External Prestressing Tendons Research Articles

Shear behavior of externally prestressed precast concrete segmental beams with both positive and negative moment regions

To investigate the shear behavior of externally prestressed precast concrete segmental beams with both positive and negative moment regions (EPCS P&N beams), eight specimens were subjected to failure under various shear span to depth ratios, moment ratios, and joint types. Throughout the testing process, critical crack initiation and development, joint slippage and opening, failure processes and modes, as well as strains in concrete, stirrups, and external prestressing tendons were meticulously recorded. At the point of failure, the concrete in the shear-compression zone near the top surface of the joint section (closest to the loading point in the positive moment region) or near the bottom surface of the joint section (closest to the interior support in the negative moment region) experienced crushing. Subsequently, the external tendons lost support and underwent elastic retraction, causing the two segments on either side of the critical web-shear crack to slide against each other. The elastic strain energy was released significantly as a consequence of the external tendons retracting, leading to the rupture of stirrups intersecting the failure cracks, followed by flange buckling. Based on the test results, a strut-and-tie model was developed to analyze the shear resistance mechanism, and a detailed flowchart for computing the shear resistance of EPCS P&N beams was established. The predictions from the proposed analytical method were compared with the test results, showing good agreement and confirming the rationality of the proposed shear resistance mechanism.

Flexural performance of precast segmental continuous box girders with corrugated steel webs

Due to the existence of joints, the flexural performance of segmental assembled girders is different from that of monolithic cast girders. In order to study the flexural performance of precast segmental assembled box girder with corrugated steel webs, a static failure test on a precast segmental assembled continuous box girder with corrugated steel webs and variable cross-section and a monolithic cast continuous box girder with corrugated steel webs of the same size was carried out. The influence of the existence of joints on the deflection, strain, and prestress increment of precast segmental continuous girder with corrugated steel webs was analyzed. The parameter analysis was further carried out by the finite element method. The results showed that, at the initial loading stage, the joint had little effect on the displacement, and the deflection of the segmental assembled girder changed more rapidly than that of the monolithic cast girder. In the monolithic girder, cracks mainly occurred at the middle-support position of the middle span and pure bending sections. In the segmental beam, cracks were concentrated in the concrete on both sides of the joint. The number of cracks was relatively small and concentrated in the concrete on both sides of the joints of the loading segment and the middle support segment. The trends in the strain growth in the segmental beam and MB01 were consistent, and the values were similar. The strain growth trend of the segmental girder and the monolithic girder was consistent, and the values were similar at the initial loading stage. The external prestressed tendons in the segmental girder had a greater role in the loading process than those in the monolithic girder, and the normal stress in the segmental girder increased more rapidly during the bending process. In the ultimate loading state, the external prestressing force of the segmental girder was 2.01% higher than that of the monolithic girder. The number of segments was inversely proportional to the flexural capacity of the structure. Excessive thickness of the adhesive layer would adversely affect the crack resistance of the structure. This study will contribute to the engineering application of continuous composite box girders with corrugated steel webs.

Bending resistance mechanism of prestressed ultra-high performance concrete - reinforced concrete beam based on a full-scale experiment

Ultra-High Performance Concrete (UHPC) is a new type of engineering material with high compressive strength, high tensile strength, and high fracture toughness. Its bending failure mechanism is different from that of traditional concrete beams, which requires a new computational model to describe the bending failure phenomena of the prestressed ultra-high performance concrete - reinforced concrete (UHPC-RC) beam without web reinforcement. Therefore, this paper, through full-scale tests on a 30m prestressed UHPC-RC beam without web reinforcement, captures unique bending failure phenomena, including initial cracking, development of local cracks, and rupture of prestressed steel strands. Considering the tension-compression constitutive relationship of UHPC material, an innovative computational model for bending bearing capacity is proposed. Based on this model, a study on the minimum reinforcement ratio of full prestressed-ordinary steel bars is conducted. The results show that in the bending failure of the prestressed UHPC-RC beam without web reinforcement, excessive tensile strain of steel strands will occur at the local crack location. At this time, the structure does not satisfy the assumption of plane sections, and the introduction of the calculation model of the limit state of external prestressed tendons can effectively match this model, which is highly consistent with the experimental results. The minimum reinforcement ratio of full prestressed-ordinary steel bars is revised to the auxiliary reinforcement ratio of full prestressed-ordinary steel bars, quantifying the minimum reinforcement requirements of ordinary steel bars. The research results of this paper can provide reference for the next step of theoretical research.

