The Magnetic Rope Testing is a non-destructive method in use for the detection of flaws and cracks in steel wire ropes. Given the severe protocol of safety certification for in-service cableway ropes, a proper methodology operating in accordance with new European standard specifications is here presented. A relevant experience about detection of multiple cracks due to fretting fatigue on a peculiar locked coil structure rope is also shown and discussed.
Dowels are used in jointed concrete pavements to provide load transfer and improve performance. Misaligned dowels could cause poor joint performance that would lead to pavement distresses. An approach to detect misaligned dowel bars in concrete pavements using GPR is proposed. The paper addresses all forms and combinations of dowel misalignment. Equations were developed to identify each misalignment type, and statistical analyses were performed on major categories for the entire project. A decision on the acceptance or rejection of a dowel bar, a joint, or a pavement section, can be made based on the results of the computations and specified tolerance values.
Footbridges are structures that may experience vibration amplification problems caused by pedestrian and/or wind actions. Design codes deal with these phenomena limiting the natural frequencies and the maximum accelerations expected. Aiming at taking into consideration these dynamic phenomena, current procedures to evaluate the structural performance of light-weight bridges based on experimental dynamic analysis are evaluated in this study. To achieve this, the dynamic response of three pedestrians walking, running and jumping was obtained. Maximum comfort limits of dynamic responses were then determined. The results indicate that codes could overestimate the level of vibration in this kind of footbridge.
Details of the investigations on the application of Electro Mechanical Impedance (EMI) technique using smart piezoelectric (PZT) sensors for damage detection of structures are presented in this paper. The behavior and the ability of this method to detect damages, in a homogenous material are studied for its effective utilization in structural health monitoring. Experimental investigations are conducted on a homogenous aluminium plate bonded with PZT patches to study the effects of external low frequency vibrations (mass loading) and boundary condition on EMI signatures and the observations are discussed using RMSD as damage index computed between pristine and damaged states. Effect of low frequency vibration on the resulting EMI signature and the corresponding RMSD is found to be less than 2%. This is the threshold upper control value (UCL) beyond which the change in RMSD shall truly reflect the damage.
Sparse sensor networks for Lamb wave-based structural health monitoring (SHM) can detect defects in plate-like structures. However, the limited number of sensor positions provides little information to characterize the unknown scatterer. This can be achieved by full wavefield analysis e.g. using Laser Doppler vibrometry measurements.
This paper proposes deconvolution processing that enhances the acoustic wavefield interpretation by increasing the temporal resolution of the underlying ultrasound signals. Applying this preprocessor to the whole wavefield allows improved non-destructive assessment of the defect. This approach is verified experimentally through a case study on an isotropic aluminum plate with four cracks.
The epoxy-bonded steel plate strengthening method has been widely applied in retrofitting reinforced concrete structures. However, using epoxy as the adhesive will bring deterioration due to its aging and delamination. Ultrasonic Nondestructive Evaluation (NDE) is an advantaged approach to detect the delamination or the bonding quality of the layered medium. The elastic property of the adhesive material can also be estimated properly by obtaining the phase velocity of surface wave through NDE test. This research proposes an approach to estimate the elastic property of epoxy layer in a steel–epoxy–concrete bonding layered medium. By solving dispersion equations, the analytical dispersion curves are plotted. Then the influence factors to the modes and shapes of those dispersion curves are discussed. An ultrasonic NDE test on a specimen is conducted, by which the relation between phase velocity and frequency is obtained. Through inversion process, the elastic property of epoxy layer is estimated. Based on the estimated elastic constants, a numerical study of steel–epoxy–concrete layered medium is also conducted using Explicit Finite Element Method, from which the numerical dispersion curves are obtained. Through analytical, experimental, and numerical studies, the dispersion property of surface waves in the layered medium is well understood.
The paper presents a study on the seismic assessment of a 21-story building having an asymmetrical plan. The study applies the approach using in-situ measurements to assess the building's seismic performance. According to preliminary observations on site, the soil may have a significant influence on the building's behaviour. That is why it is important to isolate the behaviour of the building from the soil effect (fixed-base structure). First, in-situ dynamic measurements are conducted to identify dynamic characteristics of the building. The Frequency Domain Decomposition (FDD) method is used to determine the vibration modes of the building in three dimensions (3D). First three vibration modes with close frequencies and unusual mode shapes were identified, which shows the relevance of the used method in the case of buildings having complex behaviour. Second, the relevance of the applied approach was checked by using 3D Finite Element (FE) modelling, in both cases: fixed-base structure and soil + structure system.
The paper presents a study about the monitoring of a pre-stressed reinforced concrete viaduct in Bari (Italy), by means of an optical fiber system embedded into the structural elements. The application case had two objectives: controlling the structural efficiency during the phases of construction, and allowing, in the future, the periodical check of the structural performance under service loads. Sensors were directly anchored to the prestressing strands during the manufacturing phases of the precast beams. By processing and analyzing the data acquired by the system during the different construction phases, it was possible to assess the strain variations related to load increments and stress losses, by comparing them with expected theoretical values. The specific case study shows that the availability of real-time monitoring procedures is nowadays a precious tool for checking the structural safety of critical facilities, in particular bridges.
This work investigates methods for predicting imminent wire failure during fatigue testing.
Sensors that measure changes in vibration, displacement, and infrared signatures were explored, and in-situ video recording was studied for its ability to capture changes in the shape of the wire.
Video recording appears to be the most promising of the methods investigated.
It has promise for both single and multi-strand configurations.
Further investigations could include image/video processing.
Could be used to determine if the number of fatigue cycles to complete fracture is an accurate measure of the fatigue life of multi-stranded wire.
This paper investigates the possibility of simultaneous nondestructive evaluation of material degradation and detection of sub-millimeter sized defects using magnetic methods. We confirmed by FEM simulation that assessment of both degradation and small defects in steel is possible using a single-yoke probe. This was also verified experimentally. The hysteresis loop measurements were sensitive to degradation in the material, and the scanning flux distribution could be effectively used for detecting sub-millimeter sized defects. The degradation and small defects can also be evaluated separately with this single measurement configuration.
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