second, the largest deformation area of the protective barrier is at the diagonal position when x-directional seismic loading was applied, which is at the vertical bisector position when y-directional and z-directional seismic loading was applied. Third, the maximum elongation of the protective barrier decreased with the increasing seismic wave period. But in general, the amplitude and period of seismic waves have negligible effects on the elongation, maximum normal stress, and maximum shear stress of the flexible protective barrier.