Abstract Summary
In recent years, several advanced technologies have been developed to automate inspections and monitoring processes of existing bridges [1]. Robotic platforms, as the Unmanned Aerial Vehicle (UAVs), and Artificial Intelligence (AI) techniques are capable of evaluating autonomously the actual mechanical performances of materials and structures reducing the inspection and maintenance costs. The research community has made significant progress in autonomous data acquisition, identification and localization of the damage through machine learning algorithms. In physics-based approach, the efficiency of the computational models, as for example those based on nonlinear finite element procedures, plays a crucial rule not only in the model updating of monitoring system but also in the training of deep neural network. Although the nonlinear structural response of the bridges can be efficiently analysed through two-dimensional and three-dimensional finite element (FE) models, these commonly require high computational efforts. The aim of this work is to present a high-performing 3D beam FE to model the nonlinear behaviour of reinforced concrete and prestressed reinforced concrete girders, including material degradation. In this regard, the adoption of a fiber cross-section discretization allows both to consider general material non-linearity, through the introduction of specific constitutive laws, and to identify the region of the beam section affected by the degradation mechanisms. A force-based (FB) formulation is adopted for the proposed beam element, that is proved to be more efficient than the classical displacement-based approach as it strictly satisfies equilibrium is along the element. In presence of material non-linearity, the computational advantages of the FB approach are relevant. A crucial aspect in presence of strain-softening material behaviour is the pathological mesh dependence of the FE numerical solutions. In this work, a proper regularization procedure for FB formulations is adopted to overcome this drawback [2]. The composite cross-section of the prestressed concrete girder is modelled in detail by considering concrete, reinforcing steel bars and prestressing tendons fibers. The nonlinear constitutive law of the concrete fibers is based on a plastic-damage model which considers two different damage parameters for the compression and tensile behaviour to take in account the re-closure of the tensile cracks, while a classical elasto-plastic constitutive law is adopted for steel bars and tendons. A predictor-corrector algorithm is used to solve the evolution problem of damage and plasticity. The presented force-based beam finite element based on a damage-plasticity model is implemented in the OpenSees framework. Some applications are computed to properly selected benchmarks to show the computational efficiency and the potentiality of the proposed modelling approach for nonlinear analysis repeated several times, such as in the application of the Artificial Intelligence for the assessment of existing bridges. [1] Spencer, B.F., V. Hoskere and Y. Narazaki. 2019. Advances in computer vision-based civil infrastructure inspection and monitoring. Engineering, 5: 199–222 [2] Addessi, D., and V. Ciampi. 2007. A regularized force-based beam element with a damage-plastic section constitutive law. Int. J. Numer. Methods Eng., 70 (5): 610–629