Open issues on the use of carbon composite tendons as prestressed reinforcement of concrete members

In the last decades, fiber-reinforced polymer (FRP) composites gained popularity in the field of structural engineering thanks to their high mechanical properties and limited corrosion in harsh environments. These composites are used as reinforcement of new concrete members as well as for strengthening of existing structures. For existing reinforced concrete (RC) structures, different techniques are available to increase the strength and stiffness of the existing elements. Among them, a promising technology consists in inducing to the element a bending moment opposite to that induced by the applied load by using external prestressed FRP tendons. This technique increases the load carrying capacity of the beams and induces concrete crack closure, thus reducing the exposure of steel bars to the environment.In this paper, a literature review is carried out to investigate the open issues that hinder the diffusion of prestressing made with composite carbon fiber tendons. According to the literature, the main issue is represented by the anchor system that should guarantee high stress level into the composite material avoiding local ruptures. Another open issue is the definition of the maximum stress applied to the composite with respect to its tensile strength. In fact, high levels of stress may induce premature composite failure. Finally, the exposure of CFRP bars to some harsh environmental conditions and high temperatures may negatively affect the reinforcement effectiveness.

Bond behavior of flexible braided AFRP tendons in high-performance concrete based on pull-out and beam tests

AFRP tendons are manufactured in both rigid and flexible form, where flexible AFRP tendons could be coiled and utilized as external prestressed tendons with significant curvature. This study investigates the bond behavior of flexible AFRP tendons in high-performance concrete (HPC) by examining the effects of tendon types, tendon diameter, concrete types, and test methods. Results show that pull-out failures are prone to occur in specimens with AFRP tendon, whereas splitting failures are prone to occur in specimens with steel tendon. The bond stresses for AFRP tendons reach maximum value within a slippage range of 4.5–10.5 mm, while for steel tendons, the maximum bond stresses occur within a larger slippage range of 17–44 mm. The bond strength of steel tendons is 1.12–1.26 times higher than that of AFRP tendons. Normal concrete (NC) specimens with splitting failure produced maximum 7.1 % higher bond strength compared to HPC. On the other hand, the pull-out failure is determined by the interlaminar shear strength of AFRP tendons, leading to comparable bond strength between NC and HPC. A 5 % difference in bond strength exists between pull-out tests and beam tests with similar failure modes. For AFRP tendons, changing the diameter from 13 mm to 15 mm increases the bonding strength by +6 % to −17 %, which is basically consistent with the existing research that the bonding strength decreases as the diameter increases. This study presented a formula for AFRP tendon bond strength, considering concrete strength, types, tendon diameter, and test methods. The proposed model outperforms existing ones with an average of 0.99 and a variance of 0.13.

Detection of wire breaks and corrosion in external prestressed tendons using a magnetic rope testing device

AbstractExternal prestressing tendons are a major structural element for the durability of concrete bridges. In France several cases of sudden breaks in external pre‐stressing tendon made of HDPE duct injected by cement grout directly in contact with strands have been recorded in the past decade [2].In order to prevent this sudden breaks Cerema has experimented the magnetic rope testing technology from ropeways to develop a non‐destructive inspection technic of the free length and junction of prestressing. The method is based on magnetic leakage field detection and allows to detect defaults of the strands inside the tendon such as corrosion and wire breaks.The article first focuses on the magnetic rope testing technic. Then tests previously performed on laboratory tendons with reference wire breaks will be analyzed for defaults characterization. Finally, the particular methodology adapted to the nondestructive magnetic inspection of prestressing tendons on site will be detailed. A general feedback including handling issues and analysis of non‐destructive magnetic controls completed with visual controls by removing the high‐density polyethylene (HDPE) sheath will be given.

