Post-tensioned Concrete Box Girder Research Articles

Investigation of Failures of Three Precast Post-Tensioned Segmental Concrete (PSC) Box Girder Bridges During Construction

Considering the fast pace of construction development, with a consistent increase in the volume of traffic, both road and rail traffic in developing countries like India, which are constrained by the limitation of land availability, especially in built-up or urban areas, lateral expansion in transport facilities has become increasingly challenging. Under such circumstances, vertical expansion through the construction of long flyovers or elevated structures is the most viable solution to meet traffic demand. Road and railway bridges are complex structures by nature with respect to their design and construction requirements based on a high level of knowledge, expertise and experience. Hence, some structural failures are taking place even during the construction stage of bridges owing to material quality issues as well as human error, to name but a few of the causes. This paper presents three case studies related to the investigation process and the primary cause(s) of the collapse of three different precast concrete post-tensioned segmental concrete (PSC) box girder bridges in India, with the corresponding lessons learnt and proposed recommendations. This paper covers issues relating to the investigation of the reasons leading to the failures of three precast concrete PSC box girders and a few suggestions for remedial measures.

Characterization of the static and dynamic response of a post-tensioned concrete box girder bridge with vertically prestressed joints showing vertical deflections due to concrete creep deformation

Characterization of the static and dynamic response of a post-tensioned concrete box girder bridge with vertically prestressed joints showing vertical deflections due to concrete creep deformation

Insights into structural assessment and long-term effects of a post-tensioned multispan concrete box girder bridge with vertically prestressed internal joints

The study focuses on multi-span prestressed bridges, where time-dependent effects like creep, shrinkage and prestress losses can have a significant impact on long-term behaviour. Specifically, the paper analyses a bridge constructed with the balanced-cantilever method and presenting the peculiarity of vertically prestressed internal joints, which significantly influence the deformed shape and require proper modelling approaches. The testing campaign is fundamental to achieve a deepened awareness of the actual behaviour of the bridge and to correctly reproduce it through a Finite Element (FE) model. The constructed FE model accurately predicts actual and future deformations and stresses, and allows simulating the actual service conditions of the structure. The novelty of the work presented in this paper lies in the development of a detailed model specifically tailored for the analysed bridge typology, considering real construction stages and long-term phenomena of both steel and concrete. The model has reached a high level of validation through the comparison of the results with extensive in-situ tests and theoretical formulations, so as to be able to achieve insights and learn important lessons on the long-term structural behaviour of post-tensioned bridges with special internal connections.

NONLINEAR FINITE ELEMENT ANALYSIS OF FULL-SCALE EXTERNAL POST-TENSIONED CONCRETE BOX GIRDER AT JACKING AND SERVICE

This paper presents the modelling of a 47-meter of simply supported full-scale external post-tensioned concrete box girder in a bridge using in-house software 3D-NLFEA. The Girder was designed with sections, adequate reinforcements, and the jacking force according to the codes to resist the live load. The objective of this work is to assess the global structural response i.e., the load and deflection capacity under service loading. The detailed response of anchorage and deviator segments concerning their micro-cracking behavior during jacking transfer and service load conditions was also discussed. The constitutive model of materials applied to the modelling covered the hardening and softening of concrete under tension and compression, the nonlinearity of mild steel reinforcement, and prestressing tendons. The first stage was to simulate the self-weight of the girder simultaneously with the application of jacking forces from the tendons. The second stage was to load the girder under three-point bending to replicate the typical wheel axle from vehicles. The load was in the form of displacement-controlled and it was applied at the top midspan. From the results obtained, it was shown that under service limit state conditions, the load-displacement curve of the girder was linear at elastic. Cracks in allowable limit manifested in several parts of anchorage and deviator segments by the end of prestressing sequences. This highlighted the importance of providing crack control reinforcement to alleviate the progression of cracks under jacking service load conditions.

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.

