Prestressed Concrete Bridge Research Articles

Corrosion effects on strands of PT bridges

In recent years, partial failures and collapses involving existing Post – Tensioned (PT) bridges highlighted the need for their structural assessment. Most of existing bridges are approaching the end of their nominal life and constitutive materials have undergone, over the decades, relevant degradation phenomena with dangerous consequences at both local and global level. A good knowledge of material properties, structural details and of the actual maintenance condition of the bridge is then required, especially if we consider that hidden defects – i.e. defects that are not visible without specific investigations – can be responsible of the activation of unexpected brittle failures. Corrosion of prestressing steel cables represents one of the most relevant aspect to investigate, being related to phenomena (such as localized pitting or hydrogen embrittlement) that cannot be detected without specific investigation techniques but that are responsible for relevant decrease of the mechanical properties of materials and modification of the failure modality. Predictive models calibrated basing on experimental results, may represent in presence of aggressive environmental conditions may represent an efficient tool for describing corrosion effects on the mechanical properties of strands and evaluating residual performance.The present work shows preliminary results of a wide experimental test campaign executed on corroded steel strands extracted from an existing prestressed concrete bridge with post-tensioned steel cables; hydrogen embrittlement effects are well visible on the mechanical properties of corroded strands. The peculiarity of the work lies in the availability of naturally corroded strands, with well-known external agents (rain, air, etc.) and exposure period. Preliminary results of FEM analyses on models calibrated basing on experimental tests’ results are even presented.

Finite-Element-Based Study on Girder Behavior and Load-Sharing of Shear-Connected Multigirder Prestressed Concrete Bridges

Finite-Element-Based Study on Girder Behavior and Load-Sharing of Shear-Connected Multigirder Prestressed Concrete Bridges

Construction Monitoring and Analysis of Asymmetric Prestressed Concrete Bridge Crossing Multiple-Line Railways

Construction Monitoring and Analysis of Asymmetric Prestressed Concrete Bridge Crossing Multiple-Line Railways

Influence of chloride-induced corrosion on the traffic vulnerability of simply supported Italian PC bridges: a preliminary study

In Italy, a large part of road bridges was built after the Second World War, mainly with Reinforced Concrete (RC) or Prestressed Concrete (PC) simply supported decks. Most of the bridges currently in service have been designed with outdated codes and could be inadequate to modern heavy traffic loads. Furthermore, their structural performance decrease over time due to ageing effects, like steel corrosion.Bridges are often exposed to chlorides from de-icing salts or marine environment; chloride diffusion in concrete can induce pitting corrosion of steel reinforcing, decreasing the structural resistance of bridge elements. As part of a broader study on the structural risk of existing bridges with respect to traffic loads, it is certainly of interest to investigate the influence of chloride-induced corrosion on the risk itself.In this preliminary study, four sets of simply supported decks made of precast PC beams and a cast in-situ RC slab were designed according to outdated Italian codes relating to different construction periods (60s, 70s, 80s, and 90s); each set is composed by bridges with different span, width, number of main girders and transverse diaphragms. The deck design took into account only the bending failure of the main girders, in order to determine the minimum amount of strands and steel reinforcements required. The vulnerability to traffic loads is evaluated with respect to the bending moment resistance of the main girders. Monte Carlo simulations were performed to evaluate the decrease over time of the resisting bending moment of the main girders, taking into account literature models for estimating the time to corrosion and corrosion propagation both in strands and in steel reinforcements.

The Risk of Failure Assessment in Bina Marga Standard Designed Prestressed Concrete Girder Bridges under B-WIM Load Measurement

The use of precast prestressed concrete girder bridges in Indonesia has been increasing rapidly due to their high quality, reliability, and faster construction on site. The girder components are typically designed for a specific bridge span and can be prefabricated. The Directorate General of Highways of the Ministry of PUPR (Bina Marga) has released a standard design for prestressed concrete girder bridges with a typical span of up to 40 m. This design is based on the bridge loading standard SNI 1725 2016, which determines the live traffic load through consensus due to limited data on actual traffic load measurement results. However, the Ministry of PUPR has been implementing actual traffic load measurements using weigh-in-motion (WIM) technology to directly measure the load of passing vehicles. In this study, a risk assessment of the failure risk of a standard Bina Marga bridge with a 40-m span prestressed concrete girder type was conducted based on B-WIM load measurements. The results of this assessment indicate that the standard Bina Marga bridge has a failure risk of 1.48 x 10-4, which is smaller than the acceptable risk of failure according to the AASHTO LRFD Bridge Design Specification as referenced in SNI 1725 2016.

