The paper presents the results obtained from the application of different output-only modal identification techniques to ambient response data collected in two dynamic tests of a cable-stayed bridge ...and the subsequent finite element model correlation analysis. The first test, performed by using a traditional data acquisition system with servo-accelerometers, was aimed at investigating the vertical dynamic characteristics of the bridge. In the second test, an innovative radar vibrometer was used for non-contact measurement of deflection time series of the forestays and the identification of local natural frequencies of the stay cables.
In the theoretical study, vibration modes were determined using a 3D Finite Element model of the bridge and the information obtained from the field tests, combined with a classic system identification technique, provided a linear elastic model, accurately fitting the modal parameters of the bridge in its present condition.
Skewed bridges are more vulnerable to earthquake-induced failure than straight bridges due to pounding at expansion joints between the bridge superstructure and abutments. This study focuses on ...analyzing pounding effect and rotation mechanism of highway bridges with prestressed concrete box girder and seat-type abutments when subjected to bi-directional near-fault ground motions, especially seismic response with respect to abutment skew angle. These analytical models include nonlinear characteristics of skewed bridge components, especially pounding effect between the superstructure and abutment in both longitudinal and transverse directions. Nonlinear time history analyses were performed to predict the pounding force and its effect on the seismic response of skewed highway bridges using the Kelvin model. The analytical results indicate that the pounding of skewed bridge causes significant seismic displacement response and local damage of superstructure. In addition, the pounding in the transverse initial gap reduced the rotation response of the skewed bridge, and the skew angle has significant effect on the seismic behavior of skewed highway bridges. The pounding force and back-fill response decreased with an increasing skew angle, but deck displacement in longitudinal direction and torsion response increased apparently. Bridges with skew angle increased demand on shear keys under the strong earthquake excitation.
•A model of skew bridge with consideration of pounding effect was built up.•The pounding effect on seismic response of skewed highway bridge was investigated.•The seismic response of bridge components was analyzed.
•TOMA methods are popular due to their insensitivity to natural excitation.•Verify the applicability of two different TOMA schemes to large-scale structures.•Resolve the application conditions of ...classic TOMA under ambient vibration.•Highlight the dynamic properties of different types of cable-stayed bridges.•The damping ratio is estimated by the pLSCF method.
Two transmissibility-based operational modal analysis (TOMA) schemes, i.e., the classic TOMA method utilizing measurements under multiple loading conditions, and the power spectral density transmissibility (PSDT) method resorting to multiple reference outputs under one loading condition, are further investigated in this study. For the classic TOMA approach, the issue of requiring multiple loading conditions is properly addressed in ambient vibration testing. Based on the unique properties of transmissibility, the frequencies can be extracted by varying either loading conditions or reference outputs, while the mode shapes can be estimated by a singular value decomposition of the transmissibility matrix. The applicability of TOMA approaches is evaluated through three typical large-scale cable-stayed bridges, including a railway bridge, a highway bridge, and a pedestrian bridge. A comparative study of these large cable-stayed bridges is carried out to gain more insights into the dynamic properties of large-scale cable-stayed bridges.
This paper uses the probabilistic seismic assessment to study the effects of pounding and irregularity on the seismic behavior of typical concrete box-girder bridges with four levels of altitudinal ...irregularity. To extend the results for all bridges in the same class, uncertainty related to the earthquake, structural geometries, and materials are considered. Pounding is likely to take place in two cases: the first one concerns the seat-type abutments, and the second is at the in-span hinge of multi-frame bridges. Accordingly, the present study is an attempt to investigate the behavior of irregular bridges considering the effects of pounding in both cases. In the first case, the effects of changes in the gap size on engineering demand parameters (EDPs) were investigated. Then, correlations between earthquake parameters and the pounding force were evaluated. Furthermore, the pounding force exerted on the abutment was compared for different bridge irregularity levels. In the second part of the paper, the effects of pounding of adjacent bridge segments in the decks of non-continuous bridges were studied for equivalent Two-Degree-of-Freedom structures, for which the probability of non-occurrence was estimated. In the end, the relationship between structural or seismic parameters and the pounding force was evaluated in case of pounding. The results of the study show that the gap size between the abutment and the deck has the highest effect on the abutment passive deformation, pounding force, and base shear. Also, the substructure irregularity of bridges reduces the correlation between the gap size and the EDPs, except for the column ductility. Moreover, decreasing the ratio of periods of the adjacent frames diminishes the effect of the type of the earthquake but increases the probability of pounding.