The San Francisco–Oakland Bay Bridge, CA, USA – eastern span

With daily traffic of 260 000 vehicles, the San Francisco–Oakland Bay Bridge is a major connection in the San Francisco Bay area (CA, USA). The new bridge is a designated lifeline structure (to remain open for emergency traffic after a major seismic event) with a design life of 150 years. The new bridge is 3.6 km long and consists of four distinct structures: a low-rise post-tensioned concrete box girder near the Oakland shore; a 2.4 km long segmental concrete box girder (skyway); a first-of-its-kind self-anchored suspension (SAS) bridge with a 385 m main span over the navigational channel; and a post-tensioned concrete box girder that connects to the east portal of the Yerba Buena Island tunnel. Opened in 2013, the signature span of the bridge is the SAS bridge with a length of 624 m and a total deck width of 79 m accommodating ten lanes of traffic in addition to a bike/pedestrian path. The US$6.4 billion megaproject was procured under multiple contracts and was delivered using the traditional design–bid–build method. This paper describes the key design innovations and construction methods which address the unique challenges on this project.

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...

A Localized Fire Model for Predicting the Surface Temperature of Box Girder Bridges Subjected to Tanker Truck Fire

The quantification of thermal action is important to the analysis of structural-fire performance of bridges. This study evaluates the parameters for the localized fire model adopted in SFPE Handbook for application to the fire scenario of a tanker truck burning beneath a bridge. Modification is applied first to the flame length and then to the distribution of gauge heat flux using the simulation results of various fire models established in Fire Dynamics Simulator considering parameters, including the sectional dimensions of bridge, bridge headroom, truck size and heat release rate. Spatially varied gauge heat flux or adiabatic surface temperature of the bridge can be predicted with this fire model. Implementation of this modified fire model in structural-fire analysis is illustrated with a sequentially coupled thermo-mechanical modelling of a post-tensioned segmental concrete box girder bridge exposed to tanker truck fire. The adiabatic surface temperature calculated from the modified fire model is applied as thermal boundary to the bridge. Simulation results show that, although the global structural responses are seldom influenced by fire, localized damage in concrete and tendon may result. The prestress in tendons near mid-span may be reduced even after the bridge is cooled down to ambient temperature, which may adversely affect its load-carrying capacity. The damage to concrete may also induce localized separation between adjacent segments, possibly affecting the durability of tendons.

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.

Ambient vibration test-based deflection prediction of a posttensioned concrete continuous box girder bridge

Ambient vibration test generally only outputs basic modal parameters including frequencies, damping ratios, and unscaled mode shapes, which cannot directly support decision making of structural maintenance and management. In this article, structural deep-level parameters including unscaled and scaled flexibility identification of a posttensioned concrete continuous box girder bridge are studied by performing ambient vibration test, which is able to predict structural deflections by multiplying the static load with the identified flexibility. Ambient vibration test of the bridge and basic modal identification are firstly performed. Then, the method of unscaled flexibility identification is proposed by investigating the relationship between the frequency response function estimated from ambient test data and the analytical one. Finally, a mass-changing strategy is utilized to identify the scaled flexibility from output-only data, in which the key issue is to identify mass-normalized scaling factors by performing ambient vibration tests of tested structure before and after changing its mass. Numerical simulation of a simply supported beam and field test of a three-span bridge has been conducted to verify the capability and reliability of the proposed method. The good agreement between the predicted deflections from the identified flexibility and those measured from the static test successfully illustrates the effectiveness of the proposed method.

Modal response identification of a highway bridge under traffic loads using frequency domain decomposition (FDD)

In this study, a four-span, 224m long, post-tensioned concrete box girder bridge supported on single column piers was subject to a series of controlled vehicle tests. Bridge acceleration response datasets were used to study the effect of truck speed and a sudden stop, on the modal identification of the bridge structure. Natural frequencies and mode shapes of the bridge were determined using the frequency domain decomposition technique for all datasets. The passing of the truck rendered difficult to identify the first bridge frequency. Conversely, the vehicle tests improved the identification of higher vibration modes. This is because the truck preferentially excites the bridge vertical response, which is associated with higher modes of vibrations, especially when a sudden stop of the vehicle occurs. Thus, carefully conducted vehicle-crossing tests provide detailed information about the bridge structure dynamics in the vertical direction. However, to identify lower modes, no vehicle on the bridge is preferred.

