Prestressed Concrete Beams Research Articles

Crack propagation control for a pre-stressed concrete beam utilising coupled sensitivity indices-Pareto optimisation method

Crack propagation control for a pre-stressed concrete beam utilising coupled sensitivity indices-Pareto optimisation method

Influence of chloride-induced corrosion on the traffic vulnerability of simply supported Italian PC bridges: a preliminary study

In Italy, a large part of road bridges was built after the Second World War, mainly with Reinforced Concrete (RC) or Prestressed Concrete (PC) simply supported decks. Most of the bridges currently in service have been designed with outdated codes and could be inadequate to modern heavy traffic loads. Furthermore, their structural performance decrease over time due to ageing effects, like steel corrosion.Bridges are often exposed to chlorides from de-icing salts or marine environment; chloride diffusion in concrete can induce pitting corrosion of steel reinforcing, decreasing the structural resistance of bridge elements. As part of a broader study on the structural risk of existing bridges with respect to traffic loads, it is certainly of interest to investigate the influence of chloride-induced corrosion on the risk itself.In this preliminary study, four sets of simply supported decks made of precast PC beams and a cast in-situ RC slab were designed according to outdated Italian codes relating to different construction periods (60s, 70s, 80s, and 90s); each set is composed by bridges with different span, width, number of main girders and transverse diaphragms. The deck design took into account only the bending failure of the main girders, in order to determine the minimum amount of strands and steel reinforcements required. The vulnerability to traffic loads is evaluated with respect to the bending moment resistance of the main girders. Monte Carlo simulations were performed to evaluate the decrease over time of the resisting bending moment of the main girders, taking into account literature models for estimating the time to corrosion and corrosion propagation both in strands and in steel reinforcements.

Evaluation of minimum flexural reinforcement for precast prestressed concrete NEXT beam bridges

The minimum flexural reinforcement requirement has been used in the current bridge design specifications to protect the member from brittle failure after the formation of the first flexural cracks. Several variables have been reported to affect this requirement, such as concrete strength, amount of prestressing in the member, and type of cross section. Recently, the Precast/Prestressed Concrete Institute (PCI) developed a new type of beam section (NEXT beam) to accelerate bridge construction and enhance the sustainability of bridges. As a newly developed beam section, no research on the minimum flexural reinforcement has been reported for NEXT beam bridges. This paper aimed to examine the minimum flexural reinforcement requirements in the current AASHTO LRFD Bridge Design Specifications for NEXT beam bridges. A comprehensive parametric study was analytically conducted with various parameters, including bridge section, beam section, concrete strength, and span length. The results from this study showed that the current minimum flexural reinforcement requirements were met for all bridges examined herein; the concrete strength, beam cross section, and span length could affect the levels of safety against brittle failure after first flexural cracks for NEXT beam bridges.

Analytical Performance Assessment of Deteriorated Prestressed Concrete Beams

In this paper, a new approach is developed to numerically evaluate the structural performance of deteriorated prestressed concrete beams using the finite element analysis application RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology). A prestressing steel element was modified to represent the interaction between deteriorated concrete and prestressing steel. Considering the corrosion effects—as shown by the reduction of the prestressing steel section and loss of bond—a nonlinear material model was proposed for deteriorated prestressed concrete behavior. The modified damage index is intended to provide a numerical method for quantifying the structural performance of deteriorated prestressed concrete beams. The analytical procedure developed for the performance evaluation of deteriorated beams was validated by comparison with the credible test results, thereby enabling a more reliable and rational prestressed concrete beams design process.

Experimental study on the flexural behavior of bonded prestressed concrete beams strengthened with CFRP sheets

This paper presents an experimental study on the flexural behavior of bonded prestressed concrete (PC) beams strenthening using CFRP sheet. Two (PC) beams were fabricated, with overall dimensions of 150 × 200 × 2700 mm. One specimen served as an unstrengthened control, while the other was strengthened using CFRP sheets to enhance flexural performance. The specimens were simply supported and subjected to a four-point bending test until failure, allowing assessment of their flexural behavior. The results show that the CFRP-strengthened PC beams exhibited a 24% increase in load-bearing capacity compared to the control specimen. The stiffness of the strengthened beams was also significantly enhanced, leading to a reduction in deflection. Based on the obtained results, it is evident that the application of CFRP sheets for strengthening PC beams is a viable solution.

