Precast Concrete Girders Research Articles

Composite Behavior of Precast Concrete Full-Depth Panels and Prestressed Girders

The authors evaluate the composite behavior of a bridge section consisting of a full-depth concrete slab that is connected by threaded steel bolts to an AASHTO-type concrete I-girder. The research conducts 13 push-out tests on specimens having shear pockets in the slabs to show both horizontal shear strength capacity and the behavior that threaded steel bolts exhibit when used as shear connectors to achieve composite action between the precast concrete panels and precast concrete girders. The specimens, cast and tested under static loading conditions, are used to determine the ultimate strength and failure mode of the shear connection system. Steel bolt length, along with their number, configuration in the shear pocket, and spacing are also examined. Results show that threaded steel bolts allow for full composite action between the precast concrete panels and precast concrete girders. The authors also note that their results, when applied to the load and resistance factor design guidelines of the American Association of State Highway and Transportation Officials, point to the Association's conservative estimate of design strength.

SOME FACTORS AFFECTING THE ULTRASONIC PULSE VELOSITY TEST RESULTS OF HIGH STRENGTH CONCRETE

The high strength concrete is characterized by its high strength, low porosity and good performanceunder aggressive environmental conditions. The paper presents some factors affecting the Ultrasonic Pulse Velocity test results for high strength concrete such as water/ cement ratio, type of aggregate, frequency level of transducers, dimension of the specimens and path length. An experimental equation has been derived for the prediction of compressive strength of high strength concrete from pulse velocity, which can be used for the estimation of strength. It provides more reliable prediction and can be used in precast concrete factories manufacturing precast concrete girders for bridges

Collapse during Construction of a Precast Girder Bridge

This paper describes the collapse during construction of a precast concrete girder bridge crossing Highway 15, north of Montreal. The bearing conditions for the girders at the time of collapse are discussed. The tie rods that were used to restrain the movement of the girder top flanges were tested to determine their effective stiffness and strength. Rotational and sliding tests were also performed on the pot bearing units. These experimental results were used in an analytical study to confirm the sequence of collapse of the girders. Bracing requirements during construction for precast girder bridges supported on pot bearings are discussed.

Design of Prestressed Concrete Bridges to Accommodate Future Widening

This article discusses how a two-lane prestressed concrete bridge can be designed and constructed so that it can be widened easily into a three- or four- lane bridge in the future. The author presents two methods to accomplish this task: the strutted box widening method (SBWM), which applies to concrete box girder bridges; and the strutted girder widening method (SGWM), which applies to precast concrete girder bridges. Two design examples are given. Four studies are included to demonstrate how two elevated median-based expressways (Austin, Texas and Tampa, Florida) and two major long-span crossings (the Confederation Bridge in Canada and the North Halawa Valley Viaduct in Hawaii) could have been designed and constructed using the SBWM to allow for future widening. The paper concludes with a discussion of a proposed precast segmental extradosed (cable-stayed) bridge that is to be constructed and widened using the SBWM.

A continuity method for bridges constructed with precast prestressed concrete girders

A method of making simply supported girders continuous is described for bridges with spans of 30-45 m. The splicing method takes advantage of an induced secondary moment to transform the self-weight stresses in the precast simply supported girders into values representative of a continuous girder. The secondary moment results from prestressing of continuity tendons and detensioning of temporary tendons in the girders. Preliminary sections are selected for spliced U-girder bridges with a range of span lengths. Use of the proposed technique results in girder depth reductions of 500-800 mm when compared to standard simply supported I-girder bridges. The flexural behavior of an example bridge with 40-m spans is examined to illustrate the necessary considerations for determining the optimum sequence of splicing operations.

프리스트레스트 콘크리트 합성단면에 도입되는 추가 긴장력 설계와 저항모멘트 평가

A general composite section of precast and cast-in-place concrete with prestressed and nonprestressed reinforcements was analyzed to calculate residual stresses and loss of prestressing force caused by internal constraints of concrete long-term deformation. From the analytical results, equations to design additional prestressing force and to evaluate resistant moment of the composite section were proposed. The equations shows that the additional prestressing force can be over-estimated if the loss rate of the first prestressing force is over-estimated from the lumped sum of a design code. The analytical procedure with the proposed equations has been applied to a composite section using the AASHTO Type 5 girder. The loss rates of the additional prestressing force appling to the precast concrete girder was less than those appling to the composite girder. However, the resistant moment of the additional prestressing force on the composite girder was much larger than that on the precast concrete girder. The additional prestressing force appling to the composite section was very effective for strengthening of the prestressed concrete composite girder.

