Automated classification of civil structures defects based on Convolutional Neural Network

Today, the most used method for civil infrastructure inspection is based on visual assessment performed by certified inspectors following prescribed protocols. However, the increase in aggressive environmental and load conditions, coupled with the achievement for many structures of the end life-cycle, highlighted the need to automate damage identification to satisfy the number of structures that need to be inspected. To overcome this challenge, the current paper presents a method to automate the concrete damage classification using a deep Convolutional Neural Network (CNN). The CNN is designed after an experimental investigation among a wide number of pretrained networks, all applying the transfer learning technique. Training and Validation are performed using a built database with 1352 images balanced between “undamaged”, “cracked”, and “delaminated” concrete surface. To increase the network robustness compared to images with real-world situations, different configurations of images has been collected from Internet and on-field bridge inspections. The GoogLeNet model is selected as the most suitable network for the concrete damage classification, having the highest validation accuracy of about 94%. The results confirm that the proposed model can correctly classify images from real concrete surface of bridges, tunnel and pavement, resulting an effective alternative to the current visual inspection

Two-node curved inverse finite element formulations based on exact strain-displacement solution

The inverse finite element method (iFEM) is an efficient algorithm developed for real-time monitoring of structures equipped by a network of strain sensors. The inverse element for modeling curved beams was previously developed using an approximate solution based on independently interpolated displacement components. In this study, a new formulation is proposed by the development of a least-squares variational principle using the kinematic framework of the curved beam theory. The library of existing iFEM-based elements is expanded by introducing three different inverse curved elements named iCB3, iCB4 and iCB5 respectively. This new formulation has been developed considering the exact solution of the curved beam theory that corresponds to the membrane-bending coupling and the explicit statement of the rigid-body motions. The three inverse elements, which require three, four and five measurement points respectively, extend the practical utility of iFEM for shape sensing analysis of curved structures according to the minimum available quantity of strain sensors. The effectiveness and higher accuracy of the iCB/iFEM methodology compared to other solutions present in literature are demonstrated considering numerical studies on curved beams under static transverse force and distributed loading conditions. For these problems, the effect of strain measurements error, number of sensors and discretization refinement on the solution accuracy is evaluated

A Model for the Analysis of Ultimate Capacity of RC and PC Corroded Beams

Corrosion of steel in reinforced and prestressed concrete beams is very common for structures and infrastructures. It can drastically reduce the resisting section of rebar, modify the mechanical response of the steel rebar, and also determine cracking of the surrounding concrete because of the volume expansion effect of rust. Moreover, it heavily influences the bond between steel rebar and concrete. Few experimental tests are available in the literature, where the structural behavior of reinforced and prestressed concrete beams, in presence of corrosion of longitudinal and transversal reinforcement, is analyzed. A reduction of the bearing performance is observed with an increasing level of rebar corrosion. Indeed, a changing collapse mechanism is evidenced through the tests and may be addressed to the not obvious consequences of corrosion. In this paper, a physical model based on a consistent equilibrium and ultimate strength theory is employed in order to explain the residual capacity of corroded beams. The model is based on limit analysis, and it is able to take into account the interaction between shear, bending moment, and axial forces

Estimating corrosion attack in reinforced concrete by means of crack opening

The corrosion of reinforcement in concrete is the most common degradation phenomenon of reinforced concrete structures. Reinforced concrete elements subjected to corrosion generally crack due to the expansive nature of oxides. One very important task is estimating the corrosion level using a non‐destructive method in order to establish both the actual safety of the structure and a priority intervention plan. Many researchers have studied the relationship between the corrosion phenomenon and the corresponding crack openings and their evolution; several statistical analyses, based on test data from experimental campaigns under a wide range of test conditions, are available. The present work attempts to contribute to finding a relationship between the crack opening and the amount of corrosion induced in the reinforcing bars. The result of the analysis is that only a reduced number of tests can be used to establish an empirical model based on a reliable set of test data. A simple relationship between crack opening and corrosion penetration is not recommended, due to the different parameters that are able to influence this correlation. Therefore, two fundamental parameters, the ratio of the concrete cover to the rebar diameter and the concrete strength, have also been considered. The considerations made regarding these parameter test results have been rearranged and the result is a formulation that shows reduced scatte

Study on the Probability Distribution of Pitting for Naturally Corroded Prestressing Strands Accounting for Surface Defects

One of the most urgent scientific needs from a technical and economic engineering point of view is the assessment of concrete structures suffering corrosion deterioration. However, the pursuit of this target in the case of corroded prestressed concrete (PC) members is hindered by the lack of (i) consolidated simplified formulations to be used in the engineering daily practice and (ii) works investigating the uncertainties in the correlation between the damage induced by corrosion and the structural resistance. To this aim, the present study adopts a 3D-scanning technique for the pitting morphology evaluation of several corroded prestressing strands retrieved from 10-year-old PC beams. First, the probabilistic distributions of penetration depths have been investigated. Second, the pitting factors alpha and omega(i) have been proposed and discussed to quantify the level of corrosion in longitudinal and transversal direction, respectively. Finally, correlations have been derived between the maximum and average penetration depth as a function of the level of corrosion and the surface defects mapping has been carried out on the corroded PC beams. The results show that the penetration depth of strands subjected to chloride-induced corrosion can be best fitted by a lognormal distribution function. Additionally, the simultaneous consideration of longitudinal and transversal pitting factor is found out to be essential for an exhaustive comprehension of pitting corrosion. Moreover, the outcomes highlight that the presence of longitudinal splitting cracks plays a fundamental role in the corrosion spatial variability of prestressing strands

