Adjacent Precast Research Articles

Experimental Investigation of Shear Keys for Adjacent Precast Concrete Box Beam Bridges.

Longitudinal cracking in shear keys is one of the most frequently recurring problems in the adjacent precast concrete box beam bridges. The relative displacement across the shear key (RDSK) under loads has been used as a direct indicator for shear key cracking. Therefore, accurately simulating the interface between the shear key and beam or providing the correct relationship between shear transfer and RDSK is key to evaluating the damage of the shear key. In this study, the shear transfer properties of four types of composite specimens were studied by static displacement-controlled bi-shear (SDS), cyclic force-controlled bi-shear (CFS), and cyclic displacement-controlled bi-shear (CDS) tests. Two finite element models (FEMs) were established to calibrate and validate the interfacial material parameters. The results showed that adding reinforcement bars over the joints that connect the block and the overlay could improve the bearing capacity of the shear key. Formulae were proposed for the relation between shear force transfer and RDSK in engineering applications. The values of the interfacial material parameters used in the traction–separation model to simulate the interface between the shear key and beam were recommended.

Experimental Study on Shear Behavior of a UHPC Connection Between Adjacent Precast Prestressed Concrete Voided Beams

Abstract A partial-depth, diamond-shaped, ultra-high performance concrete (UHPC) connection with embedded transverse reinforcement between adjacent precast prestressed concrete voided beams (APPCVB...

Full-Scale Evaluation of an Innovative Joint Design between Adjacent Box Beams

The longitudinal joints on adjacent precast, prestressed box beams used in bridge construction are vulnerable to cracking. These cracks provide a direct path for water and deleterious agents to enter the structural system, causing corrosion of the embedded steel bars and tendons. To avoid significant maintenance costs, safety concerns, or both, an innovative longitudinal joint between two adjacent box beams was designed in the current study. This joint is 6½ in. wide with roughened surfaces, filled with shrinkage compensating concrete and reinforced by steel bars. The joint was evaluated on a small-scale basis and satisfactory performance was obtained in resisting early-age cracks. In the current paper, the joint design is further evaluated through experiments on a 31 ft long specimen during the joint’s early age, and when it is subjected to multiple levels of cyclic loads. A finite element (FE) model that is capable of simulating the early-age concrete hardening was also developed and validated against the experimental data. The early-age, time-dependent stress development in the joint and at the interface of the joint and box beam was investigated using the FE model. Based on the results of laboratory tests and FE simulations, the innovative joint was found to remain crack free without the utilization of a shear key or transverse post-tensioning. The “compression-dominate” joint created by the expansive joint material and transverse reinforcing bars across the interface is expected to address the issues associated with early age, while ensuring the long-term durability and performance of box-beam bridges.

Structural Redundancy Assessment of Adjacent Precast Concrete Box‐Beam Bridges in Service

Present approaches for assessing bridge redundancy are mainly based on nonlinear finite element (FE) analysis. Unfortunately, the real behavior of bridges in the nonlinear range is difficult to evaluate and a sound basis for the nonlinear FE analysis is not available. In addition, a nonlinear FE analysis is not feasible for practitioners to use. To tackle this problem, a new simplified approach based on linear FE analysis and field load testing is introduced in this paper to address the particular structural feature and topology of adjacent precast concrete box‐beam bridges for the assessment of structural redundancy. The approach was first experimentally analyzed on a model bridge and then validated by a case study. The approach agrees well with the existing recognized method while reducing the computation complexity and improving the reliability. The analysis reveals that the level of redundancy of the bridge in the case study does not meet the recommended standard, indicating that the system factor recommended by the current bridge evaluation code for this bridge is inappropriate if considering the field condition. Further research on the redundancy level of this type of bridges is consequently recommended.

