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CONTENTS
Volume 1, Number 4, December 2014
 

Abstract
In the existing bridge management systems, assessment of the structural behavior is based on the results of visual inspections in which corresponding condition states are assigned to individual elements. In this process, limited attention is given to the correlation between bridge elements from structural perspective. Also, the uncertainty of parameters which affect the structural capacity is ignored. A system reliability-based assessment model is potentially an appropriate replacement for the existing procedures. The aim of this research is to evaluate the system reliability of existing conventional Steel-Reinforced bridge decks over time. The developed method utilizes the reliability theory and evaluates the structural safety for such bridges based on their failure mechanisms. System reliability analysis has been applied to simply-supported concrete bridge superstructures designed according to the Canadian Highway Bridge Design Code (CHBDC-S6) and the deterioration pattern is achieved based on the reliability estimates. Finally, the bridge condition index of an old existing bridge in Montreal has been estimated using the developed deterioration pattern. The results obtained from the developed reliability-based deterioration model and from the evaluation done by bridge engineers have been found to be in accordance.

Key Words
bridge; reliability; deterioration; conventional steel-reinforced deck

Address
Farzad Ghodoosi, Ashutosh Bagchi and Tarek Zayed: Department of Building, Civil & Environmental Engineering, Concordia University, 1455 de Maisonneuve blvd. West, Montréal, Quebec, Canada H3G 1M8
Adel R.Zaki: SNC-Lavalin Inc., 455 René-Lévesque, Blvd. West, Montréal, Quebec, Canada, H2Z 1Z3

Abstract
Long-span cable-supported bridges are flexible structures vulnerable to unsymmetric loadings such as railway traffic and strong wind. The torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds may deform the railway track laid on the bridge deck and affect the running safety of trains and the comfort of passengers, and even lead the bridge to collapse. Therefore, it is eager to figure out the torsional dynamic response of long-span cable-supported bridges under running trains and/or strong winds. The Tsing Ma Bridge (TMB) in Hong Kong is a suspension bridge with a main span of 1,377 m, and is currently the world\'s longest suspension bridge carrying both road and rail traffic. Moreover, this bridge is located in one of the most active typhoon-prone regions in the world. A wind and structural health monitoring system (WASHMS) was installed on the TMB in 1997, and after 17 years of successful operation it is still working well as desired. Making use of one-year monitoring data acquired by the WASHMS, the torsional dynamic responses of the bridge deck under rail traffic and strong winds are analyzed. The monitoring results demonstrate that the differences of vertical displacement at the opposite edges and the corresponding rotations of the bridge deck are less than 60 mm and 0.1o respectively under weak winds, and less than 300 mm and 0.6o respectively under typhoons, implying that the torsional dynamic response of the bridge deck under rail traffic and wind loading is not significant due to the rational design.

Key Words
torsional response; long-span suspension bridge; railway traffic; typhoon; structural health monitoring

Address
Yun-Xia Xia, Yi-Qing Ni and Chi Zhang: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong


Abstract
Across-wind response is often the cause of significant structural vibrations that in turn cause fatigue damage to welded and other connections. The efficacy of low-cost helical strakes to mitigate such adverse response is presented for a traffic signal structure. Field observations are made on a prototype structure in a natural wind environment without and with helical strakes installed on the cantilevered arm. Through continuous monitoring, the strakes were found to be effective in reducing across-wind response at wind speeds less than 10 m/s. Estimates of fatigue life are made for four different geographical locations and wind environments. Results for the class of traffic signal structure show that helical arm strakes are most effective in locations with benign wind environments where the average annual wind speed is not more than the vortex shedding wind speed, which for this investigation is 5 m/s. It is concluded that while strakes may be effective, it is not the panacea to mitigating connection fatigue at all locations.

Key Words
traffic signal structure; fatigue; helical strakes; vortex shedding; full-scale monitoring

Address
Kyle T. Wieghaus, Stefan Hurlebaus and John B. Mander: Zachry Department of Civil Engineering, Texas A&M University, College Station, Texas 77843, USA

Abstract
A relatively low frequency Lamb wave-based damage identification method called damage imaging method for rectangular composite plate is presented. A damage index (DI) is generated from the delay matrix of the Lamb wave response signals, and it is used to indicate the location and approximate area of the damage. The viability of this method is demonstrated by analyzing the numerical and experimental Lamb wave response signals from rectangular composite plates. The technique only requires the response signals from the plate after damage, and it is capable of performing near real time damage identification. This study sheds some light on the application of Lamb wave-based damage detection algorithm for plate-type structures by using the relatively low frequency (e.g., in the neighborhood of 100 kHz, more suitable for the best capability of the existing fiber optic sensor interrogator system with the sampling frequency of 500 kHz) Lamb wave response and a reference-free damage detection technique.

Key Words
damage detection; Lamb wave; composite plates; piezoelectric sensors and actuators; damage imaging

Address
Pizhong Qiao and Wei Fan: Department of Civil and Environmental Engineering, Washington State University, Sloan 117, Pullman, WA, 99164-2910, USA

Abstract
A hybrid optimization method for the identification of state–space models is presented in this study. Hybridization is succeeded by combining the advantages of deterministic and stochastic algorithms in a superior scheme that promises faster convergence rate and reliability in the search for the global optimum. The proposed hybrid algorithm is developed by replacing the original stochastic mutation operator of Evolution Strategies (ES) by the Levenberg-Marquardt (LM) quasi-Newton algorithm. This substitution results in a scheme where the entire population cloud is involved in the search for the global optimum, while single individuals are involved in the local search, undertaken by the LM method. The novel hybrid identification framework is assessed through the Monte Carlo analysis of a simulated system and an experimental case study on a shear frame structure. Comparisons to subspace identification, as well as to conventional, self-adaptive ES provide significant indication of superior performance.

Key Words
Evolution strategies; Levenberg-Marquardt; hybrid optimization; system identification;state-space; modal analysis

Address
Vasilis K. Dertimanis, Eleni N. Chatzi and Minas D. Spiridonakos: Institute of Structural Engineering, Department of Civil, Environmental and Geomatic Engineering,
ETH Zürich, Stefano–Franscini–Platz 5, 8093 Zürich, Switzerland


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