Long-span box beam dynamic bending ultimate strength test device

The invention discloses a long-span box beam dynamic bending ultimate strength test device. Dynamic pure bending load loading of a box beam test model is realized through an assembly type drop hammer and a distribution beam, and the dynamic load amplitude is changed by adjusting the mass and height of the drop hammer. The natural vibration frequency of the box beam test model is changed by adjusting the single weight and number of the counterweight parts, secondary impact of a drop hammer is prevented through combined control of an electromagnet and a laser sensor, insertion connection and fixation can be performed through clamping fixation and sliding contact of two fixing parts, box beam test models of different lengths can be fixed conveniently, meanwhile, the fixing parts and a guide frame of the device adopt a separated design, flexible change and adjustment can be carried out, the operation is convenient, the experiment speed is accelerated, and the box beam test model is prevented from bouncing after b