Flexibility identification and deflection prediction of a three-span concrete box girder bridge using impacting test data

Abstract Deflection is an important parameter for condition assessment of in-service bridges. However, accurately measuring bridge deflections especially that of long span bridges is still a challenging problem. In this article, field tests including multiple reference impact test (MRIT) and static test were performed on a three-span post-tensioned concrete box girder bridge to study structural deflections. Firstly, a new impacting device, which can generate high-magnitude and wide-frequency-band forces, has been developed and employed to execute the MRIT on the bridge. The output data from MRIT was utilized to estimate structural Frequency Response Function (FRF) and to identify deep-level structural parameters including modal scaling factor and structural flexibility, from which structural deflections under arbitrary loads were predicted. Field test results have shown that the developed impacting device can produce FRF with much better reciprocity than the FRF estimated from traditional sledge hammer, which demonstrates the superiority of the developed impacting device for bridge excitation and deflection prediction. Secondly, static test was also conducted on the bridge. The developed long gauge Fiber Bragg Grating (LG-FBG) strain sensors were mounted on the bottom of the box girder bridge. The measured long-gauge strains have been adopted to calculate structural deflections through a modified conjugate beam method which has high precision and there is no error accumulation from other span. Finally, data processing strategy was carried out according to the procedure of structural flexibility identification from MRIT data, and the identified flexibility matrix has been used to predict structural deflections by multiplying a static force vector corresponding to the tested truck load. The well agreement between the predicted deflections and the calculated deflections indicates that the proposed methods can be utilized to obtain structural deflections.

Deflection of in-span hinges in prestressed concrete box girder bridges during construction

Multi-span cast-in-place (CIP) post-tensioned concrete (PS) box girder bridges undergo upward deflection (curl) at hinges due to post-tensioning forces. Adjustments in falsework height are often necessary in the field to address the curl and avoid bumps, which cause traffic safety concerns and present a road hazard. A current method to estimate hinge curl has often led to results that are significantly different than those measured in the field thus causing construction delays and costly change orders. The main purpose of the study presented in this article was to measure bridge deflections at and near in-span hinges in ten hinges within five bridges during construction over a period of several months and compare the results with the current theory. Based on the analysis of data, the correlation between the measured and calculated data was studied. Both short-term and time-dependent hinge curls were evaluated. Substantial differences between the field and theoretical data were observed and quantified. The data was used to identify the causes for the differences and directions for development of a new method to more accurately estimate hinge curl. A new method was developed as part of this study to address the sources of differences. Description of the new method, however, is beyond the scope and page limits of the current article.

Constantine viaduct: a new landmark for the city of bridges

The core part of the Constantine viaduct is a 756 m long cable-stayed bridge currently under construction in Constantine, Algeria. Due to its slender appearance, clear visual lines and prominent location, it will be another landmark structure for a city already known for its historic and beautiful bridges. This paper focuses on the design and construction of the cable-stayed bridge with its 259 m main span, central pylons, central cable plane and post-tensioned concrete box girder with internal and external tendons. The architectural form is characterised by extensive use of curved structural elements. The design considerations associated with placing an aesthetically pleasing major bridge in the centre of an old city with many restrictions to alignment and consequently complex geometry are addressed. The paper outlines key structural elements and selected details such as the anchorage blocks for the stay cables in the bridge girder and the monolithic connection between the pylon and the deck. It also reports on the construction methodology and control.

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.

Railway bridge using small post-tensioned concrete box girder

A girder depth is the critical parameter for rapid construction of bridge and clearance limitation in urban area such as high-density residential district. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder depth in order to retain sufficient moment arm between compressive and tensile fiber. To elaborate this issue, a small rectangular hollowed section can be used as a replacement of I-shaped standard girder. This small post-tensioned concrete box girder allows more flexible girder depth adjustment rather than standard I-shaped posttensioned girder plus additional torsion resistance benefits of closed section. A 30 m long, 1.7 m high and 3.63 m wide actual small post-tensioned concrete box girder is designed. A laboratory test was performed for its static behaviors by applying 6400 kN amount of load in the form of 4-point bending test. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extract the dynamic characteristics, natural frequency and damping ratio of this girder, several forced vibration tests using oscillator are carried out with varying operational frequency. Nonlinear finite element analysis of this 4-point bending test under monotonic static load is discussed with the aid of concrete damaged plasticity using ABAQUS program. Finally, a series of modal dynamic analyses of different span length and girder depth of small post-tensioned girder bridge is performed in order to validate the applicability to railway bridges and compared to the UIC design criteria in the form of time dependent dynamic responses such as deflection, acceleration and end rotation.

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.