Post-tensioned Tendons Research Articles

Carbon Fiber Reinforced Polymer (CFRP) Laminates: Flexural Strengthening Method for Prestressed Concrete Beams with Anchorage Loss

Abstract Post-tensioning (PT), a method of pre-stressing, involves the use of high-strength steel strands/ tendons to reinforce concrete or other materials. On the contrary, Carbon Fiber-Reinforced Polymers (CFRP) are lightweight, high-strength materials with used to strengthen concrete structures by adhering the polymer to the concrete element. Challenges with post-tensioned elements include reverse curvature of the post-tensioning strands, tendon misplacement, and frequent damage in the anchorage and dead-end zones. These difficulties frequently cause bulging of the surrounding concrete, even at lower stress levels, and can lead to concrete bursting when tension exceeds certain threshold. This study investigates into the potential of CFRP strengthening technique to improve the flexural capacity of post-tensioned concrete beams with anchorage loss. Through an experimental program, the study compares the performance of control beams to those reinforced with different layers of CFRP. The results of this study demonstrated that there was a significant increase in flexural capacity, ranging from 45.31% to 78.62% for single layers and 87.17% to 153% for double layers of CFRP sheet. Additionally, the research examines how different levels of prestressing and CFRP wraps influence crack formation and delamination patterns of carbon fiber, with promising results. It was also noted that optimal usage of CFRP fibers and tendons is found to be critical. The study suggests exploring alternative fiber types and orientations for future study.

Seismic performance assessment and fragility analysis of concrete structures equipped with self-centered hybrid wall systems

ABSTRACT In this study, comprehensive analytical and parametric studies were conducted on seismic performance, collapse and fragility curves of concrete structures equipped with self-centered unbonded post-tensioned hybrid wall system in comparison with conventional structural wall system. For this purpose, analytical models of prototype buildings were developed and to further study the behaviour of hybrid wall, parametric analysis was performed considering four parameters: wall aspect ratio, initial stress of post-tensioned tendons, the total area of PT tendons, the total area of mild bars. The performance of buildings was evaluated under non-linear quasi cyclic and time history method considering two seismic hazard levels, the design-based earthquake level and the risk-targeted maximum credible earthquake level. Hysteresis response, energy dissipation ability and damping ratio, relative self-centering efficiency, residual drift, peak roof drift, column curvature ductility, incremental dynamic analysis data, seismic collapse assessment and fragility curves for collapse and repairable limit states were studied.

Prestressed CFRP Plates and Tendon Strengthening of Steel–Concrete Composite Beams

This study aims to enhance the ultimate capacity and stiffness of steel–concrete composite beams through external strengthening with prestressed carbon fiber-reinforced polymer (CFRP) plates and post-tensioned CFRP tendons. A 3D finite element model was developed using ANSYS and validated using experiments. The impact of various parameters on the capacity of the beam was investigated, including the level of post-tensioning in the CFRP tendons, tendon profile, degree of shear connection, and beam load level when adding strengthening CFRP tendons. Results indicate that reinforcing composite beams with bonded CFRP plates using post-tensioning tendons with trapezoidal and parabolic profiles can increase maximum load capacity by 37% and 60%, respectively, while maintaining high stiffness. This study also indicates that the optimal strengthening conditions for the composite beam are when the beam is loaded up to 70% of its capacity and has a composite action degree of 100%.

