Habib Tabatabai

Evaluation of a Permit Vehicle Model Using Weigh-in-Motion Truck Records

Permit truck models are used to consider local truck traffic in addition to national live load models in bridge design and rating practices. Weigh-in-motion (WIM) systems installed in the United States provide millions of truck records that can be used for evaluating such truck models. In this study, the standard permit vehicle in Wisconsin was evaluated by using six million WIM truck records collected in 2007. The evaluation was on the basis of statistical analyses of the maximum moments and shear in simply supported, 2-span, and 3-span continuous girders in the selected heaviest 5% of trucks in each vehicle class/group. The comparisons showed that 5-axle, short, single-unit trucks may cause larger moment/shear in bridge girders than the standard permit vehicle, and a 5-axle truck model was proposed to supplement the standard permit vehicle for possible use in bridge design and rating in Wisconsin.

Reliability of Bridge Decks in Wisconsin

An accurate reliability model for bridge decks is important for effective long-term bridge deck management. The main objectives of this paper are to identify the most suitable reliability model for bridge decks in Wisconsin, and to utilize that model for detailed analyzes of bridge deck reliability and failure rates. The 2005 National Bridge Inventory (NBI) data for the State of Wisconsin were used. In this paper, the hypertabastic, Weibull, log logistic, and lognormal distributions are investigated. The end of service life is defined as the age of deck when rehabilitation or replacement is required (herein defined as a deck rating of between 4 and 5). The effects on NBI deck rating of average daily traffic (ADT), type of bridge superstructure (steel or concrete), and the deck surface area were considered. Based on the Akaike information criteria, the hypertabastic accelerated failure time model was selected as the most appropriate model for this study. Results show that deck area, type of superstructure ...

Damage Detection in Structures Using Precursor Transformation Method

In this paper, a new concept for damage detection and long-term health monitoring of structures is presented. The Precursor Transformation Method (PTM) is based on determining the causes (precursors) of change in the measured state of the structure under non-variable loading conditions (e.g., dead loads in bridges). The PTM concept addresses the inability of the current structural monitoring methods to discriminate, in structural behavior terms, the meaning of voluminous measured sensor data on a timely and cost effective basis. This method offers advantages in sensitivity and cost efficiency when compared to conventional vibration-based or parameter estimation methods. PTM was developed as part of a research project sponsored by the Federal Highway Administration on bridge stay cable condition assessment. Measured changes in the state of a structure (displacements, strains, internal forces) can be related to precursors through a transformation matrix. This matrix is formed by determining the patterns of change in the state of structure associated with externally imposed strains (temperatures) or displacements representing possible damage scenarios. A finite element model of the undamaged structure is used to calculate these patterns. The use of an undamaged model of the structure in determining damage patterns simplifies the calculation process significantly, while introducing some approximation in results. Theoretical derivations and special case studies indicate that these approximations are limited to second order effects, and in many cases well within measurement and calculation accuracies. Examples using simulated damages on two truss structures and a cable-stayed bridge are also presented.

Laboratory Assessment of Select Methods of Corrosion Control and Repair in Reinforced Concrete Bridges

Fourteen reinforced concrete laboratory test specimens were used to evaluate a number of corrosion control (CoC) procedures to prolong the life of patch repairs in corrosion-damaged reinforced concrete. These specimens included layered mixed-in chlorides to represent chloride contamination due to deicing salts. All specimens were exposed to accelerated corrosion testing for three months, subjected to patch repairs with various treatments, and further subjected to additional three months of exposure to accelerated corrosion. The use of thermal sprayed zinc, galvanic embedded anodes, epoxy/polyurethane coating, acrylic coating, and an epoxy patch repair material was evaluated individually or in combination. The specimens were assessed with respect to corrosion currents (estimated mass loss), chloride ingress, surface rust staining, and corrosion of the reinforcing steel observed after dissection. Results indicated that when used in patch repair applications, the embedded galvanic anode with top surface coating, galvanic thermal sprayed zinc, and galvanic thermal sprayed zinc with surface coating were more effective in controlling corrosion than the other treatments tested.

Precursor transformation method for damage detection in structures

In this paper, a new concept for damage detection and long- term health monitoring of structures is presented. The Precursor Transformation Method (PTM) is based on determining the causes (precursors) of change in the measured state of the structure under non-variable loading conditions (e.g. dead loads in bridges). The PTM concept addresses the inability of the current structural monitoring methods to discriminate, in structural behavior terms, the meaning of voluminous measured sensor data on a timely and cost effective basis. This method offers advantages in sensitivity and cost efficiency when compared to conventional vibration-based or parameter estimation methods. PTM was developed as part of a research project sponsored by the Federal Highway Administration on bridge stay cable condition assessment. Measured changes in the state of a structure (displacements, strains, internal forces) can be related to precursors through a transformation matrix. This matrix is formed by determining the patterns of change in the state of structure associated with externally imposed strains (temperatures) or displacements representing possible damage scenarios. A finite element model of the undamaged structure is used to calculate these patterns. The use of an undamaged model of the structure in determining damage patterns simplifies the calculation process significantly, while introducing some approximation in results. Theoretical derivations and special case studies indicate that these approximations are limited to second order effects, and in many cases well within measurement and calculation accuracies. Examples using simulated damages on two truss structures and a cable-stayed bridge are also presented.

