Calibration of Ground Pressure on Tunnel Lining in Genetic Algorithm Application for Structural Monitoring

This article presents the evolution of an algorithm that can be applied to a diagnostic systems for tunnels developed by the same authors. The aim of this work is the analysis of typical ground trust shape functions to be introduced in the library of a genetic algorithm in order to calculate the forces acting on tunnel lining starting only from the quantities measured by a set of clinometers and pressure sensors placed inside the lining itself, without any other knowledge of geotechnical or geological parameters. The knowledge of proper trust shapes, derived from geotechnical simulations, increases the performance of the algorithm in terms of convergence and correctness of the result. Some benchmarks of the genetic algorithm applied on geotechnical f.e.m. results is also given

Cracking analysis of plane stress reinforced concrete structures

This article presents the numerical analysis' results of reinforced concrete elements subjected to plane stress in early cracking stage. The elements are modelled by a concrete two-dimensional matrix, discrete reinforcement bars and bond-slip elements. The aim of this study is to investigate the behaviour of RC structures before and after the formation of the first cracks to understand the influence on the crack spacing and width of bar orientation with respect to the crack direction, bar spacing and diameter and presence of shear stresses on the crack. Discrete crack non-linear analysis of elements with reinforcement both orthogonal and skew to the crack directions are performed. The interaction between concrete and steel is ensured by a non-linear bond slip law at the interfaces between the two materials. The crack spacing obtained numerically are compared with the ones calculated using different design codes. The analysis of models with different reinforcement geometries allows individuating and discussing the main factors governing two-dimensional plane stress concrete cracking behaviour

Structural Health Monitoring Issues Using Inclinometers on Prestressed Concrete Girder Bridge Decks

In the last decades, assessment and rehabilitation of the existing built environment constitute one of the major challenges for engineers, practitioners and code-makers all over the world. Aging, deterioration processes, lack of or improper maintenance, and increasing occurrence of extreme events have led to the need of more efficient methods for the safety assessment and retrofitting/rehabilitation of existing concrete structures like bridges. New approaches deriving from research should be able to provide solutions devoted to reduce and/or avoid the necessity of interventions, verifying the safety conditions for human life and performances for serviceability on aged infrastructures. Structural Health Monitoring (SHM) of existing bridges has become a key issue in all western world as most of the infrastructures of each Country are reaching the end of their design life. SHM can be divided classically in two approaches: static and dynamic. Static SHM is based on the measure of displacements and their derivatives like rotations or strains regardless of the dynamic behaviour of the structure. Clinometers are among the most used devices to measure angles on structures; they can provide high accuracy when used in static mode as advanced techniques of signal processing can be used to reduce the noise of the signal working on acquisitions that can last several seconds to provide one single accurate measure of angle. Nevertheless, many issues one the affidability and the correct use of measures done with clinometers have to be addressed to achieve a trustworthy SHM using such devices. In this paper the most relevant issues related to the f.e.m. modelling of a bridge deck in view of the use of clinometers for SHM are presented providing explanation using a test case bridge that has been under continuous investigation for many months. A brief explanation of the process for data cleaning and interpretation is also given, stressing out the limits of the technology and the possible outcomes

Effect of concrete tensile strength in non linear analyses of 2D structures - a comparison between three commercial finite element softwares

Non-linear finite element method (FEM) allows to take into account material and geometrical non-linearities in the simulation of the behaviour of reinforced concrete structures. However, the accuracy of the numerical solution with respect to experimental tests is often questionable, especially in the case of 2D and 3D structures. Several competitions showed in the past significant scatter of the predicted results with respect to the correct ones. Even though internationally well-known computer softwares can be used to predict the structural response, the uncertainty of the numerical simulation cannot be neglected. Therefore, the application of finite element models to the assessment of concrete structures requires a proper investigation of the uncertainty related to the results of the simulations. This paper presents a comparison of numerical simulations of sixteen case studies taken from past experimental tests and modelled with three commercial non-linear softwares. The purpose of the investigation is to show how significant could be the difference between the experimental and numerically evaluated failure load and displacement in function of the code used and the variation of only one material parameter

