Sand cushions for passive protection structures could reduce the damage that is induced by rockfall impact. Therefore, evaluation of the peak impact force generated by rockfall on the sand cushion is significant to the design of passive protection structures. This study aims to estimate the peak impact force using the elastoplastic linear strengthening model when a rockfall hits the sand cushion. Impact tests were conducted to study the effect of rockfall mass, impact velocity, and cushion thickness on the rockfall impact force. The experimental results indicate that the decreasing rockfall mass, impact velocity, and increasing cushion thickness could decrease the impact force of rockfalls. The sensitivity analysis results show that the main factor that influences the peak impact force is impact velocity, followed by rockfall mass and cushion thickness. In addition, the calculation method for the peak impact force and penetration depth of rockfall was proposed by the elastoplastic linear strengthening model. The impact force-deformation curves of this model were provided and discussed. The relationship between the strengthening coefficient and influencing factors was established. In addition, the simulation results indicate that the elastoplastic linear strengthening model showed good reliability when estimating the impact force compared with the five classical models. The strengthening coefficient of other cushion materials needs to be calibrated.

A series of numerical simulations were completed to investigate the behavior of intact, fire -damaged, and Carbon Fiber -Reinforced Polymers (CFRP) retrofitted reinforced concrete (RC) bridge columns of varying sizes subjected to vehicle collisions. Three-dimensional finite element models of isolated RC columns and their foundation systems surrounded by soil volumes were developed using LS-DYNA. A comprehensive parametric study was carried out to investigate the effects of nine demand and design parameters on the performance of bridge columns. Studied parameters included: column diameter, column height, unconfined compressive strength, steel reinforcement ratio, fire duration, CFRP wrap thickness, wrapping configuration, vehicle 's mass, and vehicle 's speed. For each studied scenario, Peak Twenty-five Milli -second Moving Average ( PTMSA ) was employed to estimate the Equivalent Static Force ( ESF ) corresponding to each vehicle collision scenario. Resulting ESF s were then utilized to assess effectiveness of the current ESF approach available in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design ( AASHTO-LRFD ) Bridge Design Specification for analyzing and helping design bridge columns under vehicle collision. Multivariate nonlinear regression analyses were used to derive an empirically based, simplified equation to predict the ESF that corresponds to a vehicle collision. Rather than constant design force, this equation established a correlation between ESF and kinetic energy, column axial capacity, and column height. Results indicated that the proposed equation is reliable and can accurately predict ESF s over a diverse range of collision scenarios that included intact, fire damaged, and CFRP retrofitted columns. To facilitate realistic implementation of the derived equation, an ESF assessment framework was also devised.

It has been found that in the event of a strong earthquake, and due to insufficient distance between two adjacent structures, the lateral movement at the top of structures may cause collisions between them. This phenomenon, commonly known as seismic collision, can generate impact forces that were not considered during the initial design of the structure. These forces can cause significant structural damage or lead to complete collapse of the structure. The main purpose of this paper is to study the coupled effects of soil flexibility and impact between adjacent buildings undergoing seismic excitation. To capture the impact forces between the structures during the collision, a modified linear viscoelastic model was used effectively. Particular attention has been paid to studying the effects of shear wave velocity, first on the soil structure interaction and then on the collision response of adjacent structures. Three configurations of adjacent structures were analyzed: light-light, light-heavy, and heavy-heavy structures. The results obtained through this analysis showed that the dynamic response and the impact force of the structures depend essentially on the interaction between the structure, the foundation, and the soil.

Currently, the simulation parameters for the model of the interaction between the transplanter, the plug seedlings, the soil, and the pot damage mechanism still need to be clarified. The optimization design of the planters and the improvement of planting quality are still urgent issues that need to be solved. In this paper, the simulation parameters of the pot and the soil were calibrated based on the pressure distribution measurement technology. With the actual collision impact force and matrix loss rate as the targets, a four-factor, three-level orthogonal test was designed to obtain the optimal parameters. Through the optimization analysis of the experimental results, it could be concluded that the pot-soil restitution coefficient, the pot-soil static friction coefficient, the pot-soil rolling friction coefficient, and the surface energy were 0.31, 0.88, 0.35, and 1.07 J/m2, respectively. The experimental verification of the optimal parameter combination showed that the relative error of the collision impact force was 1.65% and that the relative error of the matrix loss rate was 2.32%, which verified the model's reliability. Based on the optimal parameters, the movement law of the hole tray seedlings was studied at different positions during the transplanting process. The plug seedlings collided not only with the planter but also with the soil, which led to the breakage and looseness of the pot structure. The relative error between the matrix loss rate of the transplanter inserting soil, the matrix loss rate of the transplanter that did not enter the soil, and the simulated matrix loss rate was less than 10%, which further proved the accuracy of the simulation model.