Experimental study on seismic performance of post-tensioned precast segmental piers designed with multiple joint openings

In accelerated bridge construction (ABC), precast segmental piers (PSPs) have shown significant progress in shortening the construction period and reducing the cost. By combining multiple segments with post-tensioned (PT) tendons, the desired self-centering ability can be introduced; however, this may lead to a lower energy dissipation (ED) capacity and concentrated damage. To address this concern, the present study proposes a design concept that promotes multiple joint openings to achieve a better energy dissipation capacity and decentralized damage without compromising the self-centering ability. Two main approaches for this objective are discussed in detail. The first approach incorporates different arrangements of ED rebars at various joints, while the second introduces innovative damage control rubber joints (DCRJs) with varying stiffness beneath each segment. Four scaled specimens designed using these two approaches were quasi-statically tested. The observed damage, final failure mode, energy dissipation capacity, resilience index, and damage decentralization were further examined. The results revealed that for PSPs designed using the first approach, the joint openings were successfully decentralized only up to a certain level, after which they were still predominantly concentrated at a single joint, leading to strength degradation and damage concentration. PSPs designed using the second approach demonstrated decentralized joint openings, improved displacement ductility, and damage mitigation, resulting in both superior seismic and post-seismic performance.

Effects of Grout Condition on Galvanic Coupling and Hydrogen Absorption in Post-Tensioned Bridge Tendons Constructed with Galvanized Steel Ducts

There has been concern that prestressing structural steel contained within galvanized bridge tendon ducts may become embrittled due to excessive galvanic coupling with the duct which may be exacerbated by deficiencies within the grout fill. This work strives to quantify the level of galvanic coupling achievable as a function of grout conditions and assess whether such conditions may promote water reduction and hydrogen absorption. Experimental tendon assemblies were used to quantify galvanic coupling considering a single prestressing steel wire and various grout conditions. The results were related to more realistic geometric configurations by simulations considering a range of possible kinetic boundary conditions. A model is used to estimate the amount of hydrogen that may be absorbed as a function of time considering the coupling current density.

High-performance grout for post-tensioned tendons (Review Paper)

High-performance grout for post-tensioned tendons (Review Paper)

Detecting wire breaks in post-tensioned tendons of wind turbines: A signal energy spectrum analysis approach

In the wind industry, recent advancements have led to the research and development of wind turbines featuring hybrid towers, a novel combination of steel tube and precast concrete segments. These concrete modules, which absorb the high stresses caused at the intersection between the tower and its foundation, are commonly joined with post-tensioned tendons. This study focuses on the identification of wire breaks in post-tensioned tendons through the application of acoustic emission testing. Measurements involve the evaluation of wire breaks under controlled laboratory conditions and the analysis of the dynamic operational environment of a functioning wind turbine. The investigation encompasses the development and assessment of a methodology based on principles of discrete Fourier transformation and Parseval’s theorem for analyzing the frequency-dependent energy distribution of acoustic signals. This analytical approach extends to the examination of wire breaks generated under varying stress levels as well as the operational noise within the actual wind turbine. The findings demonstrate a notable concentration of energy within the frequency range of 5-20 kHz in the wire break signals. In contrast, the operational noise signals show a distinct pattern, presenting an extreme value distribution within the 0-2 kHz range. The developed methodology exhibits robustness, even in the presence of high background noise levels, establishing itself as a valuable tool for wire break detection. Additionally, its potential for integration with machine learning algorithms offers the prospect of automated wire break detection, enabling further advancements in structural health monitoring for wind turbines.

Corrosion-induced fragility of existing prestressed concrete girder bridges under traffic loads

Italian and European transportation networks include a significant number of existing bridges, built since the early ‘60s, characterised by simply supported prestressed concrete (PC) girders with post-tensioned steel tendons. Corrosion of tendons, which may lead to significant loss of structural capacity, cannot be detected by simple visual inspections and requires advanced and expensive testing by bridge owners. Therefore, procedures aimed at risk-informed prioritisation of advanced inspections and possibly retrofit are needed. The paper presents a study on the fragility of existing PC girder bridges considering traffic loads, accounting for corrosion-induced effects. An automated framework is proposed, aiming at the efficient probabilistic structural assessment of the investigated bridge typology accounting for different critical corrosion scenarios and the influence of knowledge-based uncertainty related to geometric and mechanical properties. To simulate corrosion effects, prestressing steel tendon geometric and mechanical characteristics are modified through a specific algorithm able to estimate variations in flexural and shear bearing capacity of critical cross-sections. To simulate the traffic loads, a simplified analysis is performed by using code-based traffic load models. In the paper, the framework is tested with reference to a dataset of case-study superstructures. The obtained fragility curves are deeply discussed, highlighting the effects of the number of girders and span length on the corrosion-induced increase in fragility. Although the proposed methodology presents some simplifications, it could improve the current practices of risk prioritisation, by supporting transportation authorities in ensuring the safety of the existing bridge stock.

