TY - GEN
T1 - Cost-effectiveness evaluation of MR damper system for cable-stayed bridges under earthquake excitation
AU - Hahm, D.
AU - Koh, H. M.
AU - Ok, S. Y.
AU - Park, W.
AU - Chung, C.
AU - Park, K. S.
PY - 2006
Y1 - 2006
N2 - Over the last few decades, cable-stayed bridges have attracted great interest because of their aesthetics, structural efficiency, and economy of construction. However, these structures have a vulnerability to dynamic loads such as earthquakes and strong winds as a consequence of their structural flexibility and low damping characteristics. Among various strategies for the dynamic response mitigation of cable-stayed bridges, semi-active dampers have lately become a subject of interest due to its favorable features, i.e., inherent stability and minimal power requirements. Furthermore, the recent rapid progress of the related technology on magnetorheological (MR) damper system shows the great deal of promise for introduction of semi-active dampers to real structures. Thus, it would be a worthwhile subject to investigate the feasibility and cost-effectiveness of the MR damper system for cable-stayed bridges under earthquake excitation. This paper presents cost-effectiveness evaluation of MR damper system for cable-stayed bridge with respect to the various seismic characteristics, such as magnitudes and frequency contents. The cable-stayed bridge used in this study is the Bill Emerson Memorial Bridge, which was adopted in the phase I benchmark control problem. The semi-active damper system is controlled by a modified clipped-optimal control algorithm on the basis of Linear Quadratic Gaussian (LQG) optimal controller. The cost-effectiveness of the MR damper system is defined by the ratio of life-cycle costs between a bridge structure with the semi-active control devices and a bridge structure with shock transmission units. The life-cycle cost function consists of the summation of initial construction cost and expected damage cost due to earthquake event. For the evaluation of the expected damage cost, the failure probability of a cable-stayed bridge system is estimated by use of the crossing theory and simulation methods. The cost effectiveness index of MR damper (JMR) is defined as the ratio of life-cycle costs between a bridge structure with MR dampers and a bridge structure with STU, as follows. (Equation Presented) where α(= CMR/CI) is a ratio of installation cost of MR dampers(CMR) to initial construction cost(CI), and β(= 2D/C1) is a ratio of damage cost(CD) to initial construction cost. Pf,STU is failure probability of a bridge with STU, Pf,MR is the failure probability of a bridge with MR dampers, νis earthquake occurrence rate, λ is discount rate and tlife is lifetime of a structure. In this study ν, λ and tlife are assumed to be 0.1/year, 5% and 50 years, respectively. Note that the MR damper is cost-effective when the value of JMR is larger than 1. (Graph Presented) From the results of the cost-effectiveness evaluation for the MR damper system with respect to a, it was found that the cost-effectiveness index does not show significant variation, and the index is larger than 1.0. This implies that the MR damper system is cost-effective regardless of the damper cost. However, cost-effectiveness increases remarkably in accordance with an increase in β. Especially for the case of SPC D, the cost-effectiveness is very sensitive to variations in β. Thus, the damage cost of the structural system, i.e., the socio-economic effect due to the failure of a cable-stayed bridge, should be carefully assessed when designers apply MR damper systems to cable-stayed bridges that are located in regions of high seismicity. Figure 1(a) and Figure 1(b) provide the cost-effectiveness of an MR damper system with respect to the soil profile types of the construction site when β = 10 and β = 100, respectively. Note that the scales of the cost-effectiveness index in each case are quite different although both cases show a similar tendency according to the soil profile types. In the case of ground motion with moderate seismicity, i.e., SPC B, the MR damper system shows a higher cost-effectiveness in soft soil profile types. On the other hand, in a region of high seismic intensity, SPC D, the cost-effectiveness is consistently higher compared to the case of SPC B for the overall soil profile types. Figure 2 presents evaluation results with respect to the intensities of earthquake ground motion. For SPC A and soil profile type I, the failure of a structural system even without control device is very non-probable, fhe benefit of the control system on failure probability becomes negligible, from a total life-cycle cost perspective. In soft soils, it should be noted that the MR damper system is more cost-effective for moderate seismicity, SPC C, rather than high seismicity, SPC D. The decrease in cost-effectiveness for a high-intensity earthquake may be caused by the limited capacity of the MR dampers, 1000 kN, used in this study. Therefore, a preliminary study to determine the appropriate level of MR damper capacity will be required when MR damper devices are applied to cable-stayed bridges, especially in the regions of high seismicity and soft soil profile types.
