The Effect of Blast Load and Earthquake Load on the Nonlinear Behavior of Structures

This paper examines the simultaneous effect of blast and earthquake loads on the structural nonlinear dynamic responses of the structure. For this purpose, it is assumed that an explosion occurs near the structure during the earthquake, induced by the ground motion. Initially, the pressure caused by the explosion is calculated with two different intensities (i.e., 1000 and 1500 kg TNT at a distance of five meters from the structure) and is applied to the structure at different time intervals. It is assumed that the structure is excited by the Sarpol-eZahab earthquake. In order to investigate the simultaneous effect of earthquake and blast loads on the nonlinear dynamic responses of the structure, four different scenarios are considered. In the first scenario (State A), the explosion occurs at the beginning time of the earthquake, while in the second state (State B), the explosion happens at the time that the strong ground motion will be started. In the third state (State C), the blast load is applied to the structure at the time that the maximum earthquake acceleration occurs. Finally, in the fourth state (State D), the blast load is applied to the structure at the end time of the earthquake. It is assumed that during an earthquake, or at the beginning and the end of the earthquake, the earth's motion causes an explosion near the structure, which has been observed repeatedly in previous earthquakes and causing significant financial and human casualties. Therefore, to study the simultaneous effect of blast and earthquake loads on the structural nonlinear dynamic responses of the structure, a six-story steel structure modeled in OpenSees software is considered. The frame is modeled nonlinearly, and the Steel 02 material is used to model the frame members. Finally, the acceleration, drift, displacement, and base shear curves of the structure are computed. The results show that with increasing the amount of blast load, the structural response has generally increased. In addition, considering the different scenarios, the maximum response of the structure has occurred in state C. Besides, by increasing the amount of blast load, the maximum response of the structure has not been changed by considering the simultaneous effect of the blast and earthquake loads. In the case that the structure is only excited by the blast load, the results also show that the amount of base shear and base moment is much more than the same values ​​for the state that the structure is only excited by the earthquake load. The values ​​of roof rotation, roof drift, shear, and base moment for the states A and D are similar to these values when the structure is only affected by the blast load. This is due to the short time of the blast load and also the low intensity of the earthquake at the beginning time of the earthquake. Therefore, the earthquake load could not change the response of the structure in these cases. At the end of the earthquake, due to the lack of earthquake load, only the structure was excited by the blast load, and the same results occurred. For example, in the case of using 1500 kg of explosives at a distance of five meters from the structure along with the earthquake load, the maximum displacement of the structure is 64.75% more than the amount of the responses of the structure when it is only excited by the explosive load and also 65.94% more than the amount of the responses of the structure when it is only excited by the earthquake load. These values were increased by 146.12% and 3.44%, respectively, when 1000 kg explosive is considered at a distance of five meters from the structure.