The coupled effects of corrosion and earthquake action on bridges piers are investigated in this study. Starting from a literature review to collect existing corrosion models, a bridge overpass is ...selected to perform seismic analyses. It allows to assess the degrading seismic capacity of the bridge pier at different periods due to general and pitting corrosion. The selected bridge structure belongs to the class of motorway overpass, that is a frequently used structural system all around the world. Consequently, the development of a suitable and effective tool for an in‐depth degradation analysis of this type of system, with the identification of the most appropriate time for restoration, is of paramount importance to guarantee continuous serviceability and safety.
•Nonlinear concrete deck modeling predicts earlier girder yielding with skew.•Deck concrete cracking reduces ultimate skewed system capacity.•Response fractions become conservative with increasing ...skew.•Response fractions are unrepresentative for ultimate load conditions.
Bridge designs are routinely developed using simplified 1D approximations of structural behavior and assume linear elastic behavior throughout the structure. More rigorous methods can reveal significant unquantified reserve capacity with 3D system behavior as ductile members experience yielding, but reserve capacity can be overestimated if cracking in a concrete deck is neglected. The primary objective of this study is to characterize the influence of concrete deck nonlinearity on 3D system behavior and capacity of skewed steel girder bridges. Structural behavior is examined throughout the range of potential applied loads, from initial linear elastic behavior to initial yielding and ultimate conditions. Additionally, this study provides a secondary benefit by comparing the applicability of two general load distribution characterization methods: response fractions (displacement, strain, or curvature ratios) versus extracted and integrated results from a rigorous analytical model. Analytical models, accounting for material inelasticity in the steel girders, are constructed for each of two experimentally tested bridges. Skew is varied parametrically from 0° to 60°. Concrete deck is modeled with a tension cracking stress limit consistent with typical design assumptions in United States practice. Results are also presented for the 60° case with linear elastic deck to directly compare the influence of cracking versus non-cracking deck. The analyses indicated that neglecting concrete cracking noticably affected capacity by overestimating slab plate flexure between abutments, resulting in increasingly unconservative reserve capacity evaluations with increasing skew. Bridges with small skews evaluated using only elastic analysis were found to be reasonably well characterized using response fractions feasibly obtained from diagnostic load tests. However, bridges with high skews and bridges evaluated using ultimate capacity from detailed finite element analysis, regardless of skew, will receive unnecessarily conservative flexural capacity ratings if response fractions are relied upon to represent analogous internal load effects.
•A new framework is proposed for fatigue damage prognosis of a cable-stayed bridge.•The framework considers fully-coupled vehicle-bridge dynamics.•The framework also considers deck and pavement ...interaction.•The framework has been applied to a real long-span cable-stayed bridge in Hong Kong.•The fatigue damage is underestimated if neglecting temperature and road roughness.•The fatigue damage is overestimated if neglecting transverse locations of vehicles.
