The rapid growth of the transportation market has led to a substantial increase in road freight volume, thereby subjecting existing highway bridges to elevated traffic flows and vehicular loads. Consequently, the need for accurate safety assessment techniques and rational decision-making methods to allocate resources for maintenance and repair has become paramount. Reliability-based decision-making has emerged as a robust methodology to address these challenges. Reliability-based approaches are widely adopted to quantify bridge safety and make informed decisions that ensure the longevity and safe use of bridges.
Shrinkage and creep, intrinsic behaviors of concrete, induce additional deformation in prestressed concrete bridges over time, leading to internal force redistribution and deformation. Such effects can result in unfavorable outcomes, including the cracking of bridge decks and the loss of prestress, ultimately impacting the durability of these structures. Therefore, understanding the effects of shrinkage and creep in prestressed concrete bridges is crucial. However, existing analyses often overlook the coupled effects of these phenomena on deflection evolution and stress redistribution. Recent research has begun to address this issue and considered the effects of creep and shrinkage on prestressed concrete box girder bridges. Nonetheless, these analyses often focus on specific aspects, leaving room for further exploration.
Accurate modeling of vehicle loads is paramount for calculating bridge load-carrying capacity, reliability assessment, and lifespan prediction. Previous research has often simplified traffic loads to stationary random processes. However, with the progressive increase in traffic volume, fatigue damage accumulation becomes a critical factor leading to the failure of PC bridges. Addressing these practical challenges, various researchers have introduced time-varying reliability assessment methods, considering the effects of traffic loads and material deterioration.
In a new study published in the peer-reviewed Journal Structures by Mr. Heng Zhou, Associate Professor Xueping Fan and Associate Professor Yuefei Liu from Lanzhou University, and Professor Dagang Lu from Harbin Institute of Technology introduced a methodological approach for evaluating the time-varying reliability of simply supported prestressed concrete girder bridges, taking into account the effects of traffic loads, concrete shrinkage, and creep. The significance of this research lies in its potential to inform rational decision-making for bridge maintenance and repair, ultimately extending the service life and safety of these essential structures.
The research team simulated real traffic loads and address the time-varying reliability of simply supported prestressed concrete bridges, accounting for the effects of concrete shrinkage and creep during their service life. The approach involves simulating random traffic flows using monitored Weigh-In-Motion (WIM) data. The finite element method, in conjunction with MATLAB programming, is utilized to analyze the internal forces and deformations of these bridges. Moreover, the effects of shrinkage and creep on load effects are evaluated, leading to a comprehensive understanding of bridge behavior. Reliability analysis methods are then employed to assess the safety of the bridges over time.
The authors introduced a random vehicle model that takes into account various parameters such as vehicle type, weight, distance, and speed. By leveraging statistical information from existing research, the simulation of stochastic traffic flows that closely resemble real traffic loads is achieved. This foundational work provides insight into bridge responses under the influence of vehicle flows. The Monte Carlo method in MATLAB is used to generate the sequence of random traffic flow, which is then incorporated into the DLOAD subroutine for analysis.
The study’s findings hold important implications for assessing the time-varying reliability of simply supported prestressed concrete girder bridges. By considering the effects of concrete shrinkage, creep, and traffic loads, the proposed methodology offers a comprehensive approach to bridge safety assessment. Notably, the study underscores the need to account for shrinkage, creep, and structural deterioration in the assessment of prestressed concrete bridge conditions. Comparisons across different bridge types reveal valuable insights into the effects of span length and the number of main girders on shrinkage and creep. Furthermore, the utilization of the first-passage probability method demonstrates computational efficiency without compromising accuracy.
According to the corresponding author and in a statement to Advances in Engineering: Professor Xueping Fan said: the new study presents a robust framework for evaluating the time-varying reliability of simply supported prestressed concrete girder bridges. By integrating real traffic load simulations, finite element analysis, and reliability assessment methods, the research contributes to the field of bridge safety and maintenance. This work exemplifies the synergy between engineering principles and statistical techniques, culminating in a holistic understanding of bridge behavior and performance over time.
Heng Zhou, Xueping Fan, Yuefei Liu, Dagang Lu. Time-variant reliability analysis of simply supported PC girder bridges considering shrinkage, creep, resistance degradation and vehicle load flows. Structures, Volume 56, 2023, 104885.