John O. Sobanjo

Development of a triboluminescence-based sensor system for concrete structures

The triboluminescence phenomenon has been proposed as a sensor system for detecting and monitoring damage in aerospace and civil infrastructure systems (CIS). While significant work is being done in developing such systems for aerospace structures, little or no work is being done in developing triboluminescence-based sensor systems for the critical and aging CIS. This article reports some findings in the work being done by the authors to develop such a sensor system for civil infrastructure applications. A ZnS:Mn-based cementitious patch that emits light when stressed or fractured was developed and its triboluminescence performance under loading characterized. The results show that a ZnS:Mn concentration level of 10% gives the best triboluminescence response without adversely affecting the compressive strength of the patch, while also minimizing the use of the expensive ZnS:Mn crystals. The triboluminescence response increased as the concentration of ZnS:Mn in the system increased. The highest triboluminescence response was obtained at a concentration level of 25% but resulted in significant reduction in the system’s compressive strength. Nonetheless, the presence of ZnS:Mn affects the hydration process by slowing down the conversion of the needle-shaped crystals of calcium sulfoaluminate hydrate (ettringites) into the monosulfate hydrate that makes concrete vulnerable to sulfate attack.

Causative Factors and Trends in Florida Pedestrian Crashes

A case study review of 353 fatal pedestrian crashes that occurred in Florida, primarily in 2000, identified contributing causes and trends of predominant pedestrian crash types. Researchers reviewed state records, traffic crash reports, traffic homicide investigative report narratives, diagrams, and photographs and incorporated select accident reconstructions and site visits. Results indicate that the most significant causes of pedestrian crashes are pedestrian behavior, alcohol use by pedestrians and drivers, poor pedestrian visibility at night coupled with violation of driver expectation, and lack of compliance with state laws. Some form of pedestrian behavior was the primary contributing factor in more than three-fourths of the pedestrian crashes reviewed. Alcohol use by the pedestrian or the driver was determined as the primary factor in 45% of the cases. Where alcohol use was determinable, 69% of pedestrians crossing not in crosswalks were under the influence. Dark conditions or insufficient lighting...

State transition probabilities in bridge deterioration based on Weibull sojourn times

This paper presents an investigation of the Markov property underlying the stochastic deterioration models for highway bridges, including transition probabilities between the condition states. Using historical data of sojourn times for the ‘decay’ (no improvement intervention) deterioration, hazard functions were developed and ‘instantaneous’ 1 year transition probabilities estimated for the sojourn times in the condition states, for various bridge categories, by type of material and roadway carried. The rate of transition out of each state was found to be not constant relative to time, as assumed for Markov chain models, but rather, increasing with the time spent in the state. Best-fit distributions of the sojourn times were determined to not be exponential (Markov chain), but Weibull, with the parameters established using the maximum likelihood estimate (MLE) method. A semi-Markov model of the bridge deterioration process was formulated and developed, including kernels of transition probabilities and time-based matrices of multi-step transition probability functions.

Effect of Construction Induced Vibrations on Green Concrete in Drilled Shafts

This study was concerned with vibrations induced during drilled shaft construction on green concrete in adjacent drilled shafts. To characterize the types of vibrations, a full-scale field test was conducted using a 0.9-m (3-ft)-diameter steel casing vibrated at a peak particle velocity (ppv) of 250 mm/s (10 in./s) to various depths in a sandy soil layer. In addition to the steel casing, the peak particle velocities were recorded at different distances and depths from the vibration source. Empirical relationships from measurements were developed to predict the velocity values on the surface and in the ground along the penetration depth of the steel casing. Laboratory tests were conducted on two groups of green concrete samples to determine the effect of ppv and curing time on concrete properties. These tests showed a 10% reduction in the 28-day compressive strength for samples subjected to continuous vibration at ppv of 50 mm/s (2 in./s) for a duration ranging from the initial to the final setting time. O...

Modeling the Risk of Advanced Deterioration in Bridge Management Systems

The Florida Department of Transportation (DOT) has developed a set of risk models for its bridge management system; the models are built into its existing Excel-based project-level and network-level decision support tools and are intended for eventual use in AASHTOs Pontis 5.2. One of these new models is an analysis of the risk associated with advanced deterioration. This model extends the reach of Floridas existing deterioration models to estimate the likelihood of service disruption if a badly deteriorated element should be unrepaired. The Florida DOT maintains data about demolished and replaced bridges as inactive records in its Pontis database. The condition and characteristics of the removed bridges were statistically analyzed to explore the reasons for the end of each bridges life. On the basis of the available data, including information on load posting and reconstruction, the likelihood of service disruption was reasonably quantified. The best models developed in the research used a combination of linear and lognormal forms and reflected the buildup of risk caused by repeated Markovian deterioration as well as the typical delay that occurred between the observation of the deteriorated conditions and the resulting action to replace or reconstruct the bridge. As a by-product of the research, a linear failure probability model was developed; the model is suitable for Pontis releases up to 4.5. This model will be helpful to bridge owners who do not have their own source of estimates for the probability of bridge element failure.

