Highway agencies are responsible for the optimal expenditure of taxpayer dollars allocated to highway infrastructure. Truck size and weight are regulated by federal legislation, and every state highway agency has its own legal load limits. In addition, state agencies issue permits for trucks with gross vehicle weights that are above legal load limits. However, the effect of overweight trucks on the service life of bridge structures, especially concrete decks, is not explicitly quantified. Detailed research on deterioration models for bridge decks was conducted. Condition ratings of bridge decks in New Jersey from the National Bridge Inventory were used to derive the deterioration of decks over time, and the expected service lives of decks on different highways were obtained. Weigh-in-motion data from stations in New Jersey were used to extract two data sets: “all trucks” and “legal trucks.” The “all trucks” data set was used to develop a deck deterioration model as a function of equivalent wheel load that could be used to estimate expected service life. Finally, bridge life-cycle cost analysis was conducted under two scenarios, one with and the other without overweight trucks, to quantify the economic impact of such trucks on bridge decks. The results indicate that overweight trucks caused more damage on New Jersey state highways than on Interstate highways because of a larger proportion of overweight trucks, heavy wheel loads from overweight trucks, and fewer axles per truck.
State agencies are responsible for making major decisions on allocating the available but limited funds for the maintenance and rehabilitation of bridges. Over the past two decades, the frequency of overweight trucks has kept increasing. Although the AASHTO load and resistance factor design specifications mandate a design life of 75 years, the actual service life will be affected by site-specific loading; local environmental attack, including the application of deicing salts; each agency’s bridge preservation strategy; the funding situation; and routine maintenance. Nowadays, agencies issue more permits for trucks with gross vehicle weights that exceed legal load limits. There is a need, therefore, to quantify the impact of overweight trucks on the service life of bridge girders. This study presents a procedure for investigating the impact of truck loads on bridges in New Jersey through the utilization of bridge inspection reports, truck weigh-in-motion data, and the National Bridge Inventory database. Actual bridge deterioration modes in New Jersey were identified from the bridges’ respective inspection reports, and the expected bridge service life was successfully correlated with truck loading from weigh-in-motion data. The deterioration mode of prestressed concrete (PC) girders was found to be the corrosion of prestressing tendons near the beam ends induced by cracking and spalling of enclosing concrete. The maintenance of deck joints is a major factor that affects the deterioration of PC girders. Additionally, a strong correlation was found between the expected service life of PC girders and overweight truck counts.
Specialized hauling vehicles (SHVs) are short heavy trucks within the legal weight limits but induce higher load effects than routine commercial loads. The Manual for Bridge Evaluation (MBE) adopted a series of single-unit trucks (SUs) to represent this type of vehicle. However, the SUs were introduced without rigorous reliability-based analysis due to the lack of data on SHVs. With the availability of vast amounts of data on weigh-in-motion (WIM) truck weights and configurations, the reliability of steel bridges under the SHVs should be evaluated in a more robust and quantitative manner. Through the utilization of WIM data, the authors quantified the SHVs in terms of percentages of SHVs among all truck traffic, daily average counts of SHVs, and number of axles. The gross vehicle weights (GVWs) and typical configurations of SHVs were investigated. In addition, their load effects were determined and normalized by the corresponding SUs. The maximum live loads corresponding to a return period of 5 years were also extrapolated using normal probability paper (NPP). To evaluate the effectiveness of current load-rating procedures for SHVs, the authors investigated the relationship between the load-rating factors and the corresponding reliability indices for existing bridges using the developed live load parameters based on the WIM data. Results indicated that the current live load factors were not able to provide a uniform and appropriate reliability index at different average daily truck traffic (ADTT) scenarios. This paper thus proposes new live load factors and weight adjustments of SU trucks to provide an adequate and uniform safety margin for the evaluation of steel bridges.
Truck platooning has been demonstrated to possess several advantages in relation to energy savings. To implement this technology in the future, a better understanding of the effects of truck platooning on bridges is needed in relation to safety, serviceability, and remaining service life. This research aims at investigating the effects of truck platooning on the fatigue of steel girder bridges. Different types of platoons are simulated in line girder analysis for simple spans and two-equal continuous spans bridges. Then the rainflow counting method is applied to obtain the stress ranges and cycles. Miner’s rule is used to quantify the fatigue damage. The fatigue damage of different platoons is normalized by American Association of State Highway Transportation Officials Load and Resistance Factor Design Fatigue Load for comparison. The effects of the number of trucks and gap distances of truck platoons are further investigated. In some cases, truck platooning helps decrease the fatigue damage since, although truck platooning brings higher load effects, it also decreases the number of cycles. For platoons with different truck wheelbases, there are specific span to wheelbase ratios, beyond which fatigue damage decreases as gap distance increases. In addition, depending on the platoon configurations, there are ranges of span lengths where it is more beneficial to travel as truck platoons rather than traveling individually in relation to fatigue damage.
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