State of the Art Review on Bridges Structural Health Monitoring (Model Testing)

Khaled Heiza, Ayman Khalil, Omar El Nawawy
2016 The International Conference on Civil and Architecture Engineering  
Most structural health monitoring methods focus on using dynamic responses to detect and locate damage (i.e. items I and II above) because they are global methods that can provide rapid inspection of large structural systems. These dynamic-based methods can be divided into four groups: (1) spatial-domain methods, (2) modal-domain methods, (3) time-domain methods, and (4) frequency-domain methods. Spatial-domain methods use changes of mass, damping, and stiffness matrices to detect and locate
more » ... age. Modal-domain methods use changes of natural frequencies, modal damping ratios, and mode shapes to detect damage. Introduction In the frequency domain method, modal quantities such as natural frequencies, damping ratio, and model shapes are identified. The reverse dynamic system of spectral analysis and the generalized frequency response function estimated from the nonlinear auto-regressive moving average (NARMA) model were applied in nonlinear system identification. In time domain method, system parameters were determined from the observational data sampled in time. It is necessary to identify the time variation of system dynamic characteristics from time domain approach if the properties of structural system change with time under the external loading condition. Moreover, one can use model-independent methods or model-referenced methods to perform damage detection using dynamic responses presented in any of the four domains. Literature shows that model independent methods can detect the existence of damage without much computational efforts, but they are not accurate in locating damage. On the other hand, model-referenced methods are generally more accurate in locating damage and require fewer sensors than model-independent techniques, but they require appropriate structural models and significant computational efforts. Although time-domain methods use original timedomain data measured using conventional vibration measurement equipment, they require certain structural information and massive computation and are case sensitive. Furthermore, frequencyand modal-domain methods use transformed data, which contain errors and noise due to transformation. Moreover, the modeling and updating of mass and stiffness matrices in spatialdomain methods are problematic and difficult to be accurate. There are strong development trends that two or three methods are combined together to detect and assess structural damages. For example, several researchers combined data of static and modal tests to assess damages. The combination could remove the weakness of each method and check each other. It suits the complexity of damage detection. Research on modal testing as a health-monitoring tool for civil engineering structures has been ongoing for two decades. The modal testing includes ambient vibration testing and forced WS(1) 2/4 2 vibration testing. In ambient vibration testing, the input excitation is not under control. The vibration may be induced be wind, waves, vehicle or pedestrian traffic or any other service loading. The increasing popularity of this method is probably due to the convenience of measuring the vibration response while the bridge is under in-service and also due to the increasing availability of robust data acquisition and storage systems. Since the input is unknown, certain assumptions have to be made. Forced vibration testing involves application of input excitation of known force level at known frequencies. The excitation manners include electro-hydraulic vibrators, force hammers, vehicle impact, etc. The static testing in the laboratory may be conducted by actuators, and by standard vehicles in the field-testing. A brief description of the laboratory and field-testing research on the damage assessment is given below. Among the earliest uses, Douglas and Reid [i] conducted modal tests on a five-span reinforced concrete bridge to: (1) determine the transverse modal characteristics of the bridge to help understand the bridge response to earthquakes and (2) experimentally evaluate the soil-structure interaction behavior. The authors indicated that modal characteristics are potential tools for system identification of bridge structures. At the University of Missouri, Salane and Baldwin [ ii ] monitored the modal characteristics of a bridge model as well as a three-span bridge during fatigue tests. A common trend was that frequencies of vibration decreased and the mode shapes changed Research on modal testing, as a global inspection method for civil engineering structures has been ongoing for two decades. A common trend was that frequencies of vibration decreased and the mode shapes changed as the test progressed indicating deterioration. However, reductions in the modal frequencies were small compared to changes in the mode shapes. Thus, the authors commented that changes in specific mode shapes were the best indicators for damage locating. The overall results indicated that vibration signature monitoring could have application to prevent catastrophic failures of bridge structures. Bakht and Jaeger [iii] summarized the valuable lessons learned from static and dynamic testing of more than 225 bridges in Ontario, Canada. They found that: (1) slab-on-girder bridges are stiffer than the corresponding calculated values; and (2) the floor systems of steel truss bridges may contribute substantially of the combined stiffness of the structure. In most cases, the actual loadcarrying capacities are higher than those from calculations. Kennedy and Grace [iv Mazurek and DeWolf [ ] investigated the dynamic and fatigue response of continuous composite bridges with pre-stressed concrete slabs. Four 'l4-scale models of continuous composite bridges were tested. It was shown that pre-stressing the concrete deck slab in the vicinity of the pier supports eliminated transverse cracking of the slab, enhanced the natural frequencies, and increased the fatigue life as well as the ultimate load-carrying capacity. v] conducted ambient vibration tests of a two-span aluminum plate-girder bridge in the laboratory. They used low-mass vehicular excitation and found that the ambient vibration method provided approximately the same resonant frequencies and mode shapes as those used modal analysis. Hearn and Testa [ vi] applied a perturbation method to structural inspection through vibration monitoring. They found that changes in modal frequency and damping can be good damage indicators; and demonstrated the effectiveness of this method by testing a welded four-member steel frame with progressive cracks. They found that modal parameters (except mode shapes) could be used effectively to detect damage in these test structures. Hogue, Aktan, and Hoyos [vii Pandey and Biswas [ ] carried out an impact excitation test on local region of a 262-meter long, pre-stressed, pre-tensioned concrete girders bridge. Modal parameters except for damping ratios were identified, then the mass matrix was estimated, and then the flexibility matrix was derived. A static test was conducted to validate the dynamic test-based identification. viii] used a simple supported W12x16 beam for experimental verification. The beam had a splice at the mid-span. Damage was simulated by opening bolts from the splice plates. Thirty-three measurement points were marked up on the top of the beam. They
doi:10.21608/iccae.2016.43759 fatcat:bjnt5y35yfe37hiw23ltqxuysq