Traffic Excitation Research Articles

Extrapolating specification-level dynamic load factors for bridge performance analysis using deflection measurements during ambient traffic excitations

Field-measured dynamic load factors (DLFs) are underutilized for bridge health assessment. Bridge practitioners often face confusion when comparing field-measured DLFs to specification design values owing to significant DLF variations across different traffic load levels. However, mathematical relations or methods correlating bridge DLFs and load levels are lacking. To address this challenge, this study proposes practical methods for determining specification-level DLFs using field-deflection measurements during ambient traffic excitations. Deflections from a continuous rigid-frame bridge over six months were measured, and DLFs were computed using hourly maximal total deflections and their corresponding static deflections. Two approaches were developed and validated to extrapolate the specification-level DLF using field-measured DLFs of low load levels. Extrapolated DLFs from both methods illustrated a noticeable downward trend in DLFs relative to load levels. Both methods yielded consistent results, falling within the range of 0.03–0.09, equivalent to the design DLF value of 0.05 for the bridge under study. No significant temporal-dependent changes in extrapolated DLFs were evident, indicating that bridge performance and pavement roughness met design expectations and did not deteriorate significantly. This study provides an alternative data-driven approach that utilizes field-measured DLFs to assess the health condition of bridges.

Closed-form dynamic stiffness formulation for modal and dynamic response analysis of pile group foundations

A closed-form dynamic stiffness (DS) formulation is proposed for pile group foundations. This model consists of a rigid cap and an arbitrary number of flexible piles. The rigid cap, connecting to all piles, is modeled as a rigid body resting on an elastic foundation. For each pile, a longitudinal soil–pile model and a preloaded Timoshenko beam on viscoelastic Pasternak foundation are adopted to describe the longitudinal and transverse vibration, respectively. The piles can be either friction piles or end-bearing piles, and pile sections surrounded by different soil layers can be easily modeled by the assembly of pile elements with different parameters. The proposed DS formulations essentially use very few degrees of freedom to, nevertheless, describe the broadband dynamic behaviors of complex pile group foundations in a highly accurate manner. The DS formulation is then used for modal and dynamic response analysis. For modal analysis, the Wittrick–Williams algorithm is applied, with the key issue J0 count problems resolved. The proposed method is verified against some existing results. This research provides an exact and highly efficient modal and response analysis tool for pile group foundations, which can be used for the dynamic analysis of pile foundations subjected to earthquake or traffic excitations.

Finite element model of a cable-stayed bridge updated with vibration measurements and its application to investigate the variation of modal frequencies in monitoring

Ambient vibration measurements of a cable-stayed bridge in Taiwan were first conducted to identify its dominant modal parameters with a reliable stochastic subspace identification algorithm recently developed. A finite element model is then constructed based on the identified frequencies and shape vectors of four vertically bending, one torsional, and one horizontally bending modes. This model is also updated by adjusting the girder-pier connection with the addition of a rotational spring to reflect the actual conditions and its accuracy is demonstrated with less than 1% of error for the first two vertically bending modes. As a solid application for probing the environmental effects in structural health monitoring, the vibration measurements of 24 hours were further conducted and combined with the well calibrated model to investigate the controlling factor for its variation in modal frequencies. It is found that the frequencies of the first two vertically bending modes are closely correlated to the root-mean-square velocity representing the traffic excitation intensity. Moreover, it is shown with the updated model that the daily variations in the frequencies of the first two vertically bending modes can be reasonably simulated by modifying the coefficient of the rotational spring merely in a limited range.

Study on the Damage Diagnosis of Ancient Wood Structure in Tianshui under Traffic Excitation

Three‐dimensional finite element model of the wood structure‐foundation of the North House’s main hall in Tianshui under ground traffic excitation was established, and the damage of the first‐floor longitudinal beam of the wood structure was simulated by the finite element method. The node acceleration response signals on beams were decomposed with a wavelet packet. The wavelet packet energy curvature difference index was proposed to determine the structural damage location. The results show that the wavelet packet energy curvature difference can decide the damage location of the middle part of the first‐floor longitudinal beam, and the index value increases with the increase of damage degree. If SNR is 40 db or larger, the damage index can accurately identify the damage of ancient wooden structures. When SNR increases, the damage index will have an increasingly higher sensitivity and certain ability to resist the effect of noise. The function relation between the damage index and the damage degree is obtained to determine the structural damage degree. The study results provide a theoretical basis for the damage diagnosis of the wood structure of ancient buildings along the traffic line.