Performance of RC frames strengthening by external post-tensioning tendons under vertical and lateral loads

In this study, the structural performance of reinforced concrete frames strengthened with external post-tension tendons was investigated. An experimental study was performed to investigate the failure modes and generate the data required to validate the numerical model. The experimental study includes a reinforced concrete (RC) frame control specimen without strengthening and three strengthened specimens under vertical loads. The specimens were strengthened using external post-tensioning with three different tendon layouts, including a straight tendon in the beam-positive moment zone, straight tendons in the beam-positive and column-negative moment zones, and U-shape tendons along the frame beam. The numerical model was built for the four specimens, validated using the experimental results, and used to analyze the lateral load performance. Results showed that the most effective strengthening technique for the vertical load was the beam U-shape tendons, and for the lateral load, it was the beam and column strengthening. It can be concluded from this case study that strengthening frames with external post-tensioning techniques can enhance the first crack load, yielding load, and ultimate load by 80–100 %, 180–250 %, and 35–70 %, respectively.

Grouting inspection of PC bridge girder using Ultrasonic Pulse Echo Tomography and multiparameter evaluation procedure

Assessing the condition of grouting in post-tensioned tendons within Prestressed Concrete (PC) structures stands as a challenge in the field of civil engineering infrastructure maintenance. Current non-destructive testing (NDT) techniques employed for grouting assessment have certain constraints. For instance, the Impact-Echo method exhibits relatively low accuracy, while the X-Ray method proves to be costly and demands significant time and labor resources. Simultaneously, there exist promising alternative NDT techniques that offer potential for grouting inspection. In this study the authors used commercially available Ultrasonic Pulse Echo Tomography device with an array of dry-contact sensors and multiparameter method of evaluation. The evaluation method uses amplitude of ultrasonic pulse reflected from PC sheath, backwall and phase of reflected ultrasonic pulse. The experimental study on large-scale specimens confirmed that the evaluation method allows to achieve higher accuracy, as compared to existing methods of evaluation. The developed procedure was applied for inspection of PC bridge girder on an existing road bridge. The inspection was carried out on one of the spans of the bridge, which had 4 I- shaped PC girders. The results of Ultrasonic Pulse Echo Tomography were confirmed by means of drilling and borescope inspection method The results of both methods showed good correlation.

Experimental study on grouting inspection of PC tendons by means of Ultrasonic Pulse Echo Tomography method

Evaluation of grouting condition of post-tensioned tendons in Prestressed Concrete (PC) structures is an important problem in a field of maintenance of civil engineering infrastructure. Existing methods of non-destructive testing (NDT) used for grouting inspection have some limitations. For example, Impact-Echo method has comparatively low accuracy and X-Ray method is expensive and time- and labor-consuming. At the same time, there are promising alternative methods of NDT, which can be used for grouting inspection. The authors carried out an experiment using several large-scale specimens simulating PC girders. Commercially available Ultrasonic Pulse Echo Tomography device with an array of dry-contact sensors was used. Several cases of grouting condition, PC sheath diameter and geometry and rebar placement were studied. It was confirmed that amplitude of reflected ultrasonic pulse in the case of not grouted PC sheath is larger, as compared with a case of a grouted PC sheath. However, depending on diameter of PC sheath, distance from PC sheath to concrete surface and presence of nearby reinforcement, evaluating grouting condition based only on amplitude of reflected ultrasonic pulse can be problematic. To solve this problem authors developed a more accurate method of evaluating grouting condition, which uses multiple parameters, such as amplitude of ultrasonic pulse reflected from PC sheath, backwall and phase of reflected ultrasonic pulse.

