Post-tensioned Concrete Box Girder Bridge Research Articles

Assessment and strengthening of post-tensioned concrete box-girder bridges

Post-tensioned concrete box girders have been widely adopted for the construction of medium- to long-span bridges since the mid-20th century. Since the construction of the first such bridges, there has been rapid growth in the volume and weight of heavy vehicles, as well as an increase in exposure to adverse environmental conditions. At the same time, it is estimated that more than 50% of existing bridges in higher-income countries are over half-way through their design life and thus bridge owners are challenged with the management of aging structures. When deterioration in prestressed concrete bridges is identified during inspections, it leads to specific assessments and is usually followed by the need for bespoke strengthening design solutions. In many cases, the challenge in implementing the strengthening resides in maintaining structural capacity to minimise traffic disruption before the works are complete. This article covers the technical and asset management aspects related to the assessment and subsequent strengthening design for post-tensioned concrete box-girder bridges through the lens of case studies on two successful post-tensioned bridge rehabilitations. The strengthening solutions presented have been implemented with minimal disruption to traffic and have had a positive environmental impact by avoiding demolition and full deck reconstruction.

Long-Term Health Monitoring Data Processing on Post-Tensioned Concrete Box-Girder Bridge by Wavelet-Based

The concrete box-girder bridge is designed to have a long service life of around 100 years. To ensure safety and performance degradation during long service life, a Structural Health Monitoring System (SHMS) has been implemented in the box-girder bridge. SHMS can reliably assess structural response due to real-time applied loads, detect anomaly activities and locate the structural damage in the structure. Several sensors have been implemented in the bridge to continuously record the behavior of the bridge in all environmental conditions. Due to real-time natural conditions, false alarms occur frequently in SHM due to the disruption of noises and lead to misunderstanding of who is evaluating. Nevertheless, numerous SHM data that have been collected make it complicated to determine the anomaly of the structures. Therefore, it required signal processing to maximize the potentialities of the massive SHM data, as well as the efficiency of the time work. In this study, wavelet transformation, a rapid and unsupervised signal processing approach, was used to analyze the huge signal data by removing noise, and separating different signal sources as well. Further, with time-frequency analysis and multi-resolution capabilities, the transformation of wavelet is a promising tool for analyzing long-term SHM data. The suggested approach is shown by using long-term strain data from a 40 m concrete box-girder bridge in 24h. The results showed that after the denoising process, the highest discrepancy between the reconstructed and original strain signal is 2.73 μƐ and lost their energy less than 1%. Hence, the strain gauge sensor was successfully able to eliminate the noise through wavelet technology.

An Analytical Model to Evaluate Short- and Long-Term Performances of Post-Tensioned Concrete Box-Girder Bridges Rehabilitated by an Ultrahigh-Performance Concrete Overlay

Potentially unfavorable stress redistributions could occur in post-tensioned concrete box-girder bridges upon deck rehabilitation by an ultrahigh-performance concrete (UHPC) overlay. The reason for such redistributions is that the deck forms an integral part of the load-resisting mechanism so that deck rehabilitation, namely, the process of removing the deteriorated deck and casting a fresh UHPC overlay, may cause large stress redistributions in the box girder. In addition, the significantly different shrinkage behavior between the freshly cast UHPC deck overlay and the old existing concrete deck below would result in restrained stress in the UHPC–old concrete interface. Therefore, how to evaluate the stress redistributions and the potentially unfavorable stresses in the box girder resulting from construction operations and the incompatible shrinkage is a crucial issue. Here, we propose an analytical model to assess the short- and long-term performances of the concrete box girder during and after deck rehabilitation. The analytical model was verified by using finite-element models incorporating the staged construction simulation and time-dependent behavior of materials. The model can be easily established and calculated with a great amount of time-saving compared with finite-element modeling, and it applies to different types of post-tensioned concrete box-girder bridges. The analytical model involves the balancing-load concept and the age-adjusted effective modulus method (AEMM). The balancing-load concept in the short-term analysis is to account for the prestressing force, and the AEMM in the time-dependent analysis is an effective tool to determine how stresses and strains vary with time due to the creep and shrinkage of a UHPC deck overlay. A parametric study was then conducted based on the analytical model, which involved the thickness of the deck layer to be rehabilitated and the addition of steel reinforcement in the new UHPC deck overlay. Analysis results indicated that pronounced tensile stresses developed in the UHPC deck overlay, which resulted from the restraint of the free shrinkage of the UHPC overlay by the subjacent concrete deck. An increase in the thickness of the newly cast UHPC deck overlay resulted in a decrease of the tensile stress in the UHPC deck overlay, and a rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) was deemed appropriate for the selected bridge according to the analysis.