Stochastic Dynamic Response and Long-Term Settlement Performance of Superstructure-Underground Tunnel System Subjected to Subway Traffic Excitation

Stochastic Dynamic Response and Long-Term Settlement Performance of Superstructure-Underground Tunnel System Subjected to Subway Traffic Excitation

EVALUATION OF VIBRATION-BASED GLOBAL STRUCTURAL HEALTH MONITORING METHOD FOR MEDIUM-RISE BUILDINGS

The automated monitoring of a building’s structural health during its exploitation is a way to extend its design life without compromising structural safety. In turn, it helps increase the rate of building renovation works compared to demolition works, which reduces future construction and demolition waste levels.This research explores the vibration-based global monitoring method application to structurally stiff medium-rise reinforced concrete buildings by analysing predicted building vibration amplitudes and spectrum under regular city traffic excitation. These predictions are based on the results obtained from finite element calculations of building models with variated structural stiffness and inertial mass of the building.Regular traffic-generated ground frequency spectrum differs from the first natural frequencies of medium-rise reinforced concrete buildings, and the vibration energy is low. Nevertheless, it is found that the structural identification of such building dynamic parameters is still possible, particularly natural frequencies. It was found that the ratio between fundamental frequency for the fixed base model of the building and elastic spring foundation model is the decisive parameter for selecting the building part to be monitored. Structural health monitoring vibration-based methods are also a promising technology for medium-rise mass house buildings when tailored according to some damage sensitive feature.

Impact of rigid central clamps on longitudinal deformation of long-span suspension bridges under vehicle excitations

The presence of rigid central clamps (RCCs) minimises the damage potential of short suspenders and expansion joints in in-service long-span suspension bridges. The study presented in this paper evaluated the impact of the presence of RCCs on the longitudinal deformation of a long-span suspension bridge under live load with vehicle braking and random traffic flow excitations. Two finite element (FE) models of the bridge were developed – one with RCCs and the other with a traditional suspender (TS) at mid-span. The impact of RCCs and TS on the structural system response was evaluated by comparing the dynamic characteristics of the models. The exceeding probabilities of longitudinal deformation under different traffic flow levels during the design reference period were obtained. The simulation results show that the RCCs are capable of reducing the longitudinal deformation by 35% to 45%. The unfavourable exceeding probabilities of longitudinal deformation over the design threshold decreased from 1.0 to 0.0002, showing that the RCCs could be an effective measure to enhance the service life of the shortest suspender and expansion joints of long-span suspension bridges.

Exploiting the inter-correlation of structural vibration signals for data loss recovery: A distributed compressive sensing based approach

Compressive Sensing (CS) is a novel signal sampling technique that can enhance the resiliency of the data transmission process in Structural Health Monitoring (SHM) systems by projecting the raw signal into another domain and transmitting the projected signal instead of the original one. The original signal can later be recovered in the fusion center using the received projected vector and the corresponding projection matrix. In this study, data loss recovery of multiple signals with variable loss ratio is investigated. Unlike previously proposed CS-based single-signal approaches, the inter-correlation across vibration signals is exploited in this study. The inter-correlation type for vibration signals is characterized as having common sparse supports (the same location of non-zero elements in the sparse domain) and is dealt with in the context of Distributed Compressive Sensing (DCS). In this approach, vibration signals are encoded separately without extra inter-sensor communication overhead and are decoded jointly. Adopting the DCS-based approach enabled handling non-uniform data loss pattern across channels by allowing the use of a different projection matrix for each channel. Furthermore, a new projection matrix, named Permuted Random Demodulator (PRD), is proposed that not only reduces the coherence of the sensing matrix and enhances the reconstruction accuracy, but also makes the proposed approach robust to continuous data loss. The performance of the proposed method is evaluated using acceleration responses of a real-life bridge structure under traffic excitation. Modal parameters of the bridge are also identified using the recovered signals with reasonable accuracy.

Fusion of structural damage identification results from different test scenarios and evaluation indices in structural health monitoring

There are many existing algorithms and damage indices that can effectively meet the engineering need in damage diagnosis. However, all of them (except those with an exact formulation) are based on certain assumptions with approximations, and their performances depend on the combination of test parameters, for example, type, number, and location of excitations and sensors; identification algorithm adopted; and environmental noise effect. Results obtained from different combinations of these test parameters are different and they may be mathematically biased or contradicting. Existing practice adopts the general indication of result for further maintenance decisions or by subjective screening the results with engineering sense. This article demonstrates the possibility to have a better design of the structural health monitoring system where the benefits of different damage indices and evaluation methodologies can be reaped via the fusion of the identified results. The scenario for discussion is the vibration-based damage localization problem. The change in mode shape in the modal domain and change in the covariance of impulse response function change in the time domain are selected as damage indices for the illustration. An exact form of the covariance of impulse response function is also proposed for this purpose. The demonstration is conducted via a simulated truss structure, an experimental beam, and 280 days valid recorded data from an in-service suspension bridge deck. Different measurements are analyzed to produce large number of identified results for reducing traffic excitation effect, the temperature effect, and so on, and to enhance the structural damage information in the final set of results. Experiences in handling the structural health monitoring data for monitoring the movement of a structural joint before and after a typhoon are also presented. The proposed strategy does not need a mathematical model of the structure, but this leads to heavy sensor requirement for a fine spatial resolution of the local damage.