Study on the Shear Behavior of Prismatic and Tapered Continuous Beams with Corrugated Steel Webs under External Prestressing Force

This paper analyzes the shear behavior of prismatic and tapered continuous beams with corrugated steel webs (CSWs) under different external prestressing tendon layouts. For girder bridges with CSWs, the existing design specifications consider only the shear force caused by the external prestressing force when calculating the shear stress of CSWs under the external prestressing tendons. However, in a tapered continuous beam with CSWs, in addition to the shear force caused by the prestressing force, the prestressing bending moment and the horizontal component of prestressing can also induce additional shear stress, which results in a redistribution of the shear stress on the section. This finding has not been reported previously. Then, the reasons for the shear behavior differences of tapered and prismatic continuous beams with CSWs under external prestressing tendons are explored. The study reveals the factors affecting the distribution of shear stress on indeterminate static beams with CSWs under external prestressing and proves that the traditional method used for predicting the shear stress on CSWs is not applicable to tapered cases. In addition, it is found that the direction of the internal forces and moments also affects the shear-bearing ratios of CSWs and concrete slabs. Consequently, a unified analytical formula is proposed for calculating the shear stresses of the CSWs induced by external prestressing, and it can be applied to both tapered and prismatic continuous beams with CSWs under external prestressing tendons.

The Interfacial Friction Loss of Prestressed Carbon-Fiber Tendons in a Bending State

Carbon-fiber reinforced plastic (CFRP) is ideal for bridge reinforcement due to its high strength, light weight, and corrosion resistance. Studies on the friction loss of CFRP tendons in a bending state form an important part of advancing the application of CFRP materials to external prestressing strengthening technology. To understand the magnitude and variation of interfacial friction loss of prestressed CFRP tendons under bending conditions, 12 single-bending prestressing tension tests and 4 three-consecutive-bending prestressing tension tests were conducted in this study. Two bending radii of 1.5 m and 2 m, two bending angles of 20° and 30°, and three contact surfaces with different friction coefficients were selected for the steering block condition to measure the friction loss under each stage of tensioning prestress. On this basis, a model for calculating the friction loss rate on the surface of prestressed CFRP tendons was derived for the change of contact stress between CFRP tendons and deflectors during the installation and tensioning stages. The results show that the friction loss of external prestressed CFRP tendons is mainly related to four external factors: bending radius, steering angle, friction coefficient, and the magnitude of tensioning prestress; with the increase of prestress, the friction loss rate goes through three stages, the rising stage, the falling stage, and the stable stage; in the process of friction loss rate change, the main influencing factor controlling the magnitude of friction loss rate changes from bending radius to steering angle. In the theoretical calculation model of friction loss rate, the calculation model of the prestressed CFRP tendons under multiple successive bends can be simplified to a combination of several calculation models for a single bend. This study provides a reference for the engineering field of strengthening reinforced concrete (RC) beams using external prestressed CFRP tendons.

Durability enhancement of half-joints in RC bridges through external prestressed tendons: The Musmeci Bridge’s case study

This paper numerically investigates the effect of post-tension interventions to strengthen the deteriorated half-joints of the Musmeci Bridge in Potenza (Italy), with the primary objective of increasing the ultimate load-bearing capacity and monitoring the secondary effects in terms of preventing or limiting cracking patterns. Bearing this in mind, the study aims to investigate the role of the reinforcement detailing, of the post-tension stress and of the corroding time in the presence of chlorides, outlining the intervention ability to improve the structure’s durability. To this end, nonlinear finite element models are provided with chloride ions diffusion analysis to investigate corrosion initiation and progress in reinforced concrete elements and account for deterioration due to two scenarios (45 and 95 years). Results show the significant impact of reinforcement layout as the presence of inclined bars increases the ultimate load by about 86 %. The ultimate load improvement is in the range 50–55 % when the intervention is carried out after 45 years while it is equal to about 30–35 % if a period of 95 years is last since the construction. This latter highlights the significant influence of the intervention timeliness on structural durability.

