NUMERICAL AND EXPERIMENTAL INVESTIGATIONS OF ANTI-RAM BARRIERS UNDER VEHICULAR IMPACT
Open Access
- Author:
- Yoo, Tae Kwang
- Graduate Program:
- Acoustics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 29, 2018
- Committee Members:
- Tong Qiu, Dissertation Advisor/Co-Advisor
Victor Ward Sparrow, Committee Chair/Co-Chair
Daniel Allen Russell, Committee Member
Robert Lee Campbell, Committee Member
Sean N Brennan, Outside Member - Keywords:
- Anti-Ram Barriers
Smoothed Particle Hydrodynamics
Soil-Structure Interaction
LS-DYNA
Crushable Concrete
Response Surface Methodology
Dimensionless Analyses
Pendulum Test - Abstract:
- As terrorist attacks have frequently occurred in recent years, security measures to stop or mitigate the damage they cause have been increasingly discussed and researched. Vehicle anti-ram systems have been widely used for protecting sensitive buildings and facilities against vehicular impacts. Numerous researchers have investigated vehicle anti-ram systems under vehicular impact using the LS-DYNA research/commercial code and field-scale crash tests. However, comparisons between different formulations in LS-DYNA for the interaction between soil and embedded anti-ram systems involving large soil deformation are remarkably sparse in the literature, particularly when the comparison is validated using instrumented, field-scale crash tests. The aim of this study is to numerically investigate several vehicle anti-ram systems with comparisons to experimental results to improve the accuracy and efficiency of the simulation models and the impact performance of the systems. In the first part of the dissertation, two field-scale crash tests of Streetscape Vehicle Anti-Ram (SVAR) barrier systems and LS-DYNA simulations to predict the global response of each system under vehicular impact were conducted. Tests 1 and 2 consisted of a five-post welded bus stop and a welded bollard, respectively. Test 1 resulted in a P1 rating, where minimal foundation uplift and rotation were observed; however, test 2 failed to result in a P1 rating, where significant foundation uplift, rotation, concrete cracking, and large deformation of surrounding soil were observed. For each test, two LS-DYNA models, namely an FEM-only model and a hybrid FEM-SPH model, were created to predict the global response of the system. The hybrid FEM-SPH model did a much better job in matching the crash test than the FEM model did. This research suggests that the hybrid FEM-SPH approach is more appropriate in simulating the field performance of embedded structures under impact loading when large deformation of the surrounding soil is expected. In the second part of the dissertation, a series of experimental testing and numerical modeling studies to optimize the parameters of a constitutive material model were conducted to accurately simulate the behavior of polystyrene crushable concrete during impact loading using LS-DYNA. Quasi-static compression tests and confined drop impact tests were performed. To model the quasi-static compression tests, the response surface methodology was used to optimize the Poisson’s ratio and friction angle in the pseudo-tensor model in LS-DYNA. Using the optimized model parameters, the simulated compression stress vs. strain relationship showed an excellent agreement with those from the compression tests. To model the confined drop impact tests, the strain rate sensitivity parameter in LS-DYNA was optimized by comparing the drop impact simulations at different strain-rate sensitivity values with the drop impact tests. This study suggests that the pseudo-tensor material model is suitable for modeling crushable concrete. Although the optimized constitutive model parameters are specific for the polystyrene concrete mix used in this study, a similar approach can be used to optimize model parameters for other polystyrene concrete mixes. In the third part of the dissertation, a series of tests were designed and conducted to determine the angle of a boulder face at which the impact of a vehicle changes from preventing override to allowing override. Medium-scale pendulum tests were performed for the vehicular override research of a boulder with the impact face angled at 55°, 60°, and 65° from the horizontal plane. A dimensionless analysis was conducted to properly relate the pendulum test results to full-scale field situation. LS-DYNA simulations were conducted to yield the input parameters needed for the dimensionless analysis. Vehicle override is predicted to occur for the 55° override angle under both M30 and M50 scenarios, but not to occur for the 65° override angle under both scenarios. This prediction is consistent with the results of high-fidelity LS-DYNA simulations of the full-scale crash tests.