Innovative Methods to Improve the Seismic Performance of Precast Segmental and Hybrid Bridge Columns under Cyclic Loading

This paper investigates the seismic performance of prefabricated segmental bridge columns (PSBCs) with hybrid post-tensioned tendons and energy dissipation (ED) bars under cyclic loading. PSBCs with unbonded and hybrid bonded prestressed tendons and columns incorporating ED bars are designed to improve the lateral strength, energy dissipation, and limit the residual drift. The PSBCs under cyclic loading were investigated using the three-dimensional finite element (FE) modeling platform ABAQUS. The FE model was calibrated against experimental results, with an overall error of less than 10%. The seismic performance of the proposed PSBCs was evaluated based on critical parameters, including lateral strength, residual plastic displacement, and the energy dissipation capacity. The results show that bonding the tendons in the plastic hinge region as opposed to the overall bonding along the column leads to a better cyclic performance. The lateral strength, and recentering abilities are further improved by bonding tendons up to 2/3 of the length in the plastic hinge region, along with 100–300 mm in the footing. It was also found that selecting a longitudinal length of ED bars crossing multiple precast segmental joints and having a circumferential spread of 70–90% of core concrete results in a higher bearing capacity and energy dissipation compared to ED bars crossing the single joint.

Self-centering concrete-filled steel tubular column-steel beam joint: Experiment and numerical modeling

This paper studied the seismic behavior of a novel self-centering concrete-filled steel tubular column-steel beam (SCSTCSB) joint. The restoring force was provided by the post-tensioned tendons arranged in the CFST columns. Cyclic loading tests were performed on five 1/3 scaled specimens by varying the parameters of steel tendon type, concrete strength (fc), and axial compression ratio (n). The failure modes, hysteresis behavior, stiffness and strength degradation, energy dissipation, post-tensioned tendons response, residual deformation, and strain distribution were studied in detail. The finite element models were established to capture the stress distribution of the joints. In addition, parameter analysis was performed by expanding 17 finite element models. The results show that the ratio of residual deformation to beam rotation angle of the specimens ranged from 0.068 to 0.172. And the proposed joints demonstrated excellent self-centering ability. The self-centering (SC) performance of joints with ordinary steel tendons was better than that of joints with high-strength steel tendons. With the increase of n, the SC performance of the joints intensified at the lower ratio (n from 0.1 to 0.3) and weakened after n = 0.3. The flexural capacity of the joints improved with the increase of axial compression ratio (n), width-thickness ratio (D/t), diameter of steel tendons (d), and assembly part strength (fy,a).

Experimental research on seismic performance of dry-wet combined precast concrete beam-to-column connections

In order to enhance on-site assembly efficiency and construction organization flexibility, a new type of dry-wet combined precast concrete beam-column connection was proposed. The prefabricated beams and columns were joined together using local post-tensioned tendons to create a temporary frame structure with dry connections. Subsequently, the wet connections between the prefabricated beams and slabs were established by pouring cast-in-place top concrete. A monolithic connection and four full-scale precast connections were subjected to reversal cyclic loading, with each designed incorporating distinct types of post-tensioned (PT) tendons, bonding conditions, and grouting materials. The test results indicate that the new connection exhibits flexural failure at the beam ends. In comparison to cast-in-place connections, it demonstrates enhanced deformation capacity, comparable ductility, higher stiffness, and reduced energy dissipation due to slippage of the PT tendons and steel bars. However, the viscous damping exceeds 15 %, thereby satisfying the seismic resistance requirements. The high-strength mortar grouting material satisfactorily fulfills the anchoring requirements of steel bars within the corrugated steel ducts, whereas the prestressed grouting material falls short in this regard. The overall performance of the new connection can be further enhanced by improving the grouting material and implementing local unbonded measures.