Seismic performance and damage control of large-span prestressed concrete rigid-frame bridges with high piers crossing strike-slip faults

Post-earthquake surveys show that fault-crossing simply supported beam bridges or continuous beam bridges suffer from severe seismic damage, such as falling beams and even collapse. Currently, there is a lack of understanding of the seismic performance of fault-crossing prestressed concrete rigid-frame bridges (PCRFBs). In this study, a representative PCRFB was used as a case study, and typical strike-slip fault cases were discussed, including fault-crossing angles and permanent displacement. The results revealed that different from other bridge structure types, the mid-span section was prone to yield failure because of the significant plastic deformation demands when the fault crossed the middle span. Positive and negative moment failures of the mid-span girder occurred when the fault-crossing angle was greater than or less than 90°, respectively. The fault-crossing angle is an important factor that affects the seismic performance of PCRFBs. A value of 90° is a favorable fault-crossing angle with minimal damage. The deformation demands of the mid-span were larger than the internal force effects when there was an increase in the permanent ground displacement of the fault. The proposed shock-absorbing hinge system (SAHS) can effectively reduce the vertical displacement of the girder and can significantly avoid the occurrence of plastic hinges, so the main girder is protected.

Evaluation of minimum flexural reinforcement for precast prestressed concrete NEXT beam bridges

The minimum flexural reinforcement requirement has been used in the current bridge design specifications to protect the member from brittle failure after the formation of the first flexural cracks. Several variables have been reported to affect this requirement, such as concrete strength, amount of prestressing in the member, and type of cross section. Recently, the Precast/Prestressed Concrete Institute (PCI) developed a new type of beam section (NEXT beam) to accelerate bridge construction and enhance the sustainability of bridges. As a newly developed beam section, no research on the minimum flexural reinforcement has been reported for NEXT beam bridges. This paper aimed to examine the minimum flexural reinforcement requirements in the current AASHTO LRFD Bridge Design Specifications for NEXT beam bridges. A comprehensive parametric study was analytically conducted with various parameters, including bridge section, beam section, concrete strength, and span length. The results from this study showed that the current minimum flexural reinforcement requirements were met for all bridges examined herein; the concrete strength, beam cross section, and span length could affect the levels of safety against brittle failure after first flexural cracks for NEXT beam bridges.

Reliability-Based Service III Evaluation for Prestressed Girder Bridges Under Platoon Loads

Platooning may benefit heavy truck transportation through fuel savings, reduced congestion, enhanced safety, and lower emissions. In the future, platoons may be able to act as mobile-WIM stations, and their permit process and allowable load limits may differ from unregulated trucks in a convoy. Previous reliability-based studies have focused on the Strength I limit state and have shown that trucks can operate at weights exceeding standard legal load limits even with short headways at operating-level reliability. However, the Service III limit state often governs prestressed concrete bridges. The AASHTO Manual for Bridge Evaluation does not specify a target reliability index (β) nor reliability-based evaluation guidance for the Service III limit state. The work presented here performed reliability analyses to investigate implicit reliability indices (βImplicit) inferred from bridges designed according to current and past AASHTO criteria, as well as cracking probabilities. Design live loads were used to evaluate the Service III limit state for prestressed concrete NU I-girder bridges, optimally designed using LRFD and LFD/allowable stress design (ASD). Various span lengths, numbers, continuity conditions, prestress loss methods, and allowable tension stress levels were considered. Cracking probabilities ranged between 10% and 67%, which indicates that optimally designed bridges may crack during their service life. Although beyond the scope of the study, the present work suggests a reexamination of service behavior and performance is appropriate, using an alternate mechanistic approach to estimate potential cyclic damage and aid life-cycle assessment. Such assessments could provide a more rational framework for platoon operations while maintaining bridge health and safety.

