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GNSS-Based Long-Span Bridge Deformation Monitoring (Dissertation Review Sample)
the task was to write the literature review dissertation chapter on the given topic. the sample is about showing that the writer can also do lengthy jobs well.source..
GNSS-BASED LONG-SPAN BRIDGE DEFORMATION MONITORING
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Bridges are undoubtedly one of the fundamental civil structures for any given society. As important infrastructures in the economy of a given nation, bridges serve as the crucial links in the transportation network, thus influencing how productive an economy is. A bridge failure would therefore affect the performance of an economy as it would mean disruption of the transportation network. This implies that there is need for the responsible authority to invest in monitoring of bridges so that defects are identified early and any rectification needed is done or before the extent of defects is such that the entire structure has to be brought down.
The state of a long-span bridge is ascertained through structural health monitoring. By definition, Structural Health Monitoring or simply SHM, may be perceived as referring to the integration of sensory technologies system, system for data processing and data archiving, data acquisition system, damage protection and modelling system, and a communication system for the acquisition of knowledge of in-service bridges or structures generally on a continuous basis (Xu & Xia, 2012). When implementing SHM of a long span bridge, the objectives normally entail to make an assessment of a structureâ€™s performance under different service loads, to monitor loading conditions of the structure, to update or verify the rules used during design, to form guidelines for its maintenance and inspection and to detect the structureâ€™s deterioration or damage (Afonso Costa & Figueiras, 2012).
In the recent past, there has been rapid technological advancement. The structural health monitoring field has seen development of new technologies that provide better solutions for various problems of concern to bridge engineers. Current structural health monitoring technologies are based on a sophisticated system for data processing, combined with a comprehensive sensory system, which is implemented with various advanced structural analysis algorithms and advanced information technology. A critical component of the technologies applied for the monitoring of long span bridges are the surveying technologies of satellite based positioning. These technologies have proven critical with regard to dynamic monitoring of long span bridges. In the following discussion, the application of GNSS (global navigation satellite systems) for the monitoring of a long span bridgeâ€™s deformation is addressed. The discussion focuses on reviewing literature on long span suspension bridges, structural health monitoring (SHM), particularly bridge deformation monitoring, individual global satellite based positioning systems, other deformation monitoring methods, current bridge management system (BMS) research and bridge dynamics and evaluation.
Long span Bridges
Advancement in bridge engineering has a long history that spans over centuries. According to structural configuration, a bridge may categorized as being beam bridge, arch bridge, cantilever bridge, cable-supported bridge or truss bridge. With regard to long span bridges, the competitive options are mainly bridges that are cable supported, which may be either cable-stayed bridges or suspension bridges. Currently, the cable stayed bridge with the longest span is Russky Bridge of Russia, which has a span of 1104m, while the suspension bridge with the longest span is the Akashi-Kaikyo Bridge, which is located in Japan and has a span of 1991m (Laboratory of Bridge Engineering (LBE), 2014). Increase in the size of large-scale bridges has been aided largely by rapid development in computation techniques and hardware, which has resulted in a more detailed, realistic and accurate analysis (Afonso & Figueiras, 2012). Particular techniques in this regard are finite element which allows modeling and dealing with nonlinearity, computational fluid dynamics (CFD), which helps in ensuring the flutter stability of long span bridges and wind tunnel testing (Yu et al., 2014).
The nature of a long span bridge is such that it is usually located in an environment that has unique and in some cases, extreme conditions. The design loads considered for these bridges mainly include traffic loads, seismic loads, wind loads, dead loads and temperature loads. Other loads that might be considered include impact loads, erection loads and support movement. The structural systems for a long span suspension bridge consists of stiffening trusses or girders, anchorages, main cables and hangers (also referred to as suspenders) and towers. The configuration of a typical long span suspension bridge is as shown in figure 1
Figure SEQ Figure \* ARABIC 1: Components of a typical suspension bridge (Source: Xu & Xia, 2012)
Long Span Bridgesâ€™ Structural Health Monitoring
There are several considerations that necessitate the constant monitoring of a long span bridge. First, apart from dead loads, other loads that were considered during design are measured from scaled laboratory models and design standards and the implication here is that they do not fully represent the actual loads on the bridge. Furthermore, it is impossible for ideal conditions on which laboratory models and tests are based to offer a loading environment that is realistic and to which a long span bridge is subjected. Second, while laboratory experiments and numerical analysis techniques have advanced, their accuracy with regard to the prediction of the structural response is limited due to the assumptions on which mathematical models are based do not match real life conditions. Third, during the structural design of a long span bridge, some parameters and assumptions are adopted which must be verified through on-site monitoring. Fourth, long span bridges are exposed to man-made and natural hazards such as strong earthquakes, fire, typhoons, collisions and flooding. Through online SHM, it becomes possible to continuously monitor the structural response of a long span bridge and any abnormality identified early (Xu & Xia, 2012).
Long span bridges are inherently vulnerable to and constantly subjected to environments that are aggressive. Deterioration begins even before construction is fully completed and the bridge commissioned for access to the public. This implies the considerations for maintenance and inspection have to be factored in the design and construction process and their implementation must begin immediately the bridge is completed (Flamand et al., 2014). The scope, frequency and depth, however, is dependent on the traffic, age, known deficiencies, and so on and is determined by the bridge owner. Once inspection is done (a regular interval for inspection should not exceed two years), reports should be filed in order to maintain a history file for the bridge. The number of elements required for inspections are dependent on the bridge. In general, each element is normally characterized by discrete condition states, which describe the type and also offer prediction of the probability of transitions among various conditions (Xu & Xia, 2012).
Bridge Deformation Monitoring
At this juncture, it is important to distinguish two terms that are easily confused: deformation and displacement. By definition, displacement refers to the movement of individual points on a structural system as a result of various externally applied loads (Xu & Xia, 2012). Once the displacements induced by applied loads result in the alteration of the shape and/or size of the body, relative movement of individual points relative to one another is experienced. The change in dimension as a result of the relative displacements experienced is by definition referred to as deformation (Cury et al., 2012). A long span suspension bridge is normally characterized by several kinds of deformations that may ultimately affect its performance. These include movement in the long-term due to stress relaxation and bridge deck creep and dynamic motion of the bridge in the short term such as motion that is induced by wind, temperature, traffic and tidal current. In order to ascertain the occurrence of these deformations, there are a number of technologies required. These include sensory system (SS), structural evaluation system (SES), DATS (data acquisition and transmission system), portable inspection and maintenance system (PIMS), DPCS (data processing and control system), portable data acquisition system (PDAS) and data processing and data management system (DMS).
Sensors and Sensing Technology for Bridge Displacement Measurement
The extent to which a bridge experiences displacements may serve to indicate its performance structural wise. Occurrence of large displacements or deformations may lead to the creation of hazardous conditions for traffic using the bridge, while excessive deformations will ultimately have a profound effect on the structural integrity of the bridge. This implies that displacement monitoring is a must for any long span bridge. Equipment used for the measurement of displacement includes level sensing station, variable differential transformer, and GNSS(Global Navigation Satellite System) such as GPS.
By definition, positioning that is satellite based may be perceived as referring to the activity of determining positions of sites of observation at sea or on land, in space and in the air through the use of artificial satellites. Global navigation satellite system (GNSS) in the context is a generic term referring to individual satellite positioning systems such as GPS, GLONASS and Galileo among others and the combination of the positioning systems. In the f...
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