Structural health monitoring systems of long-span bridges in Turkey and lessons learned from experienced extreme events

Long-span bridges constitute one of the most critical lifelines in countries where they are constructed since they shorten transportation by providing passage through large waterways, such as rivers, channels, dams, and the sea. Owing to its geographical location, Turkey is a transit country between Asia and Europe. As long-span bridges are subject to heavy traffic and seismic hazards in Turkey, monitoring their structural health and performing their maintenance in a timely and cost-effective manner is essential. These bridges pose maintenance challenges due to their sizes. Because of their high towers and hard-to-access cables in general, the most reliable method of monitoring the structural condition of such bridges under service is to build structural health monitoring (SHM) systems. This paper reports on the results of a study in which the SHM systems of long-span bridges in Turkey, which are among the largest bridges across the world, are described. The characteristics of these systems utilized are explained in detail. In addition, SHM data acquired on the Fatih Sultan Mehmet Bridge during a recent offshore event on 26th September 2019, the Silivri Earthquake (M-w 5.8), are analyzed. The findings are validated using experimental research results presented in the literature, and the comparison was indicated good agreement to identify the bridge's dynamic characteristics. Finally, problems encountered in SHM systems because of extreme loads are explained, and recommendations are provided for future applications

Response of the Fatih Sultan Mehmet Suspension Bridge under spatially varying multi-point earthquake excitations

The study aims at investigating the structural behavior of the Fatih Sultan Mehmet Suspension Bridge, i.e. the second Bosphorus Bridge in Turkey, under multi-point earthquake excitations, and determining the earthquake performance of the bridge based on the results obtained from this analysis. For this objective, spatially varying ground motions in triple direction were produced for each support of the bridge considering the Mw=7.4 scenario earthquakes on the main Marmara Fault. In order to simulate the ground motions, modified stochastic finite-fault technique was utilized. Taking the ground motions into account, non-linear time-history analysis was carried out, and the results obtained from the analysis were compared to those from uniform support earthquake excitation to identify the effects of multi-point earthquake excitations on the seismic performance of the bridge. From the analysis, it was determined that modal response of the towers and the deck was mostly effective on dynamic response of the entire bridge rather than other structural elements, such as cable and approach viaduct. Compared to the results obtained from simple-point earthquake excitation, noticeable axial force increase in the cable elements was obtained under multi-point earthquake excitation. The changes at the main cable and the side span cable were determined as 21\% and 18\%, respectively. This much increase in the cable elements led to increase in axial force at the towers and in shear force at the base section of the tower column. These changes in the structural elements were closely related to response of the deck and the towers since they had considerable contribution to response of the entire bridge. Based on the findings from the study, spatially varying ground motions has to be considered for long span suspension bridges, and the multi-support earthquake analysis should be carried out for better understanding and obtaining reliable results necessary for retrofitting and performance evaluation. (C) 2016 Elsevier Ltd. All rights reserved

Multi-Point Earthquake Response Of The Bosphorus Bridge To Site-Specific Ground Motions

The study presents the earthquake performance of the Bosphorus Bridge under multi-point earthquake excitation considering the spatially varying site-specific earthquake motions. The elaborate FE model of the bridge is firstly established depending on the new considerations of the used FEM software specifications, such as cable-sag effect, rigid link and gap elements. The modal analysis showed that singular modes of the deck and the tower were relatively effective in the dynamic behavior of the bridge due to higher total mass participation mass ratio of 80%. The parameters and requirements to be considered in simulation process are determined to generate the spatially varying site-specific ground motions. Total number of twelve simulated ground motions are defined for the multi-support earthquake analysis (Mp-sup). In order to easily implement multi-point earthquake excitation to the bridge, the practice-oriented procedure is summarized. The results demonstrated that the Mp-sup led to high increase in sectional forces of the critical components of the bridge, especially tower base section and tensile force of the main and back stay cables. A close relationship between the dynamic response and the behavior of the bridge under the Mp-sup was also obtained. Consequently, the outcomes from this study underscored the importance of the utilization of the multi-point earthquake analysis and the necessity of considering specifically generated earthquake motions for suspension bridges

Finite element modeling of the Fatih Sultan Mehmet Suspension Bridge

This study presents the 3D finite element model of the Fatih Sultan Mehmet Suspension Bridge located In Istanbul, Turkey. All the towers and the deck are modeled with four node thin shell finite elements with the inclusion of internal diaphragms. The main suspension cable, the back-stay cable, and the hanger cables are modeled with two node beam finite elements. An initial nonlinear static analysis utilizing the geometric stiffness is performed in order to obtain the correct pre-stressing forces in the cables. An eigenvalue analysis of the bridge is performed once a converged solution is obtained by the non-linear static analysis. The results of the eigenvalue analysis are compared with the available ambient vibration test measurements and the results of the finite element model of the bridge with only beam elements. The results show that the 3D numerical model utilizing thin shell finite elements can accurately represent the modal periods of the suspension bridge