Research on In Situ Stress Measurements in Reinforced Concrete Beams Based on the Core‐Drilling Method

Abstract

To increase the accuracy of the core-drilling method in measuring the in situ stresses within concrete beams, this paper developed a special core-drilling machine system, studied the surface stress release rule of concrete beams through finite element simulations, and then carried out verification tests. The effects of the borehole diameter, drilling depth, strain sensor size, and borehole position on the measurement accuracy were studied. The results showed that borehole diameters of 100 mm, 75 mm, and 50 mm can achieve stress release and that the smaller the borehole diameter was, the easier it was to release the stress. When using the smallest borehole, the stress concentration range around the borehole was narrow, and there was little damage to the original structure. The strain gauge size influenced the actual measurement results. An excessively large strain gauge will be disturbed by drilling because of the limited size of the borehole. An excessively small strain gauge will be easily influenced by the inhomogeneity and randomness of the concrete materials, resulting in large measurement error. The difference between the measured concrete stress and the theoretical value was less than 10%, and the average error was only 6.03%, indicating the feasibility of the proposed method.

Parametric Study of Drilling Method Performed on One-Way Post-Tensioned Slabs

“…Since then, this approach has become standard for the determination of residual stresses in steel structures. In the case of metal materials, the drilled hole is small (diameter only circa 1.5 mm) [15][16][17]. Therefore, such small holes are not applicable for concrete members (need for longer strain gauges and heterogeneity of concrete) [17].…”

“…Moreover, they have considered the effects of water during drilling, the shrinkage of concrete, and the presence of reinforcement. In 2020, Deng and Tang [15] described a new system of this approach that combines strain gauges with a core-drilling machine to measure the released strain. This way, they managed to solve the problem of borehole strain gauge wiring (the strain gauge is placed inside the core) in case of uniaxially stressed concrete beam which was experimentally and numerically analysed.…”

“…If we cut the steel reinforcement, it is important to consider its influence. Hence, the identification of the reinforcement in advance is very important, so we can avoid its cutting [15]. In [23], the authors presented an analysis performed on steel members instead of concrete elements.…”