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.
The dynamic analysis using computational models is an important tool to simulate the dynamic of structures that have
specific uncertain behavior like the cable stayed bridges which nowadays is an alternative to solve long span bridges
with a slim structure. In this work we developed a 3D non linear model of a cable in order to evaluate the wind effect on
the Papaloapan cable stayed bridge located on Veracruz Mexico, under different scenarios. The health of the structure is
an important factor to analyze and there are many different fail causes, one of them is the fatigue fall that is relevant in
the anchorage elements of the cable stayed bridges. It is possible to modify the behavior of the structure using dampers
to minimize that effect. The geometry and all the forces and stress on the structures are a challenge also for the
specialists of the structures, in this work the developed methodology resulted very successful to analyze the behavior of a
cable on a cable stayed bridge using damping.
KEYWORDS: Bridges, Chemical elements, Reliability, Statistical analysis, Failure analysis, Monte Carlo methods, Inspection, Chemical analysis, Finite element methods, Ultrasonics
This work describes the experimental and theoretical approach used for the development of a structural reliability model for the upper anchorage of a cable-stayed bridge. Experimental and field analysis are used to establish the statistical models for uncertainty in material constitutive laws, fracture toughness, external loads (traffic and wind), and material defects (inclusions and pores). A standard reliability method is used for the evaluation of probabilistic characteristics of parameters and for the failure probabilities. Finite element analysis is used within two levels; the first level considers the model of the whole bridge to calculate the loads on the anchorages under different external load conditions. The second level considers the detailed model for the anchorage to calculate stresses on critical points. A particular semi-empirical model is proposed to analyze fatigue and to predict structural life. The reliability model is evaluated through the simulation of different scenarios of load conditions.
A bridge management system developed for the Mexican toll highway network applies a probabilistic-reliability model to estimate load capacity and structural residual life. Basic inputs for the system are the global inspection data (visual inspections and vibration testing), and the information from the environment conditions (weather, traffic, loads, earthquakes); although, the model takes account for additional non-destructive testing or permanent monitoring data. Main outputs are the periodic maintenance, rehabilitation and replacement program, and the updated inspection program. Both programs are custom-made to available funds and scheduled according to a priority assignation criterion. The probabilistic model, tailored to typical bridges, accounts for the size, age, material and structure type. Special bridges in size or type may be included, while in these cases finite element deterministic models are also possible. Key feature is that structural qualification is given in terms of the probability of failure, calculated considering fundamental degradation mechanisms and from actual direct observations and measurements, such as crack distribution and size, materials properties, bridge dimensions, load deflections, and parameters for corrosion evaluation. Vibration measurements are basically used to infer structural resistance and to monitor long term degradation.
A novel measurement technique, based on a laser beam, is proposed to measure the amplitude of vibration by using fractal analysis of speckle patterns. Experimental measurements of nodes and antinodes, and its respective speckle pattern structures in the two sates, are presented in terms of fractal dimensions. It is shown that a correlation with the fractal dimension of the speckle pattern and each amplitude of vibration can lead to a new method for amplitude of vibration analysis.
KEYWORDS: Corrosion, Modal analysis, Wave propagation, Sensors, Beam controllers, Calibration, Finite element methods, Data acquisition, Data modeling, Intelligence systems
Experimental corrosion damage and dynamic behavior of nine 3 meter concrete beams (15x15 cm cross section) pre-stressed with four strands (6-wire, 0.8 cm in diameter) were evaluated by visual inspection (crack morphology) and vibration testing. Corrosion was induced in the embedded strand under controlled conditions and different levels of degradation were achieved. The Sub-Domain Inverse Method (SDIM), which is a dynamic method based on the wave propagation analysis of impact loads, was used to evaluate the damage. Stiffness reductions were calculated using a non-corroded control beam for reference and to calibrate a FEM. SDIM results compared with modal analysis, show reasonable agreement for low damage levels, while for the high damage levels differences is found. From the modal analysis, it is observed that the fundamental frequency is primary affected by the pre-stressing load reduction and none effect is recorded due to the longitudinal cracks generated by the corroded strands. Results show that the SDIM is sensitive to both, pre-stress reduction and concrete cracking damage.
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