•The shear behavior of externally prestressed UHPC beams without stirrups is experimentally investigated.•Effects of the a/d ratio, stirrups, and longitudinal reinforcement ratio are discussed.•An ...equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed.•Effects of key parameters on the shear strength of prestressed UHPC beams without stirrups are analyzed.•Prediction equations of shear strength of prestressed UHPC beams without stirrups are proposed.
Externally prestressed ultra-high-performance concrete (UHPC) beams without stirrups (EPUBs-WS) that simplify the reinforcement design and construction procedure are becoming a competitive option in bridge engineering. To investigate the shear behavior of EPUBs-WS, five specimens were designed and tested considering several critical parameters, such as the shear span-to-depth ratio (λ), shear stirrups, and longitudinal reinforcement ratio. The EPUBs-WS exhibits diagonal tension failure as the fibers pull out and the specimen shears off into two parts along the critical diagonal crack. However, the beam with λ = 3.67 exhibited flexural failure due to the large λ. The stiffness, shear-cracking strength, and shear strength of EPUBs-WS decrease as λ increases. Stirrups enhance the shear resistance of EPUBs but result in a more brittle shear failure mode. A higher reinforcement ratio augments the dowel action in EPUBs-WS, which contributes to a ductile shear failure mechanism. The web-shear cracking force accounts for 46% to 87% of the shear capacity, implying that the shear-cracking strength is a significant factor in the design of EPUBs-WS. An equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed and validated using a database of experimental results reported in the literature. A parametric analysis is performed using 40 available specimens to investigate the effects of compressive strength, λ, reinforcement ratio, fiber reinforcing index, and prestressing level on the shear strength of prestressed UHPC beams without stirrups. By considering the key parameters, equations for estimating the shear strength are proposed and exhibit good accuracy.
•A tension stress upper limit of 50%fu and a deviator angle of 2° were determined.•Flexural performance of RC beam can be improved greatly with BFRP external tendons.•Deviated tendon profile and ...higher tension stress are preferable.•Standards show various validities for different design contents.
This paper investigates the feasibility of newly developed basalt fiber reinforced polymer (BFRP) as prestressing material and the structural behavior of reinforced concrete (RC) beams strengthened with externally prestressing BFRP tendons. Three main factors potential controlling structural strengthening effects, including tension stresses, bending angles and anchorages of the tendons, were first discussed based on literature review and finite element (FE) simulation. In the structural experiment, the effects of tension stresses and the tendon profiles on the flexural behavior of RC beams were discussed and the evaluation on the ultimate bearing capacity, cracking moment, crack width and deflection of strengthened beams was conducted by theoretical calculation and experimental results. The results show that the prestressing level of BFRP tendon can be determined to be 0.50fu and 0.38fu (fu is the tensile strength) according to creep rupture limit. The bending angle at the deviator is optimized to be 2° and the bond anchorage with resin epoxy was adopted to maximize strength utilization. For strengthening behavior, the second-order effect of the externally prestressed beam can be effectively relieved by using proper deviators, which is demonstrated by enhanced ultimate capacity. All of the strengthened RC beams are failed by concrete crushing, with satisfactory crack patterns and superior ductility compared to the control beam, which demonstrates the simultaneous working of internal steel reinforcements and external prestressing BFRP tendons during loading. The evaluation on mechanical behavior of strengthened RC beams indicates theoretical calculation according to several existing standards can well predict strengthening effect.
•A new model for Segmental Bridges with reduced computational cost is presented.•The model shows very good agreement with results from the literature.•The model requires an adequate estimation of the ...point of contact between segments.•Friction at the deviators affects significantly the stresses in external tendons.•The use of epoxy at the joints does not affect significantly the global behaviour.
Precast Concrete Segmental Bridges are nowadays a well-established alternative for bridge construction that presents significative advantages related to the construction process. Numerous bridges have been built using this technology in the past decades and extensive research has been conducted, including the development of different numerical models to study their behaviour. This paper proposes a new Finite Element model for Precast Concrete Segmental Bridge decks capable of reproducing the main characteristics of their behaviour at a reduced computational cost.