Simulation Research on Continuous Concrete Beams Reinforced with External Prestressed CFRP Tendons.

This paper examines the effects of different loading patterns on the static characteristics of continuous concrete beams reinforced with external prestressed carbon fiber-reinforced polymer tendons (EPCFRPT) and qualitatively analyzes the results for two continuous concrete beams: SB-1 under symmetrical loading, and SB-2 under asymmetrical loading. Then, a finite element analysis model is introduced and calibrated by tests conducted at Southeast University and data collected from a literature review. Based on the FEA model, the initial prestress, cross-section area, and eccentricity of CFRP tendons as well as the steel reinforcement configuration were selected by a parametric study. The results indicated that the initial prestress and tendon cross-section area had the most influence on the tendon stress increment and the secondary bending moment of the middle support, while the reinforcement distribution and eccentricity of the tendons had little effect. The secondary bending moment had a linear positive correlation with the stress increment of tendons. These results allow a simplified equation for calculating the external load bending moment amplitude coefficient at ultimate to be proposed.

Shear performance of prismatic and tapered beams with corrugated steel webs under external prestressing force

This paper analyzes the shear performance of prismatic and tapered beams with corrugated steel webs (CSWs) under different layouts of external prestressing based on finite element (FE) simulations. The results show that when the external prestressing tendon distribution is straight, there is no shear stress in the prismatic beam with CSWs, but there is shear stress in the tapered beam with CSWs. Therefore, it is not generally accurate that only the vertical component of the external prestressing force can induce shear stress when calculating the shear stresses caused by external prestressing in the existing design specifications. In theory, it is proven, for the first time, that the axial force and prestressing bending moment generated by external prestressing will generate additional shear stresses, which will cause the shear stress redistribution in tapered beams with CSWs. However, these two factors were not taken into account in existing design specifications, which resulted in a significant error in predicting the shear stress for tapered beams with CSWs when ignoring the contribution of the axial force and prestressing bending moment. Consequently, a unified analytical formula is proposed for predicting the shear stresses caused by an external prestressing force on the CSW, and this formula can be appropriate for both tapered and prismatic beams with CSWs under both straight and bent external prestressing tendons. In addition, this study quantitatively investigates the ratios of shear stresses in the CSWs induced by the vertical and horizontal components of the external prestressing force, and their corresponding bending moments. Finally, the study reveals the factors affecting the distribution of shear stress on beams with CSWs under external prestressing and proves that using the traditional method to calculate the shear stress neglects the shear capacity of the inclined concrete bottom slab will produce a significant error when applied to tapered cases.

Effect of External Tendon Profile on Improving Structural Performance of RC Beams

The objective of the research is to improve the structural behavior of reinforced concrete (RC) T–beams by applying various techniques of external pre-stressing tendons, thus enhancing the load-carrying capacities and raising the resistance to applied forces. Seven identical RC T–beams were subjected to four-point loading to study the influence of the deviator number, tension mechanism, and tendon profile on flexural behavior. Of these, one beam was an original specimen without any tendons. The other six beams were strengthened with external tendons: two identical specimens with straight–line tendons but with a different number of inner deviators; two identical specimens with V–shaped tendons but with a different tension direction; and finally, two identical specimens with U–shaped tendons but with a different tension direction. The results and discussion were achieved using finite element (FE) software, ANSYS WORKBENCH. The results from all specimens were listed and analyzed for the failure mechanism, load-carrying capacity, deflection, and ductility. According to the FE results, external tendons greatly enhance the load-carrying and stiffness of RC beams. In addition, strengthening beams with external pre-stressing techniques can delay the early cracking load, yield load, and ultimate load by approximately 250%, 570%, and 30%, respectively, when compared to an unstrengthened beam. Moreover, the straight-line tendon with inner deviators was obtained to be the most effective technique for simple beams.

