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Keywords = unbonded tendons

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21 pages, 3633 KiB  
Article
Shear Mechanism of Precast Segmental Concrete Beam Prestressed with Unbonded Tendons
by Wu-Tong Yan, Lei Yuan, Yong-Hua Su and Zi-Wei Song
Buildings 2025, 15(15), 2668; https://doi.org/10.3390/buildings15152668 - 28 Jul 2025
Viewed by 230
Abstract
The shear tests are conducted on six precast segmental concrete beams (PSCBs) in this paper. A new specimen design scheme is presented to compare the effects of segmental joints on the shear performance of PSCBs. The failure modes, shear strength, structural deflection, stirrup [...] Read more.
The shear tests are conducted on six precast segmental concrete beams (PSCBs) in this paper. A new specimen design scheme is presented to compare the effects of segmental joints on the shear performance of PSCBs. The failure modes, shear strength, structural deflection, stirrup strain, and tendon stress are recorded. The factors of shear span ratio, the position of segmental joints, and hybrid tendon ratio are focused on, and their effects on the shear behaviors are compared. Based on the measured responses, the shear contribution proportions of concrete segments, prestressed tendons, and stirrups are decomposed and quantified. With the observed failure modes, the truss–arch model is employed to clarify the shear mechanism of PSCBs, and simplified equations are further developed for predicting the shear strength. Using the collected test results of 30 specimens, the validity of the proposed equations is verified with a mean ratio of calculated-to-test values of 0.96 and a standard deviation of 0.11. Furthermore, the influence mechanism of shear span ratio, segmental joints, prestressing force, and hybrid tendon ratio on the shear strength is clarified. The increasing shear span ratio decreases the inclined angle of the arch ribs, thereby reducing the shear resistance contribution of the arch action. The open joints reduce the number of stirrups passing through the diagonal cracks, lowering the shear contribution of the truss action. The prestressing force can reduce the inclination of diagonal cracks, improving the contribution of truss action. The external unbonded tendon will decrease the height of the arch rib due to the second-order effects, causing lower shear strength than PSCBs with internal tendons. Full article
(This article belongs to the Special Issue Advances in Steel-Concrete Composite Structure—2nd Edition)
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14 pages, 12026 KiB  
Proceeding Paper
Numerical Modeling of Post-Tensioned Concrete Flat Slabs with Unbonded Tendons in Fire
by Ya Wei, Daoan Fan and Francis T. K. Au
Eng. Proc. 2025, 98(1), 31; https://doi.org/10.3390/engproc2025098031 - 4 Jul 2025
Viewed by 181
Abstract
The structural fire of post-tensioned concrete flat slabs with unbonded tendons has not been well investigated so far. An investigation based on experimental results was conducted in this study using a numerical model. Three-dimensional nonlinear finite element models of the flat slabs were [...] Read more.
The structural fire of post-tensioned concrete flat slabs with unbonded tendons has not been well investigated so far. An investigation based on experimental results was conducted in this study using a numerical model. Three-dimensional nonlinear finite element models of the flat slabs were established by employing the software ABAQUS, where nonlinear material models of concrete and prestressing steel tendons at elevated temperatures were incorporated. Meanwhile, both the transient creep strain of concrete and thermal creep strain of prestressing steel were explicitly considered, based on which the numerical results obtained agreed well with those of the tests for vertical displacements and crack patterns of slabs. The variations in the tendon stresses were examined as well. The effects of tendon distribution, level of prestressing, and slab soffit area exposed to fire were investigated in relation to the structural responses of the slabs. Tendon distribution had a minor effect, while the level of prestressing and area exposed to fire had significant effects. Full article
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22 pages, 13341 KiB  
Article
Research on the Mechanical Behavior of External Composite Steel Bar Under Cyclic Tension-Compression Loading
by Xiushu Qu, Jialong Yang, Hongmeng Liu and Kexin Sun
Buildings 2025, 15(12), 2019; https://doi.org/10.3390/buildings15122019 - 12 Jun 2025
Viewed by 816
Abstract
A self-centering prefabricated concrete frame structure has good seismic performance, and its seismic capacity is mainly provided by the recovery force of the unbonded prestressing tendons and the energy-dissipation deformation capacity of embedded steel reinforcement. Relocating embedded reinforcement to external positions enables replaceability [...] Read more.
