Enabling an automated, remote and rapid detection of structural damage, sensor-based structural health monitoring is becoming a powerful tool for maintenance of civil engineering structures. In this study, a baseline-free, time-domain damage detection method was developed for concrete structures, which is based on analysis of nonlinear damping from measured structural vibration responses. The efficacy of the proposed method was demonstrated through a large-scale concrete bridge model subjected to different levels of seismic damage caused by shaking table tests. By applying the random decrement signature technique, the proposed method successfully identified, from its ambient vibration responses, nonlinear damping of the bridge associated with the seismic damage. The amount of the nonlinear damping increases as the seismic damage becomes more severe. This paper also compares the damage detection results with those obtained by stiffness-based methods, demonstrating a strong correlation between the increase in nonlinear damping and the decrease in structural stiffness associated with the increase in damage severity. valuable for post-seismic damage detection by improving the current visual inspection, which is time consuming, subjective, and potentially dangerous for inspectors.Research on vibration-based damage detection began in late 1970s in aerospace structures [1][2][3]. Then in the early 1980s, the research emerged to the civil engineering structures, especially for bridges and monumental structures. Many system identification techniques and damage detection methods have been developed over the past 30 years. Some full-scale tests were conducted, but researchers had difficulties to completely validate the efficacy of the proposed methods, mainly due to the unavailability of undamaged structures as a baseline. Of considerable interest was the research on large civil engineering structures developed since 1995 at the Los Alamos National Laboratory, as it allowed researchers to compare the dynamic response of a structure before and after the introduction of different levels of damage [4,5]. Most of these studies were based on changes in the dynamic characteristics of structures, since changes in physical properties cause detectable changes in modal parameters [6,7]. Usually these techniques are based on the measurement of changes in dynamic parameters including natural frequencies, mode shapes, and damping ratios. They are based on linear analysis, and their reliability and application range are widely known [8].The main issue that must be addressed, when the frequency-domain modal identification techniques are applied for seismic damage detection, is the presence of nonlinearity in the structural response. Most of the methods developed so far are based on frequency-domain analysis, which assumes linear structural responses. In case of civil engineering structures, this assumption is difficult to accept. As suggested by some studies [9,10], a nonlinear analysis is necessary during extreme events, because most civ...
This article presents a damage detection method for prestressed reinforced concrete (PRC) ele- ments based on free vibration tests and nonlinear damp- ing identification. Integrated static and dynamic exper- iments were carried out on three precast PRC beam specimens. The static loading induced different levels of damage to the beams. At each damage level, impul- sive loading was applied to the beams and the free vi- bration response was measured. The dynamic response data were processed using different methods including the multi-input multi-output (MIMO) curve fitting and the Hilbert transform techniques. A strong correlation is observed between the level of concrete damage (cracks) and the amount of nonlinear energy dissipation that can be modeled by means of quadratic damping. The non- linear damping can be extracted from the free vibration response for each vibration mode. The proposed method is suited for quality control when manufacturing precast PRC members, and can be further extended for in situ detection of damage in concrete structures under ambi- ent vibration
Abstract.A vibration based structural assessment campaign was carried out on a r.c. segmental bridge in North East Italy. The bridge has a cantilever static scheme, fixed at the top of the piers and with a hinge at the centre of the span. The particular configuration of the hinge consists in a couple of steel elements, each one composed by a tongue and groove joint. Since the year 1960, the hinge was subjected to consumption and degradation, that caused a malfunctioning of the device. An intervention of rehabilitation of the bridge led to a reinforcement of the existing hinges with the coupling of new metallic devices: new tongue and groove hinges were applied, that by one side allow the horizontal displacements and rotation, by the other side strongly reduce the relative vertical displacements of the two parts of the bridge. A dynamic test campaign was set up in order to assess the effectiveness of the intervention. The principal dynamic parameters were calculated and analysed with respect to the intervention that was realized.The tests clearly showed the effectiveness of the intervention, and helped the designer to have a better understanding of the structural behaviour of the bridge.
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