Theoretical Study on the Flexural Behavior of Structural Elements Strengthened with External Pre-Stressing Methods

This study aims to strengthen the flexural behavior of structural elements with external pre-stressing tendons, thereby improving their load-carrying capacity and increasing their resistance against the external load. Different techniques were used to apply external pre-stressed strengthening to RC beams and RC frames. Seven identical RC frames were analyzed: an original sample without an external tendon, two strengthened samples with external tendons at the positive bending zone, two strengthened samples with external tendons at the beam–column connection zone, a strengthened sample with external straight line tendons along the beam and, finally, a strengthened sample with external U-shape tendons along the beam of the frame. The analysis and the results were obtained using ANSYS WORKBENCH finite element (FE) program. Comparisons were performed between these techniques to determine which technique is better for strengthening. The failure mode, vertical deflection, column stress, load-carrying capacity, and ductility of the samples were listed and analyzed under four-point vertical loading. The results show that using external tendons significantly increases the load capacity and the stiffness of structural frames. Moreover, the tendon in the beam zone is more effective than the tendon in the column zone.

Parametric analysis of steel-concrete composite beams prestressed with external tendons

The use of external prestressed tendons in steel-concrete composite beams can improve the performance of beams by strengthening their structure, increasing the ultimate moment resistance, and reducing deflections. The present research aims to investigate the behavior of simply supported steel-concrete composite beams, prestressed with external tendons and under positive bending moment through the development of a parametric study. Firstly, for the beam strength determination, an analytical model is discussed. To predict the ultimate increment in tendon stress Chen and Gu method is used. Additionally, a numerical model that can adequately simulate the behavior of prestressed composite beams is developed using the Abaqus software. The accuracy of this model is validated through comparisons between the obtained results and existing experimental tests. Then, a parametric study is carried out to identify the influence of the following variables: positioning and shape of the tendons, initial prestressing force, and tendon and span lengths. The effect of prestressing at the steel-concrete interface is also investigated. The results of the ultimate moment from the finite element models, are compared by applying the analytical procedure. It can be concluded that all the different tendon configurations considered in the parametric study improved the ultimate moment resistance in the composite beams, but some designs are more efficient than others, increasing the resistance even more, and significantly reducing the deflections and cracking in the concrete under service loads. Regarding the analytical procedure, it was found that the method can adequately estimate the strength capacity of the beams.

A nonlinear geometric model for pre-stressed steel–concrete composite beams

Steel–concrete composite beams are commonly employed in civil constructions such as multi-storey building floors and long-span bridges. In case of significant span to depth ratios, excessive deflections and noticeable crack widths at the concrete slab may occur at the serviceability stage. In this context, internal or external pre-stressed tendons can be used as a remediation. In the latter case, significant effects of geometric non-linearity may arise due to the strain incompatibility between the external tendon and the composite member, resulting in a variable tendon eccentricity during deformation. In this paper, second-order effects are evaluated in eight pre-stressed steel–concrete composite beams for which experimental results are available. Hence, a three-dimensional finite element model using a Lagrangian description is proposed. The external tendons are represented by one-dimensional catenary elements, whereas the reinforced concrete slab and steel profile are modeled by shells finite elements. Slipping at the slab-beam interface and tendon-deviator locations are also included in the analysis. For the studied externally pre-stressed beams, the introduction of nonlinear geometric behavior yields lower collapses loads in relation to its linear counterpart, varying this difference between 6.4 and 9.1%.