Bearing capacity of UHPC‐NC connection structure in negative moment zone of PC beam bridges

AbstractA new type of UHPC‐NC (normal concrete) structure in the negative moment zone was proposed to improve the bearing capacity of the connection structure in the negative moment zone of prefabricated prestressed concrete (PC) beam bridges. First, the distribution characteristics of the crack, cracking load, ultimate moment, and ductility coefficient of the new structure were obtained by the 1:4 scale model tests. The feasibility of the connection structure is verified. Then, the value ranges of critical structural parameters affecting the bearing capacity of the connection structure based on the plane section assumption analysis, including the reasonable thickness of the UHPC layer, the reinforcement ratio of the longitudinal tensile reinforcement, and the diameter of the reinforcement, are obtained. At the same time, based on the verification of the finite element model, the influence of crucial research parameters on the bending capacity of the connection structure is obtained by using the finite element method. Finally, a theoretical method for the bending moment capacity of the connection structure of the UHPC‐NC structure is proposed, considering the high ductility characteristics of UHPC materials. The average relative error between the calculation results and the finite element method is within 7.2%, which verifies the reliability of the calculation method in this paper and provides a reference for its design and engineering application.

Assessment of Deflection Prediction Models for Cracked Prestressed Concrete Beams

Assessment of Deflection Prediction Models for Cracked Prestressed Concrete Beams

Experimental study on flexural behavior of segmental precast large-cantilevered prestressed concrete cap beam

This study investigates the influence of epoxy joint configuration and longitudinal reinforcement continuity at the joints on the mechanical properties of segmental precast assembled large-cantilevered prestressed concrete (PC) cap beams under the co-action of flexural and shear internal forces. Accordingly, a practical project is considered, and five segmental precast-assembled large-cantilevered PC cap beam models as well as a comparative model of a monolithic precast large-cantilevered PC cap beam are designed and produced. The five segmental precast cap beam models were designed with a 1/5 scale ratio, and the joint interfaces were all connected using an epoxy resin binder. Three of these models whose longitudinal reinforcements at the joints were discontinuous utilized a large key tooth, a small key tooth, and corbel joint structures. The other two models whose longitudinal reinforcements at the joints were connected by grouted sleeves adopted large key-tooth and corbel joint configurations. Throughout the static loading test process of these six cap beam models, key results, such as the initial stiffness, cracking load, yield load, ultimate load capacity, concrete strain, deflection, and crack width, were obtained. The experimental results are as follows. The failure process and crack distribution patterns of each precast segmental cap beam model are fundamentally the same as those of the monolithic precast cap beam model. The crack distribution is sparse, cracks are wide, and the failure modes are all due to bending. Additionally, the mechanical properties of the three precast segmental cap beam models with discontinuous longitudinal reinforcement compared with those of the monolithic precast cap beam model were considerably degraded. The initial stiffness, yield load, ultimate load capacity, and ultimate deflection were only 81.4%, 80.4%, 81.1%, and 66.4%, respectively, of those of the monolithic precast cap beam model. Moreover, penetrating cracks formed in the concrete of the tensile zone on both sides of the epoxy joint interfaces during failure. Compared with the segmental precast cap beam models with discontinuous longitudinal reinforcement, the initial stiffness, yield load, ultimate load capacity, and ultimate deflection of the segmental precast cap beam models with continuous longitudinal reinforcement significantly improved. The mechanical properties of the latter were similar to those of the monolithic precast concrete cap beam model. Based on the experimental results, effective technical measures (such as grouted sleeves) were proposed to connect the longitudinal reinforcement at the joints. This ensured that the static performance of the segmental precast-assembled large-cantilevered PC cap beam was similar to that of the monolithic precast cap beam.

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.

Effect of Tendon-Related Variables on the Behavior of Externally CFRP Prestressed Concrete Beams.

This work assesses the flexural performance of prestressed concrete beams with external carbon fiber-reinforced polymer (CFRP) tendons, focusing on tendon-related variables. A finite element analysis (FEA) method is verified. A numerical parametric analysis of prestressed concrete beams with external CFRP tendons is carried out. Four tendon-related variables are considered, namely, the area, initial prestress, depth and elastic modulus of tendons. The analysis shows that flexural ductility decreases as the tendon area, initial prestress or elastic modulus increases but is insensitive to the tendon depth. The ultimate tendon stress increment (Δσp) is influenced by all of the four variables investigated. JGJ 92-2016 (Chinese technical specification for concrete structures prestressed with unbonded tendons) significantly underestimates Δσp and, hence, is over-conservative for the strength design of these beams. An equation is proposed for calculating Δσp, taking into account all four variables investigated. An analytical model is then developed to estimate the flexural strength (Mu) of prestressed concrete beams with external CFRP tendons. The proposed analytical model shows good agreement with FEA, i.e., the mean discrepancy for Δσp is 0.9% with a standard deviation of 11.1%; and the mean discrepancy for Mu is -1.6% with a standard deviation of 2.1%.