Bridge deck analysis of transversely post-tensioned concrete box girder bridges

For rural bridges in Australia, a common design practice is pouring in-situ concrete on top of beams in order to tie all the beams together and distribute load. However, pouring concrete on-site creates more risk and contractors prefer to avoid it. Another method is using transverse post tensioning to tie beams. This article investigated the behaviour of transverse post-tensioning bars in providing load distribution between beams and ultimately comment on their effectiveness compared to in-situ poured decks. Currently, the industry has not completely investigated this matter in order to design post-tensioning accurately. Conservative estimates are currently used in industry today. Current practice is 50% of the design load on the beam where the load is applied in their design assumptions which is quite high. The team modelled concrete box girder bridges with transverse post-tensioning using grillage method. Several factors were investigated including bridge length and width, bridge skew and beam type. From the models, the team concluded that increasing the bridge span increases the load distribution, the load distribution difference is negligible for skew between 0 and 20 degrees and larger shear actions are observed with increased skew and width. It was determined that the worst-case total load on the beam where the load as applied was found to be 40.5%, 9.5% less than current practice. It is recommended that a similar investigation is conducted using a finite element method to gain a deeper understanding.

Time-Dependent Reliability Assessment and Updating of Post-tensioned Concrete Box Girder Bridges Considering Traffic Environment and Corrosion

AbstractIn the reliability assessment of a bridge in operation with regards to its ultimate limit state, it should be noted that the strengths of members and effects of traffic load vary continuous...

Numerical analysis of bridge deck rehabilitation by ultra-high-performance concrete (UHPC) overlay

Rehabilitating the deteriorated deck of post-tensioned concrete box-girder bridges by ultra-high-performance concrete (UHPC) overlay is studied in this paper. Three post-tensioned concrete box-girder bridges in California were selected for the deck overlay analysis. Rehabilitation construction procedures for each bridge were described, including the practical lane closure and traffic re-routing. Detailed finite element models were established incorporating the staged construction modeling of the rehabilitation process, the time-dependent properties for existing concrete and prestressing tendon, and a “double-layer” modeling technique for the simulation of the deck. The time-dependent curves and equations of a specified UHPC were fitted based on experimental data, including creep, shrinkage, and elastic modulus, and this particular mix has been assumed in the FE analysis. How the thickness of the deck layer to be replaced affected the stress distributions in the UHPC overlay and the existing box girder was parametrically studied. Results indicated that stress variations in the existing box-girder were acceptable during the deck rehabilitation construction, but significant tensile stresses were developed in the newly placed UHPC deck overlay. Shrinkage-mitigation measures, such as adding the shrinkage-reducing admixture (SRA), should be considered during the placement of the UHPC overlay to control the shrinkage-induced tensile stress. Steel reinforcement may be adopted in the negative bending moment region to resist the flexural tensile stress by the live loads. The rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) is deemed appropriate for the bridges selected in this study.

Bridge Deck Replacement of Posttensioned Concrete Box-Girder Bridges

Abstract This paper studies the feasibility of replacing damaged deck of posttensioned concrete box-girder bridges without the use of falsework to support the superstructure span. Parameters of the...

Method and monitoring approach for distributed detection of damage in multi-span continuous bridges

A method for distributed detection of damage along the lengths of multi-span continuous Bridges is introduced. It is based on monitoring the distributed strains along the length of the bridge by using Brillouin scattering based optical fiber sensors. Identification of damage beyond the signal to noise limits of the instrument is achieved by normalization of the measured distributed strains during multiple positions of a truck with respect to the theoretical influence line of the bridge. Formulation of the method leads to the introduction of a damage index for identification of microcrack locations along the spans of the Bridge. Effectiveness of the proposed method was evaluated by load testing of a five span continuous precast post-tensioned concrete box girder bridge. Locations of detected microcracks by the distributed sensor system were further verified by visual inspections.

