Qindan Huang

Probabilistic Seismic Demand Models and Fragility Estimates for Reinforced Concrete Highway Bridges with One Single-Column Bent

In performance-based seismic design, general and practical seismic demand models of structures are essential. This paper proposes a general methodology to construct probabilistic demand models for reinforced concrete (RC) highway bridges with one single-column bent. The developed probabilistic models consider the dependence of the seismic demands on the ground motion characteristics and the prevailing uncertainties, including uncertainties in the structural properties, statistical uncertainties, and model errors. Probabilistic models for seismic deformation, shear, and bivariate deformation-shear demands are developed by adding correction terms to deterministic demand models currently used in practice. The correction terms remove the bias and improve the accuracy of the deterministic models, complement the deterministic models with ground motion intensity measures that are critical for determining the seismic demands, and preserve the simplicity of the deterministic models to facilitate the practical application of the proposed probabilistic models. The demand data used for developing the models are obtained from 60 representative configurations of finite-element models of RC bridges with one single-column bent subjected to a large number of representative seismic ground motions. The ground motions include near-field and ordinary records, and the soil amplification due to different soil characteristics is considered. A Bayesian updating approach and an all possible subset model selection are used to assess the unknown model parameters and select the correction terms. Combined with previously developed capacity models, the proposed seismic demand models can be used to estimate the seismic fragility of RC bridges with one single-column bent. Seismic fragility is defined as the conditional probability that the demand quantity of interest attains or exceeds a specified capacity level for given values of the earthquake intensity measures. As an application, the univariate deformation and shear fragilities and the bivariate deformation-shear fragility are assessed for an example bridge.

Predicting Concrete Compressive Strength Using Ultrasonic Pulse Velocity and Rebound Number

This paper shows how, as a general index of concrete strength, the compressive strength of concrete f(c) is important in the performance assessment of existing reinforced concrete (RC) structures. The paper shows how many nondestructive testing methods have been developed to estimate the in-place value of f(c). In particular, the combination of rebound hammer and ultrasonic pulse velocity tests, known as SonReb, is frequently used. With the SonReb measurements, regression models are commonly applied to predict f(c). The available regression models are not sufficiently valid, however, because of the limited range of data used for their calibration. This paper proposes a probabilistic multivariable linear regression model to predict f(c) using SonReb measurements and additional concrete properties. The Bayesian updating rule and the all possible subsets model selection are used to develop the proposed model based on the collected data with a wide range of concrete properties. The proposed model is compared with currently available regression models, concluding that the proposed model gives, on average, a more accurate prediction.

Cost-benefit evaluation of self-centring concentrically braced frames considering uncertainties

Abstract Self-centring concentrically braced frame (SC-CBF) systems have been developed to reduce post-earthquake damages in braced frames. However, due to special details required by the SC-CBF system, the construction cost of an SC-CBF is expected to be higher than that of a conventional CBF. In this study, the seismic performance and economic effectiveness of two prototype buildings utilising SC-CBFs are assessed and compared with buildings utilising conventional CBFs by evaluating the annual probabilities of exceeding various damage levels, expected annual losses, life cycle costs (under seismic hazard) and economic benefit of using SC-CBFs considering prevailing uncertainties. The results of this study show that the SC-CBF buildings have lower drift-related losses but higher acceleration-related losses. The SC-CBF is found to be beneficial for the 6-storey configuration, but not for the 10-storey configuration. For the 6-storey buildings studied here, if the construction cost of the SC-CBF is assumed to be twice that of the CBF, the pay-off time is expected to be 12 to 21 years, with a probability of 68%, considering the uncertainties in the demand, capacity, loss parameters and initial construction costs. Finally, appropriate probabilistic engineering demand parameter model formulation is critical for generating accurate loss analysis results.

Time-Dependent Reliability Analysis on the Flexural Behavior of Corroded RC Beams before and after Repairing

It has been recognized that the quantitative performance evaluation of corroded reinforced concrete (RC) structures could aid in developing effective repair strategies. However, the current performance evaluation only focuses on the ultimate strengths criteria and do not consider the serviceability requirements. To consider both criteria and to facilitate the analysis, an analytical procedure is proposed for predicting the load-deflection behavior of intact and corroded RC beams. The corrosion effects considered here include the effects of corrosion on the area and yielding strength of the rebars, and the bond stress-slip behavior at the steel-concrete interface. The proposed procedure is then utilized to evaluate the time-dependent reliability of an RC beam with and without repair in terms of flexural strength and deflection performances. The effects of relative humidity and mixture design are also studied.