Determining the number of measurements for compressive sensing of traffic-induced vibration data

Compressive Sensing (CS) is an emerging signal sampling technique, which can be useful in the long-term monitoring of civil infrastructures by reducing the storage space and transmission bandwidth drastically. In this paper, a fully deterministic approach is adopted to enhance the previously proposed CS-based methods. First, the sparsifying dictionary is trained using a vibration data set. Then, a deterministic projection matrix is computed based on the trained dictionary. Second, a new index is defined to determine the number of measurements in advance, without any trial and error in the reconstruction stage. This index which is coined as NPI (Normalized Power Index) is derived using the singular value decomposition of the trained dictionary. The capability of the proposed method is investigated using vibration signals of the Tianjin Yonghe Bridge with traffic excitation. Both accuracy and computational time of the deterministic CS was compared to different data compression algorithms.

Influence of Traffic Vehicles Against Ground Fundamental Frequency Prediction using Ambient Vibration Technique

Ambient vibration (AV) technique is widely used nowadays for ground fundamental frequency prediction. This technique is easy, quick, non-destructive, less operator required and reliable result. The input motions of ambient vibration are originally collected from surrounding natural and artificial excitations. But, careful data acquisition controlled must be implemented to reduce the intrusion of short period noise that could imply the quality of frequency prediction of an investigated site. In this study, investigation on the primary noise intrusion under peak (morning, afternoon and evening) and off peak (early morning) traffic flows (only 8 meter from sensor to road shoulder) against the stability and quality of ground fundamental frequency prediction were carried out. None of specific standard is available for AV data acquisition and processing. Thus, some field and processing parameters recommended by previous studies and guideline were considered. Two units of 1 Hz tri-axial seismometer sensor were closely positioned in front of the main entrance Universiti Tun Hussein Onn Malaysia. 15 minutes of recording length were taken during peak and off peak periods of traffic flows. All passing vehicles were counted and grouped into four classes. Three components of ambient vibration time series recorded in the North-South: NS, East-West: EW and vertical: UD directions were automatically computed into Horizontal to Vertical Spectral Ratio (HVSR), by using open source software of GEOPSY for fundamental ground frequency, Fo determination. Single sharp peak pattern of HVSR curves have been obtained at peak frequencies between 1.33 to 1.38 Hz which classified under soft to dense soil classification. Even identical HVSR curves pattern with close frequencies prediction were obtained under both periods of AV measurement, however the total numbers of stable and quality windows selected for HVSR computation were significantly different but both have satisfied the requirement given by SESAME (2004) guideline. Besides, the second peak frequencies from the early morning HVSR curve was clearly indicated between 8.23 to 8.55 Hz at very low amplitude (Ao < 2), but it should be neglected according to the similar guideline criteria. In conclusion, the ground fundamental frequency using HVSR method was successfully determined by 1 Hz seismometer instrument with recommended to specific parameters consideration on field as well as data processing, without disruption from the nearest traffic excitations.

Mode identifiability of a cable-stayed bridge under different excitation conditions assessed with an improved algorithm based on stochastic subspace identification

Deficient modes that cannot be always identified from different sets of measurement data may exist in the application of operational modal analysis such as the stochastic subspace identification techniques in large-scale civil structures. Based on a recent work using the long-term ambient vibration measurements from an instrumented cable-stayed bridge under different wind excitation conditions, a benchmark problem is launched by taking the same bridge as a test bed to further intensify the exploration of mode identifiability. For systematically assessing this benchmark problem, a recently developed SSI algorithm based on an alternative stabilization diagram and a hierarchical sifting process is extended and applied in this research to investigate several sets of known and blind monitoring data. The evaluation of delicately selected cases clearly distinguishes the effect of traffic excitation on the identifiability of the targeted deficient mode from the effect of wind excitation. An additional upper limit for the vertical acceleration amplitude at deck, mainly induced by the passing traffic, is subsequently suggested to supplement the previously determined lower limit for the wind speed. Careful inspection on the shape vector of the deficient mode under different excitation conditions leads to the postulation that this mode is actually induced by the motion of the central tower. The analysis incorporating the tower measurements solidly verifies this postulation by yielding the prevailing components at the tower locations in the extended mode shape vector. Moreover, it is also confirmed that this mode can be stably identified under all the circumstances with the addition of tower measurements. An important lesson learned from this discovery is that the problem of mode identifiability usually comes from the lack of proper measurements at the right locations.

