This paper addresses the application of a Bayesian parameter estimation method to a regional seismic risk assessment of curved concrete bridges. For this purpose, numerical models of case-study ...bridges are simulated to generate multiparameter demand models of components, consisting of various uncertainty parameters and an intensity measure (IM). The demand models are constructed using a Bayesian parameter estimation method and combined with limit states to derive the parameterized fragility curves. These fragility curves are used to develop bridge-specific and bridge-class fragility curves. Moreover, a stepwise removal process in the Bayesian parameter estimation is performed to identify significant parameters affecting component demands.
•Two 1:5 scale models of composite beams with CSWs and trusses are tested.•The effects of bottom trusses and concrete in steel tubes are examined.•Finite element simulation is used to simulate the ...full behavior of tested specimens.•Theoretical model is developed to predict the nonlinear behavior.
The composite box girder with corrugated steel webs (CSWs) and trusses is a bridge structure developed on the basis of traditional box girders with CSWs. In this research, experimental, numerical and analytical studies were carried out to investigate the flexural performance of simply supported composite box girders with CSWs. Two 1:5 scale models of a real bridge were fabricated and tested, including one with concrete filled steel tubes and another with hollow steel tubes. The test results show that the two specimens have good ductility and failed in a ductile manner. The concrete filled inside steel tubes reduces the deflection and increases the yield load. The cross sections of the two specimens basically satisfy the “plane section assumption”. Finite element models were also developed for the two specimens and validated based on the experimental results. Afterwards, a parametric study was carried out with the validated finite element models, which shows that the steel ratios and the structure of bottom trusses strongly influences the flexural behavior. At last, a theoretical model is developed to calculate the bending moment of composite beams at the ultimate load.
•Prediction model of effective prestress for two prestress tensioning techniques are established.•Probability analysis method of web cracking considering both aleatory and epistemic uncertainties is ...proposed.•Impacts of corrosion and different prestress tensioning techniques on the web cracking are discussed.•Sensitivity analysis of the epistemic uncertainties of corrosion parameters is conducted.
Reasonable assessment of web cracking probability is essential to ensure the service performance of corroded prestressed concrete (PC) bridges. In this paper, a time-dependent prediction model of effective prestress for different prestress tensioning techniques and a corrosion propagation model are established. Meanwhile, an assessment approach of web cracking probability considering both aleatory and epistemic uncertainties is proposed. The case analysis results show that the doubled-tensioned prestress technique is obviously more effective in decreasing the web cracking probability than the traditional prestress tensioning technique. The existing probabilistic method that only considers the aleatory uncertainty may greatly underestimate the probability of web cracking. In comparison, the fastest time to reach the threshold value of web cracking probability when considering the epistemic uncertainty is over 11% earlier than that of using the existing methods. Additionally, the epistemic uncertainty of the chloride diffusion coefficient among the selected corrosion parameters has a most significant impact on the probability of web cracking. Therefore, the epistemic uncertainty of corrosion parameters, especially for the chloride diffusion coefficient, should be minimized as much as possible in this assessment process.
•A novel tuned mass-damper-inerter with a Maxwell element is proposed to mitigate the vortex-induced vibration in bridges.•The effect of the inerter location on the optimal M-TMDI parameters is ...considered.•The optimal M-TMDI parameters are developed in closed-form expression for the VIV mitigation.
This paper investigates the optimal design of the Maxwell tuned mass-damper-inerter (M-TMDI) for mitigating the vortex-induced vibration (VIV) in bridges. The M-TMDI consists of a three-element tuned mass damper (TMD) and an inerter. Considering that the bridge deck is a multiple-degree-of-freedom (DOF) system, the inerter location is considered as a design variable of the M-TMDI in our study. The optimal parameters of a specific M-TMDI, in which the end of the inerter is connected to the fixed ground, are analytically given based on a two-DOF system. Furthermore, the optimal parameters of the M-TMDI with any inerter location on the bridge deck are developed in closed-form based on a multiple-DOF system. Finally, numerical analysis on a continuous steel box-girder bridge subjected to the VIV is performed to confirm the optimal design and superiority of the M-TMDI control. The result demonstrates that the optimally designed M-TMDI outperforms the TMD and three-element TMD in the transient amplitude mitigation, steady-state amplitude mitigation, stroke limitation, and static stretching reduction. The optimal control effect of the M-TMDI greatly depends on the defined effective mass ratio, which is function of the inerter location, mode shape, physical mass, and inertial mass.
