Study On Impact Behavior Of Prestressed Concrete Beam

The prestressed concrete structure, a great invention in the nineteenth Century, is widely used in the construction of large span, high-rise and complex structures. Under the influence of high speed impact, a closely related feature with loading rate is shown by the intensity constitutive relation and damage performance of prestressed concrete beam. With the increase of loading rate, the dynamic strength of prestressed concrete beam is obviously higher(i.e., rate effect), which is of great significance to the evaluation of dynamic safety and stability of large structures. Based on the drop-weight tests of prestressed concrete beam, the relationship between dynamic constitutive and strain rate is studied in this paper, and thus observes different rates of fracture damage process and failure modes. The main contents are as follows.Firstly, a drop hammer rig is designed and produced, which can obtain enough energy to meet tests requirement. The suitable aluminum hammer and gasket are determined to be used in tests through the impact condition testing. Besides, a series of related tests are carried out to verify the stability and repeatability of this drop hammer rig, and general good results were achieved.Then the static tests of prestressed concrete beam and concrete beam were completed, which get the bearing capacity, displacement and failure modes. The test results showed that the static bearing capacity of concrete beam is far less than that of prestressed concrete beam.Thirdly, the drop-weight tests of prestressed concrete beam are carried out with a strain rate from 1s-1 to 3s-1. The main parameters of tests contain height and quality of drop hammer, prestressing force and reinforcement ratio. Meanwhile, the concrete beams are also tested under the same condition. A high speed camera is used in tests to record the impact process, and the force histories, acceleration histories, strain histories and crack width in tensile are also recorded by measuring. The test results suggested that with the increase of drop height and quality, the input energy is on the rise, and the width of cracks in tensile is larger. Improving the prestressing force and reinforcement ratio can effectively delay the produce of the crack as well as inhibit its development.Statistical analysis of input energy of system and the energy absorbed by prestressed concrete beam showed that there have energy loss in the process of impact, including the plastic energy dissipation of aluminum hammer, pad and force transducer. Meanwhile,the conversion and dissipation of energy in the beam are simply analyzed.Drop-weight tests for prestressed concrete beam are numerically simulated by the aid of the meso-scale DEM model in this paper, and general good results were achieved. By the comparison and analysis of tests and numerical results, the mechanism of strain rate effect is further explained, which also verify and improve the meso-scale model.