With the increasing installation cases of underground explosive facilities (e.g., ammunition magazines, hydrogen tanks, etc.) in urban areas in recent years, the risk of internal explosions is also increasing. However, few studies on the measures for reducing damage by the ground vibration have been conducted except for maintaining safety distance. In this study, a method for attenuating the vibration propagated outward by installing a blast-proof panel was numerically and experimentally investigated. Two cubical reinforced concrete structures were manufactured according to the concrete strength and a blast-proof panel was installed on only one side of the structure. Then, acceleration sensors were installed on the external surface to evaluate the propagation of vibration outward depending on the installation of a blast-proof panel. Before a field experiment, a preliminary numerical simulation was performed. The results showed that the acceleration propagated outward could be effectively reduced by installing a blast-proof panel. Even though the performance of a blast-proof panel on vibration reduction was also investigated in the field experiment, significantly larger absolute accelerations were estimated due to the different experimental conditions. Finally, the vibration reduction effect of the blast-proof panel was numerically evaluated according to its thickness and the internal explosion load. A blast-proof panel more effectively reduced the acceleration propagated outward as its thickness increased and the explosion load decreased.
A full-scale precast prestressed concrete pavement (PPCP) system was constructed and evaluated under actual traffic load conditions to develop the design guideline under Florida conditions. This test section showed good load transfer efficiency and riding quality. However, information was lacking about its structural response and potential performance. A three-dimensional finite element model was developed for stress analysis of PPCP under critical loading conditions. The developed three-dimensional model was calibrated by using deflection data obtained with a falling weight deflectometer. The model was used to perform a parametric analysis to determine the effects of critical loading location, concrete modulus, coefficient of thermal expansion of concrete, loss of prestress force, and subgrade stiffness under typical Florida conditions. Results of the parametric study indicate that the maximum stresses in the concrete increased significantly as the concrete modulus and coefficient thermal expansion increased. Because of the increase in flexural strength associated with the increase in elastic modulus of the concrete, an increase in elastic modulus of the concrete results in a decrease in the computed stress-to-strength ratio under critical loadโtemperature conditions. The PPCP system that was evaluated appeared to have a good predicted pavement performance with a computed stress-to-strength ratio of less than 0.5, with up to an additional loss of 20% of prestress force in the longitudinal and transverse directions. Variations in the base and subbase properties were found to have a minimal effect on the maximum induced stresses in concrete. This finding indicates that the PPCP system is appropriate for a wide variety of subbase and subgrade conditions.
The use of impact rollers has increased for many decades due to its diverse advantages. However, the current lack of theoretical verification and research-based technical guidelines that can effectively describe the effect of impact rollers is probably the greatest deficiency in our ability to accurately predict the benefits of deep compaction provided by impact compaction rollers. The 3-D Finite Element Analysis (FEA) was conducted using LS-DYNA to simulate the depth of influence for various impact rollers. Results indicated that the width of the contact area between the drum and the soil primarily controls the depth of compaction. The softer the soil is, the deeper the roller sinks in the soil. Also, the wider the contact area is, the deeper the compaction depth is. Thereby, the depth of compaction is highly dependent upon the stiffness of the soil. It was found that the surface pressure controls the degree of compaction and the surface pressure of the impact rollers is higher than that of the cylindrical rollers due to the dynamic effect. However, the distribution of the pressure is significantly variable for the impact rollers than the cylindrical rollers. It was concluded that the impact rollers seem to have more potential for use in final compaction of thicker layers.
Three full-scale instrumented test slabs were constructed and tested using a heavy vehicle simulator (HVS) to evaluate the structural behavior of internally cured concrete (ICC) for use in pavements under Florida condition. Three mix designs selected from a previous laboratory testing program include the standard mixture with 0.40 water-cement ratio, the ICC with 0.32 watercement ratio, and the ICC mixture with 0.40 water-cement ratio. Concrete samples were prepared and laboratory tests were performed to measure strength, elastic modulus, coefficient of thermal expansion and shrinkage properties. The environmental responses were measured using strain gages, thermocouples, and linear variable differential transformers instrumented in full-scale concrete slabs. A 3-D finite element model was developed and calibrated using strain data measured from the full-scale tests using the HVS. The results indicate that the ICC slabs were less susceptible to the change of environmental conditions and appear to have better potential performance based on the critical stress analysis.
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