Computational models are increasingly being used for the dynamic analysis of structures with nonlinear or uncertain behavior, such as cables in stayed bridges, which nowadays are progressively more used as an alternative for long span and slim structures. In this work, a 3D nonlinear model is described to evaluate the wind dynamic effects on cables for this type of bridges under different scenarios, but also for health monitoring and structural simulation to guarantee performance, evaluate load capacity and estimate life prediction. Fatigue is one of the most relevant and complex failure causes in highway bridges, particularly on the anchorage elements of the cables in stayed bridges; where dampers may be used to minimize the dynamic behavior of the structure and reduce fatigue damage. With this nonlinear simulation model, different damper locations and configurations are evaluated to find the optimal position. A feasibility function is used as a weighting function to take into account the damper's size and design. Analysis is particularly focused for a real cable stayed bridge in the state of Veracruz in México.Although the geometry, the forces and the stresses on cable structures are a challenge, even for structural specialists, the results from this work using the proposed 3D nonlinear model showed to be accurate for the simulation of many different wind scenarios, and damper's location and orientations. Finally, the feasibility weighting function enabled the geometrical limitations to estimate the best location of a damper system to minimize the risk for fatigue failure.

The main objective of this work is to develop an active damping system that can be used to reduce the vibrations of cables in stayed bridges. As a first stage, a laboratory physical scale model of a prestressed cable was used to characterize and test the dynamic performance of the damping system that comprises accelerometers to measure cable vibrations, an electromagnetic actuator which interacts with the cable to compensate for externally induced vibrations, and a digital controller in which control strategies and algorithms are defined. In the experiment, an additional actuator was used to excite vibration disturbances on the cable modifying its frequency and amplitude, and the location for the accelerometers was defined from simulations with a linear model of the cable to optimize the damping control method. Two different system identification approaches were used to calculate the frequency response function of the whole system (cable, accelerometers and actuators); the first approach used the spectral analysis to get initial dynamic results of the cable system, while the second employed the parametric identification to obtain the transfer function of the system, by which different models were assessed. Model reduction techniques and the direct synthesis approach were selected to get a second-order model for the controller. The active damping system was first evaluated with simulation studies and then, in the laboratory. Results show that the damping system reduces the vibration amplitude up to 50% for the resonance frequency. Complementary simulations using a full scale cable model of the stayed bridge with an equivalent active damping system, showed the same damping efficiency as for that in the laboratory experiment; however, a practical application must consider the scaling factor and the limitations of possible locations and orientations of the damping actuator to get the best dynamic performance.

After an extensive analysis, the Río Papaloapan Bridge in the state of Veracruz, Mexico, was scheduled for maintenance to replace the upper anchorage element of 20 cables that were identified as structurally deficient. For this rehabilitation, an extensive monitoring was implemented to ensure the integrity of the bridge. As a result, abnormal vibration levels were detected in one cable (cable 9 in semi-harp 1), particularly for winds over 50 km/h. To determine the origin of this behavior, additional vibration measurements were implemented to evaluate the dynamic vibrations of the different elements involved.Comparison of the frequency spectrum of different cables with same characteristics and tensions, it was found that the abnormal cable had high vibration levels within the range of 10 to 20 Hz. At the same time, the frequency spectrum for their corresponding upper anchorage of the cable also showed significant differences for the same range of frequencies and higher levels were detected for the same atypical cable in the semi-harp plane (xy plane).Analysis from the vibration data concluded that the tension of the cable was within specifications and the abnormal behavior was not due to distension. Simulation studies confirmed that reduction in the structural stiffness for the anchorage element induced high vibration levels in the range within 20 Hz and the dynamic coupling with the higher vibration modes of the cable was the most probable cause for the extensive vibration in the cable. Also, simulation analysis showed that a damping system could minimize significantly the vibration levels between 8 and 25 Hz.The foregoing gave us the opportunity to conclude that the cable # 9 o semi-harp 1, is under an abnormal conditions due to a dynamic vibration coupling to its upper anchorage element and the higher vibration in the xy plane in this anchorage element was most probably to stiffness reduction. Based on the previous, monitoring and detailed inspection of the anchorage element was recommended, and at the same time, consideration of a damping system is highly recommended to reduce vibration damage.