Damage localization on Reinforced Concrete Structures

It is known that the occurrence of structural damage, for any kind of structure, it is able to changes its dynamic characteristics over time. Generally, the main parameters conditioned by this problem are periods of vibration, damping factors and mode shapes. Several authors showed that also the variations of the modal curvature are strictly related to the damage occurred on a structure. Moreover, using the mode curvature as a control parameter it is also possible to localize where the damage occurred on the structure. In order to analyze the nonlinear behaviour of a general structure, and localize a possible damage, we propose a band-variable filter based on the Stockwell Transform. This paper shows through many examples as comparing mode shapes and the related curvature variations over time it is possible to easily identify the damage and also localize it on the structure

Effect of non-structural elements on the dynamic behaviour of moment-resisting framed structures.

Effects of earthquakes on building structures have studied from many researchers on the recent scientific and technique literature. The phenomenon is clear: inertia forces are governed from structural and non-structural stiffness and masses. The distribution of seismic lateral loads and their magnitude are strongly correlated to the fundamental period of the structure. Therefore, an accurate evaluation of the fundamental period is a crucial aspect for both static and dynamic seismic analyses. In fact, the fundamental period determines the global seismic demand through the spectral acceleration directly evaluated from the linear and/or nonlinear acceleration response spectra (provided from codes or derived from detailed analyses of site effects). Recent earthquakes highlighted the significant effects derived from the interaction between structural and non-structural elements on the main dynamic parameters of a structure and on the lateral distribution of the inertial forces. Usually, non-structural elements acts together with the structural elements, adding both masses and stiffness. Using numerical and experimental campaigns, many researchers have studied the effects of infill walls on the dynamic behaviour of buildings and several simplified models have been proposed to take into account the presence of non-structural elements within linear and nonlinear numerical models. As example, Kliner and Bertero tested a 1/3 scaled structure (moment-resisting infilled frame model) and determine its behaviour during earthquakes. They found that the infills increased the stiffness of the frame in about 5 times. Consequently, in these cases the fundamental period reduces and the inertia forces generally increases. Meharabi et al. tested a 6-storey, three bay, reinforced concrete moment resisting frame, designed according to the provision of UBC-91, and they shown that the lateral force resistance of an infilled frame was higher than that of bare frame. It was concluded that a proper design of the infills would have beneficial effects on the seismic behaviour of frames. Elouali et al. studied the effect of inflill walls on vibration periods of frames. The infill wall was modelled as an equivalent diagonal strut. It was concluded that the fundamental period of the infilled frame could be reduced in about 50 to 70% from that of the bare frame. Considering existing mathematical models proposed in the recent scientific literature and the main geometrical and mechanical characteristics of Italian buildings, a parametric study has been conducted using several numerical analyses. Finally, a comparison between the predicted response of numerical models and the response of real structures have been done

Structural Health Monitoring of Reinforced Concrete Structures using Nonlinear Interferometric Analysis

Structural Health Monitoring (SHM) aims to improve knowledge of the safety and maintainability of civil structures and infrastructures. Within the Italian research project RELUIS-DPC 2010-2013, funded by the Italian Department of Civil Protection, a specific task deals with the possibility of set up a fast procedure to determine the damage evolution on a large number of structures after seismic events. This paper presents an upgrade of a method for damage detection based on a statistical approach that uses the most significant data recorded on both the top floor and the bottom of a building, with the purpose of extracting the value of the maximum inter-story drift expected along the building height, adopted as damage indicator. Nonlinear interferometric analyses combined with the S-Transform are used to evaluate frequencies and damping variation of the monitored structure during an earthquake. The method has been tested on numerical reinforced concrete framed structures

Damage detection on framed structures: modal curvature evaluation using Stockwell Transform under seismic excitation

The key parameters for damage detection and localization are eigenfrequencies, related equivalent viscous damping factors and mode shapes. The classical approach is based on the evaluation of these structural parameters before and after a seismic event, but by using a modern approach based on time-frequency transformations it is possible to quantify these parameters throughout the ground shaking phase. In particular with the use of the S-Transform, it is possible to follow the temporal evolution of the structural dynamics parameters before, during and after an earthquake. In this paper, a methodology for damage localization on framed structures subjected to strong motion earthquakes is proposed based on monitoring the modal curvature variation in the natural frequency of a structure. Two examples of application are described to illustrate the technique: Computer simulation of the nonlinear response of a model, and several laboratory (shaking table) tests performed at the University of Basilicata (Italy). Damage detected using the proposed approach and damage revealed via visual inspections in the tests are compared

A Fast Method for Structural Health Monitoring of Italian Reinforced Concrete Strategic Buildings

The growing number of demand for a widespread of health monitoring for strategic buildings in seismic areas has emphasized the need to realize in-depth scientific studies, in order to verify the feasibility of economic and fast methods to detect anomalous vibrations, to execute post earthquake warning and monitoring, damage assessment and first damage scenarios. Generally, an effective system for structural health monitoring requires an appropriate number of sensors, suitably located in the structures, and complex elaborations of big amounts of data. The simplified method presented in this paper is based on a statistical approach that uses the most significant data recorded on the top floor of the building, with the purpose of extracting information on the maximum inter-story drift, used as damage indicator. The parameters considered in the method are (i) maximum top acceleration, (ii) the first modal frequency variations and (iii) the equivalent structural viscous damping variation. A big amount of experimental data relevant to several tests carried out on scaled R/C models and numerical non linear dynamic analyses have been used to verify the feasibility of this approach

