Precast Prestressed Concrete Beams Research Articles

Experimental Study on Flexural Performance of Precast Prestressed Concrete Beams with Fiber Reinforcement

Fiber-reinforced concrete (FRC) has good toughness and a gentle stress–strain softening section, which can improve the inherent defects of concrete material such as high brittleness, easy cracking, and poor fracture toughness. In this paper, carbon fiber, aramid fiber and mixed fiber are introduced to enhance the performance of precast prestressed concrete beams (PPCB). The effects of different fiber types and adding rate on mechanical properties of FRC were studied via axial compression test and four-point bending test. Based on the flexural performance test of precast FRC beams, the failure form and the improvement degree of flexural ability of the beams were analyzed. Moreover, the load–deflection curve and the quantified ductility index obtained by the test were discussed, and the law of the improvement effect of fiber type on flexural property was revealed. The results show that the optimal addition rate of fiber is 0.6%. In addition, the addition of fiber significantly increased the cracking load and ultimate bearing capacity of the test beam, whereby the average increase in cracking load and ultimate bearing capacity was 40% and 20%, respectively. At the same time, the ductility of the beam is obviously enhanced by the action of fibers, among which the hybrid fiber has the best effect. Specifically, the ductility coefficient analysis verifies that aramid fiber plays an important role in improving the ductility of the components.

Experimental study of moment redistribution before yielding in precast prestressed concrete beams made continuous

AbstractThe bending stiffness distribution of beams composed of simple‐span precast prestressed beams, which are made continuous by deck reinforcement at intermediate supports, is not constant. As the structure undergoes loading, the deck slab at the intermediate support cracks earlier than the prestressed span soffit and due to that the bending stiffness distribution changes along the beam length. The effect of nonconstant bending stiffness distribution on the moment redistribution of the structure before the yielding is studied experimentally and analytically. Two continuous beams with spans of 10 m + 10 m were manufactured, loaded to failure, and studied. It was concluded that the studied structure undergoes considerable moment redistribution before yielding although it would be designed for zero redistribution at the ultimate limit state. If this elastic redistribution is neglected in the structural analysis, the service limit state sagging moment at midspan may end up on the unconservative side. Elastic redistribution can be predicted quite accurately with the help of nonlinear analysis or roughly with simplified idealization as proposed in this article.

RESTORING FORCE CHARACTERISTICS OF PRECAST CONCRETE BEAMS POST-TENSIONED BY UNBONDED TENDONS AT WIDENED BEAM END

Modeling on restoring force characteristics of unbonded precast prestressed concrete beams with widened beam end was proposed in this paper. One model has rotational springs at both the outer end of the general and widened beam end, and another model has one spring with a rigid zone at the end. Ten unbonded precast prestressed concrete beams whose parameters are beam longitudinal rebar amount, widened beam end size, prestressing force, etc., were constructed and tested. The proposed method captured the restoring force characteristics of the test results in good accuracy.

Shear design of precast prestressed concrete NEXT beam bridges: A critical assessment

Northeast extreme tee (NEXT) precast prestressed concrete beams have recently emerged as a promising solution to accelerate bridge construction and enhance the sustainability of bridges. To date, several studies on the live load distribution factor (LLDF) for moment and shear in NEXT F beam bridges have been reported, which indicated that using the AASHTO LRFD LLDF for moment in NEXT F beam bridges could provide a sufficient safety margin; however, a 20% increase in the LRFD LLDF for shear was recommended for the safety of shear design. This paper intended to investigate the required transverse shear reinforcements in NEXT F beam bridges by using a factor of 1.2 for the LRFD LLDF for shear. A comprehensive study was carried out by considering various parameters, including concrete strength, beam section, bridge section, and span length. Results from this study showed that providing the minimum transverse shear reinforcement could offer a sufficient safety margin for the shear design of NEXT F beam bridges, even with an increase of 20% on the LRFD LLDF for shear. It is recommended that a factor of 1.2 be used for the LRFD LLDF for shear to ensure a safe design of NEXT F beam bridges, though the minimum transverse reinforcements will be likely to control the shear design.