A self-centering prefabricated concrete frame structure has good seismic performance, and its seismic capacity is mainly provided by the recovery force of the unbonded prestressing tendons and the energy-dissipation deformation capacity of embedded steel reinforcement. Relocating embedded reinforcement to external positions enables replaceability of energy dissipation components. And the configuration of external energy dissipation components is the primary factor influencing their energy dissipation capacity. Based on the existing external “Plug & Play” configuration, the internal steel bar size and material properties such as those of steel bar and filling material were varied in this study, and then, cyclic tension-compression experimental studies and numerical simulations were conducted to investigate the energy dissipation performance index and key influencing factors of this type of external composite steel bar. The research results showed that the composite steel bars designed in the experiments exhibited superior overall energy dissipation performance. Specimens utilizing Q345B steel as the core material outperformed those with Grade 30 steel. Moreover, the slenderness ratio of the composite steel bars and the diameter ratio between the end region and weakened segment of the internal steel bars were identified as critical parameters governing energy dissipation performance, and recommendations for optimal parameter ranges were discussed. This study provides a theoretical foundation for implementing external composite steel bars in self-centering structural systems. Full article
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24 pages, 33810 KiB  
Article
Effect of Tendon Profile Layout on Flexural Strength of Unbonded Post-Tensioned Prestressed Concrete Bridge I-Girder
by Swar I. Hasib, Assim M. Lateef and Omar Q. Aziz
Appl. Sci. 2025, 15(7), 3669; https://doi.org/10.3390/app15073669 - 27 Mar 2025
Viewed by 533
Abstract
The main objective of this research is to evaluate the optimal design of the tendon profile layout and to examine the effect of the tendon profile layout on the flexural strength of unbonded, post-tensioned prestressed concrete bridge I-girders. In this study, the experimental [...] Read more.
The main objective of this research is to evaluate the optimal design of the tendon profile layout and to examine the effect of the tendon profile layout on the flexural strength of unbonded, post-tensioned prestressed concrete bridge I-girders. In this study, the experimental investigation involved casting and testing ten unbonded, post-tensioned bridge girders under four-point loads. The main variable studied was the tendon profile layout. The experimental results showed that the flexural behavior of the tested specimens is divided into three stages, including the elastic stage, elastic–plastic stage, and plastic stage, and all specimens exhibited flexural failure. It can be concluded that for each tendon profile layout (trapezoidal, parabolic, harped), the tendon profile with eccentricity at the end of the beam (ee) = 0 had the maximum ultimate load capacity. It also can be concluded that specimen GF-2 HA (harped tendon profile with ee = 0 mm) had the maximum ultimate load capacity among all of the specimens. These enhancements in specimen stiffness, ultimate load capacities, and deflections are due to an increase in resisting capacity, a reduction in stresses, especially at the supports, a decrease in deflection, and an increase in the resisting bending moment, which lead to a reduction in the production cost of the girder. Full article
(This article belongs to the Section Civil Engineering)
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21 pages, 70620 KiB  
Article
Experimental Investigation on Flexural Behavior of Precast Segmental Ultra-High-Performance Concrete Box-Girder with External Tendons for Long-Span Highway Bridges
by Hua Zhao, Sui Luo, Junde Hu, Chengjun Tan, Peirou Qian, Huangguo Qian, Zhilian Liao, Zhentao Hu and Dutao Yi
Buildings 2025, 15(4), 642; https://doi.org/10.3390/buildings15040642 - 19 Feb 2025
Cited by 1 | Viewed by 731
Abstract
A precast concrete segmental box-girder bridge (PCSBGB) is one of the most popular styles of Accelerated Bridge Construction (ABC). To address some common challenges (low durability, poor integrity, and construction inconvenience) in PCSBGBs, this paper proposes a precast ultra-high-performance concrete (UHPC) segmental box-girder [...] Read more.
