Theoretical development of the core-drilling method for nondestructive evaluation of stresses in concrete structures

This research establishes the theoretical basis for the core-drilling method for the nondestructive evaluation of in-situ stresses in the concrete in an existing structure. In the core-drilling method, a circular core-hole is drilled in to the concrete in a structure under stress, and the displacements that occur on the surface of the concrete as the core hole is drilled are measured. These measured displacements are then related to the in-situ stresses in the structure before drilling the hole.; Relieved displacement equations, equations for measured displacements from relieved displacements, and equations for in-situ stresses from measured displacements were derived for two stress states: (1) biaxial uniform normal and shear stress; (2) biaxial linear normal stress gradient and uniform shear stress. These closed-form equations are first developed for infinite plates in which these stresses were uniform through the plate thickness, and then applied to bounded objects. The closed-form equations were verified by finite element analyses. The evaluation of the applicability of the closed-form equations to objects with finite dimensions was conducted by finite element analyses.; Semi-analytical equations were developed for objects with finite dimensions and a core-hole for in-situ stresses uniformly distributed through the object thickness. This development is done by introducing empirical coefficients called calibration constants. Accurate analytical definitions of calibration constants were defined with dimensionless coefficients that make calibration constants material independent.; In addition to first two in-situ states of stress that are uniformly distributed through the depth, a third in-situ stress state comprised of biaxial normal stress and shear stress that are non-uniform through depth is also considered in this research. The incremental core-drilling method is developed primarily for applications in which in-situ stresses are non-uniform through the drilling depth. The incremental core-drilling method involves measuring displacements after successive increments of core-hole depth. Then these measured displacements are related to the in-situ stresses that vary through the depth. Finite element analyses were performed to verify the incremental core-drilling method.