Negative bending tests on precast prestressed concrete beams made continuous

AbstractThe objective of the current study is to investigate and evaluate the flexural behavior of the continuity connection of precast prestressed concrete beams in negative bending when the tendons are located at the compression side. The experimental program included four T‐shaped composite cantilever beams which were loaded up to failure. The main variable of the tests was the amount of prestress force of the connected precast beams. The reinforcement ratio of continuity connection was high. The ultimate flexural capacities and moment‐curvature relations were calculated theoretically. A comparison was then carried out between both the experimental and theoretical results. These experiments revealed that prestress force did not influence the ultimate hogging moment capacity of the continuity connection, but it had an effect on its soffit's compression cracking and spalling of the concrete cover before failure. This study also indicated that confinement of the concrete had a massive influence on the connection's behavior, and it increased both its negative moment capacity and ductility.

Analysis of Prestressing in Precast Prestressed Concrete Beams

Abstract Knowledge of prestressing force’s value is in the case of prestressed concrete structure the most important basis for defining load-carrying capacity and remaining service life. Numbers of prestressed concrete structures are about to reach their limit of service life and they are exhibiting signs of deterioration due to the conceptional errors, inadequate maintenance and environmental distress. All of these factors negatively influence the actual state of prestressing. Thus, it is essential to determine the value of prestressing force considering the degradation of materials, such as corrosion of prestressing strands or wires. While assessing structure in service, it is difficult to apply magnetoelastic sensors or use other direct methods for determining the state of prestressing. Hence, the indirect methods enable to analytically calculate the prestressing force based on the results of measurement, e.g. strain, stress, deflection, or width of the crack. The present paper focuses on numerical analysis of prestressing in a twosome of precast prestressed concrete beams. For the numerical analysis, two indirect methods are applied, specifically Saw-cut method and Crack initiation method. Finally, the results are discussed and recommendations for the experimental campaign are summarized.

Indirect Determination of Residual Prestressing Force in Post-Tensioned Concrete Beam.

A diagnostic survey on the precast prestressed bridge Nižná confirmed significant deterioration due to environmental distress. Evidently, decisive failures of the structure have a similar character as in the previous precast prestressed bridge in Podbiel in the northern part of Slovakia. These failures result from the unsuitable concept of the first generation of precast prestressed concrete beams, which was used in the former Czechoslovakia in the second half of the 20th century. Subsequently, experimental verification using the proof-load test was also executed. This bridge was built in 1956, so at the time of testing, it was 60 years old. The paper presents the indirect determination of prestressing level in one precast post-tensioned concrete beam using the saw-cut method. Experimental measurement was executed during the bridge demolition. Subsequently, a 2D numerical model in ATENA 2D Software, with the assumption of nonlinear material behavior for verification of experimental results, was performed. Finally, the residual prestressing force was evaluated and compared with the expected state of prestressing according to Eurocodes after 60 years of service.

Nonlinear deformation analysis for precast pre-stressed concrete beam systems

The structural systems such as road bridge beam systems (span superstructure) or beam systems used in high-rise buildings with precast pre-stressed reinforced concrete might be subjected to the load higher than the calculated load of the design process. In the process of operation the internal forces of the beams reach to a certain value, the section stiffness in elements will be changed. The change in section stiffness will lead to redistribution of internal forces in the whole system. However, that has not been included in the design process. The paper presents nonlinear deformation analysis of precast pre-stressed beam system used in road bridge span superstructure or high-rise buildings using nonlinear model of materials according to Russian construction codes to build the relationship between internal forces and section stiffness. From the calculation results, some comments will be recommended about increased load capacity in comparison with the results obtained from analysis using linear model of material.

Experimental Study of a New Precast Prestressed Concrete Joint

Precast monolithic structures are increasingly applied in construction. Such a structure has a performance somewhere between that of a pure precast structure and that of a cast-in-place structure. A precast concrete frame structure is one of the most common prefabricated structural systems. The post-pouring joint is important for controlling the seismic performance of the entire precast monolithic frame structure. This paper investigated the joints of a precast prestressed concrete frame structure. A reversed cyclic loading test was carried out on two precast prestressed concrete beam–column joints that were fabricated with two different concrete strengths in the keyway area. This testing was also performed on a cast-in-place reinforced concrete joint for comparison. The phenomena such as joint crack development, yielding, and ultimate damage were observed, and the seismic performance of the proposed precast prestressed concrete joint was determined. The results showed that the precast prestressed concrete joint and the cast-in-place joint had a similar failure mode. The stiffness, bearing capacity, ductility, and energy dissipation were comparable. The hysteresis curves were full and showed that the joints had good energy dissipation. The presence of prestressing tendons limited the development of cracks in the precast beams. The concrete strength of the keyway area had little effect on the seismic performance of the precast prestressed concrete joints. The precast prestressed concrete joints had a seismic performance that was comparable to the equivalent monolithic system.