Precast Concrete Light Rail System Provides Mass Transit Solution for JFK International Airport

John F. Kennedy International Airport in Queens, New York, is one of the world's busiest hubs, a vital facility where travelers might expect to find state-of-the-art surface transportation systems. Prior to 2003, however, travel to and from the various airport terminals and parking areas required curb-access bus transportation that was often inconvenient and slow. After years of failed attempts to rectify the situation, a rapid transit plan emerged that successfully solved right-of-way, environmental, and public opinion obstacles. The new 8.2 mile (13.2 km) light rail line was built at a cost of $1.9 billion under a design-build-operate contract using a consortium of design and construction firms. The light rail system comprises over 5400 precast concrete segments. One of the greatest accomplishments of the project was the rapid truss erection of precast concrete girders within a narrow 10 ft (3.0 m) median with minimal disruption to major roadway traffic on either side.

Creep and Shrinkage Effects in Spliced Prestressed Concrete Girder Bridges

This paper reviews and demonstrates the age-adjusted concrete modulus approach to the time-dependent analysis of spliced precast concrete girder composite bridges. The method is illustrated by example of one of the post-tensioned spliced girder bridges built during the recently completed 1-15 Reconstruction Project in Salt Lake City, Utah. Sixteen simple-span bridges up to 67 m (220 ft) in span length were constructed using a 2400 mm (94.5 in.) deep modified girder developed by the Washington State Department of Transportation. With a more accurate method for prestress loss calculations for such bridges, designers can take advantage of the higher concrete age at time of post-tensioning and the resultant reduction in creep and shrinkage strains.

Cable-Stayed Bridge over the Guamà River, Brazil

The Guama Bridge crosses the Rio Guama in the State of Para in Brazil. It is almost 2 km in length and includes two approach viaducts and a central three-span cable stayed bridge. Decks are composed of precast prestressed concrete girders with I-shaped cross sections connected by transverse beams and supporting a top concrete slab. The girders were prefabricated at the job-site plant and transported by barges before being lifted and installed by launching gantries. Details are given of the design, the aerodynamics of the bridge and the bridge construction. The problems posed by the initial inaccessibility of the site by road and by high tides and strong currents are discussed. Details are given of the owner, designer, contractor, costs and service date.

Strengthening of Precast Concrete Girder Bridges by Post-Tensioning for Continuity

Simple-span precast concrete girders have frequently been used in bridge superstructures. However, to accommodate today's heavy traffic loads, their carrying capacity can be strengthened by providing moment continuity between adjacent spans. This study investigates the use of external tendons to provide partial continuity. It is shown that such a strengthening scheme results in stiffer beam response than individual spans. The effective tendon force governs the beam deflections and opening of the joint between adjacent spans. An analytical method is presented to predict the piece-wise linear response of two-span continuous beams derived from two simple-span beams. Good agreement of both the calculated deflections and widths of joint opening with the observed test results was obtained. Based on a parametric design study, charts are provided for strengthening precast simple-span beams using external prestressing. A design example illustrates the proposed method.

Strengthening of the West Gate bridge with carbon fibre composites - a proof engineer’s perspective

The world’s biggest project of structural strengthening by means of bonded, high tensile carbon fibre reinforced polymers (CFRP) has recently been accomplished at the West Gate Bridge in Melbourne. The West Gate Bridge consists of two multi span precast concrete segmental box girder approach viaducts and a central cable stayed steel box girder Bridge. As a relief measure for traffic congestion an extra lane was provided on the western approach viaduct by utilising the former hard shoulder. This together with the increased (current) traffic loadings has resulted in higher traffic loads being applied to the bridge. The most critical areas of overstress that were identified were the torsional and shear capacity of the spine girder and the capacities of the deck slab and the precast cantilever frames. The main spine beam girder was strengthened by draped tendons to increase the global sag and hog capacity. For the other strengthening requirements, VicRoads decided on a solution proposed by the Design and Construct Contractor, of using high-strength CFRP materials due to their advantages as externally bonded reinforcement (EBR) or near surface mounted reinforcement (NSMR). This paper concentrates on this strengthening using CFRP materials. At the time of the design, these strengthening techniques were not very well established in Australia. They require not only knowledge about the mechanical properties of the innovative materials but also thorough understanding of and particular attention to bond and anchorage issues. The detailing and dimensioning by the Designers was carried out with the assistance of a German Engineering sub-consultant. The EBR and NSMR applications also posed a new challenge for the engineering consultants, Hyder Consulting, acting as Proof Engineers for the entire project. The proof engineering was in fact a gradual and stepwise process of assessment and improvement of the various details and was performed in co-operation with a German expert in Carbon Fibre technology (Prof Rostasy and Dr. Neubauer). This paper will cover the entire project, especially focusing on the EBR and NSMR issues. The authors hope by this, to make Australian engineers more familiar with these innovative techniques but also sensitive to their specific requirements.