Rank-revealing QR decomposition applied to damage localization in truss structures

The purpose of this work is the development of an efficient and high-sensitive damage localization technique for truss structures, based on the rank-revealing QR decomposition (RRQR) of the difference-of-flexibility matrix. The method is an enhancement of the existing techniques of damage detection, which rely on the set of so-called damage locating vector (DLV). The advantages of the RRQR decomposition-based DLV (RRQR-DLV) method are its less computational effort and high sensitivity to damage. Compared with the frequently used stochastic DLV (SDLV) method, RRQR-DLV offers higher sensitivity to damage, which has been validated based on the presented numerical simulation. The effectiveness of the proposed RRQR-DLV method is also illustrated with the experimental validation based on a laboratory-scale Bailey truss bridge model. The proposed method works under ambient excitation such as traffic excitation and wind excitation; therefore, it is promising for real-time damage monitoring of truss structures. Copyright © 2016 John Wiley & Sons, Ltd.

Output-only damage detection using vehicle-induced displacement response and mode shape curvature index

Most of the existing bridge superstructure damage detection methods are based on acceleration or strain response due to ambient excitation. This paper proposes a bridge damage detection procedure that utilizes vehicle-induced displacement response without requiring prior knowledge about the traffic excitation and road surface roughness. This study is partially motivated by the recent advances in convenient measurement of structural displacements enabled by video-based sensors. Vehicle–bridge interaction analysis shows that when subjected to moving vehicles, the bridge displacement response is dominated by the first-order mode component. This justifies the proposed damage detection method that only requires the first-order mode shape curvature. While conventionally the mode shapes are extracted based on operational modal analysis, the first-order mode shape is extracted by directly analyzing the power spectral density functions of measured bridge displacement responses under vehicle excitations. Numerical simulations are carried out to investigate the feasibility and performance of the proposed damage detection method using three damage scenarios including damage at single, double, and multiple locations, each involving several extents of damage defined by the reduction in element stiffness. The results reveal that all the damage cases can be successfully identified. Furthermore, the damage detection performance is evaluated for cases involving different classes of road surface roughness and less measurement points. The study demonstrates the potential of the proposed model-free and time-efficient method for damage detection of bridge structures. Copyright © 2016 John Wiley & Sons, Ltd.

Impact of vibrations on people residing in buildings from different types of traffic loads according to the VDV scale

Development of communication lines as well as reducing the distance of its location from buildings contributes to the deterioration of human comfort residing in buildings. For that reason it is necessary to determine the size of this nuisance. This paper presents a comparative analysis in order to determine influence of vibrations originating from selected means of transport for people in buildings using ISO 2631-1, British BS 6472-1 and Polish pr PN/B-02171 standards. The analysis focuses mainly on the parameter called dose of vibrations - VDV. In the comparative analysis - as the load acting on the human - vibration acceleration of ceilings caused by crossing subway, truck, tram and train were used. Presented in the paper analysis show, that each types of considered traffic excitations gives similar results for all concerned standards. In case of BS648 standard values of VDV are smaller in vertical direction than for other standards. However, for extortions, in which in the amplitude-frequency characteristics dominate lower natural frequencies, difference between obtained results decreases.

Dynamic performance of existing high-speed railway bridges under resonant conditions following a retrofit with fluid viscous dampers supported on clamped auxiliary beams

This contribution investigates the application of Passive Control techniques to reduce the severe transverse vibrations that railway bridges of moderate lengths may experience under resonant conditions. The proposed solution consists in connecting the slab to a series of auxiliary beams clamped between the bridge abutments through a set of fluid viscous dampers. A particular configuration minimising the space occupied by the devices and the auxiliary beams under the bridge deck is proposed for two typical typologies in the aforementioned lengths: slabs and girder bridges. First, the dynamic response of a double-beam analytical model is obtained in closed-form under harmonic excitation in order to detect the main governing parameters, capturing the essence of the response at resonance of the main beam fundamental mode. Then conditions are obtained for the optimal damper constants that minimise the main beam amplification. Finally the effectiveness of the solution and the adequacy of the expressions derived from the harmonic case are proven under railway traffic excitation taking into account the three-dimensional deformation of the deck. Throughout the study special attention is given to the beneficial effect arising from clamping the auxiliary beam supports when compared to the simply-supported case, analysed by the authors in previous works. Partial rotational restrictions are admitted to take into consideration the expectable deviation from ideally clamped conditions. Two case studies are presented showing that the auxiliary beams size, if partially clamped, could be significantly reduced for the same main beam vibration mitigation level. If the beams are to be installed under a railway bridge deck in a practical application, this is a crucial issue in order to minimise the free space occupied with the retrofit.

