•Experimental evidence of modal property changes in vehicle-bridge systems.•Changes in shape of mode of vibration reported for the first time.•Theoretical interpretation of results through a ...simplified model.•Improved visualization in time–frequency domain of acceleration signals.
This paper reports an experimental campaign that aims at measuring the evolution of bridge modal properties during the passage of a vehicle. It investigates not only frequency shifts due to various vehicle positions, but also changes in the shape of the modes of vibration. Two different bridges were instrumented and loaded by traversing trucks or trucks momentarily stationed on the bridge. The measurements were analysed by means of an output-only technique and a novel use of the continuous wavelet transform, which is presented here for the first time. The analysis reveals the presence of additional frequencies, significant shifts in frequencies and changes in the modes of vibration. These phenomena are theoretically investigated with the support of a simplified numerical model. This paper offers an interpretation of vehicle-bridge interaction of two particular case studies. The results clearly show that the modal properties of the vehicle and bridge do change with varying vehicle position.
•Quantifies low frequency noise errors & gives guidance on accelerometer selection.•Provides in built quality control check of the calculated displacement signal.•Method is verified using laboratory ...and field testing.
Bridge failure to pass load capacity assessment is unfortunately not an uncommon problem in bridge engineering and it is a potentially expensive problem for the bridge owner. Using load test data to justify increase in assessed load capacity is recognised as a viable approach in professional codes of practice. However, load tests are rarely carried out in practice because traditionally they are expensive to conduct and may not always justify an increase in assessed load capacity. Therefore this paper proposes a simple, quick and reliable approach for bridge load testing. In particular a procedure to calculate the bridge displacement to a moving truck by double integration of bridge acceleration is presented. Integrating acceleration to calculate displacement is not a new approach, with authors reporting difficulties due to errors in acceleration signals and unknown initial conditions. Many of the previous approaches have focused on developing signal processing algorithms to correct for the signal errors and while some good results have been reported, typically the derived displacements are very sensitive to parameters used in the correction algorithm, such as passband filter frequencies. Consequently, without comparison with directly measured displacement data, reliability of the procedure cannot be established and errors quantified. Therefore in this study a stripped down procedure is applied placing emphasis instead on minimising the errors in the recorded acceleration by using appropriate hardware and developing a quality control procedure that allows the user to assess the likely accuracy of the calculated displacement signal. The effectiveness of the proposed approach is trialled in the laboratory and in the field, with an accuracy of ±0.5mm observed.
•Propose a novel blind source separation method for operational modal analysis.•Validated on ambient and non-stationary vibrations from in-operation bridges.•Evaluated by comparing with two classic ...operational modal analysis methods.•The method could capture mode shape changes due to heavy truck passage.•The method could identify low-energy and closely-spaced modes.
Blind source separation receives increasing attention as an alternative tool for operational modal analysis in civil applications. However, the implementations on real-life structures in literature are rare, especially in the case of using limited sensors. In this study, an enhanced version of sparse component analysis is proposed for output-only modal identification with less user involvement compared with the existing work. The method is validated on ambient and non-stationary vibration signals collected from two bridge structures with the working performance evaluated by the classic operational modal analysis methods, stochastic subspace identification and natural excitation technique combined with the eigensystem realisation algorithm (NExT/ERA). Analysis results indicate that the method is capable of providing comparative results about modal parameters as the NExT/ERA for ambient vibration data. The method is also effective in analysing non-stationary signals due to heavy truck loads or human excitations and capturing small changes in mode shapes and modal frequencies of bridges. Additionally, closely-spaced and low-energy modes can be easily identified. The proposed method indicates the potential for automatic modal identification on field test data.
Structural Health Monitoring (SHM) is critical in the observation and analysis of our national infrastructure of bridges. Due to the ease of measuring bridge rotation, bridge SHM using rotation ...measurements is becoming more popular, as even a single DC accelerometer placed at each end of span can accurately capture bridge deformations. Event detection methods for SHM typically entail additional instrumentation, such as strain gauges or continuously recording video cameras, and thus the additional cost limits their utility in resource-constrained environments and for wider deployment. Herein, we present a more cost-effective event detection method which exploits the existing bridge rotation instrumentation (tri-axial MEMS accelerometers) to also act as a trigger for subsequent stages of the SHM system and thus obviates the need for additional vehicle detection equipment. We show how the generalised variance over a short sliding window can be used to robustly discriminate individual vehicle loading events, both in time and magnitude, from raw acceleration data. Numerical simulation results examine the operation of the event detector under varying operating conditions, including vehicle types and sensor locations. The method’s application is demonstrated for two case studies involving in-service bridges experiencing live free-flow traffic. An initial implementation on a Raspberry Pi Zero 2 shows that the proposed functionality can be realised in less than 400 ARM A32 instructions with a latency of 47 microseconds.