Flexural behaviours of pretensioned prestressed concrete-UHDC composite beams reinforced with CFRP bars

Prestressing fiber reinforced polymer (FRP) bars is widely acknowledged as an effective method for exploiting their high strength. However, compared to FRP reinforced concrete structures, prestressed FRP reinforced concrete structures exhibit weaker deformation capacity. To address this issue, ultra-high ductile concrete (UHDC) was employed to enhance the flexural behaviours of pretensioned prestressed concrete (PPC) beams reinforced with carbon fiber reinforced polymer (CFRP) bars, while additional aluminium alloy ribs (ARs) were utilized to ensure proper anchorage. A total of eight beams were designed and tested, consisting of four PPC beams and four PPC-UHDC composite beams, which featured different types of CFRP bars, reinforcement ratios and UHDC placement. The test results revealed that the CFRP-reinforced PPC-UHDC composite beams exhibited significantly improved flexural performance in terms of cracking load, ultimate load and ultimate displacement. For specimens with lower reinforcement ratio, the UHDC effectively controlled the cracks and promoted uniform strain in the CFRP bars, leading to increased ultimate load capacity and ultimate displacement. For specimens with higher reinforcement ratios, the flexural performance was comprehensively improved when the UHDC was placed in the compression zone. Numerical analysis was conducted to further investigate the flexural behaviours of PPC-UHDC composite beams under various conditions.

Calibrating of a Simulation Model to Predict the Flexural Capacity of Pre-Stressed Concrete Beams

Simulation models based on finite elements are currently indispensable tools for predicting the structural behavior of both reinforced and pre-stressed concrete elements. This work develops a simulation model of structural linear elements of pre-stressed concrete, using the finite element method (FEM). The main aim was to calibrate the model to predict the flexural capacity of structural elements, and so be able to undertake a double optimization through the design and the resistant behavior of the elements. Different flexural experiments were conducted in laboratory conditions on real concrete elements of different types (pre-stressed joist and tubular pre-stressed joist). In parallel, the same structural elements were analyzed by MEF simulation to calibrate the model to the real experiments. FEM analysis was performed using the ATENA software developed by Červenka Consulting (Czech Republic), especially recommended for the analysis of structural concrete elements using non-linear methods. The model was calibrated using the results obtained in real load test experiments obtained in a loading frame of 500 kN capacity. The calibration analysis shows a good fit of the results to the actual test experiments, obtaining average errors of 6% in the analysis–experiment comparison. The results of the simulation suggest that to obtain the optimum strength levels for the different typologies analyzed, it is essential to control the pre-stressing losses in the manufacturing process of the joist. The flexural capacity of all elements can be increased by around 20–30% when the real pre-stressing losses are fitted to the theoretical ones estimated.

Effect of strand debonding on the shear strength of existing pretensioned PC hollow slab

Pretensioned PC (prestressed concrete) beams experience strand debonding failure at the ultimate loading stage, which leads to bond-loss failure of the beams. To study the effect of strand debonding on the shear strength of pretensioned PC hollow slabs, the existing PC hollow slabs of 19 specimens with spans of 10, 13, 16 and 20 m used in Chinese expressway bridges were loaded to bond-loss failure. The strand slip, bond- loss failure mode and shear strength of 19 specimens and 31 shear tests were analyzed. The test results showed that the angles of the failure diagonal cracks were not consistent with the Ross model. Therefore, a refined model to predict the shear strength subjected to pretensioned PC hollow slabs was developed. Other factors were also considered in the refined shear strength model, including the dowel action of longitudinal reinforcements, the prestressed strand development length and the compression zone height. Compared with the shear failure controlled by strand yielding, the shear strength controlled by strand debonding was decreased by approximately 27 %. The test results showed that the debonding induced bond-loss failure could be described as follows: after the formation of the failure diagonal crack, the strand will clearly slip, and concrete parts on both sides of the failure diagonal crack rotate around the crack tip. Due to the debonding induced bond-loss failure of the pretensioned PC hollow slab, the shear strength could not be improved even by increasing the concrete strength of the compression zone. Finally, the validity of the refined model was verified by 23 test specimens.