Estimating agency cost of maintenance, repair, and rehabilitation for Florida bridges

The Florida Department of Transportation (FDOT) recently conducted a study to develop agency cost factors for maintenance, rehabilitation, and repair (MR&R) of bridges, for the state’s implementation of the AASHTOWare Pontis® Bridge Management System. The study analyzed three information systems on maintenance and construction history available at the FDOT. Pontis defines many combinations of bridge element, environment, condition, and feasible action, resulting in more unit cost values than can be estimated from the available data. To simplify cost determination, a classification scheme (MR&R Action Sub-category) was devised to group the Pontis combinations. Statistical analysis was performed on the raw cost data to extract useful numbers from the available data sources. The results were supplemented with the judgment of an FDOT panel of experts. Although the panel found the analysis of historical data to be useful for 70% of the actions considered, only 50% of the actions had a statistically significant sample, and only 15% were usable directly from a statistical analysis. The main issues were differences in data collection units and differences or uncertainties in the scope of recorded actions. The study recommended improvements in the automated systems to enhance the ability to use the data in future updates of the agency cost model.

Evaluating Transportation User Costs Based on Simulated Regional Network Models

Bridges are important infrastructure and essential components of a transportation network. Temporary, long-term, and partial closures of bridges can result in enormous cost implications. However, bridge closures are inevitable not only because of the likelihood of hazard-induced damages but also because routine maintenance, repair, and rehabilitation activities may also warrant closures. It is current practice that vehicles are rerouted to the shortest alternative route during bridge closures (the detour approach). In this study, a scenario-based network approach for evaluating the impact of bridge closures on transportation user cost was undertaken and is proposed in this paper. Both the detour-based and network-based approaches were applied to the Tampa Bay, Florida, regional network model, and five bridge closure scenarios were considered. User costs were computed in terms of delay and vehicle operating costs. For closures to the I-275, Gandy, Highway 580, and West Courtney Campbell Causeway bridges, there were increases of about 42%, 18%, 61%, and 45%, respectively, in total user costs for the network-based approach compared with the current detour-only approach. These findings indicate that a significant network impact was captured by the network-based approach. The proposed method captures the effects of bridge closures on all road segments within the regional network jurisdiction; provides a more rigid framework for analysis by ensuring that user costs are computed efficiently but without overestimation; takes into account that road users may have advance knowledge of roadway conditions before trips and that this knowledge may significantly influence route choices; and provides sufficient information for agencies to implement preemptive measures to cater for network-level disruptions attributable to bridge closures.

Framework for incorporating nondestructive evaluation (NDE) into pavement and bridge management systems

One of the major components of an infrastructure management system is the condition assessment or deterioration modeling. With application to highway pavements and bridges, this paper presents conceptually how nondestructive evaluation (NDE) results can be utilized to provide a quantitative assessment of the infrastructure condition in a format usable for network-level pavement management systems and bridge management systems. NDE techniques typically applied to pavements include Visual Rating, Falling Weight Deflectometer, Dynaflect, Seismic Pavement Analyzer, and the Ground Penetrating Radar (GPR). Bridges can also be evaluated using the GPR. NDE is particularly useful at the network level of infrastructure management because of the mobility of conducting the tests. Detailed mechanistic methods have been suggested for NDE interpretation but this method may not be practical at network level. Interpretation of NDE results, through knowledge-based systems and intelligent databases indicate the defects and residual capacity of infrastructures. Measured physical properties and defects in the infrastructure component materials can be correlated to existing scales of condition assessment such as in the NBI and PONTIS formats for bridge management and also to an index or rating such as the PSI in highway pavements.

Bridge Health Index: Study of Element Condition States and Importance Weights

The AASHTO Pontis bridge management system has been used to support network-level and project-level decision making on the condition and functional obsolescence of bridges. State departments of transportation often develop bridge inspection data collection methods, deterioration models, cost models, and other preservation analysis capabilities to comply with the requirements of the federal Government Accounting Standards Board. The bridge health index (BHI) in the Pontis bridge management system has been used in the evaluation of the condition of bridges and elements at the project and network levels. This paper investigates three issues in the computation of the BHI: the effects of using linear and nonlinear scales for the condition state weights when computing the element health index (EHI); the application of amplification weights to EHI values to emphasize bridge elements in bad condition; and the development of element weights based on element replacement costs, element long-term costs, element vulnerability to hazard risks, and a combination of these measures. Historical condition data from element-based inspection were used to evaluate these effects at the network level.

Modeling Hurricane Hazards and Damage on Florida Bridges

The state of Florida is developing a risk-based decision support model, specifically for its state-maintained bridges, to handle the occurrence of natural hazards, such as hurricanes, tornadoes, floods, landslides, and wildfires. Many bridges in Florida are vulnerable to damage caused by these hazards. With a focus on hurricanes, this paper develops prediction models (estimates of likelihoods) based on historical data of hazard events in Florida, as well as on existing national models. The Poisson process was assumed for the occurrence of natural events; predictions were estimated for the annual probability of occurrence. It was observed that, on average, the probability of hurricane occurrence at bridge locations decreased with the hurricane intensity (category number). In comparison, wildfires, another common hazard, had the highest likelihood estimates of the natural hazards. With a focus on physical damage to bridges, the consequences of hurricanes were also estimated on the basis of historical data within Florida. The damaged bridge components and elements were identified, and the levels of damage and the associated repair costs were assessed.