A precast concrete segmental box-girder bridge (PCSBGB) is one of the most popular styles of Accelerated Bridge Construction (ABC). To address some common challenges (low durability, poor integrity, and construction inconvenience) in PCSBGBs, this paper proposes a precast ultra-high-performance concrete (UHPC) segmental box-girder bridge (PUSBGB). In comparison to conventional PCSBGBs that use three-dimensional prestress, the PUSBGB adopts only one-dimensional (longitudinal) prestress. In addition, the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin, and as a result, the self-weight is significantly reduced. Considering the fact that the thickness of box-girder is thinner than the NC structure, the shear lag effect and risk of girder cracking may correspondingly increase when a PUSBGB is adopted in a long-span bridge. Thus, it is of essential necessity to explore the flexural behavior of a PUSBGB. In this work, a specimen with a scale (1:4) associated with a field bridge (a 102 m long simply supported PUSBGB with externally unbonded tendons) is fabricated and experimentally investigated. The mechanical behaviors of the PUSBGB are discussed, including the failure mode, the crack distribution pattern, the longitudinal strain of the UHPC plate, and the variation of tendon strain. It is found that in the elastic stage, the top slab of the UHPC box girder exhibits a significant shear lag effect, and this phenomenon is even more obvious after cracking. With the development of the cracks, the effective flange width is decreased (with a minimum value of 0.76), and the second-order effect is kept the same before the dominant crack appears (the reduction factor is around 0.95). Moreover, four existing code equations, e.g., ACI 440, ACI 318, ASSHTO, BS 8100, used to predict the stress in the externally unbonded tendons are examined. Furthermore, a finite element analysis (FEA) of the field bridge is conducted, and the theoretical calculation demonstrates that the flexural resistances of the proposed PUSBGB can comply with the design requirements of Chinese code under the ultimate limit states (ULSs). Full article
(This article belongs to the Section Building Structures)
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22 pages, 12681 KiB  
Article
Seismic Behavior of Precast Prestressed Concrete Frame with Hinge-Relocated Mortise–Tenon Connections
by Hanxi Zhao and Noriyuki Takahashi
Buildings 2024, 14(9), 3007; https://doi.org/10.3390/buildings14093007 - 22 Sep 2024
Cited by 2 | Viewed by 1529
Abstract
To satisfy the easy-construction demands of precast concrete (PCa) frames after an earthquake, a PCa frame with mortise–tenon (MT) connections is proposed in this paper. MT connections are secured solely through the binding force of unbonded prestressed tendons without grouting for easy construction. [...] Read more.
To satisfy the easy-construction demands of precast concrete (PCa) frames after an earthquake, a PCa frame with mortise–tenon (MT) connections is proposed in this paper. MT connections are secured solely through the binding force of unbonded prestressed tendons without grouting for easy construction. The design and construction of the joint are detailed. During an earthquake, the hinge system of the connection allows for slight rotational movements. Finite element analysis was employed to assess the joint’s hysteresis behavior, revealing a three-stage earthquake response mechanism: closing, hinge relocation, and self-centering. Based on the hysteresis performance of the beam and column in the precast prestressed concrete (PCaPC) frame, a seismic response model for PCaPC buildings was established. Full article
(This article belongs to the Section Building Structures)
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28 pages, 14140 KiB  
Article
Study on Prestressed Concrete Beams Strengthened with External Unbonded CFRP Tendons
by Longlong Chen, Xuhong Qiang, Xu Jiang, Hao Dong and Wulong Chen
Materials 2024, 17(18), 4622; https://doi.org/10.3390/ma17184622 - 20 Sep 2024
Cited by 1 | Viewed by 1061
Abstract
This study builds a refined finite element (FE) model to research the flexural behavior of a reinforced beam with prestressed CFRP tendons. The precision of the FE model is validated through a comparison with the experimental outcomes. The numerical findings align well with [...] Read more.
This study builds a refined finite element (FE) model to research the flexural behavior of a reinforced beam with prestressed CFRP tendons. The precision of the FE model is validated through a comparison with the experimental outcomes. The numerical findings align well with the experimental outcomes, encompassing the failure mode, load-deflection curve, load-strain curves of concrete, steel reinforcements and CFRP tendons. The variances between predicted values and experimental results are within 10%. Leveraging the verified FE model, an extensive parametric study has been carried out to examine the effects of various parameters, including the CFRP tendon prestress, the CFRP tendon diameter, the deviator layout, the anchorage height and the prestressing strand prestress. Leveraging the findings from the parametric study, some refined design recommendations are proposed for practical reinforcement applications: Increasing the CFRP tendon prestress in practical reinforcement designs is recommended; CFRP tendons with larger diameters are recommended for use in practical reinforcement designs; Employing a linear CFRP tendon profile for reinforcement is not considered optimal in practical applications; The prestress loss in the prestressing strands of PC beams should be considered in practice. Full article
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14 pages, 12302 KiB  
Article
Post-Tensioned Hollow-Core Concrete Slabs with Unbonded Tendons for Truck Scale Platforms: Design Assumptions and Tests
by Rafał Stanisław Szydłowski, Barbara Łabuzek and Łukasz Bednarski
Materials 2024, 17(16), 4154; https://doi.org/10.3390/ma17164154 - 22 Aug 2024
Viewed by 1312
Abstract
At Cracow University of Technology, attempts were made to develop national truck scale platforms with a capacity of 60 tons, made from prestressed concrete. For this work, we designed slabs partially prestressed with unbonded tendons featuring a cross-section of 1.00 × 0.28 m [...] Read more.