Acoustic monitoring of containment tendons

Assured safety and operational reliability of post-tensioned concrete components of nuclear power plants are of great significance to the public, electric utilities and regulatory agencies. Prestressing tendons provide the principal reinforcement for 40% of the containment structures in the United States. This paper briefly examines current in-service inspection requirements for prestressed containments and also reviews the feasibility of developing a passive surveillance system for identification of ruptures in tendon wires and its application to a one-tenth scale ring model containment structure.

Residual Tensile Strength and Bond Properties of GFRP Bars after Exposure to Elevated Temperatures

The use of fiber reinforced polymer (FRP) bars in reinforced concrete members enhances corrosion resistance when compared to traditional steel reinforcing bars. Although there is ample research available on the behavior of FRP bars and concrete members reinforced with FRP bars under elevated temperatures (due to fire), there is little published information available on their post-fire residual load capacity. This paper reports residual tensile strength, modulus of elasticity, and bond strength (to concrete) of glass fiber reinforced polymer (GFRP) bars after exposure to elevated temperatures of up to 400 °C and subsequent cooling to an ambient temperature. The results showed that the residual strength generally decreases with increasing temperature exposure. However, as much as 83% of the original tensile strength and 27% of the original bond strength was retained after the specimens were heated to 400 °C and then cooled to ambient temperature. The residual bond strength is a critical parameter in post-fire strength assessments of GFRP-reinforced concrete members.

Evaluation of the Low-Cycle Fatigue Life in Seven Steel Bar Types

AbstractThe low-cycle fatigue (LCF) behavior of steel in energy-dissipating seismic connections is an important consideration, especially in light of the interest in performance-based seismic design. In this study, the LCF performance of seven steel bar types (AISI 8620, 1018, 1045, 1117, 1215, 4140 and ASTM A36 steel) was experimentally examined and compared. The bar specimens were subjected to sinusoidal strains of constant amplitude from zero to peak strains of 4%, 6%, or 8%. Equations that relate the applied strain amplitudes with the number of cycles to failure were developed and compared. In addition, relationships for calculating the total dissipated energy corresponding to the applied strain amplitude were proposed based on the experimental results. This study demonstrated that, in general, the LCF resistance of AISI 1045 steel type outperformed the other steel materials at a strain amplitude of ±2%. However, at ±3 and ±4% strain amplitudes, the LCF lives of ASTM A36 and AISI 1117 bars outperforme...

Reliability of bridge decks in the United States

Deterioration of bridge decks in the United States is an important issue due to its major impact on bridge maintenance costs nationwide. In this paper, results of survival (reliability) analyses performed on bridge data for all fifty states and Puerto Rico are presented. Data were obtained from the 2011 National Bridge Inventory (NBI) database. The end of service life is defined as a recorded NBI bridge deck rating of 5. Only non-reconstructed bridges and conventional bridge types and decks were considered. The NBI-derived parameters included in the analyses were age, average daily traffic (ADT), deck surface area, and deck rating. Each state’s data were analyzed separately to assess and compare relative performance among the states. Deck reliability at an age of fifty years ranges from less than 20% to over 90% . The geographic regions with the highest overall 50-year reliability are generally in the northeastern and northern United States.

Influence of Aggregate Base Layer Variability on Pavement Performance

The objective of this research was to investigate the variability of base layer construction in hot-mix asphalt (HMA) pavements and to assess the impact of base layer variability or nonuniformity on pavement performance. Subjective acceptance criteria of base layer construction may lead to variable pavement performance and may result in early pavement distresses and failure. Eleven existing HMA pavement projects with aggregate base course layers constructed in the past few years were selected for falling weight deflectometer (FWD) testing and visual distress surveys. In six of these projects, issues with aggregate base performance (stability and uniformity) had been observed and reported during paving of the HMA surface layer. Later, these pavements exhibited various levels of early distresses, including cracking (longitudinal, transverse, and alligator), aggregate base failure, and pavement surface roughness or irregularities (for ride quality). The remaining five HMA pavement projects, for which no issues related to aggregate base layer behavior were reported during construction, performed well after construction. A test section of approximately 1 mi on each project was subjected to FWD testing. The existing HMA pavements that showed early distresses exhibited high levels of spatial variability and nonuniformity in aggregate base course layers, as demonstrated by FWD testing and backcalculated base layer modulus values and distributions. The existing HMA pavements that performed well exhibited low levels of spatial variability and good uniformity in aggregate base course layers, as shown by the FWD test results and the backcalculated base layer modulus values and distributions.