Bayesian-optimized interpretable surrogate model for seismic demand prediction of urban highway bridges

Urban highway bridges are crucial for regional economic development and population mobility, but they are vulnerable to seismic hazards. Accurately predicting the seismic demands of bridges is essential. Several commonly-used methods for seismic demand estimates, such as cloud analysis, incremental dynamic analysis, and multiple stripe analysis, are computationally expensive and subject to theoretical assumptions and convergence issues, especially for portfolios of bridges. Machine learning techniques can be effective, but their lack of interpretability hinders understanding of the surrogate model's predictions. To address these challenges, this study develops a Bayesian-optimized interpretable ensemble learning surrogate model for predicting and interpreting the critical seismic demands of urban highway bridges.Thousands of continuous prestressed concrete girder bridges with typical geometric configurations in China are generated, and 120 ground motion records with different frequency, waveform, and duration characteristics are chosen. The seismic demand dataset is established based on nonlinear time-history analyses for urban highway bridges, accounting for different types of uncertainties. The surrogate models are developed based on the XGBoost ensemble learning method, with hyperparameters automatically and efficiently determined by Bayesian optimization technique. Compared to the random search and grid search methods, Bayesian optimization is approximately 8 times and 29 times faster, respectively, and it also achieves the highest prediction accuracy. Meanwhile, the relationship of each hyperparameter in the surrogate model is also revealed. The prediction results of the proposed model are compared with other machine learning models. The SHAP algorithm is subsequently used to explain the model predictions regarding the feature importance, global interpretations, and feature dependency analysis. The study quantifies the contribution of each structural feature and seismic intensity measure to the selected critical seismic demand and identifies the interaction effects between different input variables in the prediction.

Structural behavior of skewed prestress concrete superstructure

The construction of span-skewed bridges has become widespread worldwide and in Turkey. This article focuses on the structural behavior of simply supported prestressed concrete bridges with varying skewness angles. Specifically, supported I girder pretensioned prestressed concrete bridges are investigated using different models (five models) with skewness angles 0° - 21°- 37.6°- 57°–66.6°. These models are analyzed using the Midas Civil software to analyze and design various bridge components and types through the finite element method. This method employs the most commonly accepted codes worldwide. This research showed that shear forces and bending moments were significantly affected by increasing the degree of skewness angle when it exceeds 37.5°. External I-girders behavior was similar yet inversely proportional behavior. Internal I-girder behavior was also identical but inversely, too.

Finite Element Analysis of Chloride Ingress in Prestressed Concrete Bridge Girders Accounting for Service-Life Ambient Conditions

Finite Element Analysis of Chloride Ingress in Prestressed Concrete Bridge Girders Accounting for Service-Life Ambient Conditions

Strengthening of Precast Segmental Bridge built in 1960s using External Tendons

AbstractRecently more attention has been paid to ageing infrastructure under increased traffic on the roads in Slovakia. As a result, selected prestressed concrete bridges have been inspected. Evidence of their poor technical condition has been discovered including serious faults such as large permanent deflection, wide cracks, extensive prestressing degradation, and others. The original conceptual design and poor quality of prestressing steel protection are often the decisive factor. This paper provides an example of bridge rehabilitation design of the concrete precast segmental bridge in an emergency condition. The bridge in question which is located over the water reservoir Ruzin was built in 1967 as one of the first‐generation precast segmental bridges in Slovakia. Its service life was successfully extended using structural system modification and strengthened using external prestressing. The initial assumptions for the rehabilitation have been based on the detailed analysis of the defects, and assessment of existing conditions including the analytical approach of residual prestressing determination. This concept represents the potential solution for achieving enhanced service life of similar bridges.