Layout and Optimization of the External Prestressing Tendons of Hybrid Beam Rigid Frame Bridges

External prestressing tendon systems can be set to alleviate the problem of excessive mid-span deflection of hybrid beam rigid frame bridges in the long-term use. Based on the Anhaiwan Bridge in Quanzhou of Fujian province, the effects of external prestressing tendons on reducing the deflection of the main span and improving the stress of concrete sections were studied by the shell- solid finite element models. Then the effects of the external prestressing tendons in the steel beams and the concrete beams were analyzed respectively. The effects of each prestressing tendon were further calculated. The final optimized layout was obtained by these studies, which can be used as a design reference for the external prestressed tendons of the hybrid beam rigid frame bridge. Finally, the deflection of the steel beam of the hybrid beam rigid frame bridge was analyzed under the impact of long-term effects such as shrinkage and creep. The comparative analysis of the different tensioning schemes for the external prestress tendons was carried out in order to provide a reference for the operation and maintenance management of the bridges.

Modeling fire performance of externally prestressed steel–concrete composite beams

This paper examines the fire performance of uninsulated and uncoated restrained steel-concrete composite beams supplemented with externally prestressed strands through advanced numerical simulation. In this work, a sequentially coupled thermo-mechanical analysis is carried out using ABAQUS. This analysis utilizes a highly nonlinear three-dimensional finite element (FE) model that is specifically developed and validated using full-sized specimens tested in a companion fire testing program. The developed FE model accounts for nonlinearities arising from geometric features and material properties, as well as complexities resulting from prestressing systems, fire conditions, and mechanical loadings. Four factors are of interest to this work including effect of restraints (axial vs. rotational), degree of stiffness of restraints, the configuration of external prestressed tendons, and magnitude of applied loading. The outcome of this analysis demonstrates how the prestressing force in the external tendons is primarily governed by the magnitude of applied loading and experienced temperature level. Interestingly, these results also show that the stiffness of axial restraints has a minor influence on the failure of restrained and prestressed steel-concrete composite beams. When the axial restraint ratio does not exceed 0.5, the critical deflection of the composite beam is lower than that of the composite beam with a restraint ratio of 1.0.

Corrosion Detection in PSC Bridge Tendons Using Kernel PCA Denoising of Measured MFL Signals.

The construction of prestressed concrete bridges has witnessed a steep increase for the past 50 years worldwide. The constructed bridges exposed to various environmental conditions deteriorate all along their service life. One such degradation is corrosion, which can cause significant damage if it occurs on the main structural components, such as prestressing tendons. In this study, a novel non-destructive evaluation method to incorporate a movable yoke system with denoising algorithm based on kernel principal component analysis is developed and applied to identify the loss of cross-sectional area in corroded external prestressing tendons. The proposed method using denoised output voltage signals obtained from the measuring device appears to be a reliable and precise monitoring system to detect corrosion with less than 3% sectional loss.

Second Remediation of Long-Term Deflection and Cracking of PT Box-Girder Bridge Using External Post-Tensioning

AbstractThis study involves examining a second technique for improving external prestressing tendons to remediate the deflection and cracking of an 18-year-old strengthened four-span continuous pos...

FIELD TEST ON THE COOPERATION OF NSM STRENGTHENING AND EXTERNAL TENDON RETROFITTING TECHNIQUE

In this paper, post-tension and steel plate near-surface mounted (NSM) strengthening systems are proposed to strengthen deteriorated and cracked large box girder rigid frame bridge without altering appearance and dimension of the bridge. The reinforcement method mainly improves the bearing capacity through external prestressed tendons, and bonding steel plate can enhance the shear resistance of the bridge. The main purpose is to study the structural mechanical properties before and after the reinforcement of rigid frame bridges. Take a 540m rigid frame box girder bridge as an example. The static load test of the bridge before and after reinforcement is carried out. The deflection and strain of the middle cross section of the span are measured in the static test. A finite element analysis model was also developed and verified static loading test data. The results show that structural bearing capacity and performance of the bridge were enhanced with the post-tension and NSM strengthening systems cooperatively.