Vibration-based damage identification is a non-destructive method that enables the health monitoring of civil infrastructures. It aims to detect the presence and location of damage by measuring changes in the vibration characteristics of these structures. Unfortunately, the most popular vibrational parameters – natural frequencies and modal displacements – have a low sensitivity to certain types of local damage. Modal strains and curvatures, on the other hand, can be sufficiently sensitive to local damage, but monitoring modal strains is challenging. Indeed, the strain amplitudes can be in the sub-microstrain range (<1 με) when considering ambient excitation which is too small for most conventional techniques. Here we show that such measurements can be successfully carried out in a quasi-distributed manner with fibre Bragg grating–based sensors that have been mounted on a dedicated strain-amplifying transducer. First, we report on lab-scale dynamic tests on a 5-m-long concrete beam, equipped with such transducers having a strain amplification of 62. Our results show that we can identify the first three bending modes while the average strain level on the beam was only 0.06 με. Second, we present the first field test for these transducers conducted on a high-speed railway viaduct. We have succeeded to obtain six strain modes of the viaduct from the data collected with fibre Bragg gratings on the transducers at an average strain level of 0.067 με. To the best of our knowledge, this is the first time that strain mode identification in operational conditions using strain-amplifying transducers was successful. This demonstration can be a starting point for the implementation of vibration-based damage identification in civil structures allowing the fulfilment of its long-standing promise.
Built-up wall and floor systems such as roof panels, floors with floating screeds, etc., have found widespread application in building construction. Achieving sufficient sound insulation with these systems is challenging because of their relatively low weight and complex vibro-acoustic behavior. A fast and sufficiently accurate acoustic design tool is needed. The semi-analytical transfer matrix method is able to efficiently compute the response of a thick or multilayered structure in the frequency-wavenumber domain but has important limitations. First, the system is assumed to be of infinite extent. At lower frequencies however, neglecting the modal behavior of the wall can lead to large prediction errors. Second, integration over all possible incident plane waves is necessary to obtain the diffuse transmission loss, resulting in a high computation time. The transfer matrix approach is therefore extended in two ways. The modal behavior of rectangular walls and floors with simply supported boundary conditions is approximately accounted for. Using the diffuse reciprocity relationship, a hybrid modal transfer matrix-statistical energy analysis method is then developed such that integration of plane-wave transmission over all angles of incidence is no longer necessary, largely decreasing the computational effort. The model is validated against alternative numerical prediction models and experimental data.
No abstract is provided for this article.
No abstract is provided for this article.
Vibration monitoring of civil engineering structures has gained a lot of interest over the past few years, due to the relative ease of instrumentation and the development of new powerful system identification techniques. The damage assessment step consists of relating the dynamic characteristics to a damage pattern of the structure. The presented technique makes use of the calculation of modal bending moments and curvatures to derive the bending stiffness at each location. The basic assumption is that damage can be directly related to a decrease of stiffness in the structure. Eigenfrequencies are sensitive damage indicators. Modal curvatures seem to be more sensitive to local damage than the modal displacements. The technique is validated on a reinforced concrete beam, which is gradually damaged and is instrumented with accelerometers, displacement transducers and strain gauges.
A construction can be identified by vibration measurements, from which are derived the intrinsic properties of the structure like eigenfrequencies and modeshapes. Heavy structures like bridges, buildings and dams, having very low natural frequencies, are difficult to put into vibration. In this case ambient vibrations, caused by wind, traffic, microtremors, ... are generally used. One of the advantages is that normal operation is not disturbed by the measurement. Substantial damage will affect these properties: so their use for health monitoring is an interesting and intensively explored research topic. However, the measured values do not necessarily return the exact properties of the bridge. Under the influence of environmental factors, like e.g. temperature and humidity variations, the dynamic properties will undergo changes. In this paper the influence of traffic loads on the identified modal parameters will be investigated. For this purpose, finite element simulations are used, in which a vehicle moves over a bridge model. Different vehicle-models are considered. Using the simulated bridge response, the eigenfrequencies and modeshapes of the bridge vehicle system are determined by the stochastic subspace identification method and afterwards compared with those of the original, unloaded structure.
No abstract is provided for this article.
No abstract is provided for this article.
Service loads, environmental and accidental actions may cause damage to constructions. Regular inspection and condition assessment of engineering structures are necessary so that early detection of any defect can be made and structure’s remaining safety and reliability can be determined. When the structural damage is small or it is in the interior of the system, its detection cannot be done visually. A useful more elaborate nondestructive evaluation tool is vibration monitoring. It relies on the fact that occurrence of damage or loss of integrity in a structural system leads to changes in the dynamic properties of the structure. In this paper, different techniques will be presented and compared to derive from experimentally determined modal characteristics of a reinforced concrete beam its dynamic bending stiffness. The degradation of stiffness, due to the cracking of the reinforced concrete, gives information on the position and intensity of the occurred damage.
paper introduces a methodology for shape and size optimization of shell structures with variable thickness. A model is defined that reduces the number of variables without losing freedom. Several optimization methods are compared. The method of the Coupled Local Minimizers (CLM) offers the certainty of the identification of the global minimum. This methodology is implemented by using MATLAB and ANSYS. It is used successfully for two instructive examples.