Sustainable bridge design by metamodel-assisted multi-objective optimization and decision-making under uncertainty

Today, bridge design seeks not only to minimize cost, but also to minimize adverse environmental and social impacts. This multi-criteria decision-making problem is subject to variability of the opinions of stakeholders regarding the importance of criteria for sustainability. As a result, this paper proposes a method for designing and selecting optimally sustainable bridges under the uncertainty of criteria comparison. A Pareto set of solutions is obtained using a metamodel-assisted multi-objective optimization. A new decision-making technique introduces the uncertainty of the decision-maker's preference through triangular distributions and thereby ranks the sustainable bridge designs. The method is illustrated by a case study of a three-span post-tensioned concrete box-girder bridge designed according to the embodied energy, overall safety and corrosion initiation time. In this particular case, 211 efficient solutions are reduced to two preferred solutions which have a probability of being selected of 81.6% and 18.4%. In addition, a sensitivity analysis validates the influence of the uncertainty regarding the decision-making. The approach proposed allows actors involved in the bridge design and decision-making to determine the best sustainable design by finding the probability of a given design being chosen.

Lifetime reliability-based optimization of post-tensioned box-girder bridges

Abstract This paper presents a lifetime reliability-based approach for the optimization of post-tensioned concrete box-girder bridges under corrosion attack. The proposed approach is illustrated by determining the optimal life-cycle cost and CO 2 emissions of several initial designs of post-tensioned box-girder bridges with different objectives, i.e. the lowest initial costs, the longest corrosion initiation time, or the maximum safety. The study was conducted in two steps. Firstly, the Pareto set presents initial designs considering the cross-section geometry, the concrete strength, the reinforcing steel and the prestressing steel. Secondly, the maintenance optimization was conducted with the proposed method, aimed at minimizing the economic, environmental and societal impacts of the bridge while satisfying the reliability target during its life-span. Effective maintenance is able to extend the service life of the bridge with the minimum cost and CO 2 emissions. It is indicated that a durability-conscious initial design is particularly beneficial for life-cycle performance. Besides, the emphasis on the initial design can also have an effect on the life-cycle performance of bridges. It is found that designs with longer corrosion initiation time are associated with lower life-cycle cost, especially when using concrete of higher strength. Findings from the current paper also indicate that optimal maintenance strategies are more likely to be those with fewer maintenance actions that repair all deteriorating structures simultaneously.

A direct monitoring approach for the fatigue safety verification of construction joint details in an existing post-tensioned concrete box-girder bridge

To date, there have been few reports of fatigue problems in medium-span reinforced or prestressed concrete road bridges, primarily due to the high ratio of the dead load to live load in such structures. Where fatigue problems have arisen, they have generally been due to poor detailing issues, sometimes combined with durability problems. One such example is the construction joints of certain post-tensioned concrete road bridges built in Europe during the 1960s and 1970s, which have been found to be fatigue vulnerable. This paper outlines a new approach to the fatigue safety verification of such details incorporating a direct monitoring approach. The study examines the remaining life of construction joint details in a real case study in Switzerland where detailed modelling combined with traditional fatigue load models were found to be insufficient in explaining the real structural behaviour. A long-term monitoring study was performed over three years to accurately determine the real action effects in the reinforcement elements due to thermal and traffic effects and this information is subsequently injected into fatigue damage calculation models. The seasonality of fatigue damage is assessed and the influence of the monitoring duration is examined.

Action effects in post-tensioned concrete box-girder bridges obtained from high-frequency monitoring

In this paper, an investigation into the action effect behaviour on two post-tensioned concrete highway box-girder bridges is performed. The focus is on the determination of the action effects induced in the bridges’ structural elements resulting from both traffic and thermal loading. Long-term monitoring campaigns were carried out, generating over 3 years of measured data. The strain cycles in the reinforcement bars were determined using measurements of the reinforcement bars themselves with strain gauges as well as indirectly through measurement of crack widths. The seasonal effects in the measurements are presented for both cases and thermal strain behaviour is described. The influence of the seasonal behaviour of action effects at an element level is used to demonstrate the differing fatigue damage throughout the year for specific elements. The concept of the average daily damage curve is introduced for fatigue verification based on short-term measurements to accurately account for the seasonal effects.