Infrared thermography detection of grouting defects in post-tensioned tendon ducts under active thermal excitation

The efficacy of employing infrared thermography (IRT) for concrete bridge deck inspection has been well established. Although an IRT detection method during construction stage under hydration heat excitation had been proposed in old works, it is also essential to be applicated in the existing large amounts of bridges in service, while it can be challenging due to factors, such as the substantial depth of the ducts and the variation in duct materials. Therefore, this study presents an IRT detection method for grouting defects in post-tensioned tendon ducts under the stimulation of a shortwave infrared heater. The investigation explores the influence of different factors, such as duct depth, length, grouting compactness level, and duct material, on the detection results and the corresponding heating durations required. Results indicate that with a thermal radiation intensity of approximately 550 W/m2 with a heating duration of 45 mins and followed by a cooling period of 90 mins to 130 mins, the detection of fully grouted void defects within 350 mm long ducts made of polyvinyl chloride (PVC) at burial depths of 50, 70, and 90 mm is feasible. For the best detection results, grouting void defects buried at a depth of 50 mm should be detected after a maximum heating duration of 75 mins and 90 mins corresponding to the PVC ducts and metal ducts. The detection effectiveness is higher for PVC ducts than for metal ducts. Furthermore, an environmental impact analysis should be carried out in the future to make this method into practice.

Post-tensioning tendon force estimation of in-service prestressed concrete structure using cylindrical lamb waves

This paper proposes an ultrasonic-based force estimation technique for the post-tensioning (PT) tendon of an in-service prestressed concrete structure. First, three macro fiber composite transducers are installed on the surface of an in-service PT tendon subjected to an unknown tensile force for the generation and measurement of cylindrical Lamb waves. Then, the velocities of the longitudinal and shear waves are calculated using the measured cylindrical Lamb waves at two ultrasonic input frequencies. Subsequently, the Poisson’s ratio, elastic modulus, and strain induced by the PT tendon force are estimated from the longitudinal and shear wave velocities. Finally, the PT tendon force is obtained from the estimated mechanical property values. The experimental validation was performed using a mono-strand PT tendon under various temperature conditions, and the developed technique estimated the unknown PT tendon force in the range of 10–100 kN with a 6.22 kN maximum error and a 2.99 kN root-mean-square error. The uniqueness of this paper includes (1) no requirement for temperature compensation for field deployment, (2) PT tendon force estimation without calibration of the PT tendon force and cylindrical Lamb wave relationship, and (3) easy sensor installation and no interference with the PT construction process.

Shaking table test of a controlled rocking reinforced concrete frame with column-end hinge joint

A controlled rocking reinforced concrete frame with column-end hinge joint (CR-RCFC) is proposed, in which the pure hinged joints are adopted, the post-tensioned (PT) tendons are arranged in the columns to provide lateral stiffness and self-centering capacity, and the inter-story metal dampers are utilized to dissipate earthquake energy and control displacement response. Based on the quasi-static cyclic tests of the CR-RCFC, the rotation stiffness of the joint was obtained. Shaking table tests were carried out on the 1/3-scale CR-RCFC and conventional reinforced concrete frame (RCF) test models. The test results are studied in terms of damage observations, dynamic characteristics, peak floor accelerations, peak inter-story drifts, and force changes in the PT tendons. The results indicated that the CR-RCFC can effectively protect concrete members from damage even under rare earthquakes. Meanwhile, the CR-RCFC can significantly reduce the acceleration response compared with the RCF, and the metal dampers can effectively control the displacement response.

Experimental and Analytical Investigation of Self-Centering Precast Composite Walls with Sloped Plane Friction Dampers.

