18 research outputs found
Simultaneous Identification of Bridge Structural Damage and Moving Loads Using the Explicit Form of Newmark-β Method: Numerical and Experimental Studies
Get PDFBridge infrastructures are always subjected to degradation because of aging, their envi-ronment, and excess loading. Now it has become a worldwide concern that a large proportion of bridge infrastructures require significant maintenance. This compels the engineering community to develop a robust method for condition assessment of the bridge structures. Here, the simultaneous identification of moving loads and structural damage based on the explicit form of the Newmark-β method is proposed. Although there is an extensive attempt to identify moving loads with known structural parameters, or vice versa, their simultaneous identification considering the road roughness has not been studied enough. Furthermore, most of the existing time domain methods are developed for structures under non-moving loads and are commonly formulated by state-space method, thus suffering from the errors of discretization and sampling ratio. This research is believed to be among the few studies on condition assessment of bridge structures under moving vehicles considering factors such as sensor placement, sampling frequency, damage type, measurement noise, vehicle speed, and road surface roughness with numerical and experimental verifications. Results indicate that the method is able to detect damage with at least three sensors, and is not sensitive to sensors lo-cation, vehicle speed and road roughness level. Current limitations of the study as well as prospective research developments are discussed in the conclusion
EVALUATING THE GAP SIZE IN BRIDGE STRUCTURES BY CONSIDERING THE EFFECTS OF POUNDING AND SOIL-STRUCTURE INTERACTIONS
No full textIn order to reduce the cost and time of seismic analyses, due to lack of correct understanding of structural characteristics and the forces acting on, usually simplified assumptions are applied in the structural modeling that could lead to unrealistic responses. One of these simplified assumptions in bridge modeling is ignoring the pounding phenomenon and soil-structure interaction. Nowadays, the bridges are considered as a vital component in urban and inter-urban transportation systems that the disruption in their operation due to partial or full collapses could lead to disruptions in the transportation system and heavy costs and consequences. One of the major factors, which is considered by the researchers after some earthquakes such as Northridge, Kobe and Chi Chi and their destructive effects on bridges in recent decades, is the pounding phenomenon. This phenomenon is a result of a collision
between two parts of the deck and/or deck and lateral piers (abutments) in the gaps during the earthquake. The pounding in bridges could cause damage in the deck and abutment or the dislocation of deck from the pier. In conventional bridge designs with a few centimeters gap, pounding in severe earthquakes will be unavoidable. Therefore, in this study, with modeling two- and three-span bridges with different periods and considering the gaps of 2.5, 5, 7.5, 10, 12.5 and 15 cm, the effects of the gap size on seismic parameters, including maximum absolute displacement of the deck, the maximum pier bending moment, the maximum pounding force, and the number of pounding, are analyzed. The bridges are subjected to 8 far-field and 8 near-field accelerograms. The results show that increasing the size of gap reduces the number of poundings and increases the maximum deck displacement. However, the trend of changes in maximum pounding force is subject to the bridge period and applied earthquake specifications. In addition, the near-field earthquakes lead to greater seismic responses than that of the far field ones
Robust multi-objective optimization design of active tuned mass damper system to mitigate the vibrations of a high-rise building
No full textTHE EFFECT OF LEAD RUBBER BEARING SEISMIC ISOLATOR ON PROGRESSIVE COLLAPSE POTENTIAL OF STEEL MOMENT FRAMES
No full textProgressive collapse is defined as a local failure that may occur due to various factors in structural members; then, it can spread to adjacent members and ultimately result in the total collapse of the structure or a large portion of it. Though the abnormal loads could cause progressive collapse, many structures have experienced progressive collapse due to seismic actions in our modern history. Recently, some code specifications and guideline requirements such as Unified Facilities Criteria (UFC) have introduced different analysis methods for the assessment of progressive collapse in buildings based on increasing strength, ductility, and continuity. Many research works have been conducted in relation to the phenomenon of progressive collapse almost considering the gravity loads and, in recent years, seismic progressive collapse has attracted much attention and is an open research area for researchers. Lead Rubber Bearing (LRB) is considered as one of the most conventional isolation systems that has been studied and examined theoretically and developed widely in practice.This study investigates the potential of LRB base isolation under progressive collapse. For this purpose, the behavior of intermediate steel moment frames in the two cases of fixed and with the LRB seismic isolator with 4, 8, and 12 number of stories under progressive collapse is compared using nonlinear static and dynamic analysis in different situations of the column removal. At first, two fixed and isolated 3D structures were designed by SAP2000 software according to Iranian codes; then, analysis was performed under gravity load (consist of nonlinear static and dynamic analysis) according to UFC guild-lines and seismic loading (by nonlinear time history analysis) using Perform-3D software. The base isolation is modeled with an isolator element in the Perform-3D software, and these separators provide hysteresis damping through the sink of lead core.The addition of seismic base isolation system to structures averagely reduces the response of the frames under earthquakes by 61\%. The progressive collapse potential of fixed and base isolated structures in the middle and corner column removal conditions is the same as the results of nonlinear static and dynamic analysis according to loading UFC instructions. Furthermore, the results of the progressive collapse analysis show that increasing the number of structural members leads to a reduction in progressive failure potential. It is observed that the use of base isolation system has a significant impact on the localization of the failures under seismic loads and prevention of their expansion in the structure
Dynamic analysis of Vehicle-bridge systems based on Explicit Form of Newmark-β Method
Full text link© 2017 International Society for Structural Health Monitoring of Intelligent Infrastrucure. All rights reserved. In the present study, a new method is proposed to analyse dynamic responses of the bridge subjected to a moving vehicle. Analysing the vehicle-bridge interaction system is useful for moving load identification and bridge structural damage detection. In this study, the algorithm based on explicit form of Newmark-β is proposed for dynamic analysis of the vehicle-bridge system. A three-span continuous bridge is used as a numerical example to investigate the efficiency of the proposed method and the results are compared with the existing results by the conventional state-space method. From the results, the proposed method is reliable and efficient for the vehicle-bridge interaction analysis
Seismic control of a building structure equip with hybrid mass damper using sliding mode control
No full textThis paper addresses the issue of the impact of controllers in suppressing the vibration of structural building during seismic. It is important to implement an appropriate controller to avoid a huge impact to the building structure from damage and collapse while earthquake occur. Sliding mode controller (SMC) and proportional-integral-derivative (PID) are proposed to alleviate the vibration. SMC is selected as control strategy because of its robust control technique that can reject the disturbances while PID is known as simple control design. The simulation for two storey building equipped with structural control device which known as hybrid mass damper placed at the top floor of the structure that represent by mass, spring and damper are constructed by using Matlab/Simulink. The input excitation to the structure is taken from El Centro earthquake with magnitude of 6.9 Mw. The output response for the system generates displacement, velocity, control input, and frequency response. Based from the result, SMC has better performance compared to PID and overall SMC is success to suppress the building vibration according to the displacement performance obtained
Genetic algorithm-based integrated optimization of active control systems for civil structures subjected to random seismic excitations
No full textSeismic Response Control Performance Evaluation of Tuned Mass Dampers for a Retractable-Roof Spatial Structure
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