Investigation of Thermal Gradient Effects in the I-35W St. Anthony Falls Bridge

Thermal gradients were measured through the section of the I-35W St. Anthony Falls Bridge, a posttensioned concrete box girder bridge in Minneapolis, Minnesota, over the course of 3 years. The magnitudes and shapes of the measured thermal gradients were compared with various design gradients, and a fifth-order curve was found to best approximate the shape of the gradients. The responses of the structure to the largest measured thermal gradients were compared with stresses and deformations predicted by finite-element modeling given applied design gradients. The measured structural response was found to be best predicted when the finite-element model of the bridge was subjected to a fifth-order design thermal gradient scaled to match maximum top surface temperature values proposed by AASHTO LRFD Bridge Design Specifications for the region. Stresses and deformations predicted by finite-element modeling using the AASHTO LRFD bilinear design gradients were found to be considerably lower than those derived from measured results. Recommendations for design thermal gradients are proposed.

Finite-Element Analysis of Reinforced-Concrete Box Girder Bridges under Close-In Detonations

Localized spalling/cratering of concrete structures subjected to close-in detonations may lead to global structural failure. This paper presents the details and results of a numerical study conducted on posttensioned concrete box girder bridges under close-in detonations. A bomb explosion within or near the bridge deck may cause catastrophic damage to the bridge components. Blast causes highly dynamic loads much larger than the conventional design loads applied relatively locally. In contrast to the bridge superstructure, significant research has been performed on the response and retrofit of buildings under blast loads. The published research on the response prediction and protection of bridges under near-field blast loads are limited. This study focuses on the evaluation and assessment of box girder bridges under blast loads. The objective of this research is to develop a reliable numerical model to predict the damage (spalling/cratering) size in a concrete deck under blast loading and the corresponding dynamic response of the damaged bridge system. The key parameters evaluated were the charge weight, charge location, and concrete deck properties. The results of this study make finite-element (FE) modeling an attractive alternative when blast testing is not feasible such as in the case of bridges. The numerical model was verified using close-in detonations on concrete slabs. Verification of the numerical model results using blast field testing on bridge systems is still necessary before this study can be expanded for additional parametric studies and comprehensive design recommendations. The damage sizes of the RC box girder bridges were predicted and assessed using a nonlinear dynamic FE code. Nonlinear regression analyses were conducted and an equation to predict the damage size depending on the scaled distance was introduced.

Reliability-based optimisation design of post-tensioned concrete box girder bridges considering pitting corrosion attack

Since the mid-twentieth century, prestressed concrete (PC) bridges have been significantly developed to become the most important type of bridge in the world. However, only a few studies have dealt with the reliability-based design optimisation (RBDO) of PC bridges despite the fact that RBDO demonstrates the real behaviour of structures. Moreover, the corrosion of post-tensioned tendon in PC bridges seriously caused sudden failures which have been recorded in the world. Since then, this study presents the probabilistic model and approach to formulate and analyse the RBDO of PC box girder bridges which consider the pitting corrosion phenomenon of shear, torsion reinforcements and post-tensioned tendon. A practical example of a typical PC box girder bridge is presented and discussed. Sensitive analyses are performed to evaluate the influence of ultimate target reliability index on the optimal solution. For the simple support PC box girder bridge, the ultimate target reliability index should be in the range of βult: 3.5–5 in order to produce the optimal design.

