FINITE ELEMENT AND EXPERIMENTAL STUDIES OF STRESS-INTENSITY FACTORS FOR CONCRETE BEAMS

In an attempt to evaluate the feasibility of a numerical method and a testing procedure to determine the fracture toughness of concrete, a finite element computer program for calculating stress-intensity factors has been developed. In addition, an experimental program evaluating plain concrete beams tested in bending to failure has been presented.; The finite element method utilizing a singular element around the crack tip and regular elements in the region away from the tip was developed to model a structural component with a single edge crack subjected load. Generalized parameters including displacements and their derivatives were used as unknowns at each nodal point. Results indicated that the total number of unknowns needed for a given level of accuracy was reduced as compared to that used in ordinary finite element analysis.; Plain concrete beams were notched and then precracked by static or fatigue loading prior to loading to failure. The effects of three-point and four-point bending, two sizes of beams and two different mix designs were investigated. Test results showed that the "fracture toughness" of statically-precracked beams is higher than that of fatigue precracked beams and fracture toughness of concrete is associated with its strength in compression. It is further noted that results obtained for the specimens in four-point bending are more consistent than those for three-point bending.