DInSAR–SBAS satellite monitoring of infrastructures: how temperature affects the “Ponte della Musica” case study

Continuous monitoring of the structural health of strategic structures and transport infrastructures plays a crucial role in providing an effective assessment of the safety conditions and in timely planning of the ordinary and extraordinary maintenance programme. Deformation monitoring and dynamic characteristic identification are some commonly used strategies for this purpose. One of the main challenges of recent years in the field of structural health monitoring is the use of data deriving from satellite interferometry, capable of providing information on structural deformations at a local and territorial scale. Despite the solidity and dependability of satellite-based methods for assessing ground deformation over time, when it comes to structural surveillance, there are certain circumstances under which satellites are incapable of accurately assessing displacements. This is particularly true for structures that are sensitive to temperature variations. The paper uses the “Ponte della Musica–Armando Trovajoli” in Rome as a case study to explore these aspects in more depth. This bridge has a steel arch structure with a prestressed concrete deck below it. It represents an example in which satellite differential interferometry does not allow obtaining useful information on displacement, at least for the most deformable portion of the deck, and therefore also on any pathological movements. This work proposes a 3D digital twin of the bridge, appropriately calibrated through experimental measurements of the environmental vibrations performed on the bridge. This will allow to evaluate the role played by thermal deformations related to air temperature variations and thus better understand the connection between physiological deformations and satellite limits

Numerical Model Calibration of a Bridge by Using Inverse Engineering: A Case Study

In recent years, existing transport infrastructures have experienced significant safety criticalities implying expensive repairs, significant business downtime and occasionally demolition with a relevant economic and social impact. Vibration Based Monitoring (VBM) represents a strategic tool for real time assessment of potential damages suffered by civil/strategic structures and infrastructures due to aging and/or after a critical event. As a part of VBM, experimental dynamic identificationmethods allowto characterize modal properties of existing structures both in stationary and non-stationary conditions. The process used to calibrate the numerical model (digital twin) minimizing the errors between considered parameters of real and numerical structure can be considered an inverse engineering application. This paper focuses on the dynamic calibration of a Finite Element (FE) model related to the “Ponte della Musica – Armando Trovajoli” bridge locate in Rome (Italy), built by means design documentation and visual inspection. The model calibration has been performed in terms of eigenfrequencies and equivalent viscous damping factor evaluated by means of accelerometric recordings. Several numerical FEM models were built using different boundary conditions. Uncertainties derived from external constrains and executive details have been accounted by varying stiffness and other mechanical parameters within several parametric analyses with the aim to fit experimental dynamic properties with simulated ones. The present study has been performed within the TaskWP6 “Monitoring and Satellite Data” of the DPC-Reluis 2022–2024 agreement, with the aim to further analyse the influence of temperature on the vertical displacement of monitored bridge and compare them with satellite data information

REINFORCED CONCRETE FRAMED STRUCTURES: NUMERICAL VALIDATION OF TWO PHYSICAL MODELS CAPABLE TO CONSIDER THE STIFFNESS CONTRIBUTION OF INFILL PANELS ON FRAMED STRUCTURES IN OPERATIVE CONDITIONS

The present work proposes two different models to estimate, with adequate approximation, the stiffening contribution of an infill panel for low stress levels (elastic phase). The need for such models arose from a comparison previously carried out by some authors between the fundamental period values calculated with the formulation of the NTC 2008 and those obtained experimentally through a dynamic identification campaign on ambient noise conducted with reinforced concrete framed structures. After defining the problem, the study proceeds with the description of the various phases of the infill panel behaviour for various levels of action in the plane and then discusses the major numerical modelling techniques of the infill panel currently available. Based on considerations deduced from the analysis of various bibliographic contributions, the proposed calculation models are tested against experimental results obtained from various studies

Numerical investigation on the effects of non-structural components on the elastic fundamental period of buildings

In this work a parametric study has been performed in order to evaluate the elastic fundamental period of vibration of buildings as function of structural morphology (height, plan area, ratio between plan dimensions) and infills distribution. Recent earthquakes highlighted the significant effects derived from the interaction between structural and non-structural elements on the main dynamic parameters of a structure and the lateral distribution of the inertial forces. Usually, non-structural elements acts together with the structural elements, adding both masses and stiffness. The presence of infill elements is generally not taken into account in the design process of structural elements, although these elements can significantly increase the lateral stiffness of a building leading to a modification in dynamic properties. Particularly, at the Damage Limit State (where an elastic behaviour is expected), soil-structure interaction effects and non-structural elements may further affect the elastic natural period of buildings, changing the spectral accelerations compared with those provided by seismic codes in case of static analyses. Using a numerical campaign, the effects of these parameters on the elastic dynamic behaviour of buildings have been studied taking into account presence and distribution of non-structural elements