Experience with the Precast Span Method on the Korean High-Speed Rail Project

The Korean High-Speed Rail Project, Korean Train Express, has 109 km (67 mi) of bridges that comprise about 27% of the entire alignment. The successful construction of these bridges significantly affects overall project progress. To meet tight schedule and quality control standards, in addition to cost savings, contractors proposed the precast span method (PSM) versus the original girder designs on some segments of the line. This first application of PSM to high-speed rail in Korea has posed some challenges: design requirements for high-speed railway bridges are stricter than those for road bridges because of stringent deformation requirements. The adoption of PSM girders has improved the construction quality and schedule. PSM requires no falsework and is not limited by ground and weather conditions, thus being well suited for the construction of long viaducts under stringent budget and construction schedule requirements. With PSM, one full span of a precast-concrete box girder is manufactured in a casting yard, lifted by hydraulic jacks, transported with a special carrier, and placed by the launching girder into the final position. The PSM units are then tied into two or three 25-m (82-ft) or continuous spans using cast-in-place concrete in place of concrete and posttensioning. The contractors manufactured the PSM girders in a temporary manufacturing facility and reduced the installation cycle time for one 25-m (82-ft) long box girder to 11/2 days. The design, fabrication, transportation, and installation of the box girders for the Korean high-speed railway viaducts with PSM are discussed. Project and economic implications of PSM are compared with the movable scaffolding system method.

Shrinkage cracking at interior supports of continuous pre-cast pre-stressed concrete girder bridges

This study deals with the control of cracking at interior supports of continuous pre-cast pre-stressed concrete (PCS) girder bridges. Since PCS-girder bridges are constructed by placing in-situ concrete decks on the PCS-girders at time intervals, the differences in material properties and age at loading between the deck and girder lead to time-dependent material behaviors. In addition, the continuous deck by providing a negative moment connection at interior supports, also causes the transverse cracking of the concrete deck at interior supports. In that way, cracking at interior supports is predicted with the analytical model introduced in the companion paper. Based on the ACI model, the ultimate shrinkage strain is expressed as a function of concrete slump and the relative humidity while the other remaining factors such as unit weight of cement and air content are assumed, in accordance with the typical values in mixed concrete. Finally, field recommendations in terms of concrete slump and relative humidity are suggested to minimize early transverse cracking of concrete decks at interior supports.

Numerical analysis of time-dependent behavior of pre-cast pre-stressed concrete girder bridges

This paper deals with the analysis of uncertainties associated with the behavior of bridges constructed with pre-cast pre-stressed girders and a continuous deck. To analyze the long-term behavior of bridges, an analytical model which can simulate the effects of creep, the shrinkage of concrete, and the cracking of concrete slabs in the negative moment regions is introduced. Based on the equilibrium of forces and the compatibility of strains with time, the prediction of stresses and strains in the constitutive materials at any time is achieved. To consider the different material properties across the sectional depth, the layer approach in which a section is divided into imaginary concrete and steel layers is adopted. An element stiffness matrix is constructed according to the assumed displacement field formulation, and the creep and shrinkage effects of concrete are considered in accordance with the first-order recursive algorithm based on the expansion of the compliance function. Correlation studies between analytical and experimental results are conducted with the objective of establishing the validity of the proposed model. Also, many parameters related to the continuity of spans are analyzed to minimize deck cracking at the interior supports.

超高層RC建物用プレテンション方式PCaPC大梁の開発

RC造建物における大スパン梁の構築技術であるPCaPC (プレキャストプレストレストコンクリート) 大梁の更なる合理化を図り, プレテンション方式による工法を開発した。地震後におけるPC鋼材の付着性能を実験で確認し, 仙台市内に建設中の超高層集合住宅に初めて適用した。同建物での実測結果も併せて報告する。

Effect of Bearing Stiffness and Skew Angle on Performance of Precast Concrete Bridge

