Dynamic Response Of Reinforced Concrete Frame To Underground Explosive And Impact Loads

Recently, the underground blasting events are rising year by year. These accidents not only threaten the people's life underground, but also cause damage to the civil, industrial and public buildings on the ground. The numerical model was set up in a finite element software LS-DYNA. The size of the model and the properties of the materials used in the model were decided according to some literature and experimental results. The frame structure used in this paper is a three storey reinforced concrete frames. The different underground accelerations were obtained from simulating the underground explosion with the same weight of the explosive but different distance to explosion center. The dynamic response of the frame structure was investigated under the underground acceleration. The following results can be obtained from the numerical simulation:1. When the blasting wave gets to the elements, the pressure, velocity and acceleration increase to the peak transiently, and then descend to the balance point with time. The value of the pressure, velocity and acceleration all decrease as the scaled distance( R|- = R/W^3/2) increases. The peak value of the horizontal, vertical velocity and acceleration are very close, so the vertical loads can't be ignored. After the explosion, there is a circular cavity in the soil with high pressure and temperature. The radius of the cavity in the soil is 7.0 times of the explosive original volume, which is close to the test result. The prominent characteristic of blast is high velocity, and the process can occur in several microseconds. Then the soil can get to the maximum vibrate state in a very short time and absorbs the most energies.2. As the explosive spreading from the bottom to the top of the frame, the forces at the first story columns transfer to the beam, and then to the slab. Meanwhile, the forces transfer from the columns of the first story to the second story. And the maximum stress occurs on the joints of columns and beams. Underground explosion generates high-frequency, short-duration, and large-amplitude ground motions which is different from the earthquake vibration. And the frame is not controlled by the whole offset or the displacement between the stories, so it can't be the standard to decide the damage of the frame.3. When the scaled distance is fixed, the maximum equivalent stress, strain, plastic strain and the displacements in the X, Y direction of the frame under the explosion are not equal as the quantity of explosive increasing, but increase. When the scaled distance is less than 1.0m/kg^1/3, the weight of explosive has significant influences on the structure response. And in this case both the scaled distance and the weight of the explosive should be considered. When the scaled distance is more than 1.0m/kg^1/3 and with the same value, the effect of the weight of explosive can be ignored. Therefore the scaled distance can be used only to evaluate the response the frame structure. And the scaled distance 1.0m/kg^1/3 can be taken for thesafety distance. When out of the range, the frame is safe and the weight of explosive has less influence on the response of the frame.The model for simulating the blast in the soil was set up in this paper. The acceleration produced by the explosion was obtained. A three-storey frame structure model is loaded with the acceleration and the dynamic response was investigated. The influences of the weight of the explosive and the scaled distance were summarized. These results can be used as the reference for protective design.