Orthotropic steel deck (OSD) in a long-span cable-stayed bridge is vulnerable to fatigue damage at the deck-to-rib (DTR) joints due to excessive vehicle-induced dynamic stresses. A framework for fatigue damage prognosis of OSD in long-span cable-stayed bridges is thus presented in this paper. The main features of the framework include hourly traffic loading simulation and prediction, multi-scale finite element bridge model, coupled vehicle-bridge system, mesh-insensitive equivalent stress responses at a DTR joint, response surface models for equivalent stress responses, OSD and pavement interaction, asphalt pavement temperature effect, fatigue test-generated S-N curve, and fatigue damage prognosis. To evaluate the feasibility of the proposed framework and to manifest the effects of pavement roughness, asphalt temperature, and vehicle transverse locations on fatigue damage accumulation, a real long span cable-stayed bridge is investigated as a case study. The results indicate that the developed framework is applicable and that the fatigue damage of a DTR joint is underestimated if the time-variant temperature of asphalt pavement and road surface condition are not considered but the fatigue damage is overestimated without consideration of variable transverse locations of vehicles.
•Holistic seismic vulnerability of curved steel bridge inventory was evaluated.•Curved bridges in Pennsylvania, New York and Maryland were used.•System level fragilities were developed via response ...surface metamodels.•Effects of optimal parameters on seismic susceptibility were examined.•Radius of curvature and span number significantly influenced system fragilities.
Fragility curves that have been developed for curved steel bridges have not extensively addressed horizontal curvature and do not sufficiently account for major contributing curved bridge components that influence their seismic response (e.g., radius of curvature, cross-frame spacing, etc.). This study considers a group of horizontally curved steel I-girder bridges located in Pennsylvania, New York and Maryland to examine the influence of important parameters on their seismic response and develop system level fragility curves for the bridge group. The developed methodology is then applied to specific bridges. This paper provides description of the procedure used to generate representative curved bridge fragility curves using input from select component fragilities. The curves were generated for representative bridge systems, and utilized fragilities from important bridge seismic components created using Response Surface Metamodels (RSMs). The critical components included items at the bearings and the supporting pier columns. A statistical screening approach, using design of experiments and incorporating seismic response information obtained from nonlinear time history analyses, was used to determine critical curved bridge component seismic response ranges. Monte Carlo simulation was then implemented to assist with fragility generation for both the group of bridges and sample bridges. Using the generated fragility, case studies were performed to investigate the effects of the certain bridge parameters on seismic vulnerability. Findings indicated that parameters that significantly influenced seismic fragilities were the number of spans, radius of curvature, and maximum span length.
This paper investigates the vortex-induced vibration of a twin steel box girder suspension bridge with a centre span of 1650 m based on field measurements. Two ultrasonic anemometers, two tri-axial ...accelerometers and 52 wind pressure sensors are installed at the quarter span section. The other 20 pressure sensors are installed in another 5 sections, and each section has 4 pressure sensors. Four vortex-induced oscillation events are measured. The analytical results indicate that the vortex-induced vibration more likely occurs in a low wind speed range of 6–10 m/s, with the wind direction nearly perpendicular to the bridge line, and low turbulence intensity. The mean pressure distribution on the surface of the bridge deck is obtained and the characteristics of fluctuant pressures are analysed by proper orthogonal decomposition (POD) method. Moreover, the spatial–temporal evolution of flow around the bridge deck is investigated. The results indicate that in the beginning stage of vortex-induced resonance, the regular vortex shedding phenomena occur only in the gap of the deck and at tailing region of downstream deck; however, when in the lock-in stage, the vortex shedding is strengthened due to the dramatic vibration, and the regular vortex shedding phenomena extend to the entire lower surface of downstream deck and the tail of upstream deck, the vortex shedding regions in the gap and lower surface link together. In the lock-in range, the span-wise correlation of the wind pressure is analysed, and the correlations of wind pressure along the bridge line are very high and do not decrease with the increase in distance.
This paper presents an experimental study on the box girder of a low-tower cable-stayed railway bridge with a W-shaped section that consists of prestressed concrete diagonal braces. A 1:6 scale test ...model was designed and constructed for the experiment. The mechanical behavior of the test model was investigated under two loading conditions: a double-track train symmetrical load and a single-track train unsymmetrical load. The experimental results were validated against a finite element model. Furthermore, the torsional performance of the box girder section was analyzed and discussed.
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