Seismic Performance Study on Side-Strengthened Concrete Beam Using Finite Element Analysis Method

Side-strengthened reinforced concrete or precast prestressed concrete beam for inadequate seismic performance is proposed in this paper. The factors are simulated by ABAQUS software for the impact of seismic performance, which are difference of material strength grade, initial load and the order of prestressing and pretightening. The strengthening technology can improve the seismic performance of side-strengthened beam. The meterials with different strength grades which used for beams give full play to their role. The initial load has little effect on the seismic performance. The way of prestressing after pretightening plays a favorable effect for the seismic performance. The simulation results can accurately reflect the impact of these factors on the side-strengthened beam.

Modelling and integrity assessment of shear connectors in precast cast-in-situ concrete bridges

Precast-cast insitu concrete bridge construction is widely practiced for small to medium span structures. These bridges consist of precast pre-stressed concrete beams of various cross-sections with a cast in-situ reinforced concrete slab. The connection between the beams and the slab is via shear links often included during the manufacturing process of the beams. This form of construction is attractive as it provides for standardisation, reduced formwork and construction time. The assessment of the integrity of shear connectors in existing bridges is a major challenge. A procedure for assessment of shear connectors based on vibration testing and finite element model updating is proposed. The technique is applied successfully to a scaled model bridge model and an existing bridge structure.

STRUCTURAL TEST OF PRECAST PRESTRESSED CONCRETE BEAMS USING LARGE DIAMETER PRESTRESSING STRANDS WITH PRETENSIONING SYSTEM

Precast prestressed concrete (PCaPC) beams with a pretensioning system are often used for constructing long-span reinforced concrete buildings. It is important to clarify the bond characteristics of the prestressing strands, because the concrete is prestressed through the bond between the strands and the surrounding concrete. A bond test and a loading test were carried out to clarify the bond characteristics and the structural performance of PCaPC beams using large diameter strands. As a result, the anchorage length of strands for prestressing and after large deformation, and the load-displacement relationship of the PCaPC beam under seismic loading were clarified. Based on these results, it is concluded that large diameter strands can be used as prestressing steel in PCaPC beams.

Longitudinal shear strengthening of composite bridge beams

A number of composite concrete bridges (i.e. bridges with precast prestressed concrete beams designed to act structurally in combination with a cast-in-situ concrete slab) were constructed in Western Australia in the 1960s and 1970s. Newer editions of bridge design codes have altered the requirements to which these bridges were designed. Recent assessments made on the basis of the new requirements have indicated that these structures exceed current stress limits in longitudinal shear and therefore need strengthening. To implement effective non-destructive retrofit strategies, Main Roads Western Australia (MRWA) initiated a testing programme to investigate the application of non-intrusive strengthening schemes comprising epoxy-bonding of carbon-fibre reinforced polymer (CFRP) and glass-fibre reinforced polymer (GFRP) products to reduced-scale specimens representing the connection between concrete elements in a bridge deck. A total of 32 specimens were tested. The tests were specifically designed to assess the strength of the connection under the small deformations generated in bridge decks under service conditions. The performance of the tested specimens has been compared in terms of relative slip and separation between the connected concrete blocks at peak force. The results have provided insight into the key variables that govern the strength of retrofitted connections under longitudinal shear (e.g. concrete roughness at the interface, concrete strength, reinforcement at the interface, anchorage/bonding, fibre direction, weaving pattern and thickness of the epoxy-bonded fibre composites). While the results were obtained for a specific Australian problem, they might have application to similar situations elsewhere.

Loading Behaviors of Superposed Aqueduct Affected by Segregating Layer Between PPCBs and Cast-<i>In Situ</i> RCF

Combined with the structural design of left-shore drainage aqueducts in China South-to-north Water Transfer Project, the structure of cast-in-situ reinforced concrete flume (RCF) with wide and shallow drainage section superposed on longitudinal precast prestressed concrete beams (PPCBs) was drafted. The 3D finite element models were built to study the normal service behaviors of the aqueduct with or without segregating asphalt layer between RCF and PPCBs. The results show that the segregating asphalt layer changes the structural compositions of aqueduct subjecting water loads and results in some effects on loading capacities of the PPCBs and the RCF, such as the larger displacement and tensile stress of PPCBs, the many longitudinal sections of subplate in whole tensile state with larger tensile stresses and the larger vertical tensile stresses at internal surface of sidewall. It provides valuable reference for designing the same kind of aqueduct.