Reinforced elastomeric bearing pads generally support precast concrete bridge girders. The condition of these bearing pads and the pad-bridge interface defines the support boundary conditions of the bridge super-structure. The interface between bearing pads and bridge girders affects the performance of the superstructure and the substructure. The pads are designed to carry vertical loads and to accommodate horizontal movements of the bridge girders. A study was conducted to determine the effects of various parameters on bridge superstructure performance and to compare the girder performance with simple support conditions corresponding to the current Florida Department of Transportation design. A parametric study on the interaction of the support boundary conditions and bridge girders was performed. The parameters studied included the skewness of the bridge and the effect of the bearing stiffness on the bridge system. A finite element model of a bridge superstructure containing Florida bulb tee 78 girders was created using ANSYS software. The model was subjected to an HL93 truck load according to the AASHTO load and resistance factor design specifications. The results indicate that pads with higher bearing stiffness are beneficial to bridges with higher skew angles. However, the reductions in deflections and stresses are smaller for increasing skew angles.

Design of Route 895 Bridge over James River in Virginia

The Route 895 bridge over the James River in Virginia will be a 1453-m (4,766-ft) long design-build river crossing directly downstream from the Port of Richmond. The highway will have two three-lane roadways in either direction at the James River crossing. East and west approach spans consist of two precast segmental concrete box girders connected by a longitudinal cast-in-place construction joint supported by single circular column piers with hammerhead pier caps. The east approach span segments are erected in cantilever from the piers using ground-based cranes, whereas the west approach is erected using overhead methods because of access limitations beneath the bridge. The main span super-structure will be a two-celled cast-in-place segmental box girder supported by twin-walled piers at the river crossing and single-walled piers at all other locations. The eastbound river crossing span arrangement is 115, 205, and 124 m (377, 672, and 406 ft), and the westbound river crossing spans are 75, 129, 205, and 118 m (246, 423, 672, and 388 ft). Because this was a design-build project, coordination within the design team was a key factor in the project’s success.

Continuous precast concrete girder and slab bridge decks

The availability of powerful means of lifting and transportation, high-performance building materials and refined structural analysis methods, along with the use in the same structure of pretensioning, post-tensioning, prefabrication and in situ construction techniques, has led to considerable changes in the design and construction of concrete bridges. Such advances allow engineers to design and build, for example, continuous precast concrete girder bridges, constant or variable in depth and curved or straight in plan, which are comparable to those cast in place, due to their structural efficiency, aesthetic appearance and economical competitiveness. This paper describes the geometric characteristics, conceptual design, analysis and construction of a new type of continuous precast concrete girder bridge. A typical bridge consists of precast prestressed concrete beams with a U cross-section, monolithically interconnected by post-tensioning of the end diaphragms. A cast-in-place reinforced concrete slab, positioned on top, provides longitudinal continuity and shapes the box section with side cantilevers. Particular aspects related to the influence of the segmental construction on the structural behaviour at service of these bridges are discussed. Finally, some actual bridges are presented along with proposals for future applications to long-span bridges.

Long-Term Behavior of Continuous Precast Concrete Girder Bridge Model

Continuous concrete box girder bridges composed of precast reinforced and prestressed concrete beams with a U cross section and a cast-in-place top slab are frequently used for medium spans due to their competitiveness. The service behavior of such bridges is very much influenced by their segmental construction, due to time-dependent materials behavior that makes it difficult to accurately predict the stresses, strains, and deflections at long term. A 1:2 scale model of a two-span continuous bridge was tested in order to study its behavior during the construction process and under permanent loads. Time-dependent concrete properties, as well as support reactions, deflections, and strains in concrete and steel, were measured for 500 days. Important time-dependent redistributions of stresses and internal forces throughout the bridge were also measured. The test results were compared with analytical predictions obtained by means of a numerical model developed for the nonlinear and time-dependent analysis of segmentally erected, reinforced and prestressed concrete structures. Generally good agreement was obtained, showing the adequacy of the model to reproduce the structural effects of complex interactive time-dependent phenomena.

A Precast Segmental Substructure System for Standard Bridges

A precast segmented substructure system for standardization is presented. This system is intended to support precast concrete girder superstructures in non-seismic regions and provides an alternative to current cast in place systems, particularly for areas where reduced construction time is desired. The substructure system is made up of predominantly precast elements. Four different column sizes with one basic cap shape are proposed to be assembled as single column, straddle and frame bents for varying heights and widths of standard bridges. Precasting allows for increased use of high performance concrete in the substructures, thus improving durability. In addition, the greater compressive strength of the high performance concrete is utilized to reduce the handling weight and dead load of the substructure units, facilitating construction. The construction method proposed will significantly shorten on site construction time. Shortened construction time, in turn, leads to important safety and economic advantages when traffic disruption or rerouting is necessary.