Load-Deflection Behavior Prediction of Intact and Corroded RC Bridge Beams with or without Lap Splices Considering Bond Stress-Slip Effect

AbstractIn the design and performance evaluation of RC structures, different quantities, such as ultimate strength, serviceability, and ductility, need to be considered. Because these quantities deal with both strength and deflection, the nonlinear load-deflection prediction of RC bridges becomes essential. In this paper, an analytical procedure is proposed for predicting the flexural behavior of intact and corroded RC beams with or without lap splices considering the bond stress-slip behavior at the steel–concrete interface. The accuracy of the proposed procedure is verified through several experimental and numerical case studies. Last, the proposed procedure is applied to predict the flexural behavior of intact and corroded T-beams of a RC bridge, and the results are verified through the finite-element analyses.

Structural and Nonstructural Performance Evaluation of Self- Centering Concentrically Braced Frames Under Seismic Loading

Self-centering concentrically braced frame (SC-CBF) systems have higher drift capacity than conventional CBF systems prior to damage. To fully demonstrate the effectiveness of SC-CBF systems, a comparison study is performed considering both structural and nonstructural seismic performance. First, two prototype buildings are designed with the same configuration but different lateral load resisting systems (CBF or SC-CBF exclusively). Nonlinear dynamic analysis is conducted using finite element numerical modeling to obtain seismic responses under a suite of earthquake records with various hazard levels. The numerical results are then utilized to build probabilistic demand models of inter-story drift, floor acceleration, and roof acceleration. Finally, fragility curves for structural and nonstructural components are generated for various performance levels with demands and capacities. The comparison of the fragilities of the two structural systems reveals that the SC-CBF has better seismic performance than the conventional CBF; however, nonstructural components must be designed for higher force demands in the SC-CBF.

Adaptive reliability analysis of reinforced concrete bridges using nondestructive testing

Seismic fragility reflects the ability of a structure to withstand future seismic demands. To obtain an accurate assessment of seismic fragility, it is critical to incorporate information about the current structural properties. This paper describes a probabilistic framework to incorporate information from nondestructive testing (NDT) in the estimates of the seismic fragility of a reinforced concrete (RC) bridge. The proposed framework combines global and local damage detection methods to incorporate information from nondestructive testing (NDT) on the properties of an existing bridge. As an illustration, the proposed probabilistic framework is used to assess the seismic fragility of an example reinforced concrete bridge.

Reliability-Based Multiobjective Design Optimization of Reinforced Concrete Bridges Considering Corrosion Effect

AbstractChloride-induced corrosion is known as the dominant cause of premature damage in reinforced concrete (RC) bridges in the United States. However, the current corrosion management strategies ...

Life cycle cost-benefit evaluation of self-centering and conventional concentrically braced frames