Low-cost, DC micro-electromechanical systems (MEMS) accelerometers can be employed to provide a mechanism to capture the relatively small levels of rotation typically seen on some bridges allowing ...their structural response to be measured. The effect of ambient vehicle traffic loads crossing the bridge can offer a cost-effective, less disruptive alternative method for continuous bridge structural health monitoring (BSHM). However, utilising moving traffic loads to assess the quasi-static structural behaviour is more challenging as the measured sensor data contains additional signal components due to the dynamics of the vehicle-bridge interaction system. To overcome this challenge, this paper presents a simplified approach for the specification of an appropriate filtering scheme to extract the desired quasi-static bridge response based on only the bridge's geometry and the vehicle speed. The originality of the method proposed herein lies in its wide applicability and extensibility due to its basis on the widely accepted principles of bridge influence lines. For both BSHM researchers and practitioners alike, the significance of the proposed method lies in its systematic approach, thus helping to unlock the potential for long-term monitoring of bridge quasi-static response under ambient traffic loading. The approach is demonstrated through its successful application in a field trial on an in-service highway bridge.
Various approaches have been proposed for bridge structural health monitoring. One of the earliest approaches proposed was tracking a bridge’s natural frequency over time to look for abnormal shifts ...in frequency that might indicate a change in stiffness. However, bridge frequencies change naturally as the structure’s temperature changes. Data models can be used to overcome this problem by predicting normal changes to a structure’s natural frequency and comparing it to the historical normal behaviour of the bridge and, therefore, identifying abnormal behaviour. Most of the proposed data modelling work has been from long-span bridges where you generally have large datasets to work with. A more limited body of research has been conducted where there is a sparse amount of data, but even this has only been demonstrated on single bridges. Therefore, the novelty of this work is that it expands on previous work using sparse instrumentation across a network of bridges. The data collected from four in-operation bridges were used to validate data models and test the capabilities of the data models across a range of bridge types/sizes. The MID approach was found to be able to detect an average frequency shift of 0.021 Hz across all of the data models. The significance of this demonstration across different bridge types is the practical utility of these data models to be used across entire bridge networks, enabling accurate and informed decision making in bridge maintenance and management.
Structural Health Monitoring (SHM) is a technique that involves gathering information to ensure that a structure is safe and behaving as expected. Within SHM, vibration-based monitoring is generally ...seen as one of the more cost-effective types of monitoring. However, vibration-based monitoring has mostly been undertaken on long-span bridges using data collected with a dense network of sensors. Historically, the logistical difficulty of collecting data on short- and medium-span bridges has meant that the usefulness of vibration-based methods on these bridges is largely unknown. Therefore, this study proposes Minimal Information Data-modelling (MID). MID is an approach that utilises low-cost, easily implementable sensors that are potentially feasible for operators to purchase and operate across a network. This approach will be investigated to determine whether MID is a feasible approach for monitoring short- and medium- span bridges. The results from MID were assessed to determine whether they could detect a suitably small shift in frequency, which is indicative of damage. It was determined that the data models could reliably detect frequency shifts as low as 0.01 Hz. This magnitude of frequency shift is similar to the level of frequency shift reported for a range of bridge damage cases found by others and validated with FE models. The accuracy achieved by the data models indicates that MID could potentially be used as a damage detection method. The cost of the equipment used to collect the data was approximately £370, demonstrating that it is feasible to use MID to monitor bridges across an entire network.
This study proposes the new condition monitoring concept of using features in the measured rotation, or 'pitch' signal, of a crossing vehicle as an indicator of the presence of foundation scour in a ...bridge. The concept is explored through two-dimensional vehicle-bridge interaction modelling, with a reduction in stiffness under a pier used to represent the effects of scour. A train consisting of three 10-degree-of-freedom carriages cross the model on a profiled train track, each train varying slightly in terms of mass and velocity. An analysis of the pitch of the train carriages can clearly identify when scour is present. The concept is further tested in a scaled laboratory experiment consisting of a tractor-trailer crossing a four-span simply supported bridge on piers. The foundation support is represented by four springs under each pier, which can be replaced with springs of a reduced stiffness to mimic the effect of scour. The laboratory model also consistently shows a divergence in vehicle pitch between healthy and scoured bridge states.
•Inertial measurement units (IMUs) from biomechanics research are introduced.•IMUs are compared to a conventional sensor (CS) network during modal tests on: A laboratory floor structure where the ...IMU’s performed as well as the CS.•A road bridge where IMU’s and CS both identified the mode shapes correctly.•An office tower where IMUs performed well but had some limitations with respect to CS.
This paper explores the use of wireless Inertial Measurement Units (IMU) originally developed for bio-mechanical research applications for modal testing of civil engineering infrastructure. Due to their biomechanics origin, these devices combine a triaxial accelerometer with gyroscopes and magnetometers for orientation, as well as on board data logging capability and wireless communication for optional data streaming and to coordinate synchronisation with other IMUs in a network. The motivation for application to civil structures is that their capabilities and simple operating procedures make them suitable for modal testing of many types of civil infrastructure of limited dimension including footbridges and floors while also enabling recovering of dynamic forces generated and applied to structures by moving humans. To explore their capabilities in civil applications, the IMUs are evaluated through modal tests on three different structures with increasing challenge of spatial and environmental complexity. These are, a full-scale floor mock-up in a laboratory, a short span road bridge and a seven story office tower. For each case, the results from the IMUs are compared with those from a conventional wired system to identify the limitations. The main conclusion is that the relatively high noise floor and limited communication range will not be a serious limitation in the great majority of typical civil modal test applications where convenient operation is a significant advantage over conventional wired systems.
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