Effect of Environmental Parameters on Structural Health Status Assessment Using OMA Techniques

Featured Application: The work presented in this paper is an investigation of the limitations of precision due to environmental disturbances (like thermal effects) in traditional algorithms based on operational modal analysis (OMA) that are used in dynamic structural health monitoring in civil and mechanical engineering. The data from a laboratory test on two aluminum rods are analyzed in this work. The rods are subjected to environmental excitation in an uncontrolled environment, attempting to replicate real operational conditions of structural health monitoring with external disturbances. Different damage levels are simulated on one of the two tension rods. Three of the most frequently used OMA methods are applied to evaluate the effects of the simulated damage on the dynamic behavior of the system. The complexity of the three applied OMA methods is gradually increased. The difference between the results from the different approaches is assessed. The aim of this work is to assess the performance of the proposed OMA methods, to understand their limits, and to assess the role of environmental disturbance parameters, such as temperature, in the evaluation of the health status of structures

Autogenous Crack Control during Construction Phases of MOSE Venice Dams

The design of concrete structures exposed to severe environmental attack, like in marine environment, requires serious attention for concrete durability. Early age cracking due to autogenous deformations can be detrimental to the performance of tidal structures. The study of the structural effects of hydration heat and rheological behaviour of a set of huge concrete structures of the Mobile Venice Dams known with the MOSE acronym (Experimental Electromechanical Module) is presented in this paper. Together with other measures such as coastal reinforcement, the raising of quaysides, and the paving and improvement of the lagoon, MOSE is designed to protect Venice and the lagoon from tides of up to 3 meters. Construction began simultaneously in 2003 at all three lagoon inlets, and the project has been completed in 2014. Floods have caused damage since ancient times and have become more frequent and intense as a result of the combined effect of eustatism (a rise in sea level) and subsidence (a drop in land level) caused by natural and man-induced phenomena. Nowadays, towns and villages in the lagoon are about 23 cm lower with respect to the water level than at the beginning of the 1900s. Each year, floods can cause serious problems for the inhabitants as well as deterioration of architecture, urban structures and the ecosystem. Over the entire lagoon area, there is also a constant risk of a catastrophic event such as that of 4 November 1966, when a tide of 194 cm submerged Venice, Chioggia and the other built-up areas

Effect of Environmental Parameters on Structural Health Status Assessment Using OMA Techniques

The data from a laboratory test on two aluminum rods are analyzed in this work. The rods are subjected to environmental excitation in an uncontrolled environment, attempting to replicate real operational conditions of structural health monitoring with external disturbances. Different damage levels are simulated on one of the two tension rods. Three of the most frequently used OMA methods are applied to evaluate the effects of the simulated damage on the dynamic behavior of the system. The complexity of the three applied OMA methods is gradually increased. The difference between the results from the different approaches is assessed. The aim of this work is to assess the performance of the proposed OMA methods, to understand their limits, and to assess the role of environmental disturbance parameters, such as temperature, in the evaluation of the health status of structures

Comparison between non-linear numerical models for R.C. shear walls under cyclic loading