The model proposed has shown very good agreement with experimental results existing in the literature. After calibration, the influence of different modelling choices has been analysed. The results point out to a high impact of the modelling strategy adopted for the joints in the compression areas, requiring an adequate estimation of the point of contact between the segments. Additionally, consideration of friction of external tendons at the deviators showed limited relevance in the global behaviour of the model but was important for the correct estimation of stress increments in the tendons. Finally, considering or not the presence of epoxy at the joints did not seem to influence significantly the behaviour of the models. The use of shell elements combined with the modelling strategy adopted for the joints offers better accuracy than existing models with a significantly lower computational time.
This study concerns the effect of the external prestressing strand shape profile on the flexural behavior of steel beams. Seven steel beams that have the same cross-section are strengthened by ...external strands fixed by using Saddle Points of Deviation (Deviators). Based on two criteria, beams tested are divided into two categories whether external prestressing with fixity strands is present. The first group includes only one beam as a reference, while the second group deals with beams strengthened by two external strands. Six samples have been separated according to the eccentricity for external prestressing at a jacking stress of 815 MPa. During testing, it was discovered that the moment-curvature responses at the bottom and top flange region were stiffer than those in the reference, and the degree of hardening increases with eccentricity increasing. However, failure occurs with a slight warning as a result of insufficient ductility. Due to the presence of external prestressing, the ultimate moment capacity is enhanced by approximately 6.1%, 31.7%, 38.5%, 57.6%, 29.4%, and 80.2% as compared to the reference. Finally, the radius of curvature at the top flange region for strengthening samples has grown by approximately -16.7%, 8.0%, -26.9%, 21.5%, 17.5%, and 17.4% as compared to the reference case. In contrast, the percentage of the radius of curvature at the bottom flange region for strengthened samples dropped to 24,9%, 73.9%, 83.2%, 83.6%, 69.2%, and 89.0%, respectively, with an increase in the eccentricity position as compared to the reference.
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.
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•An analytical method for externally prestressed steel-concrete composite beams is discussed.•A numerical parametric analysis is developed.•Divergences between the numerical analyses and analytical procedures were verified.•Tendon configuration influences the beam's resistance, deflections, slab cracking and the steel-concrete interface.•The analytical procedure can adequately estimate the ultimate resistance of the beams.
•Seismic failure-behavior of old medieval and bell towers is accurately simulated.•Numerical failure modes by FEM are in good agreement with real earthquake observations.•The seismic energy ...dissipation is obtained by external prestressing.•Proposal of two prestressing levels and one unbonded smart materials device.•Medium prestressing is the optimum for towers failing ductile and quasi-brittle.
Medieval and masonry bell towers are highly vulnerable to suffer strong earthquake damage due to the mechanical and physical characteristics of masonry and other important factors. An approach for the seismic vulnerability reduction of masonry towers with external prestressing is proposed. The devices are vertically and externally located in order to be removable when needed. The characteristic flexural failure mode of medieval towers and the shear mechanism of bell towers are simulated. Both failure modes are in agreement with earthquake damage in similar towers. Medium prestressing level enhances force capacity of towers failing by bending without reducing ductility. High prestressing level slightly reduces the displacement capability of towers failing ductile. In case of belfry failure, both prestressing levels permit to increase displacement but lower force than towers failing by bending. The proposed medium prestressing level is the optimal for masonry towers and other slender structures failing by bending and shear.
This study conducted a comprehensive investigation into the shear stress migration of a tapered prestressed concrete (PC) continuous box girder bridge with trapezoidal corrugated steel webs (TCSWs) ...throughout the entire construction process, including cantilever construction, structural system transformation and external prestressing tendon tensioning. The results revealed that the basic assumptions, which state that TCSWs bear all the shear force and that only the vertical component of the external prestressing contributes to shear stress when considering its contribution, are not valid for the shear design of tapered PC girder bridges with TCSWs. The horizontal component of the external prestressing and bending moments can cause additional shear forces via the Resal effect, which results in the migration of the shear stresses between the curved bottom concrete slabs and TCSWs. This study investigated the mechanism through which the Resal effect and external prestressing influence the migration of shear stress in the entire construction process. The results revealed that within continuous girders, the Resal effect exhibits both positive and negative implications. Specifically, the negative Resal effect exerts an unfavorable influence, resulting in an increase in the shear stress experienced by the TCSWs. Moreover, this study introduced a modified shear method that that takes into account the influence of bending moments and the horizontal component of external prestressing. In contrast to basic shear methods, this approach provides notably heightened accuracy.