Muscle and skin sympathetic nerve traffic during physician and nurse blood pressure measurement

Previous studies have shown that blood pressure assessment by a nurse markedly attenuates the pressor and tachicardic responses triggered by the physician blood pressure measurement. Whether and to what extent this attenuation reflects a different pattern of the neuroadrenergic responses to doctor or nurse blood pressure evaluation is unknown. In 19 lean untreated mild essential hypertensive patients (age 39.1 ± 2.4 years, mean ± SEM), we measured beat-to-beat mean arterial pressure (Finapres), heart rate (ECG), and efferent postganglionic muscle and skin sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA), respectively, by microneurography], before, during, and following a 10-min sphygmomanometric BP measurement by a doctor or by a nurse unfamiliar to the patients. Measurements were repeated at a 30-min interval to obtain, in separate periods, muscle and skin sympathetic nerve traffic recordings. Both the sequences (doctor vs. nurse and muscle vs. skin sympathetic nerve traffic) were randomized. A doctor visit induced sudden, marked, and prolonged blood pressure and heart rate increases, accompanied by a muscle sympathetic nerve traffic inhibition (average response: -18.1 ± 4.3%, P < 0.01) coupled with a skin sympathetic nerve traffic excitation (average response: +46.1 ± 5.5%, P < 0.01). In contrast, a nurse visit elicited blood pressure and heart rate responses markedly and significantly reduced (-72.1 ± 11 and -81.7 ± 13% respectively, P < 0.01) as compared with those seen during the doctor's visit. This was the case also for muscle and skin sympathetic neural responses (-44.3 ± 9 and -65.6 ± 13%, P < 0.01). These data provide the first evidence that the blunted pressor and tachicardic responses to nurse's blood pressure measurements are accompanied by an attenuation of the adrenergic neural responses seen during the alerting reaction accompanying doctor's blood pressure measurement.

A new joint application of non-invasive remote sensing techniques for structural health monitoring

This paper aims at analysing the potentialities of a new technological approach for the dynamic monitoring of civil infrastructures. The proposed approach is based on the joint use of a high-frequency thermal camera and a microwave radar interferometer to measure the oscillations due to traffic excitations of the Sihlhochstrasse Bridge, Switzerland, which was selected as test bed site in the ISTIMES project (EU—Seventh Framework Programme). The good quality of the results encourages the use of the proposed approach for the static and dynamic investigation of structures and infrastructures. Moreover, the remote sensing character of the two applied techniques makes them particularly suitable to study structures located in areas affected by natural hazard phenomena, and also to monitor cultural heritage buildings for which some conventional techniques are considered invasive. Obviously, their reliability needs further experiments and comparisons with standard contact sensors.

Dynamic Assessment of the Iron Bridge at Paderno d’Adda (1889)

The paper presents the experimental modal analysis recently carried out on the historic iron bridge at Paderno d’Adda (1889). The dynamic tests were performed in operational conditions (i.e. under traffic and wind-induced excitation) between June and October 2009 and different output-only identification techniques were used to extract the modal parameters from ambient vibration data. The described tests represent the first experimental investigation carried out on the global characteristics of the bridge, since the load reception tests of 1889 and 1892.

In-Service Diagnostics of a Highway Bridge from a Progressive Damage Case Study

Development of diagnostic and prognostic routines for application to in-service measurements from highway bridges necessitates analysis of experimental measurements from in-service highway bridges under natural or prescribed induced damage. This is generally limited to the unique opportunity of investigating end-of-service life bridges prior to reconstruction and consequently only a limited library of such case studies exist. This paper documents a field test of an end-of-service bridge span with prescribed progressive damage to a bearing as well as several diaphragm connections. Thirty dual-axis accelerometers were distributed across the bridge span with data acquisition and transmission facilitated by a real-time lossless wireless sensor network. A highway department service truck applied traffic excitation to the structure through routine passes on a consistent lane of traffic. Output-only system identification was applied to the baseline time history response to develop a state-space model of the brid...