휨과 비틀림을 받는 프리캐스트 PSC 역T형 보와 직사각형 보의 거동 비교

This study presents the behaviors of the typical architectural precast prestressed concrete beams, inverted tee and rectangular beams, subjected to combined flexural and torsional loads. For this purpose, two inverted-tee beams were designed with a parking live load, , and a market load according to the currently used typical shape in the domestic building site. Also, two rectangular beams were also designed as the same bottom dimension and area, and reinforced for similar strength as in the cases of inverted tee beams. Total of four beams were tested, under combined bending and torsion, analysed and compared. Test results showed that the cracking and ultimate flexural strength of the beams decreased under torsional loading. However, two different shaped-beams had roughly the same load resisting capacity in service and ultimate states.

Design and Construction of a Bridge in Very High Performance Fiber-Reinforced Concrete

The design, technology, and construction of a small road bridge made of very high performance fiber-reinforced concrete is described in this paper. The bridge consists of precast prestressed concrete beams with a cast-in-place ordinary concrete deck. A preliminary experimental investigation was conducted to define the mix design, to establish the properties of the material and its durability, and to study the flexural behavior of the prestressed concrete beams with and without the concrete deck. The effect of steel fibers at the structural level, where there is an influence of constitutive behavior and size effects, was analyzed by testing a prestressed beam using very high performance fiber-reinforced concrete without fibers. The establishment of the structural properties of the material then allowed the design of the final section of the bridge beams and the definition of a model to justify the design rules adopted. This project represents an attempt to demonstrate the industrial feasibility of very high performance concrete structural elements manufactured with conventional raw materials and usual production techniques and to evaluate the production technology when utilizing steel fibers.

鋼材と付着すべりと曲げせん断ひび割れを考慮したPCaPC梁の曲げ変形解析法

A flexural analysis method of precast prestressed concrete beams considering bond-slip characteristics of prestressing steels and deformations of flexural shear cracking was proposed. In this analysis method, the widths of flexural shear cracks are evaluated as the pullout of stirrup, based on the bond force distributions of prestressing steels and tension reinforcements due to the bond-slip analysis. It is concluded that the load-deflection relationships, the crack patterns and the strain distributions of prestressing steels and stirrups in test beams can be simulated by using this analysis method.

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.

The first incrementally launched bridges in Hong Kong

The Hong Kong Government invested HK$1760 million (US$225 million) to build a 24 km trunk road with a dual 3-lane carriageway from Sha Tin to Fanling in the eastern New Territories to serve the new towns and also to cater to the increase in cross-border traffic with China. The section Tai Po Bypass, which is 2.9 km long, required the construction of four viaducts ranging from 116 to 242 m long with columns up to 30 m high. The original design of these bridges adopted precast prestressed concrete beam construction. An alternative design using the incremental launching method to construct these bridges was proposed by the contractor with a saving of HK$10 million in contract costs. Specialist subcontractor and consultants from overseas were involved in the design and construction of these launched bridges, which were the first to be constructed in Hong Kong. With the effort of engineers from four continents, this project was completed ahead of schedule, and the road system was open to traffic in September 1985. Key words: prestressed concrete, alternative design, incremental launching.

Development of Continuity Between Precast Prestressed Concrete Beams

THE WIDESPREAD USE OF PRECAST PRESTRESSED CONCRETE ELEMENTS IN THE CONSTRUCTION OF BUILDINGS AND BRIDGES IS AMPLE EVIDENCE OF THE ECONOMY WHICH CAN OFTEN BE GAINED BY THIS TYPE OF CONSTRUCTION. THIS PAPER IS CONCERNED WITH THE DEVELOPMENT OF CONTINUITY BETWEEN PRECAST PRESTRESSED BEAMS, WHICH CAN LEAD TO FURTHER ECONOMY IN MANY CASES. THIS CONTINUITY CAN BE DEVELOPED IN SEVERAL WAYS TO PRODUCE SERVICEABLE MEMBERS. THE USE OF PRECAST PRESTRESSED CONCRETE RODS AS REINFORCEMENT APPEARS TO HOLD SOME ADVANTAGE AS FAR AS CRACK CONTROL IS CONCERNED. NO POST TENSIONING IS REQUIRED FOR DETAILS USING THESE RODS. BEAMS WITH SOME POSTTENSIONED STRANDS COMBINED WITH PRETENSIONED AND UNSTRESSED REINFORCEMENT ALSO GIVES VERY SATISFACTORY RESULTS. /AUTHOR/