Jong-Su Jeon

Machine Vision-Enhanced Postearthquake Inspection

AbstractCurrent postearthquake inspection of structures relies on certified inspectors to make an assessment of the existing safety of the structure based primarily on qualitative measures. Completing the required inspection takes weeks to complete, which has adverse economic and societal impacts on the affected population. This paper proposes an automated framework for rapid postearthquake building evaluation. Under the framework, the visible damage (cracks and spalling) inflicted on RC members (columns) is detected using machine vision. The damage properties are then measured in relationship to the column’s dimensions and orientation, so that the existing state of the column can be approximated as a damage index. The column damage index is then used to query fragility curves of similar buildings, constructed from the analyses of existing and ongoing experimental data. The framework is expected to automate the collection of building damage data, to provide a quantitative assessment of the building damage...

An innovative seismic bracing system based on a superelastic shape memory alloy ring

Shape memory alloys (SMAs) have great potential in seismic applications because of their remarkable superelasticity. Seismic bracing systems based on SMAs can mitigate the damage caused by earthquakes. The current study investigates a bracing system based on an SMA ring which is capable of both re-centering and energy dissipation. This lateral force resisting system is a cross-braced system consisting of an SMA ring and four tension-only cable assemblies, which can be applied to both new construction and seismic retrofit. The performance of this bracing system is examined through a quasi-static cyclic loading test and finite element (FE) analysis. This paper describes the experimental design in detail, discusses the experimental results, compares the performance with other bracing systems based on SMAs, and presents an Abaqus FE model calibrated on the basis of experimental results to simulate the superelastic behavior of the SMA ring. The experimental results indicate that the seismic performance of this system is promising in terms of damping and re-centering. The FE model can be used in the simulation of building structures using the proposed bracing system.

Automated Damage Index Estimation of Reinforced Concrete Columns for Post-Earthquake Evaluations

The safety of buildings which have been affected by a natural disaster such as an earthquake is currently evaluated manually by certified inspectors who identify visible damage on the structural elements. This process has been proven to be time-consuming, costly, and can delay the response and recovery. In order to automate this type of assessment, it is necessary to automatically determine the damage state of the individual structural members. Previously, the writers have created novel methods for automated detection of RC columns as well as significant damage on the column surfaces (spalling and cracking). This paper presents a novel method of automatically determining the damage state of RC columns in RC frame buildings based only on the automatically detected damage and column information. In addition, the novel method automatically determines an associated engineering demand parameter, residual drift capacity. All of the methods previously developed by the writers are combined with the method presented in this paper and the results are compared with those of manual assessment procedures. The method was implemented using computer software and its effectiveness was confirmed with this comparison

Parameterized Seismic Fragility Curves for Curved Multi-frame Concrete Box-Girder Bridges Using Bayesian Parameter Estimation

ABSTRACT 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.

Modeling and Fragility Analysis of Non-Ductile Reinforced Concrete Buildings in Low-to-Moderate Seismic Zones

Reinforced concrete buildings in low-to-moderate seismic zones are often designed only for gravity loads in accordance with the non-seismic detailing provisions. Deficient detailing of columns and beam-column joints can lead to unpredictable brittle failures even under moderate earthquakes. Therefore, a reliable estimate of structural response is required for the seismic evaluation of these structures. For this purpose, analytical models for both interior and exterior slab-beam-column subassemblages and for a 1/3 scale model frame were implemented into the nonlinear finite element platform OpenSees. Comparison between the analytical results and experimental data available in the literature is carried out using nonlinear pushover analyses and nonlinear time history analysis for the subassemblages and the model frame, respectively. Furthermore, the seismic fragility assessment of reinforced concrete buildings is performed on a set of non-ductile frames using nonlinear time history analyses. The fragility curves, which are developed for various damage states for the maximum interstory drift ratio are characterized in terms of peak ground acceleration and spectral acceleration using a suite of ground motions representative of the seismic hazard in the region.

Seismic fragility assessment of long-span cable-stayed bridges in China

In the existing fragility assessment, most bridges are short-span bridges and a few bridges have long spans such as cable-stayed bridges. In this study, a procedure is proposed to conduct the component and system seismic fragility analysis of long-span cable-stayed bridges. Three critical issues are addressed in the procedure: (1) the optimal intensity measure of cable-stayed bridges, (2) limit state models of various components, and (3) contribution of individual components to the entire system failure of bridges. This study chooses a long-span cable-stayed bridge with the most common configuration in China and builds the numerical model of its multiple components using OpenSEES that can account for their nonlinear response and uncertainties in the ground motion and material properties. Four typical intensity measures are compared with respect to four characteristic properties including efficiency, practicality, sufficiency, and proficiency. Peak ground velocity turns out to be the optimal intensity measure. Limit states of pylon sections are derived by a numerical simulation based on pushover analysis and China’s guidelines. The pushover results indicate that the limit state of their section curvature depends highly on the section type and axial compression coefficient. A joint probabilistic seismic demand model and Monte Carlo simulation are employed to obtain an accurate system fragility estimate of cable-stayed bridges by accounting for the contribution of each component to the overall bridge system. The system fragility curves based on Monte Carlo simulation lie much closer to the upper bound fragilities given small correlation coefficients, implying that seismic demands of various components conditioned on the peak ground velocity are not correlated.

