Dan Su

Cracking in concrete deck has been the major concern to bridge designers as well as owners. Excessive cracking not only would affect the performance and serviceability of the bridge but also reduce the service life of the concrete deck and increase the maintenance cost. It is proven that many factors could cause the cracking of concrete deck including restrained shrinkage, temperature effects, applied live load, and improper construction sequence. Among these factors, appropriate construction staging plays an important role in minimizing the cracking of concrete deck, especially for multiple span continuous bridges. However, the construction staging has not been subjected to detailed research in the past. Therefore, it is important to evaluate the current concrete deck construction staging practice and propose an optimized construction staging for multiple span continuous bridges, if needed. In this study, the research approach adopted is aimed at investigating the cracking of a typical multiple-span continuous bridge, evaluating the construction staging, and providing an optimized practice for deck construction staging. A typical three-span continuous bridge was selected for investigation and various types of sensors were instrumented on the bridge to monitor the behavior of the structure during and after construction. The finite-element (FE) model was developed and validated with the data collected from field testing. Based on FE analysis and experimental data, the cracking of the bridge deck was investigated and alternative construction staging scenarios were simulated and compared. Moreover, based on analysis results, an optimized deck construction staging practice was recommended for future use.

Transit agencies own and operate thousands of bridge structures subjected to repetitive train loading. The majority of these bridges were built at the turn of the century and many have exceeded their theoretical fatigue life spans. In New Jersey, the recent increase of the railcar weight limit from 1,170 kN (263,000 lb) to 1,272 kN (286,000 lb) raised concerns for railway bridges that have been in service for more than a century. To prioritize and schedule repairs and rehabilitation events, there is a need to establish refined procedures that would be able to estimate the impact of the increased railcar weight on the remaining life and damage accumulation of bridges. In this paper, three typical railway bridges with various span lengths were selected. Field testing was performed to validate the three-dimensional (3D) finite-element (FE) models of the bridges. A probabilistic approach was developed for fatigue evaluation. For fatigue resistance, a new model was proposed based on previous full-scale fatigue tests. The variance of fatigue resistance increases when the stress range increases based on test results. The new 1,272-kN freight car and its frequency are found to have a significant effect near the supports in terms of remaining fatigue life. Midspan location would not always be the most critical location of the bridge when operating the heavier railcars. An increase of 1,000 freight trains annually will decrease the remaining fatigue life by approximately 2 years. Last, the introduction of heavier railcars will have more significant effects on shorter spans.

Highway flyover bridges in New Jersey experienced extensive early-age cracking on the high performance concrete deck recently. There were transverse cracks observed predominantly in the positive moment regions and spider cracks concentrated in the negative moment region over the box beam. A typical two-span curved continuous bridge with high performance concrete (HPC) deck, steel girders and integral box-beam was selected to identify factors that affect early-age HPC deck cracking so as to mitigate the cracking issues on existing concrete continuous bridges. Extensive field tests were performed and various structural responses were collected for model calibration and structural analysis. Cracking issues due to effects of vertical temperature differentials, staging, shrinkage, settlement, tilt of piers, dead load, live load, etc., were quantitatively investigated and summarized through parametric study. Of prime interest has been the identification of the contributions of various effects on deck cr...

Structural health monitoring provides an efficient way to monitor and evaluate the performance of infrastructure. With the introduction of new materials and construction methods, various types of bridges are being instrumented with monitoring devices to determine their performance as well as their response to various loading conditions. Among many other objectives, this includes monitoring concrete deck cracking behavior, measuring time-dependent deformations such as camber and deflection, evaluate and load rate existing bridges, and validation of new design or construction provisions. In this study, various types of instrumentation techniques were used to monitor and test bridges. The monitoring and testing results incorporated with Finite Element Modeling (FEM) hereafter can be used to evaluate the performance and cracking potential of new concrete deck for highway bridges, which would improve the construction techniques and extend the service life of the structure. Moreover, since most of the railway bridges in New Jersey are approaching 100 years of age and these bridges experiences different degree of deterioration due to repeated live loads and environmental effects during their service years. This paper developed a refined method to load rate and evaluate the performance of the bridge using structural health monitoring and field testing.

This paper presents a simplified live load model based on a general solution in order to allow a rigorous and more accurate fatigue analysis procedure due to vehicular loads. Based on the least square estimation technique, truck loads measured using an elaborate Weight-In-Motion (WIM) database were categorized into limited groups and each group of trucks was represented by one truck model with determined parameters such as axle number, axle spacing and axle load ratio. The performance of the proposed simplification approach was demonstrated using numerical simulations. Results show that the proposed approach is quite effective in simplifying vehicular loads with acceptable error of equivalent stresses and in further estimating fatigue service life of orthotropic steel deck (OSD) bridges.