AB - Over the last few decades, cable-stayed bridges have attracted great interest because of their aesthetics, structural efficiency, and economy of construction. However, these structures have a vulnerability to dynamic loads such as earthquakes and strong winds as a consequence of their structural flexibility and low damping characteristics. Among various strategies for the dynamic response mitigation of cable-stayed bridges, semi-active dampers have lately become a subject of interest due to its favorable features, i.e., inherent stability and minimal power requirements. Furthermore, the recent rapid progress of the related technology on magnetorheological (MR) damper system shows the great deal of promise for introduction of semi-active dampers to real structures. Thus, it would be a worthwhile subject to investigate the feasibility and cost-effectiveness of the MR damper system for cable-stayed bridges under earthquake excitation. This paper presents cost-effectiveness evaluation of MR damper system for cable-stayed bridge with respect to the various seismic characteristics, such as magnitudes and frequency contents. The cable-stayed bridge used in this study is the Bill Emerson Memorial Bridge, which was adopted in the phase I benchmark control problem. The semi-active damper system is controlled by a modified clipped-optimal control algorithm on the basis of Linear Quadratic Gaussian (LQG) optimal controller. The cost-effectiveness of the MR damper system is defined by the ratio of life-cycle costs between a bridge structure with the semi-active control devices and a bridge structure with shock transmission units. The life-cycle cost function consists of the summation of initial construction cost and expected damage cost due to earthquake event. For the evaluation of the expected damage cost, the failure probability of a cable-stayed bridge system is estimated by use of the crossing theory and simulation methods. The cost effectiveness index of MR damper (JMR) is defined as the ratio of life-cycle costs between a bridge structure with MR dampers and a bridge structure with STU, as follows. (Equation Presented) where α(= CMR/CI) is a ratio of installation cost of MR dampers(CMR) to initial construction cost(CI), and β(= 2D/C1) is a ratio of damage cost(CD) to initial construction cost. Pf,STU is failure probability of a bridge with STU, Pf,MR is the failure probability of a bridge with MR dampers, νis earthquake occurrence rate, λ is discount rate and tlife is lifetime of a structure. In this study ν, λ and tlife are assumed to be 0.1/year, 5% and 50 years, respectively. Note that the MR damper is cost-effective when the value of JMR is larger than 1. (Graph Presented) From the results of the cost-effectiveness evaluation for the MR damper system with respect to a, it was found that the cost-effectiveness index does not show significant variation, and the index is larger than 1.0. This implies that the MR damper system is cost-effective regardless of the damper cost. However, cost-effectiveness increases remarkably in accordance with an increase in β. Especially for the case of SPC D, the cost-effectiveness is very sensitive to variations in β. Thus, the damage cost of the structural system, i.e., the socio-economic effect due to the failure of a cable-stayed bridge, should be carefully assessed when designers apply MR damper systems to cable-stayed bridges that are located in regions of high seismicity. Figure 1(a) and Figure 1(b) provide the cost-effectiveness of an MR damper system with respect to the soil profile types of the construction site when β = 10 and β = 100, respectively. Note that the scales of the cost-effectiveness index in each case are quite different although both cases show a similar tendency according to the soil profile types. In the case of ground motion with moderate seismicity, i.e., SPC B, the MR damper system shows a higher cost-effectiveness in soft soil profile types. On the other hand, in a region of high seismic intensity, SPC D, the cost-effectiveness is consistently higher compared to the case of SPC B for the overall soil profile types. Figure 2 presents evaluation results with respect to the intensities of earthquake ground motion. For SPC A and soil profile type I, the failure of a structural system even without control device is very non-probable, fhe benefit of the control system on failure probability becomes negligible, from a total life-cycle cost perspective. In soft soils, it should be noted that the MR damper system is more cost-effective for moderate seismicity, SPC C, rather than high seismicity, SPC D. The decrease in cost-effectiveness for a high-intensity earthquake may be caused by the limited capacity of the MR dampers, 1000 kN, used in this study. Therefore, a preliminary study to determine the appropriate level of MR damper capacity will be required when MR damper devices are applied to cable-stayed bridges, especially in the regions of high seismicity and soft soil profile types.
UR - http://www.scopus.com/inward/record.url?scp=56749157091&partnerID=8YFLogxK
U2 - 10.1201/b18175-113
DO - 10.1201/b18175-113
M3 - Conference contribution
AN - SCOPUS:56749157091
SN - 0415403154
SN - 9780415403153
T3 - Proceedings of the 3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost
SP - 301
EP - 302
BT - Proceedings of the 3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performane and Cost
PB - Taylor and Francis/ Balkema
T2 - 3rd International Conference on Bridge Maintenance, Safety and Management - Bridge Maintenance, Safety, Management, Life-Cycle Performance and Cost
Y2 - 16 July 2006 through 19 July 2006
ER -