At Cracow University of Technology, attempts were made to develop national truck scale platforms with a capacity of 60 tons, made from prestressed concrete. For this work, we designed slabs partially prestressed with unbonded tendons featuring a cross-section of 1.00 × 0.28 m and a span of 5.94 m. To reduce the weight of the slabs, four channels made from commonly used ø110 × 2.2 mm PVC pipes were used. In this way, we created post-tensioned hollow-core slabs. Due to the unpredictable behavior of slabs operating in a cracked state under a repetitive load, two slabs were subjected to cyclic loads amounting to 1,000,000 cycles with different load values. This paper presents the basic design principles and design details of the slabs, as well as the methodology and results of the research conducted. Lastly, we provide appropriate conclusions directed at further optimizing the slabs. Full article
(This article belongs to the Section Construction and Building Materials)
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19 pages, 3138 KiB  
Article
Modeling Schemes and Performance Comparisons of Unbonded and Partially Bonded Tendon in Post-Tensioned Concrete Beam
by Shangzhi Chen, Fangxin Jiang, Yue Sun and Wutong Yan
Buildings 2024, 14(6), 1682; https://doi.org/10.3390/buildings14061682 - 6 Jun 2024
Cited by 1 | Viewed by 1610
Abstract
The modeling method of unbonded effects is a challenging and hot topic for the structural performance analysis of unbonded and partially bonded post-tensioned concrete beams. The main concerns accounting for the unbonded effects are the longitudinal free-slip behaviors and the vertical deformation compatibility [...] Read more.
The modeling method of unbonded effects is a challenging and hot topic for the structural performance analysis of unbonded and partially bonded post-tensioned concrete beams. The main concerns accounting for the unbonded effects are the longitudinal free-slip behaviors and the vertical deformation compatibility relationship between the unbonded tendon and concrete beam. Three modeling schemes, namely, the beam–truss element model, the slipping cable element model, and the slack spring model, are presented in this paper. These modeling schemes are, for the first time, systematically compared regarding applicability, convenience, and accuracy. Then, these modeling schemes are applied to experimental beams with different tendon layouts and bonding conditions, including external tendons, internal unbonded tendons, and partially bonded tendons. The beam–truss element model and the slipping cable element model are only applicable to the fully bonded and unbonded members, respectively. The slack spring model is recommended as the generally applicable model for analyzing post-tensioned concrete beams with different bonding conditions. Crucial suggestions are put forward as to the zero-length slack spring element, which have the potential to improve the prediction accuracy for tendon stress. In addition, parametrical analysis is conducted to determine the influence of unbonded length on flexural performance. With the increase of unbonded length, the flexural capacity of the beam will decrease, but the self-centering performance can be improved. Interestingly, the effects of unbonded length on the structural deformability are not monotonic, and the reasons for this are clarified. Full article
(This article belongs to the Section Building Structures)
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24 pages, 6051 KiB  
Article
Innovative Methods to Improve the Seismic Performance of Precast Segmental and Hybrid Bridge Columns under Cyclic Loading
by Jahangir Badar, Tariq Umar, Muhammad Akbar, Nadeem Abbas, Qamar Shahzad, Weizhen Chen and Muhammad Usman Arshid
Buildings 2024, 14(6), 1594; https://doi.org/10.3390/buildings14061594 - 31 May 2024
Cited by 3 | Viewed by 1251
Abstract
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 [...] Read more.