Self-centering concentrically braced frame (SC-CBF) systems have been developed to increase the drift capacity of braced frames prior to structural damage. To achieve the improved seismic performance of SC-CBF system, the construction cost of an SC-CBF is expected to be higher than that of a conventional CBF. In this study, economic effectiveness of using an SC-CBF instead of a CBF in one prototype building is calculated to indicate the time that initial SC-CBF construction costs are compensated by lower earthquake-induced losses in the lifetime of the building (pay-off time). The results of this study show lower business interruption is the most significant component of the economic benefit of the SC-CBF compared to the CBF. Moreover, the pay-off time increases dramatically if the initial construction cost of the SC-CBF is more than 4% higher than the CBF. Earthquake-induced damages of buildings can cause social and economic disturbances. Selfcentering concentrically braced frame (SC-CBF) systems (Roke et al. 2009) have been developed to address the limitations of conventional CBFs by increasing drift capacity of the structure prior to damage and decreasing residual drift; thus SCCBF can mitigate losses due to earthquakes. This improved seismic performance of the SC-CBF system has been found experimentally and numerically (e.g., Roke et al. 2009; Dyanati et al. 2014, 2015). However, the construction cost of an SC-CBF is expected to be higher than that of a conventional CBF due to the special details and elements required by the SC-CBF. Therefore, it is necessary to investigate if the higher construction cost of SC-CBF system would be offset by lower earthquake-induced losses (due to better seismic performance of SC-CBF) during the life time of the building, which would demonstrate the economic effectiveness of SC-CBF systems compared with conventional CBF systems. Life cycle cost assessment has been used as a measure of the economic effectiveness of a structure. Wen & Ang (1991) and Wen & Shinozuka (1998) developed a life cycle cost formulation to investigate the cost effectiveness of an active control system in structures during earthquakes. Goda et al. (2010) used life cycle cost assessment to investigate the cost effectiveness of a seismic isolation technology. Kang & Wen (2000) used the minimum life cycle cost concept to develop an optimal design for structures under single and multiple hazards. Padgett et al. (2009) developed a retrofit strategy for bridges based on cost-benefit analysis using life-cycle cost to determine the most costeffective retrofit method that differs based on the seismic hazard characteristics of the location. Available software such as HAZUS (FEMA 2014) and PACT (FEMA 2012) have been used in the seismic performance and loss evaluation of buildings (Erberik & Elnashai 2006, Parvini sani & Banazadeh 2012) and can also be used for life 12 International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP12 Vancouver, Canada, July 12-15, 2015 2 cycle cost estimation. However, there is a major drawback in both software packages: they both define engineering demand parameter (EDP) models as a function of only one seismic intensity measure (IM), pseudo spectral acceleration (PSA), which may not be accurate for CBF and SC-CBF structures (as studied by Dyanati et al. 2015), eventually leading to inaccuracy in the loss estimation. In this study, the economic benefit of the SC-CBF will be studied using life cycle cost formulation. The economic benefit of the SCCBF, which is the difference between life cycle cost of SC-CBF and CBF structures, will clarify if the higher construction cost of SC-CBF will be compensated by better performance of SC-CBF. 1. SC-CBF SYSTEM The general configuration of an SC-CBF is shown in Figure 1(a). There are two sets of columns in the SC-CBF: SC-CBF columns and adjacent gravity columns. As shown in Figure 1(b), the SC-CBF columns are allowed to uplift at the base, causing a rocking response under higher levels of lateral force. Vertically oriented post-tensioning (PT) bars and gravity loads are used to resist column uplift and provide selfcentering (i.e., reducing residual drift). The rocking behavior softens the lateral force-lateral drift response of the system, thereby permitting larger lateral displacements while limiting the member force demands, avoiding yielding or buckling in the braces. 2. SEISMIC LIFE-CYCLE COST-BENEFIT MODEL Life cycle cost of a building system subjected to seismic hazard includes three components (Kang & Wen 2000): initial construction cost, including structural and non-structural component costs (C0); earthquake-induced losses or life cycle loss of the building (e.g., repair cost, business interruption, injuries) (LCL); and operation/maintenance costs during the life cycle of the building (Cm), as shown in Equation (1).         x x x x m C t LCL C t LCC    , , 0 (1) where LCC = life cycle cost of the structure; t = life time of the structure; and x = vector of design variables for the structure. Figure 1: (a) Configuration of SC-CBF; (b) Rocking behavior of SC-CBF; (c) configuration of CBF. Construction cost estimation is straightforward and can be generally estimated using expert opinions or tools such as R.S. Square Foot Costs (RS Means 2013). Maintenance and operation costs are highly related to the occupancy of the building, rather than the structural system, and can be estimated using handbooks and standards such as Facilities Maintenance & Repair Cost Data Online (RS Means 2013). The life cycle loss (LCL) estimation, on the other hand, involves more complex procedures including hazard, response, damage, and loss analysis for calculating the losses from earthquakes. If the expected annual loss (EAL) from earthquakes is known, the expected value for life cycle loss (E[LCL]) can be evaluated as follows (Porter et al. 2004):     EAL e t LCL E t      1 ] , [ x (2) where e -γt = discounted factor over time t and γ = constant discount rate per year, which is used to calculate the present value of the future losses. Assuming C0,SC-CBF = a C0,CBF (a = relative cost coefficient and a > 1) and equal maintenance/operation costs for CBF and SCCBF systems, the expected economic benefit of using an SC-CBF instead of a CBF in a building, E[BSC-CBF], can then be calculated as follows: 12 International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP12 Vancouver, Canada, July 12-15, 2015 3         CBF SC CBF t CBF CBF SC

Adaptive Reliability Analysis of Reinforced Concrete Bridges Subject to Seismic Loading Using Nondestructive Testing

AbstractSeismic fragility reflects the reliability of a structure to withstand future seismic demands. It is defined as the conditional probability that a structural demand attains or exceeds a specified capacity level for given values of earthquake intensity. In order to obtain an accurate assessment of the seismic fragility, it is critical to incorporate information about the current structural properties, which reflects possible aging and deterioration. This paper proposes an adaptive reliability analysis of bridges using the actual structural properties identified through nondestructive testing (NDT). The proposed methodology combines global and local damage detection methods. Global damage detection uses the dynamic responses of a structure obtained from a vibration NDT to assess the global/equivalent structural properties of the structure and detect potential damage locations. Local damage detection uses local measurements from an NDT technique to identify the local characteristics of the structure ...