The Study On The Spall Strength Of Concrete

Performances on spall fracture of concrete and steel fiber reinforced concrete are discussed in the dissertation: technique of spall experiment, spall strength of concrete material, load rate effect, mechanism of spall fracture, the influence of compressive damage on spall and characteristic of spall fracture about steel fiber reinforced concrete.When the concrete components are subjected to impact or explosive loading in the applications, compressive waves are generated and then propagate through the concrete components. The compressive waves will be reflected back at the free surface of construction as tensile waves such that the concrete constructions may be fractured by the tensile waves in the form of spalling. Spall fracture is the most common failure form of concrete components subjected to impact or explosive loading. The studies about concrete material are few, due to the difficulties of experimental techniques, and have the important values in engineering applications and academic research domain. The review of survey on the traditionary indirect methods to measure the spall strength of concrete material is presented first in the dissertation. The shortcomings of those traditionary experimental methods are expatiated and amendments are submitted to modify the influence of dispersion and attenuation of stress waves. The novel experimental method , that the buffer bar behind the specimen bar can record the spall signal, may measure the spall strength and the evolution of spall damage directly. The results of three dimensional finite element analyses indicate the validity of the postulate about the one dimensional stress state. The influence of damage evolution to spall signal and the experiential formula on the spall strength of different kinds of material at different load rates are presented in the dissertation. The Stefan effect and inertial effect are used to explain the load rate effect of the spall strength respectively and the result is that the difference of propagation pattern of cracks is the main physical sources of the load rate effect. The viewpoint that the spall fracture of concrete may be influenced by the damage due to the load compressive wave is confirmed by way of the phenomena...