Multidimensional nonlinear numerical simulation of post‐tensioned concrete girders with different prestressing levels

AbstractMost of the Italian infrastructures have been built since the mid‐twentieth century. Prestressed concrete (PC) has been widely used, especially for bridges and viaducts. These structures have proved effective over time, but their performance could be affected by degradation phenomena (i.e., corrosion of the tendons and residual prestressing) or construction defects (i.e., grouting of the ducts), which need to be accurately modeled. This paper focuses on the flexural response of two reduced‐scale, posttensioned, PC bridge girders, prestressed with two different jacking forces and tested under four‐point bending configuration. Four multidimensional numerical models were developed to simulate the experimental behaviors of the selected specimens, using two alternative computational strategies, namely, the finite element method (FEM) and applied element method (AEM). Three FEM modeling were considered, ranging from one‐dimensional lumped‐plasticity models to two‐dimensional and three‐dimensional (3D) spread‐plasticity models. Besides, 3D AEM models were developed into another software package. The accuracy and the computational costs of the two numerical strategies are discussed in this paper. Also, the main features of each numerical modeling technique are addressed, including comparisons between numerical and experimental global response data as well as the statistical characterization of the model error. Based on these different features, the authors also suggest the most suitable numerical strategy for future studies on PC girders.

Rapid Prestressed Concrete Retrofit with Prestressed Mechanically-Fastened Fiber-Reinforced Polymer: Field Performance and Observation for a Deteriorated Prestressed Concrete Bridge

This paper presents repairs to rural bridges in North Carolina that deteriorated as a result variously of aging, overweight traffic, and exposure to salts and sulfates. The prestressed concrete C-channel superstructures exhibited prestressing strand loss and displayed significant concrete spalling, with one structure having to be closed to traffic after a routine inspection. Analysis conducted using the American Association of State Highway and Transportations Officials (AASHTO) bridge load rating criteria concluded that repair techniques which strengthen deteriorated flexural elements without also restoring lost prestressing forces are insufficient to maintain load ratings in C-channel structures with heavily damaged prestressing tendons. A prestressed mechanically-fastened fiber-reinforced polymer (MF-FRP) retrofit solution was developed and successfully installed on three structures by the authors and North Carolina Department of Transportation maintenance crews. The most extensive of these three repairs is presented here in detail. The field applications and associated analysis show the temporary MF-FRP repair system is capable of restoring lost prestressing forces, allowing original inventory and operating ratings to remain in place until a permanent superstructure replacement can be scheduled. The most heavily repaired bridge remains in service after 23 months, its performance demonstrated by long-term monitoring data. As currently implemented, the MF-FRP repair is a viable temporary solution for maintaining traffic on a degraded structure while a replacement structure is designed, programmed, and implemented. Efforts to expand the MF-FRP repair into a longer-term solution are underway.

Comparison of Seismic Upgrading Techniques Applied to an Existing Prestressed Concrete Bridge

Comparison of Seismic Upgrading Techniques Applied to an Existing Prestressed Concrete Bridge

Stochastic analysis for bending capacity of precast prestressed concrete bridge piers using Monte-Carlo simulation and gradient boosted regression trees algorithm

The use of precast prestressed concrete bridge piers is rapidly evolving and widely applied. Nevertheless, the probabilistic behavior of the bending performance of precast prestressed concrete bridge piers has often been overlooked. This study aims to address this issue by utilizing actual precast bridge piers as the engineering context. Through the implementation of the Monte-Carlo simulation and Gradient Boosted Regression Trees (GBRT) algorithm, the stochastic distribution of the bending performance and their critical factors are identified. The results show that the normal distribution is the most suitable for the random distribution of bending performance indicators. The variability of the elastic modulus of ordinary steel bars, initial strain of prestressed steel hinge wires, and constant load axial force has little effect on the bending moment performance, while the yield stress of ordinary steel bars, elastic modulus of concrete, compressive strength of unrestrained concrete, and elastic modulus of prestressed steel hinge wires have a greater impact on the bending performance. Additionally, the compressive strength of unrestrained concrete has a significant influence on the equivalent bending moment of the cross-section that concerns designers.

A simplified ANN-based evaluation method for creep sensitive girder bridge identification at preliminary design stage

