Jong-Wha Bai

Fragility estimates of smart structures with sensor faults

In this paper, the impact of sensor faults within smart structures is investigated using seismic fragility analysis techniques. Seismic fragility analysis is one of the methods used to evaluate the vulnerability of structural systems under a broad range of earthquake events. It would play an important role in estimating seismic losses and in the decision making process based on vibration control performance of the smart structures during seismic events. In this study, a three-story building employing a highly nonlinear hysteretic magnetorheological (MR) damper is analyzed to estimate the seismic fragility of the smart control system. Different levels of sensor damage scenarios for smart structures are considered to provide a better understanding of the expected fragility estimates due to the impact of sensor failures. Probabilistic demand models are constructed with a Bayesian updating approach while the seismic capacity of smart structures is estimated based on the approximate structural performance of semi-actively controlled structures. Peak ground acceleration (PGA) of ground motion is used as a measure of earthquake intensity. Then the fragility curves for the smart structures are developed and compared with those for the semi-active control systems with different levels of sensor damage scenarios. The responses of an uncontrolled structure are used as a baseline. It is shown from the simulations that the proposed methodology is effective in quantifying the impact of sensor faults within smart structures.

Seismic vulnerability assessment of tilt-up concrete structures

This paper focuses on seismic vulnerability assessment for one-story tilt-up concrete structures. To capture the potential failure mechanisms, an analytical modelling approach using nonlinear properties is developed and verified with measured data from a shake table test documented in the literature. Nonlinear dynamic analyses using synthetic ground motions for Memphis, Tennessee, are performed to assess dynamic behaviour of the buildings. Then, probabilistic demand models for multiple limit states that represent potential failure mechanisms are developed with a Bayesian updating approach. These demand models are used in conjunction with appropriate capacity limits to develop fragility curves that provide a probabilistic measure of the seismic vulnerability of typical tilt-up concrete buildings. This study shows that the vulnerability of typical tilt-up structures in Mid-America is significant when seismic hazards are high. In addition, it is found that the aspect ratio of building geometry has a significant impact on the seismic performance and fragility estimates of tilt-up buildings.

Case Study: Scenario-Based Seismic Loss Estimation for Concrete Buildings in Mid-America

This paper focuses on probabilistic loss estimation of concrete buildings subject to seismic activity in the Central United States. The scenario earthquakes under consideration have three moment magnitudes, and Shelby County, Tennessee, is selected as the case study region. The buildings considered are typical reinforced concrete frame buildings and tilt-up concrete buildings in this region. Fragility curves based on recently developed demand models are used to represent the seismic vulnerability of the buildings. The structural damage of the selected buildings is assessed with a probabilistic approach that uses empirical structural damage factors and accounts for the prevailing uncertainties. Finally, corresponding losses for the buildings are estimated using a probabilistic framework. Through this approach, critical structures that might be expected to have extensive damage are identified. Additionally, the result of the scenario-based approach provides decision makers with information needed to prioritize mitigation options for high risk structures due to potential earthquakes.

Probabilistic Shear Capacity Models for Concrete Members with Internal Composite Reinforcement

AbstractThis paper presents probabilistic models for estimating shear capacity of concrete members reinforced internally with fiber-reinforced polymer (FRP). The application of FRP in concrete structures has steadily gained popularity since the late 1980s; however, the wide range of mechanical properties and various manufacturing processes have made it challenging to unify the design formulation for engineers and code developers. Consequently, the conservative approach has been used to predict structural performance, particularly shear capacity, which has limited its application and resulted in excessive use of materials. In this paper, a robust prediction model is proposed to capture the variety of characteristics of FRPs based on an available database. The database includes various FRPs used as flexural reinforcement for beam members. The model was formulated using the Bayesian parameter estimation method, which takes into account the uncertainties of the parameters that are considered the potential pre...

Seismic Fragility Analysis of Faulty Smart Structures

In this chapter, seismic vulnerability of smart structures is assessed using fragility analysis framework. The fragility analysis framework is effective to evaluate the performance and the vulnerability of structures under a variety of earthquake loads. To demonstrate the effectiveness of the seismic fragility analysis framework, a three-story steel frame building employing the nonlinear smart damping system is selected as a case study structure. To investigate the impact of sensor failures, various sensor damage case scenarios are considered. The seismic capacity of the smart building is determined based on the typical structural performance levels used in the literature. The unknown parameters for the seismic demand models are estimated using a Bayesian updating algorithm. Finally, the fragility curves of the smart structures under a variety of sensor damage cases are compared. It is proved from the extensive simulations that the proposed seismic fragility analysis framework is very effective in estimating the control performance of smart structures with sensor faults.

Seismic performance and retrofit for tilt-up concrete buildings in Mid-America

Seismic risk is a concern in the Mid-America region because of the series of severe earthquakes that occurred in the New Madrid Seismic Zone in 1811-1812. Many existing concrete structures in this area are considered to be vulnerable in a moderate to significant seismic event because they were not designed for the seismic provisions of the current International Building Code. Seismic performance assessment and fragility analysis are used to evaluate the seismic vulnerability of existing structures. Based on these analyses, possible retrofit techniques are considered to reduce structural damage and corresponding losses. Based on available inventory data for Memphis, Tennessee, tilt-up concrete buildings are the most common type of concrete structure in Memphis. Tilt-up construction is commonly used for low-rise industrial buildings and has several advantages, including a large open space and low construction costs. However, many tilt-up concrete buildings were damaged during previous earthquakes in the Western U.S. and other regions. Typical damage included collapse of wall panels and roof diaphragms due connection failures. To improve seismic performance of tilt-up concrete buildings, several seismic retrofit techniques are currently used including the addition of anchors to strengthen the roof-to-wall connections.

Probabilistic Assessment of Structural Seismic Damage for Buildings in Mid-America

This paper provides an approach to conduct a probabilistic assessment of structural damage due to seismic events with an application to typical building structures in Mid‐America. The developed methodology includes modified damage state classifications based on the ATC‐13 and ATC‐38 damage states and the ATC‐38 database of building damage. Damage factors are assigned to each damage state to quantify structural damage as a percentage of structural replacement cost. To account for the inherent uncertainties, these factors are expressed as random variables with a Beta distribution. A set of fragility curves, quantifying the structural vulnerability of a building, is mapped onto the developed methodology to determine the expected structural damage. The total structural damage factor for a given seismic intensity is then calculated using a probabilistic approach. Prediction and confidence bands are also constructed to account for the prevailing uncertainties. The expected seismic structural damage is assessed ...