•The Resal effect can induce the migration of shear stress between TCSWs and the bottom slab in tapered girders with TCSWs.•The Resal effect exhibits both positive and negative effects within tapered continuous girders with TCSWs.•The horizontal component of external prestressing can influence the migration of shear stress in tapered girders with TCSWs.•A modified method is proposed for calculating the shear stress on the TCSWs in tapered girders with TCSWs.
The existing research on the deflection of girders with CSWs have mainly concentrated on prismatic cases under self-weight or external loading. There has been a lack of research on the deflection ...analysis of tapered girders with CSWs under external prestressing (EP). For the first time, in this study, the authors conducted an analysis of the deflection in prismatic and tapered girders with CSWs under EP using a combination of theoretical calculations and finite element (FE) simulations. The findings of the study revealed that shear deformation contributes over 20% to the total deflection in girders with CSWs under EP. Moreover, the results emphasize that the current standards, which assume that shear deformation in girders with CSWs is solely induced by the vertical component of the EP, are applicable only to prismatic girders. This assumption leads to substantial inaccuracies when applied to tapered girders with CSWs. This discrepancy arises because in tapered girders, the bending moments and axial force generated by EP induce additional shear deformations on the CSWs and inclined bottom slabs. Consequently, the study put forward modified theoretical formulas that considers the additional shear deformation induced by bending moments and axial force for predicting the deflection of tapered girders with CSWs under EP. This modified method yields more accurate deflection predictions for tapered girders with CSWs.
•The shear deformation cannot be neglected in deflection calculations under external prestressing for girders with CSWs.•The current design standards' assumptions regarding deflection in tapered girders with CSWs are not applicable.•The bending moment and axil force caused by external prestressing can cause additional shear deformation.•A modified method is suggested to calculate the deflection in tapered girders with CSWs.
Previous studies have confirmed the vulnerability of reinforced concrete (RC) knee joints under cyclic loading, however, there remains a lack of studies on their seismic retrofitting. This study ...proposes a retrofit strategy aimed at enhancing the seismic performance of knee joints by acknowledging their unique behavior. The strategy involves a novel arrangement of steel plates that optimizes the effectiveness of steel haunch and external prestressing methods. To evaluate this approach, six full-scale knee joint specimens—two controls and four retrofitted—were fabricated using nonseismic reinforcement details and subjected to reversed cyclic loading. Vital parameters, including load, displacement, and strain responses along the reinforcement bars and steel plates, were monitored throughout the tests. The specimens retrofitted with this newly proposed strategy demonstrated a significant improvement in seismic performance by effectively distributing the prestressing force to the core of the joint and promoting beam flexural failure. The lateral strength significantly increased, with maximum enhancements of 100 % and 200 % under closing and opening rotations, respectively. Additionally, the retrofitted specimens dissipated at least 100 % more cyclic energy compared to the control specimens. Furthermore, the proposed distribution of the prestressing force within the joint core was instrumental in restraining the expansion of diagonal cracks. Consequently, this study makes a substantial contribution to the body of knowledge on RC knee joints and promotes their practical implementation under different conditions.
•Improving the seismic performance of knee joints on closing and opening rotation.•A retrofit strategy to address knee-joint invulnerability under opening rotation.•Contributions of steel haunch and external prestressing.•Steel haunches resist beam flexural rotation and relocate plastic hinges to beams.•External prestressing prevents joint crack expansion through force distribution.
To investigate the effects of long-term prestress loss on concrete box girders strengthened with external prestressing, a large-span box girder, in service for over 20 years and strengthened with ...external prestressing, was monitored for four months. Prestress loss in the longitudinal, vertical, and transverse directions of the box girder was calculated according to Chinese code requirements. Magnetic flux rope force transducers were used to monitor the prestress loss in the external prestressing cables. Fiber Bragg Grating (FBG) sensors were used to monitor deflection changes at the mid-span of the bridge. Finally, the effect of prestress loss in the longitudinal, vertical, and transverse tendons on mid-span deflection was investigated through simulations using ABAQUS software. The results show that instantaneous prestress loss accounts for most of the total loss compared to long-term loss, and that longitudinal prestress loss has the most significant effect on mid-span deflection. The impact of longitudinal prestress loss on deflection before and after strengthening was also compared. The downward deflection and up-ward arch caused by longitudinal tendon prestress loss were reduced after strengthening, con-firming the effectiveness of the external prestressing method.