Excessive deflection which exceeded expectations has been identified as one of the main problems contributing to long-term performance degradation of long-span girder bridges. Although the 3D refined finite element model of the full bridge can improve the prediction accuracy of long-term creep deformation, there is still a lack of efficient creep-sensitive structural judgment methods in the preliminary design stage. This study was thus intended to develop a new evaluation method and model to identify the possibility of excessive deflection will occur by utilizing simple structural design parameters, which contributed to new understandings of the creep deformation of bridge structural level. A finite element model database established by 20 long-span prestressed concrete girder bridges with actual project backgrounds was used for providing training, testing, and validation sample datasets for the artificial neural networks (ANN). The Back Propagation (BP) model was chosen for creating mappings among variables and results and solving complex problems with a fairly accurate prediction even without sufficient information. The indicator of deflection-span ratio difference between creep models was proposed as the key analysis factor. A case study was conducted to validate the effectiveness of the ANN model. The mean absolute error (MAE) between the results of the ANN model and FE analysis was 6.25%, which indicated a high consistency. The analysis of bridge design parameters using the ANN model revealed that it had a high risk of excessive deformation, which was consistent with the conclusion of the actual situation. Multiparameter sensitivity analysis results from the model also suggest that the side-span ratio, the main span, and the deflection caused by the pavement are the most three significant impacts compared to different input variables in this model. Based on the results, it can be concluded that the performance of the ANN-based technique can predict possible excessive creep problems in advance.

Time-variant reliability analysis of simply supported PC girder bridges considering shrinkage, creep, resistance degradation and vehicle load flows

The long-term performance of simply supported Prestressed Concrete (PC) girder bridges exhibits dynamic characteristics because of concrete shrinkage, concrete creep, resistance degradation and vehicle load flows. The vehicle loads are non-stationary and random, which interacts with concrete shrinkage, concrete creep and resistance degradation to cause dynamic changes of bridge internal force and deformation, further, bridge dynamic reliability occurs. This study presented a reasonable method for calculating the time-varying reliability of simply supported PC girder bridges under the effects of traffic loads and concrete shrinkage creep. Stochastic truck-load models were simulated based on site-specific weigh-in-motion measurements, then the internal forces of the bridge were calculated when the mean value of vehicle loads increases by 1% per year. Considering the resistance degradation and load effect increase, the PC bridge reliability for serviceability limit state and capacity-carrying ultimate state were analyzed using first-passage probability method and Monte-Carlo method, respectively. The accuracy of the proposed method was verified by comparison. The evaluation results show that the failure probability including concrete shrinkage and creep has increased significantly, creep is affected by the bridge span and the number of main girders, and the reliability assessment results are safer for bridges with smaller spans.

Dynamic identification of an aging prestressed concrete bridge using heavy vehicle excitation

Non-destructive evaluation of aging infrastructures can be useful in evaluating the safety and assuring uninterrupted operation during earthquakes and other natural hazards. Due to the lack of information regarding the structural and material properties, non-destructive evaluation of aging bridges in operation becomes further challenging. This is because numerical modeling using structural mechanics approach is associated with large uncertainties. Such uncertainties can be reduced by dynamic identification methods. Vibration properties of such bridges inferred from dynamic identification can be used to update finite element models of such bridges, which can subsequently be used in safety evaluation. We present a case study of such an application on a 420 m long prestressed concrete bridge. Traffic induced accelerations measured on the bridge deck are used to infer vibration frequencies of the bridge using parametric as well as non-parametric system identification methods. Vibration frequencies inferred from system identification were then used to update the finite element model of the bridge. The results show that vehicle induced vibrations can effectively identify the fundamental vibration frequency of the bridge while higher mode frequencies and damping ratios are more challenging to identify.

Topology Optimization of Continuous Precast Prestressed Concrete Bridge Girders Using Shape Memory Alloys

Despite the growing interest in the concept of topology optimization, its acceptance in civil structures, especially in prestressed concrete structures, is still faced with practical obstacles primarily due to the geometric complexities of optimized structures. Quite often, complex concrete topology yields a complex distribution of tensile zones, which are hard to be effectively prestressed with continuous steel reinforcement. Shape memory alloys (SMAs), with their ability to apply localized prestressing force only at target tensile regions, can offer solutions to the issues facing conventional prestressing steel reinforcement in topology-optimized concrete structures. This paper investigates the topology optimization of prestressed concrete bridge girders using locally prestressed SMAs. A prototype continuous concrete bridge is selected to be optimized under the AASHTO loading conditions. To prove the feasibility of the optimized design, a detailed 3D finite element analysis is performed. The performance of the optimized girder is compared with that of two commonly used conventional designs. The results show that the optimized design can effectively satisfy the AASHTO limit state with less material than the conventional cases.