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. Full article
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14 pages, 6810 KiB  
Technical Note
Innovative Approaches and Challenges in the Demolition of Large-Span Post-Tensioned Beams: Insights from a Case Study
by Mohammad Jonaidi, Adam Kaplan and Ali Keyvanfar
Buildings 2024, 14(5), 1380; https://doi.org/10.3390/buildings14051380 - 11 May 2024
Viewed by 1852
Abstract
Large-span, post-tensioned (PT) beams play a crucial role in maximizing the benefits of post-tensioning techniques. Bonded and unbonded systems are prevalent, with the latter being more widespread in the United States. While bonded systems are advantageous for creating long spans when multiple tendons [...] Read more.
Large-span, post-tensioned (PT) beams play a crucial role in maximizing the benefits of post-tensioning techniques. Bonded and unbonded systems are prevalent, with the latter being more widespread in the United States. While bonded systems are advantageous for creating long spans when multiple tendons are grouped in ducts, limited studies in the literature exist on their demolition. With a case study, this paper addresses the unique challenge of demolishing large-span-bonded, post-tensioned beams that occurs due to a building’s functional change. Emphasizing insights for engineers, it explores the use of cutting and dismantling methods, thereby considering the presence of prestressed cables. The demolition process is distinctive due to the presence of numerous prestressed cables along the beams, necessitating a specialized and cautious cutting approach. This is accomplished through the use of a drilling technique that selectively distresses the tendons, ensuring they are not all affected simultaneously. An intriguing observation discussed in this paper pertains to the occurrence of horizontal cracks accompanied by loud sounds following the drilling process, thereby offering insights from the design perspective of PT systems. This paper details an innovative method for safely demolishing large-span, bonded PT beams using ground-penetrating radar and computer models to navigate structural complexities and ensure nearby structures’ safety. Full article
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17 pages, 5089 KiB  
Article
Experimental Study on Shear Performance of Concrete Beams Reinforced with Externally Unbonded Prestressed CFRP Tendons
by Hetao Qi, Haozhe Jiang, Bing Wang and Ping Zhuge
Fibers 2024, 12(3), 23; https://doi.org/10.3390/fib12030023 - 29 Feb 2024
Cited by 2 | Viewed by 2199
Abstract
To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally [...] Read more.
To investigate the reinforcing effect of externally prestressed carbon-fiber-reinforced polymer (CFRP) tendons on the shear performance of reinforced concrete beams, a set of model tests was designed. Static load comparative tests were conducted on one original beam and four reinforced beams to experimentally investigate the impacts of the prestress level and damage in the shear zone on the shear reinforcement effect and analyze the reinforcement mechanism of CFRP tendons. The results show that in the beams reinforced with CFRP, the CFRP tendons could work collaboratively with the stirrups to reduce the strain on the stirrups; the increasing rate in the yield load was 28–70%. After the stirrups yielded, the CFRP tendons did not yet reach their ultimate tensile strength and could still withstand increased shear forces, resulting in an increasing rate of the ultimate load for the reinforced beams with a CFRP content of 56–78%. The enhancements in both the yield load and the ultimate load were positively correlated with the level of prestress in the CFRP tendons. This reinforcement technique efficiently restricts the growth and delays the first appearance of diagonal cracks. The prestress can close the pre-existing diagonal cracks and provide a reserve of shear capacity for the beams. The initial damage in the shear zone decreases the initial shear stiffness and increases the width of the initial diagonal cracks. However, this effect gradually diminishes as the load increases and does not significantly impact the shear capacity. Prestressing can significantly improve the strength utilization rate of the CFRP reinforcement when the reinforced beams fail. The deformation of the CFRP tendon is directly related to the shear deformation. By combining this relationship with the truss–arch model, the shear capacity for the reinforced beam can be predicted. The predicted results exhibit an error of less than 10% when compared to the test results, offering valuable design guidance for reinforced engineering composites. Full article
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23 pages, 9517 KiB  
Article
Effects of Prestressing Magnitude and Position on Seismic Performance of Unbonded Prestressed Concrete Beams
by Dong Chen, Bin Zeng, Qing Xu, Xiaoda Xu and Man Xu
Buildings 2024, 14(2), 431; https://doi.org/10.3390/buildings14020431 - 4 Feb 2024
Cited by 4 | Viewed by 1790
Abstract
To study the effects of the jacking stress level, height and strength ratio of the prestress tendons (λ) on the seismic performance of unbonded prestressed concrete (UPC) beams, six UPC beams and one reinforced concrete (RC) beam were tested under cyclic [...] Read more.