Shape-Sensing of Beam Elements Undergoing Material Nonlinearities

The use of in situ strain measurements to reconstruct the deformed shape of structures is a key technology for real-time monitoring. A particularly promising, versatile and computationally efficient method is the inverse finite element method (iFEM), which can be used to reconstruct the displacement field of beam elements, plate and shell structures from some discrete strain measurements. The iFEM does not require the knowledge of the material properties. Nevertheless, it has always been applied to structures with linear material constitutive behavior. In the present work, advances are proposed to use the method also for concrete structures in civil engineering field such as bridges normally characterized by material nonlinearities due to the behavior of both steel and concrete. The effectiveness of iFEM, for simply supported reinforced concrete beam and continuous beams with load conditions that determine the yielding of reinforcing steel, is studied. In order to assess the influence on displacements and strains reconstructions, different measurement stations and mesh configurations are considered. Hybrid procedures employing iFEM analysis supported by bending moment-curvature relationship are proposed in case of lack of input data in plastic zones. The reliability of the results obtained is tested and commented on to highlight the effectiveness of the approach

Application of Inverse Finite Element Method to Shape Sensing of Curved Beams

Curved beam, plate, and shell finite elements are commonly used in the finite element modeling of a wide range of civil and mechanical engineering structures. In civil engineering, curved elements are used to model tunnels, arch bridges, pipelines, and domes. Such structures provide a more efficient load transfer than their straight/flat counterparts due to the additional strength provided by their curved geometry. The load transfer is characterized by the bending, shear, and membrane actions. In this paper, a higher-order curved inverse beam element is developed for the inverse Finite Element Method (iFEM), which is aimed at reconstructing the deformed structural shapes based on real-time, in situ strain measurements. The proposed two-node inverse beam element is based on the quintic-degree polynomial shape functions that interpolate the kinematic variables. The element is C2 continuous and has rapid convergence characteristics. To assess the element predictive capabilities, several circular arch structures subjected to static loading are analyzed, under the assumption of linear elasticity and isotropic material behavior. Comparisons between direct FEM and iFEM results are presented. It is demonstrated that the present inverse beam finite element is both efficient and accurate, requiring only a few element subdivisions to reconstruct an accurate displacement field of shallow and deep curved beams

Dynamic response of PC bridge beams under different damages

The present paper describes the dynamic test campaign on prestressed concrete bridge beams taken from a dismantled viaduct in Turin, Italy after a service life of 50 years in the framework of BRIDGE|50 research project. Dynamic measurements were previously performed on the decks from which the 29 beams were taken to characterize the behaviour of the viaduct in service condition. Successively the single beams are tested to analyse and evaluate the effects of the different damage levels on the dynamic properties. The vibration data have been collected before the application of static load, after the first cracking condition and after the maximum load applied on the beam to extract the principal modal components. The results highlight the correlation among the evolution of the damage and the dynamic response of the beam and then the effectiveness of vibration tests to identify the occurrence of damages and follow their evolution. The experimental findings could be used in future works to explore the effects of damages of the single beams on the global response of this bridge typology. This work presents the results of the experimental tests on the first eight beams tested

Large-scale experimental testing of 50-year-old prestressed concrete bridge girder

This paper reports on large-scale loading tests survey carried out on 50-year-oldprestressed concrete girders as part of the BRIDGE|50 research project (www.bridge50.org).The girders were retrieved from an existing viaduct in Turin, Italy. The prestressed concreteelements were 19.2 m long and had an I-shaped cross-section with a cast-in-situ slab. Variabledamages were found, due to in-service deterioration and/or subsequent lifting operations duringthe demolition phase. Each specimen was subjected to static tests using monotonic or cyclicloading up to the ultimate load. This paper reports the results of tests on the second group offour girders, comparing their load-deflection responses and strains with those of the first groupsubjected to a different static scheme. The experimental findings highlight the global structuralresponse from bending to bending/shear failure; the outcomes will define a valuable referencedatabase for assessing the residual structural performance of existing girder bridges

Load tests on dismantled 50-year-old prestressed concrete bridge deck beams

This paper presents the results of three large scale experimental tests within the survey conducted on 50-year-old prestressed concrete (PC) girders for the BRIDGE|50 research project (www.bridge50.org). The girders were retrieved from a viaduct before dismantling operations once located in the urban area of Turin, Italy. Together with other structural members they represent one of the most prominent project of this type worldwide. The PC elements have 19.2 m span length and I-shaped cross section with 14 cm cast-in situ slab with variable damage due to deterioration caused by both service and lifting operations during dismantling phase. For each specimen, static tests have carried out applying monotonic or cyclic loading up to the ultimate load, measuring deflections, loads and strains in several positions for two I beams and one box beam. The results of the tests in terms of load-deflection responses and strains are reported for each beam investigated and compared considering previous tests from the same project already reported in literature. The experimental findings highlight the specific structural response and residual capacity of the tested members in presence of damage, cyclic loading and different tested section. The outcomes of the project will provide a valuable database of reference for the assessment of the residual structural performance of existing bridges