Arch Action Model for the structural assessment of existing prestressed concrete bridges

AbstractStructural assessments of existing older prestressed concrete bridges according to the currently applicable standards and guidelines in Germany generally reveal significant deficiencies in shear reinforcement. Large‐scale tests within the scope of research activities commissioned by the Federal Highway Research Institute (BASt) were carried out at TU Dortmund University to analyze the shear load‐bearing behavior of continuous prestressed concrete beams in more detail. The Arch Action Model (AAM) was derived from the Simplified Arch Action Model (SAAM) to provide a possible analysis method for determining shear contribution from concrete. Thus, the shear capacity of prestressed beams can be determined in a more realistic manner than using the truss model underlying the current state of standardization. The paper at hand provides information and explanations about the SAAM and AAM with regard to their application to real‐world structures for structural bridge assessments.

A prediction model for flexural strength of corroded prestressed concrete beam using artificial neural network

A prediction model for flexural strength of corroded prestressed concrete beam using artificial neural network

Long-term investigations of dynamic behavior of a pre-stressed concrete ballasted railway bridge

Dynamic properties of civil structures such as natural frequencies, damping ratios, and mode shapes are essential parameters for evaluating the health condition of structures. However, dynamic properties are prone to be biased by environmental effects which may lead to fault structural health assessment. To investigate the environmental effect on the dynamic parameters of ballasted bridge, in this paper, a series of vibration experiments were performed on a multi-span pre-stressed concrete beam railway bridge. The dynamic properties of the bridge were identified and analyzed. In total, 9 experiments were conducted in 2 years. In the first 8 experiments, only sleepers and tracks had been removed. For the last experiment, the bridge was under destruction. The subsidiary components of the structure were destructed, and some holes were drilled on the slab for hoisting. The results show a clear seasonal variation in natural frequencies that in winters the natural frequencies reach local maximum values. Damping ratios show no clear variation regularity, indicating the complex correlation between the damping ratios and the environmental variation. Additionally, compression tests of concrete pieces of the slab were also conducted to investigate the degradation of material properties. The result of the compression tests indicates that there is approximately no degradation of compression strength of the concrete slab after the bridge was in service for several over 4 decades.

Comparative study on the influence of mono fibers in the behaviour of RCC & PSC beams

One of the hopeful solutions to augment flexural behaviour of reinforced cement concrete (RCC) and prestressed concrete (PSC) is the addition of fibres. All the flexural parameters namely peak load, cracking load and crack propagation improve in the presence of fibers in the matrix. Cracks are bridged well when fibers are present in concrete. The present work, intends to evaluate the influence of steel and basalt fibers in the flexural parameters of RCC and PSC beams made of M40 grade concrete. Hardened concrete properties are evaluated by adopting the volume fractions 0.25%, 0.5% and 0.75%. Results proved that the steel and basalt fibers at 0.75% and 0.25% resulted in optimum values. These fiber volume fractions were used to cast PSC and RCC beams. Later their behaviour was compared in flexure.

Synergetic concrete shape and cable layout optimization of pre-stressed concrete beams

Synergetic concrete shape and cable layout optimization of pre-stressed concrete beams

Size‐scale effects in high‐performance reinforced and prestressed concrete T‐beams

AbstractReinforced concrete (RC) and prestressed concrete (PC) structural elements need to be designed in order to guarantee large plastic deformations, avoiding any loss in their load bearing capacity. In this framework, the rotation capacity of RC and PC beams has been demonstrated to be a function of concrete mechanical properties, reinforcement characteristics, and of the structural size. On the other hand, Theory of Plasticity as well as the International Standards completely disregard size‐scale effects and ductile‐to‐brittle transitions, leading to an overlook of the strain‐softening behavior of the concrete matrix and of the rotation capacity of RC beams. On the other hand, the Cohesive/Overlapping Crack Model is able to evaluate concrete cracking in tension and concrete crushing in compression, as well as snap‐back and snap‐through unstable phenomena, steel yielding and/or slippage. This Nonlinear Fracture Mechanics model predicts a reduction in the moment versus rotation plastic plateau by increasing the beam depth and/or the reinforcement percentage. The numerical investigations carried out on reinforced and prestressed high‐performance concrete beams having rectangular or T‐shaped cross‐sections highlight the size‐scale effects on plastic rotation capacity that allow to formulate new scale‐dependent upper and lower limits of reinforcement percentage to guarantee a stable and ductile postpeak behavior of reinforced concrete structures.