•A novel thermal analysis methodology is proposed to predict the temperature distribution of steel box girders considering the actual wind field.•The convection coefficient is computed based on the ...wind speed at the thermal boundary layer thickness through the CFD simulation.•Effects of the various factors affecting the resultant temperature characteristics are quantified.
Most existing studies on bridge thermal analysis have ignored the influence of wind on the resultant temperature distribution, in which a constant value of wind speed is applied to all structural surfaces. In fact, the wind blowing across the girder exterior surface significantly affects the heat-transfer convection coefficient and consequently influences the accuracy of the thermal analysis results. For the streamlined steel box girder in particular, the local wind speeds on different surfaces even under the same inflow wind speed could vary significantly, because the steel box girder is composed of multiple surfaces with different azimuth angles. In this paper, a novel thermal analysis methodology for predicting the temperature characteristics of steel box girders is proposed considering the actual wind field distribution around the girder. Validation studies are first performed to validate the applicability of the proposed methodology. Subsequently, the proposed thermal analysis methodology is applied to a typical bridge, with which the temperature distribution characteristics of its steel box girder is investigated in detail. Meanwhile, parametric analysis, including the inflow wind speed, the season, the geometry of box girder, and the influence of vehicle are conducted to identify their effects on the temperature distribution characteristics of the girder quantificationally.
•Study the working state characteristics of SCCBG by the theory of structural stress state analysis.•Analysis of the working state parameters (strain distribution mode, deflection and crack width, ...etc.) reveals the abrupt change characteristics and material evolution behavior.•Shear-slip curves at the interface of the combined box beam indicate the differences in the three-stage stress state.•The NPI method reasonably extends the experimental strain data.
This paper uses the theory of structural stressing state to study the working characteristics of three multi-span continuous steel-concrete composite box girder (SCCBG) models with different prestress levels. Firstly, the generalized strain energy density (GSED) is constructed to reveal the working state of the structure based on the experimental strain data, the Mann-Kendall (M-K) criterion is applied to distinguish the leap characteristics load points (P and Q) of the structural stressing state and defined as the “failure load”. It is used to update the existing structural “destruction” load to more clearly reflect the entire structural failure process. Then, the working state parameters of the cross-section are described (strain distribution mode, midspan deflection, crack width, etc.) to analyze the working behavior of the box girder model. Finally, the non-sample point interpolation method (NPI) is used to reasonably expand the experimental strain data, to verify the rationality of the characteristic load points, and the stressing state characteristics of box girders with different prestressed levels are further discussed.
Summary
Recent efforts of regional risk assessment of structures often pose a challenge in dealing with the potentially variable uncertain input parameters. The source of uncertainties can be either ...epistemic or aleatoric. This article identifies uncertain variables exhibiting strongest influences on the seismic demand of bridge components through various regression techniques such as linear, stepwise, Ridge, Lasso, and elastic net regressions. The statistical results indicate that Lasso regression is the most effective one in predicting the demand model as it has the lowest mean square error and absolute error. As the sensitivity study identifies more than 1 significant variable, a multiparameter fragility model using Lasso regression is suggested in this paper. The proposed fragility methodology is able to identify the relative impact of each uncertain input variable and level of treatment needed for these variables in the estimation of seismic demand models and fragility curves. Thus, the proposed approach helps bridge owners to spend their resources judiciously (e.g., data collection, field investigations, and censoring) in the generation of a more reliable database for regional risk assessment. This proposed approach can be applicable to other structures.
•The combined effect of duration and spectral shape on bridge response is investigated.•Ia &Sa(T1) are the best predictors of the response in shallow crustal ground motions.•Duration is insignificant ...in affecting the response in shallow crustal ground motions.•The duration of ground motions from subduction sources affects bridge response.