Development of a baseline for structural health monitoring for a curved post-tensioned concrete box–girder bridge

The establishment of a baseline is essential for long-term structural health monitoring and performance evaluation. Usually, field testing data and finite element (FE) model are two critical tools used to develop the baseline. In this paper, the establishment of the baseline field database for a curved post-tensioned concrete bridge with expansion bearings is first introduced to include the effect of varying temperature conditions on the field testing data. This database uses data collected from a full year and is based on an undamaged status. The development of a baseline FE model for the bridge is then discussed. Model updating for the FE model are detailed in this paper which includes calibration of material properties, utilization of spring bearing elements, and replacement of Mindlin plate elements (MP4) on box–girder by recently developed cracked Mindlin plate elements (MP4C) to represent the bridge service conditions. A good agreement in modal results has been observed between the baseline FE model and the baseline field data. The proposed structural health baseline can be used for near real-time damage detection, development of monitoring techniques, and condition assessment. Finally, as an application of the baseline, this FE model is used for an earthquake simulation with a selected ground motion on the bridge. The seismic analysis demonstrates the beneficial effect of the guided expansion bearings on the bridge deck in the longitudinal direction.

Analysis of Structural Behaviour in Widened Concrete Box Girder Bridges

Structural performances for a widened post-tensioned concrete box girder bridge under dead load, prestressing force, shrinkage and creep of concrete and settlements of piers are analysed. The existing and new box girder bridges are connected with their flange slabs. Connection of the two bridges will cause internal force to be redistributed between them, and cause great local stress in the connecting slab. To reduce the influence of internal force redistribution, those factors such as connecting time, usage of low-shrinkage concrete and prestressing arrangement for the new bridge are discussed. The local structure of the connecting slab and factors which influence the stresses in the connecting flange slabs of box girders, are also discussed. The results of analysis show that the time for connecting the two bridges should be as delayed as possible, while the usage of low-shrinkage concrete will reduce internal force redistribution, and optimization on the prestressing design of the new bridge can improve the stress states in both the existing and new bridges. The analysis results also show that settlements of piers of the new bridge must be strictly controlled.

Development of Computer-Based System for the Temperature Monitoring of a Post-Tensioned Segmental Concrete Box-Girder Bridge

This paper describes the development and implementation of a computer-based remote monitoring system for temperature monitoring of an 11-span segmental, post-tensioned concrete box-girder bridge. Monitoring was carried out for 5 years. The extensive data collected is analyzed using software developed to provide engineers with information that can be used in the evaluation of the long-term behavior and performance of the bridge. The software was used to determine the maximum and minimum bridge temperatures, vertical temperature differences through the bridge cross section, and horizontal temperature differences in the transverse directions. Comparisons are made with design specification provisions and with recommendations proposed by previous researchers. In addition, software has been developed to determine the relationship between the daily maximum temperature differences and the air temperatures inside the box-girder. This approach is also used to develop the relationship between the maximum stresses due to temperature differences and the air temperature inside the box-girder. This paper shows the benefits from using a computer-based monitoring system to provide a continuous evaluation of data collected on the bridge.

Temperature Induced Deformations in Match Cast Segments

During the match casting operations of precast segments for segmental post-tensioned concrete box girder bridges, a problem can arise due to the heat of hydration of the newly cast segment. When the segments have a particularly high ratio of wing span to segment length, warping of the match cast segment can occur due to a thermal gradient that is caused by the high temperatures in the adjacent newly cast concrete. This warping, or bowing, has subsequently caused problems during erection operations. This paper presents the results of a field study of this phenomenon. Concrete temperatures and segment deformations measured during the casting of several segments for the San Antonio Y project are reported along with observations from the erection operations. A simple method is presented to determine whether, for a given bridge, measures to reduce the thermal gradient during match casting should be taken.

The Pitan Bridge, Taiwan

To alleviate traffic congestion near Taipei, in 1985 the Taiwan Area National Freeway Bureau planned the construction of the 108 km long Northern Taiwan Second Freeway. The majority of the Second Freeway’s alignments are on grade, on embankments, in tunnels, or on viaduct structures. At several locations however, obstacles were identified that required special bridges. The Pitan Bridge spans one of these areas. The Pitan Bridge, actually two nearly parallel bridge structures, is located about 15 km south of Taipei. It connects typical low-level viaducts to a tunnel. Both bridge units have total length of approximately 800 m, a 750 m radius curvature and a slope of approximately 1%. The structure as designed and built makes use of the well-established economy of a segmentally erected post-tensioned concrete box girder bridge, adapted for the site with the innovative use of delta-shaped piers of post-tensioned concrete construction.