Structural condition assessment of cracked RC beams based on digital crack measurements

This paper presents calibration algorithms for assessing the current deformation state and predicting the load-bearing capacity of cracked reinforced concrete structures using high-quality pictures of crack data and numerical modeling. Under typical service conditions, structural members experience loading and unloading processes that result in concrete cracking and damage to the bond between steel and concrete. These factors contribute to the development of residual strains, which lead to permanent deformation. Two iterative calibration algorithms are developed for the analysis of a cracked structure with consideration of the damage effects of the load history. In the proposed approaches, the cracked structure is discretized initially as a Macro Finite Element (MFE) based on the crack information, and each element’s cross-sections are modeled as layers of either concrete or rebar materials. In the first proposed algorithm, to consider the crack and bond damage effects, an initial pre-strain is gradually applied on the rebar layers of MFE, in such a way that causes tension stress in the cracked zone. The initial pre-strain considered shall be combined with the strain from residual loading to calculate the overall section stress. The pre-strains are iteratively updated until the calculated and measured crack widths for each MFE satisfy the tolerance limit. By this, the impact of load history damage effects are incorporated in the current analytical model of the structure. The second proposed algorithm assumes a linear maximum initial residual strain in each MFE sections to consider damage effects. The linear initial residual section strain updates each section layer material state so that the strain from residual loading follows the updated state in calculating the total section stress. Those proposed algorithms are implemented based on standard displacement-based finite element (FE) with consideration of material nonlinearity. Both approaches are successfully compared with experimental data, and the effectiveness of the methods in accurately predicting residual deformation and load–deflection responses is demonstrated. This research contributes to advancing the field of assessing cracked reinforced concrete structures, providing a comprehensive framework for condition evaluation and modeling for cracked beams. • In modern structural health monitoring, infrastructures are being inspected by taking high-resolution images, from which defects such as cracks can be detected and measured. Structural engineers need these input parameters to update structural models and analyze the structure’s safety and condition. • This paper introduces two iterative-based calibration algorithms to assess the current deformation state and residual capacity of cracked reinforced concrete beams based on digital crack data. • In the first algorithm, an initial pre-strain is gradually applied on the rebar layer of macro finite elements (MFE), resulting in tension stress in the cracked zone. The pre-strain of rebar layers is iteratively updated until the calculated and measured crack widths for each MFE meet the tolerance limit. • In the second algorithm, a linear initial residual strain distribution is assumed for each MFE, with which each sec on layer materials are updated according to material law assigned to account for residual strain from load history. • Both algorithms have been successfully validated against experimental data, confirming their effectiveness in accurately predicting residual deformation, load-deflection responses, and crack width.