Effects of Temperature Distributions on Thermally Induced Behavior of UHPC Shear Key Connections of an Adjacent Precast Prestressed Concrete Box Beam Bridge

Effects of Temperature Distributions on Thermally Induced Behavior of UHPC Shear Key Connections of an Adjacent Precast Prestressed Concrete Box Beam Bridge

Effect of Thermal Load on the Behavior of an Adjacent Precast, Prestressed Concrete Box-Beam Bridge that Contains Ultra-High-Performance Concrete Shear Keys with Transverse Dowels

Effect of Thermal Load on the Behavior of an Adjacent Precast, Prestressed Concrete Box-Beam Bridge that Contains Ultra-High-Performance Concrete Shear Keys with Transverse Dowels

Live-Load Moment-Distribution Factors for an Adjacent Precast Prestressed Concrete Box Beam Bridge with Reinforced UHPC Shear Key Connections

Live-Load Moment-Distribution Factors for an Adjacent Precast Prestressed Concrete Box Beam Bridge with Reinforced UHPC Shear Key Connections

Laboratory Evaluation of Ultrahigh-Performance Concrete Shear Key for Prestressed Adjacent Precast Concrete Box Girder Bridges

AbstractPrecast adjacent box girder bridges have become a preferred solution in several states due to their simple structure, economy, and ease of construction. However, longitudinal cracks often appear along the shear keys between adjacent box girders. With its superior strength and durability, ultrahigh-performance concrete (UHPC) has been used as an alternative grout material to reduce shear key cracking and enhance load transfer. The objective of the present research was to evaluate the performance of UHPC in shear keys using direct shear, direct tension, and flexural tests. Also, this study determined the effectiveness and functionality of shear reinforcement bars by applying direct shear load on specimens with shear reinforcement. In the direct shear test, a steel frame was placed around the specimens to allow the shear key to experience pure shear force. The direct shear test established the cracking threshold and ultimate shear strength of each shear key with and without shear reinforcement bars. ...

Non-proprietary bar splice sleeve for precast concrete construction

Over the last few decades, the use of precast concrete components have been significantly increasing in building and bridge construction due to their quality, durability, and speed of construction. Precast components need to be fully connected to ensure the integrity, serviceability, and durability of the completed structure. Several proprietary grout-filled sleeves are currently being used to splice reinforcing bars of the adjacent precast components. These sleeves require very tight tolerances in precast production to ensure the alignment of the spliced bars, which usually results in using larger and more costly sleeves than needed. The objective of this paper is to introduce a non-proprietary bar splice sleeve that accommodates current production tolerances in addition to being economical and easy to produce. The design method of the proposed splice sleeve and the analytical investigation conducted using FE analysis are discussed. The experimental investigation conducted using two alternatives of the proposed bar splice sleeve is presented. Eighteen specimens for splicing #8 and #9bars were tested using different sleeve lengths. Test results indicated that the proposed bar splice sleeve have adequate capacity to fully develop reinforcing bars while being simpler to use and more economical than current proprietary splice sleeves.

Practical assessment of magnetic methods for corrosion detection in an adjacent precast, prestressed concrete box-beam bridge

Magnetic methods are progressing in the detection of corrosion in prestressing strands in adjacent precast, prestressed concrete box-beam bridges. This study is the first field trial of magnetic strand defect detection systems on an adjacent box-beam bridge. A bridge in Fayette County, Ohio, which was scheduled for demolition, was inspected. Damage to prestressed box-beams is often due to corrosion of the prestressing strands. The corroded strands show discontinuities and a reduced cross-sectional area. These changes, due to corrosion, are reflected in the magnetic signatures of the prestressing steel. Corrosion in the prestressing steel was detected using two magnetic methods, namely the ‘magnetic flux leakage’ (MFL) and the ‘induced magnetic field’. The purpose of these tests was to demonstrate the ability of the magnetic methods to detect hidden corrosion in box-beams in the field and tackle the logistic problem of inspecting box-beams from the bottom. The inspections were validated by dissecting the bottom of the box-beams after the inspections. The results showed that the MFL method can detect hidden corrosion and strand breaks. Both magnetic field methods were also able to estimate corrosion by detecting the effective cross-sectional area of the strand in sections of the beams. Thus, it was shown that the magnetic methods can be used to predict hidden corrosion in prestressing strands of box-beams.

