Principal Investigator: Robert Peterman
Sponsors & Partners
Kansas State University
Mid-America Transportation Center
Kansas State University Department of Civil Engineering
About this Project
Brief Project Description & Background
This research is aimed at determining the existing stresses in a concrete member. The first step is to image the concrete in its in-situ stressed condition at a desired location, and then cut around the imaged area using a diamond core bit to a depth of approximately one inch. The result will be a "re-bounding" of most of the elastic strain carried by the concrete member at that point. By re-imaging the point after penetration by the core drill, the change in surface strain can be determined, and thus also an estimate of the initial internal stress.
In Phase 1 (the laboratory phase), the procedures for measuring and cutting the concrete will be established. In addition, the correlation between surface strain changes and internal forces will be evaluated, and the accuracy of the method determined.
One of the most attractive features of this new measurement technique is that there is typically no surface preparation required. The reflective properties of the member's surface serve as a "fingerprint" of the unique location. Thus, an engineer or technician can begin taking initial baseline measurements within minutes after arriving at a bridge site.
With the aging and deterioration of bridges, evaluation of existing conditions of their structural elements becomes vital to engineers and public officials when deciding how to repair or replace the structures. The ability to obtain necessary information on these conditions is often expensive and time consuming, especially for concrete bridges where the reinforcement is not available for inspection. Employing the surface-strain relief method could allow for accurate evaluation of aged or damaged prestressed members.
The surface-strain relief method was developed to measure initial or pre-existing strains in a concrete member. It involves relieving the strain in the member and measuring the change in strain. Two methods were tested in this studyâ€”one used a linear electrical-resistance strain gage and a three-inch-diameter diamond concrete core bit to cut around the gage, and the second method used a laser-speckle imaging device and a diamond cutting wheel to create notches perpendicular to the axis of maximum strain. Both methods measured the change in strain and related it to within 10 percent of the actual fse. The method of cutting notches and the laser-speckle imaging device provided a simpler method to be implemented in the field, while the coring method achieved a higher level of accuracy and precision. The selection of transportation modes are provided and promising future research tasks are suggested as well.