Response Analysis of RC Bridge Piers due In Multiple Earthquakes

In this paper, the effect of cumulative damage for reinforced concrete bridge piers subjected to both single and multiple earthquakes is investigated. For this purpose, selected are three set of accelerograms one of which represents the real successive input ground motions, recorded at the same station with three months time interval. The analytical predictions indicate that piers are in general subjected to a large number of inelastic cycles and increased ductility demand due to multiple earthquakes, and hence more damage in terms of stiffness degradation is expected to occur. In addition, displacement ductility demand demonstrates that inelastic seismic response of piers can significantly be affected by the applied input ground motion characteristics. Also evaluated is the effect of multiple earthquakes on the response with shear. Comparative studies between the cases with and without shear indicate that stiffness degradation and hence reduction in energy dissipation capacity of piers are pronounced due to the multiple earthquakes combined with shear. It is thus concluded that the effect of multiple earthquakes should be taken into account for the stability assessment of reinforced concrete bridge piers.

Application of Bayesian Methods to Probabilistic Seismic Demand Analyses of Concrete Box-Girder Bridges

This paper proposes a set of probabilistic demand models of bridge components using the Bayesian parameter estimation method. To develop probabilistic demand models of individual bridge components, the material, structural, and geometric properties used in the bridge models serve as independent variables and the response data of engineering demand parameters for individual components monitored from the analyses serve as dependent response variables. To illustrate the proposed methodology, a typical reinforced two span, three frame curved concrete box-girder bridge in California is selected as a case study. Probabilistic numerical bridge models are developed, and then nonlinear time history analyses are performed using a set of ground motions representative of the seismic hazard. The significant input parameters are identified through a stepwise removal process in the Bayesian approach. The demand models generated in the Bayesian approach provides a more reliable estimation of the seismic demand compared to the traditional approach in which the ground motion intensity measure is the only input parameter.

Adjustment Factors to Account for the Effect of Bridge Deck Horizontal Curvature on the Seismic Response of Concrete Box-Girder Bridges in California

This research suggests adjustment factors to account for the effect of bridge deck horizontal curvature on the probabilistic seismic demand model (PSDMs) and fragility curves of concrete box-girder bridges in California. For this purpose, typical configurations of horizontally curved bridges in California are selected to create detailed three-dimensional (3-D) probabilistic bridge models with different levels of bridge deck horizontal curvature. Simulation results from the nonlinear time history analysis (NLTHA) of bridges are used to compare the PSDM of individual bridge components using a statistical technique called analysis of covariance (ANCOVA). Comparison results are used to group bridge classes and to suggest adjustment factors. Grouping results indicate that the PSDMs of unseating and bearing displacement are statistically significant for bridges with different levels of deck horizontal curvature. The effect of deck curvature and the use of the modification factors are demonstrated in this paper through the generation of fragility curves.

System fragility curves for a long multi-frame bridge under differential support motions

The paper presents the seismic fragility assessment of a long multi-frame bridge subjected to differential support motions. For this purpose, a bridge experiencing the 1992 Landers earthquake is first chosen as the subject bridge and its numerical model is created using OpenSees. Nonlinear time-history analyses for the model under both uniform and multi-support motions recorded during the earthquake are performed and the simulated deck deformations are compared with the recorded sensor data. The results highlight the significance of multi-support motions along with an appropriate bridge model. For the derivation of fragility curves of the bridge, the conditional simulation of spatially variable ground motions is undertaken to obtain a set of acceleration time histories at different supports, which are converted into a set of displacement time histories. A set of analyses for the simulated motions are conducted on statistical realizations of the bridge model reflecting material and structural uncertainties to monitor the seismic demand of components. Accordingly, a new analytical formulation for the intensity measure is introduced to consider the spatial correlation of ground motions. Given the demands and limit states, component fragility curves are developed on the basis of the closed form, and system fragility curves are developed using Monte Carlo simulation. The fragility results reveal that a reduction in the average shear wave velocity results in an increase in the exceedance probabilities at higher limit states and thus the increase of bridge vulnerability.