The non-linear behaviour of concrete structures is the result of a series of phenomena, as material non-linear constitutive law and cracking process. As a consequence, in order to understand the behaviour of reinforced concrete members from elastic field to ul-timate condition, is necessary to use instruments able to simulate the material damaging evolution under growing loads. Commer-cial non-linear finite elements codes are generally able to simulate concrete behaviour with good approximation when a progressive incremental load is applied. However, the same result could not be reached under a cyclic loading. In this work two commercial non-linear finite element codes have been considered in order to assess the skill of these codes to simulate non-linear concrete be-haviour under cyclic loading. The results of six laboratory tests on shear walls have been compared with the ones obtained by means of numerical models and some conclusions on the numerical predictions are presented. / Il comportamento non lineare delle strutture realizzate in calcestruzzo è il risultato di una serie di fenomeni, come la non linearità della legge costitutiva del materiale ed il processo di fessurazione. Al fine di comprendere il comportamento degli elementi struttura-li in calcestruzzo armato è necessario disporre di strumenti in grado di simulare il progressivo danneggiamento del materiale in pre-senza di carichi crescenti. In generale, i codici di calcolo presenti in commercio sono in grado di cogliere abbastanza bene il compor-tamento delle strutture in cemento armato soggette a carichi monotoni crescenti. Risulta invece più complesso seguire il compor-tamento strutturale in presenza di un carico ciclico. In questo lavoro sono stati considerati due diversi codici di calcolo non lineare agli elementi finiti al fine di verificare la loro capacità nel simulare il comportamento di pareti a taglio soggette a un carico ciclico. Sono stati considerati i risultati di sei prove di laboratorio disponibili in letteratura; tali risultati sono stati confrontati con quelli otte-nuti numericamente per trarre delle conclusioni sull’affidabilità dei modelli numerici

Influence of Slenderness on the Evaluation of Epistemic Uncertainty Related to Non-Linear Numerical Analysis of RC Columns

This investigation is devoted to quantify the epistemic uncertainty related to the nonlinear analysis of reinforced concrete columns characterized by high slenderness using numerical codes. The adoption of refined numerical tools, which are able to consider both mechanical and geometric non linearities, implies to perform assumptions and approximations with respect to reality. Whit reference to reliability analysis, these simplifications lead, inevitably, to additional uncertainties which are of epistemic nature. In fact, these uncertainties may be reduced by the engineers/analysts by increasing the level of refinement of the numerical model and/or increasing knowledge about parameters associated to material models. However, also numerical model established by expert engineers/analysts are affected by this kind of epistemic uncertainty. Accepting that the level of uncertainty associated to the experimental tests set are minimized, the epistemic uncertainty associated to non-linear numerical simulations can be quantified characterizing the model uncertainty random variable comparing the outcomes of numerical results to the associated experimental ones. The present investigation proposes the quantification of the model uncertainty related to non-linear numerical simulations of slender RC columns. A total number of 40 experimental results known from literature are herein selected in coherence with current Eurocodes specifications. The experiments are reproduced adopting non-linear numerical analysis differentiating between several modelling hypotheses (i.e., numerical code; materials models). The comparison between experimental and numerical results is adopted to characterize the most suitable probabilistic model for the model uncertainty random variable associated to non-linear numerical simulations of RC columns subjected to significant slenderness. The outcomes of the research are useful to provide background to the characterization of partial safety factor for model uncertainty in non-linear numerical analysis using the approach of the global resistance format for safety verifications

Prediction of Cracking Induced by Indirect Actions in RC Structures

Cracking of concrete plays a key role in reinforced concrete (RC) structures design, especially in serviceability conditions. A variety of reasons contribute to develop cracking and its presence in concrete structures is to be considered as almost unavoidable. Therefore, a good control of the phenomenon in order to provide durability is required. Cracking development is due to tensile stresses that arise in concrete structures as a result of the action of direct external loads or restrained endogenous deformations. This paper focuses on cracking induced by indirect actions. In fact, there is very limited literature regarding this particular phenomenon if compared to its high incidence in the construction practice. As a consequence, the correct prediction of the crack opening, width and position when structures are subjected to imposed deformations, such as massive castings or other highly restrained structures, becomes a compelling task, not so much for the structural capacity, as for their durability. However, this is only partially addressed by commonly used design methods, which are usually intended for direct actions. A set of non-linear analysis on simple tie models is performed using the Finite Element Method in order to study the cracking process under imposed deformations. Different concrete grades have been considered and analysed. The results of this study have been compared with the provisions of the most common codes