To reduce the damage to reinforced concrete shear walls in earthquakes and repair costs, a self-centering wall with sloped plane friction dampers (SPFDs) is proposed. In addition to the SPFDs, the proposed wall includes a precast composite wall, steel wall toes, and post-tensioned (PT) tendons. The steel wall toes embedded in the base of the precast wall were used to improve its strength, and the SPFDs installed in the steel toes were used to increase its energy dissipation capacity. To investigate the effect of the initial PT force and prestressing clamping force of the friction bolt on the seismic performance of the wall, quasistatic cyclic loading tests were carried out on three precast wall specimens. The damage to the self-centering walls was slight, the residual drift was small, and the energy dissipation met the specification requirements. The wall with the greater initial PT force showed higher self-centering and bearing capacity, and the wall with higher prestressing clamping forces showed greater energy dissipation capacity. Additionally, a calculation method for the bearing capacity of the precast wall, which was verified by comparison with the test results, is suggested.

Optimal energy dissipation ratio of base-rocking walls

Base-rocking walls (BRWs) were excellent in maintaining enhanced post-earthquake serviceability and decreasing repair costs and downtime. However, little research has been aimed at finding the optimal range of energy dissipation ratio for designing BRWs. In this study, an approach was developed first for designing BRWs to obtain an intended level of energy dissipation capacity. Using the proposed approach, fifteen BRWs with different heights (i.e., 16, 25.6, and 38.4 m) and energy dissipation ratios (i.e., 0, 0.25, 0.50, 0.75, and 1.00) were designed and modeled using experimentally validated numerical models. Conducting nonlinear time history analyses using far-field (FF), near-field no-pulse (NFnP), and pulse-like (NFP) ground motions, the walls’ response features (RFs), including residual and transient lateral drifts, story acceleration, energy dissipation capacity, post-tensioning (PT) tendons strain, and structural demand were estimated and compared to the existing criteria. Proposing a desirability index (DI), the extent of criteria exceedance for the walls RFs was investigated to find the optimal range of energy dissipation ratio. The results showed that the walls designed by the developed approach could achieve the pre-assumed energy dissipation capacity. Increasing the energy dissipation ratio increases the lateral residual drift while decreasing the transient lateral drift, PT tendon strain, and wall demand. Increasing the wall height increases dissipated energy, exacerbating the adverse effects of higher modes while decreasing PT tendon strain. The obtained residual and transient drifts and PT tendon strain for NFP records are higher than those for FF and NFnP records. Moreover, the peak moment occurred at the lower wall height for NFP records. The adverse effects of higher modes are more evident in FF records. In general, for designing BRWs, the optimal energy dissipation ratio range was 0.50–0.75.

Post-earthquake fire resistance of self-centering concrete beam-column joint: An experimental investigation

Fire is an accidental disaster resulting in disastrous consequences for building. Post-earthquake fire is a secondary disaster induced by earthquake, triggering off larger destruction in a higher probability of occurrence. The potential severity of consequences to structures makes fire and post-earthquake fire safety imperative in the design of any new structures. Self-centering concrete joints are introduced as a promoting alternative to traditional reinforced concrete (RC) joints. They always exhibit excellent seismic performance and self-centering capacity, available in high-seismic zone. However, the current lack of experimental data on fire response of self-centering concrete joints means that they remain an open issue in current design codes. In this paper, full-scale quasi-static cyclic test and fire tests were conducted on two self-centering concrete joints connected with bolted angles and posttensioned (PT) tendons. The experiments aimed to explore the performance of self-centering joint in fire situations, and the impact of post-earthquake damages on fire response of self-centering joint. The deformation patterns and thermal responses of self-centering joints including temperature distribution, prestress force of PT tendons, displacements at beam ends and duration were recorded and analyzed. The results show that both self-centering joints exhibited satisfactory fire resistance with endurance over 170 min. Generally, the bolted angles and PT tendons in self-centering concrete joints showed acceptable working performance in fire. The findings unveil the actual response of self-centering concrete joints during the fire and post-earthquake fire conditions, providing experimental data for further numerical simulation and analysis. It can be used to calibrate the design approach for self-centering joints under fire and seismic-induced fire exposure.