Behrouz Shafei

Estimation of Corrosion Initiation Time in Reinforced Concrete Bridge Columns: How to Incorporate Spatial and Temporal Uncertainties

AbstractDeterioration of reinforced concrete structures has been a subject of interest for the researchers, practicing engineers, and decision makers who work on the reliability assessment and safety evaluation of civil infrastructure systems. Over the last two decades, several studies have approached this subject and developed numerical and experimental methods to quantify the extent of deterioration over time. The studies completed to date, however, lack the comprehensive probabilistic approach needed to consider the uncertainties involved in the deterioration of structural components during their service life. To address this issue, the current study develops a computational framework that examines the time-dependent effects of multiple environmental stressors on the integrity of structural components. This framework takes into account the mutual interactions of all exposure factors and provides a reliable estimate of the extent of penetration of deteriorating agents into concrete. Given the capabiliti...

Seismic Resilience of Transportation Networks with Deteriorating Components

AbstractPerformance assessment of a transportation network is naturally a complicated problem. This is mainly due to the fact that such a spatially distributed network is subjected to a variety of natural hazards and environmental stressors while it consists of a range of components with different ages. Among various components of a transportation network, bridges are known to be the most important but vulnerable components. Previous efforts to investigate the functionality of transportation networks, especially after earthquake events, have proven that damage to highway bridges may directly cause a major degradation in the functionality of the entire network. Considering the extensive socioeconomic consequences of network disruptions, the main focus of the current study is on the seismic resilience assessment of highway bridge networks exposed to deterioration processes. While this study provides a comprehensive computational framework to include several sources of uncertainty that must be taken into acc...

Assessment of Postearthquake Losses in a Network of Aging Bridges

AbstractThe current study approaches the issue of deteriorating civil infrastructure components in a systematic manner through microscale, mesoscale, and macroscale investigations. At the microscale, the integrity of individual network components is examined considering the extent of deterioration due to aggressive environmental conditions and climatic effects. For this purpose, the deterioration of structural members is evaluated through a detailed finite-element framework and the corresponding structural models are updated at regular time intervals to capture the effects of aging mechanisms. To quantify the vulnerability of deteriorating components subjected to earthquake events, a series of nonlinear time-history analyses are performed and time-dependent seismic fragility curves are generated. Based on the state of damage in the network components under a set of scenario earthquakes, appropriate damage indexes are introduced to measure the postevent functionality of the network at the mesoscale. Throug...

Reactive Molecular Dynamics Simulations to Understand Mechanical Response of Thaumasite under Temperature and Strain Rate Effects

Understanding the structural, thermal, and mechanical properties of thaumasite is of great interest to the cement industry, mainly because it is the phase responsible for the aging and deterioration of civil infrastructures made of cementitious materials attacked by external sources of sulfate. Despite the importance, effects of temperature and strain rate on the mechanical response of thaumasite had remained unexplored prior to the current study, in which the mechanical properties of thaumasite are fully characterized using the reactive molecular dynamics (RMD) method. With employing a first-principles based reactive force field, the RMD simulations enable the description of bond dissociation and formation under realistic conditions. From the stress-strain curves of thaumasite generated in the x, y, and z directions, the tensile strength, Youngs modulus, and fracture strain are determined for the three orthogonal directions. During the course of each simulation, the chemical bonds undergoing tensile deformations are monitored to reveal the bonds responsible for the mechanical strength of thaumasite. The temperature increase is found to accelerate the bond breaking rate and consequently the degradation of mechanical properties of thaumasite, while the strain rate only leads to a slight enhancement of them for the ranges considered in this study.

Management of Bridges Under Aging Mechanisms and Extreme Events: Risk-Based Approach

Current bridge management systems predict the condition state of bridge elements primarily on the basis of the extent of continuous structural deterioration. Although the existing systems deliver a range of capabilities for the management of bridges under normal operational conditions, these systems do not take into account the consequences of sudden extreme events in a systematic way. Considering the uncertainties involved in natural and manufactured hazards in addition to the ones associated with environmental exposure conditions, there is a critical need to develop risk-based approaches that not only take into account the site-specific aging mechanisms and extreme events at the same time but also accommodate the spatial and temporal randomness originated from them. This study introduced a risk-based, life-cycle analysis framework to be implemented in the current bridge management systems used by the transportation agencies. A set of representative bridges exposed to environmental stressors and seismic hazards was investigated to demonstrate the capabilities of this framework. The condition states of the bridges were predicted in accordance with the Markovian transition matrices that were generated for both aging mechanisms and seismic events. The outcome of this study highlights how the developed framework can contribute to improve the life-cycle performance and cost predictions, especially when the adverse effects of extreme events cannot be neglected in the management of bridges.

Impact of Extreme Events on Transportation Infrastructure in Iowa: A Bayesian Network Approach

Iowa’s roadway network is an important part of the state’s transportation infrastructure and plays a critical role in the functionality and economic development of the entire state. This network primarily consists of three interstate highways that pass through Iowa, connecting it to the neighboring states and eventually Canada. Various businesses are located near this roadway network and rely on it for everyday operation. In recent years, however, the growth of agricultural and biofuel industries has intensified the demand on the roads and bridges in Iowa. The state’s roads and bridges have also witnessed a number of flooding events, which have caused extensive traffic disruptions and economic losses. Thus, it is imperative to develop a fundamental approach to evaluate the impact of extreme events on the transportation infrastructure of Iowa and other similar states. Towards this goal, the current study investigates the existing condition of Iowa’s transportation infrastructure, possibility of occurrence of extreme weather events, and scenarios that may lead to the failure of transportation infrastructure components. For this purpose, the capabilities of Bayesian belief networks are utilized to quantify the effects of extreme precipitation and extreme temperature on the performance of transportation infrastructure and then predict the probability of damage to roads and bridges. This will be achieved through the identification of the most influential factors using a set of sensitivity analyses, assessment of overall vulnerability with evidence-based propagation analyses, and quantification of response to extreme weather events, taking into consideration climate projections.

Flexural Performance Evaluation of Fiber-Reinforced Concrete Incorporating Multiple Macro-Synthetic Fibers

Fiber-reinforced concrete (FRC) is a promising construction material mainly because of the crack-controlling mechanisms that discrete fibers can impart to inherently brittle concrete. Macrofibers, in particular, have been proven effective for providing post-crack ductility and toughness, while synthetic fibers are a promising solution to avoid corrosion-related durability issues. To assess the performance enhancement provided by macro-synthetic concrete fibers, this study performs flexural tests on FRC beams containing three different types of macro-synthetic fibers. The selected fibers include polypropylene (PP), polyvinyl alcohol (PVA), and alkali-resistant glass (ARG) macrofibers mixed at volume fractions of 0.5%, 1.0%, and 1.5%. Static and dynamic fresh properties are monitored using the vibrating Kelly ball (VKelly) test. Beam specimens are then placed under a third point bending configuration, as per ASTM C1609 Standard, to measure load versus mid-span deflection. Strength and toughness parameters are derived from the load–deflection data to assess the flexural performance of the FRC composite systems under consideration. The parameters of interest include first peak strength (pre-crack flexural strength) and post-crack residual strength and toughness provided by fiber addition. Of the mixtures tested, ARG fiber mixtures show the highest residual strength and toughness values, followed by PP and PVA fiber mixtures. ARG fibers produce the most workable mixtures at all fiber volumes, while PVA fibers show a tendency to encounter dispersion issues at higher volume doses. The outcome of this study is expected to facilitate the selection of fibers by giving insight into their relative contribution to fresh and hardened flexural properties of FRC.