Interpretation and optimization of internal force data of piles based on concrete damage model

The elastic modulus of concrete is one of the critical parameters in calculating the internal forces of pile structures. Due to inherent complexity and variability of elastic modulus, it directly impacts the interpretation accuracy of internal force measurements in piles. This study addresses the issue that significant discrepancies arise between the interpreted internal force data of bored piles that is interpreted by constant elastic modulus and the applied loads at the pile head during static uplift load tests, which is not compliant with mechanics principles. We foremost conduct a detailed analysis on the variation characteristics of sensor data at the calibration cross-sections of bored pile internal force measurements. By integrating the static load application conditions and the deformation characteristics of the pile body, we propose a method to inversely determine the elastic modulus and tensile strength of the pile concrete using multi-stage load data. Subsequently, a reinforced concrete damage model based on measured data is established, enabling the interpretation and optimization of internal force measurements in bored piles during uplift static load tests. Case study results demonstrate that the strain variation characteristics at calibration cross-sections during the static uplift load test are closely correlated with the magnitude of the pile head load, which can reflect the damage characteristics of the pile concrete. When calculating the elastic modulus of the pile concrete, the inverse analysis results of using damage model parameters are more consistent with actual conditions compared to the empirical parameters recommended in design codes, providing axial force calculations that align well with the pile head load. Therefore, it is suggested that the interpretation of internal force measurement results in bored piles during static uplift load tests must fully take account of the damage state of the pile concrete.