To study the effects of the jacking stress level, height and strength ratio of the prestress tendons (λ) on the seismic performance of unbonded prestressed concrete (UPC) beams, six UPC beams and one reinforced concrete (RC) beam were tested under cyclic loads. The hysteretic characteristics, skeleton curves, ductility properties, energy dissipation capacity, strain distribution of reinforcement and self-centering capability of the specimens were studied and discussed. Numerical parameter analysis was also carried out by using OpenSees. The results indicate that three failure modes of UPC beams under cyclic loading were observed, namely the tension-failure mode involving a broken rebar, the compression-failure mode involving concrete crushing and the balanced failure. By considering the influence of the prestress position and magnitude, the modified reinforcing index ω was proposed to determine the failure mode. The ω is suggested to be less than 0.3 to ensure sufficient ductility. The effective stress level is linearly and positively related to the stiffness from cracking to yield Kcr and the ultimate bearing capacity of the UPC beam under cyclic loading. The stiffness of the UPC beam is slightly larger than that of the RC beam before yielding, and significantly greater than that of the RC beam after yielding. Due to the large strength reserve after yielding, the integrated seismic performance of the UPC beam is similar to that of the RC beam. When the λ was unchanged, the increase in the relative height of the prestressed tendons αh is beneficial for the overall performance factor F, ductility and crack control. The stiffness degradation performance depends on the λ but is independent of the αh. The total energy dissipation of the non-tensioned UPC specimen was 59% higher than that of the RC beam. The cumulative total energy dissipation of the tensioned UPC specimen was only 13% lower than that of the RC beam with the same number of cycles, indicating that the UPC specimen had a considerable energy dissipation capacity. Full article
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27 pages, 12310 KiB  
Article
Flexural Stiffness and Crack Width of Partially Prestressed Beams with Unbonded Tendons
by Bernardo T. Terán-Torres, Adolfo A. Elías-Chávez, Pedro L. Valdez-Tamez, Jose A. Rodríguez-Rodríguez and César A. Juárez-Alvarado
Buildings 2023, 13(11), 2717; https://doi.org/10.3390/buildings13112717 - 28 Oct 2023
Cited by 2 | Viewed by 1422
Abstract
The original concept of “Total Prestress” consists of creating compressions in concrete without generating tension stresses for service load, while in "Partially Prestressed” elements, tensions are allowed in the service stage, which would produce some cracking depending on applied loads that will be [...] Read more.
The original concept of “Total Prestress” consists of creating compressions in concrete without generating tension stresses for service load, while in "Partially Prestressed” elements, tensions are allowed in the service stage, which would produce some cracking depending on applied loads that will be taken with non-prestressed reinforcement. Using criteria and design recommendations can guarantee maximum flexural capacity and admissible serviceability requirements of partially prestressed elements; however, there is insufficient research for estimating more accurately the required parameters for the design and review of these types of elements. Because of this, the present investigation consisted in the realization of experimental studies in continuous partially prestressed beams with unbonded tendons for the evaluation of the flexural behavior for different stages of load determining the actual stresses and the strains taking into account the structural stiffness decrease and its effect on deflections. The dimensions of the specimens were selected based on common dimensions presented on slabs. The tested specimens considered variables such as the relationship between the length of the continuous spans, the cross-section, and the partial prestressing ratio. Afterward, equations were proposed to predict the decrease in the structural stiffness, depending on the degree of cracking, the type of cross-section, the partial prestressing ratio, and the magnitude of the applied load and the tension and compression stresses to estimate the probable deflections for a particular loading stage. The crack width equation presented a difference of −16% to +18% with respect to the experimental data, while the flexural stiffness equation showed a highly accurate correlation to the experimental data. Full article
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16 pages, 6259 KiB  
Article
Effect of Tendon-Related Variables on the Behavior of Externally CFRP Prestressed Concrete Beams
by Tiejiong Lou, Han Hu and Miao Pang
Materials 2023, 16(14), 5197; https://doi.org/10.3390/ma16145197 - 24 Jul 2023
Cited by 4 | Viewed by 1585
Abstract
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 [...] Read more.
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%. Full article
(This article belongs to the Special Issue Novel Fiber Reinforced Polymer (FRP) Technologies for Structures)
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