The design practice of Box-Girder Seat-Type (BGST) bridges in the Western U.S. is continuously evolving based on the results of advanced modeling and analysis techniques. This is mainly to help engineers and researchers to better understand the behavior of BGST bridges during seismic excitations. Within this backdrop, this study fills the gaps in the current knowledge of assessing the combined effect of strong motion duration and spectral shape on the response of bridges using a comprehensive set of numerical simulations and statistical analyses. Three-dimensional finite element models of two real BGST bridges are analyzed using a large set of ground motions obtained from crustal sources and subduction sources. By means of Step-wise regression – and other statistical procedures – the sensitivity of bridge response parameters to various ground motion parameters including Arias Intensity (Ia), RotD50 spectral acceleration at the bridge’s first natural period (Sa(T1)), Significant Duration (D5-95), mid-frequency (f), the derivative of the mid-frequency (f’) and time at 30% of cumulated Arias Intensity (tmid) are evaluated. Results indicate that in the case of ground motions arising from shallow crustal sources, Ia and Sa(T1) are the best predictors of the bridge response, and strong motion duration (D5-95) has no statistically meaningful impact on the response of bridges. However, it is observed that the D5-95 of the ground motions ascending from the subduction sources highly affects the bridge response; utilizing D5-95 alongside Sa(T1), or Ia, can significantly increase the accuracy of bridge response estimates. Hence, it is concluded that D5-95 is not an important ground motion intensity measure for ground motion selection for bridges located in areas with crustal earthquakes. In contrast, D5-95 is important in subduction zone ground motions and must be given proper consideration in the design and analysis of BGST bridges.
AbstractThis study investigates the vortex-induced vibration (VIV) behavior of a twin-box girder bridge by means of aerodynamic sectional wind tunnel test and particle image velocimetry (PIV) ...measurements. The effect of grid plates on suppressing the VIV of twin-box girder model is examined and the influence of four design parameters of grid plates porosity, flat plate width (FPW) ratio, composition type, and installation position is studied. The primary causes of VIV and the suppression mechanism of grid plates are discussed in detail. It is found that torsional VIV is more vulnerable to the change in wind attack angle than is vertical VIV. The installation of grid plates noticeably suppresses the VIV of test model and its effect depends on the variation of different design parameters. For the porosity and FPW ratio, there is an optimal range in which the improvement of VIV suppression is more significant; the optimal value of porosity is about 42%–67%, and the optimal value of FPW ratio is about 0.042–0.167. Moreover, the uniform distribution of grid plates is more preferable in terms of suppressing VIV than is nonuniform distribution, whereas the installation of grid plates on the upper side leads to better performance of VIV suppression than does installation on the lower side. The primary cause of VIV of the twin-box girder is closely related to the formation of large-scale vortex shedding at the tail of the upstream box girder. The generation of large-scale vortex can be eliminated by appropriate selection of the design parameters of grid plates.
Wind-induced nonlinear oscillations of twin-box girder bridges are very sensitive to the aerodynamic shape of the deck (i.e., slot width ratio (SWR) and wind fairing shape) due to the complicated ...flow characteristics around the bridge deck. This paper presents a fully integrated finite element (FE) model in time domain, involving a nonlinear aerodynamic force model and a bridge FE model, to allow the investigation of nonlinear oscillation behaviors of long-span twin-box girder bridges with various SWRs and wind fairing shapes. The parameters in integrated FE model were firstly identified by using CFD simulation, and then, the proposed model was validated by conducting wind tunnel testing using sectional models and full-bridge aeroelastic models. It demonstrates that the developed integrated model has the capability of simulating the nonlinear flutter behaviors of twin-box girder bridges with various aerodynamic shapes. Furthermore, the prediction results show that the wind fairing shape has significant impact on the degree of freedom participation in coupled oscillation and failure modes, as well as flutter performance of the bridges. In addition, there is an increase in amplitudes of the limit cycle oscillations with the increase in the SWR of the twin-box girder bridges, and the relationships between the bending-torsional coupled oscillation, failure modes, and SWR of the bridges with anti-symmetric wind fairings are opposite to those with symmetric wind fairings.
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