Field Test of Magnetic Methods for Corrosion Detection in Prestressing Strands in Adjacent Box-Beam Bridges

Magnetic methods are progressing in the detection of corrosion in prestressing strands in adjacent precast, prestressed concrete box-beam bridges. This study is the first field trial of magnetic strand defect detection systems on an adjacent box-beam bridge. A bridge in Fayette County, Ohio, that was scheduled for demolition was inspected. The prestressed box beams had significant strand corrosion. The corroded strands showed discontinuities and a reduced cross-sectional area. These changes are reflected in the magnetic signatures of the prestressing steel. Corrosion in the prestressing steel was detected using two magnetic methods; namely, the magnetic flux leakage method and the induced magnetic field method. The purpose of these tests was to demonstrate the ability of the magnetic methods to detect hidden corrosion in box beams in the field and tackle the logistic problem of inspecting box beams from the bottom. The inspections were validated by dissecting the bottom of the box beams after the inspections. The results showed that the magnetic flux leakage method detects hidden corrosion and strand breaks with a sufficient amount of accuracy. Both magnetic field methods were also able to estimate corrosion by detecting the effective cross-sectional area of the strand. Thus, it was shown that the magnetic methods can be used with sufficient reliability to predict hidden corrosion in prestressing strands of box beams. The recommended actions to make magnetic inspection practical are discussed.

Transverse Posttensioning Design of Adjacent Precast Solid Multibeam Bridges

Adjacent precast, prestressed multibeam bridges have often been used for medium- and short-span bridges. However, there have been longitudinal cracking problems in shear keys and overlays commonly seen on some adjacent precast multibeam bridges during their service years. The fundamental reason for the problem is the poor transverse connection. Transverse posttensioning is important to the transverse connection design, although the posttensioning varies largely from state to state. Especially for adjacent precast solid multibeam bridges without diaphragms, there are no theoretical justifications for designing the transverse posttensioning. In this study, an approach based on the concept of shear friction, which is used for designing the transverse posttensioning in adjacent precast solid multibeam bridges, is presented. Furthermore, a newly rehabilitated bridge was load tested with the primary purpose of evaluating the effect of transverse posttensioning under truck load. Also, the calibration of a numerical model was conducted. At last, suggestions about design and construction of shear keys, with reference to the experience in other states, are presented for the practice in the state of Maryland.

Forensic Examination of a Noncomposite Adjacent Precast Prestressed Concrete Box Beam Bridge

On the evening of December 27, 2005 the fascia beam supporting the east side parapet wall of the third span of the Lake View Drive Bridge failed under the action of dead load. To gain insight into the potential causes of the failure a series of forensic analyses were conducted on the beams decommissioned from the bridge. The study correlates external observations of surface condition with internal chloride profile, depth of carbonation, and existing corrosion. The forensic investigation indicated that strand cover was reduced due to the construction methods of the time. The chloride level in the concrete at the lower layer of strands was high enough that corrosion would be expected. Chloride attack was identified to have come from the leakage of water between beams from the bridge deck surface above. Based on the research findings recommendations are made for visual inspection, and guidelines are provided for condition rating of noncomposite prestressed concrete box beam bridges.

Full-Scale Testing of Shear Keys for Adjacent Box Girder Bridges

Adjacent precast, prestressed box girder bridges are widely used in the United States, but the shear keys between the girders tend to crack and leak. Three different shear key configurations were studied, i.e., a current detail where the shear key is approximately 10 in. (250 mm) from the top of the girder and grouted with non-shrink grout, this same detail grouted with epoxy rather than non-shrink grout, and a proposed mid-depth keyway grouted with non-shrink grout. The tests were conducted on a full scale, four-beam assembly which represented part of the bridge. The results showed that the currently used shear key detail cracks due to thermal stresses generated as the beams deflect upward and downward due to daily heating and cooling. The mid-depth shear key is less susceptible to these stresses and was found to be more resistant to cracking. Loading did not appear to cause new cracking, but rather seemed to propagate existing thermal cracks.

Transverse Design of Adjacent Precast Prestressed Concrete Box Girder Bridges

American and Japanese design and detailing practices of prestressed concrete box girder bridges are compared. A new precast, prestressed box girder design suitable for U.S. practice is proposed. The design is based on requiring the deck to act as a rigid assembly of longitudinal and transverse members. This is consistent with Japanese practice and fulfills the intent of several state DOT initiatives. The proposal advocates quarter-point diaphragms with relatively large amounts of transverse post-tensioning. A design chart and recommended details are provided for bridges up to 80 ft (24 m) long. The amount of post-tensioning was found to be unaffected by bridge span length. A fully worked numerical design example is included to demonstrate the proposed design procedure.