Post-tensioned Concrete Beams Research Articles

Investigation of Bursting Force In I-Section Post-Tensioned Anchorage Zone

In post tensioned concrete beam the high transverse tensile stress is generated and if proper reinforcement is not given, bursting may occur. To study the effect of these stresses and to find bursting stress in end region the analytical study was carried out. In present work the end block of post-tensioned prestressed concrete beam is modelled in finite element based software with eccentric tendons. The bursting zone of beam is evaluated and parametric study was carried out by varying eccentricity, anchorage ratio and web thickness of girder. The 3D modelling was done and results are compared in terms of bursting force. The results are compared with Indian Standard 1343:2012 and inferences are drawn towards the usability of IS code equation of bursting force for I-section.

New trends in assessing the prestress loss in post-tensioned concrete bridges

The evaluation of the current prestress force represents often a challenging issue during the assessment of existing post-tensioned concrete (PTC) members. In this contribution, two case studies are presented to show the efficiency of some experimental methods applied both to laboratory beams and to an in-service PTC bridge. First, the outcomes of an experimental campaign carried out on three PTC beams with a straight post-tensioned, non-grouted tendon are discussed. For each beam, three-point bending tests (3PBTs) were carried out applying increasing load steps until failure and varying the prestress force; at each load step, non-destructive tests (NDTs) were performed, namely, dynamic free vibration and ultrasonic tests. The variation of non-destructive parameters was evaluated as a function of the prestress force and of the structural damage. The second case study deals with a 50-year-old PTC bridge with grouted ducts. In this case, other than evaluating the existing geometry, structural details, and material properties, the following NDTs were performed: endoscopies, tests based on stress release, i.e., both saw-cut and wire-cut tests, and lastly, X-ray diffractometries (XRDs). The results indicate the high potential of this latter technique, which resulted more reliable and less invasive than the previous ones.

Flexural behavior of Corrosion-Damaged prestressed concrete beams

This paper presents an experimental study and theoretical analysis on corroded prestressing tendons and corroded prestressed concrete beams. 68 steel strands and steel wires were artificially corroded and monotonically tested under tensile loads. Results indicated significant degradation in both deformability and strength of the corroded tendons. A bilinear model was consequently developed to characterize the constitutive relationship of the corroded prestressing tendons. Afterward, six post-tensioned prestressed concrete beams were electrochemically corroded and flexurally tested using a four-point bending set-up. Different variables were considered, including the corrosion degree, yield strength ratio and corrosion of non-prestressed rebars. It was found that, corrosion of prestressing tendons led to a deteriorated flexural bearing capacity of a beam. The cracking load, yield load, and ultimate load all decreased with the corrosion degree. Thereafter, a theoretical approach based on the stress–strain model of corroded steel tendons was proposed to predict of flexural behavior of corroded prestressed concrete beams. Good agreement with experimental results of current study and from literature was observed.

Effect of prestressing corrosion on failure in bridges

AbstractInfrastructures (viaducts, bridges, tunnels, railways, and roads) are fundamental to allow people and goods move around a country. In particular, in Italy, due to its orographic and morphological complexity, the ratio between the number of viaducts and the national geographical extension is the largest in Europe. This kind of structure constitutes a weakness of the road networks, especially those over 50 years old, and among these, prestressed concrete structures are the most vulnerable. Therefore, the study of the robustness of an infrastructure network is a quite useful topic for modern societies and public mobility managers. The aim of the present work is to develop a reliable and fast analysis tool capable of processing many structures in a relatively short time. In order to calibrate the most suitable instrument, starting from the study of an experimental campaign on six prototypes of artificially corroded posttensioned concrete beams, the reliability of concentrated plasticity models was investigated to reproduce force‐displacement diagrams and in particular, the effect of corrosion on the moment‐curvature relationship. In fact, this method could provide a well‐defined nonlinear analysis of prestressed elements, especially in the case of grillage decks where external girders could be more affected by corrosion damage in opposition to internal girders or diaphragms. A numerical model by FEM analysis is also presented to reproduce a vulnerability study on an actual structure.

Effect of Transverse Reinforcement on Shear Response of Fiber-Reinforced Polymer Post-Tensioned Concrete Beams

Effect of Transverse Reinforcement on Shear Response of Fiber-Reinforced Polymer Post-Tensioned Concrete Beams

The effect of carrier system materials used in an Olympic swimming pool on the perceptual evaluations of respondents

PurposeThis study aims to determine the effects of three different carrier system materials (laminated wooden beams, post-tensioned concrete beams and steel beams) used widely in interior spaces on the perceptual evaluations of respondents.Design/methodology/approachThe large opening Olympic swimming pool space was chosen as the research environment. A total of 376 university graduates participated. After experiencing the 360-degree virtual images of the experimental spaces, a “spatial perception” questionnaire was applied to these respondents.FindingsThe spaces using the laminated wood beams in the carrier system were perceived as warmer, lighter, more attractive, more spacious, more informal, closer, more well-planned, freer, simpler, more peaceful, more exciting, and uncrowded compared to the spaces that used post-tensioned concrete beams and steel beams. The architect respondents made more negative perceptual evaluations for all the adjective pairs compared to the respondents in the other professional groups. Respondents who were males, and in the 26–35 years of age group, perceived more positively the physical environmental factors of the virtual swimming pools compared to females, and the 36 years of age or above age group.Originality/valueThe results set forth that the structural elements of buildings, such as ceilings, walls and furnishings, were not only systematic elements used in the formation of the structure, they were also important environmental factors in the perceptual evaluation of the space.

Re-evaluation of shear contribution of CFRP and GFRP sheets in concrete beams post-tensioned with unbonded tendons

Contemporary design guidelines for the shear resistance of post-tensioned concrete (PC) beams retrofitted with fibre reinforced polymer (FRP) sheets are developed from the results of reinforced concrete (RC) beams. The accuracy of these guidelines for calculating the shear resistance of PC beams wrapped with FRP sheets is still questionable due to the difference in the shear behaviour of RC vs PC beams. The effects of the essential factors (e.g. tendon profile and anchorage system) on the shear resistance of PC beams have not been sufficiently studied, particularly for unbonded post-tensioned concrete (UPC) beams. This study presents an experimental investigation on the shear behaviour of UPC T-beams and the shear contribution of CFRP/GFRP sheets. The experiment consisted of 26 large-scale UPC T-beams with various factors including the tendon profile (harped or straight), concrete strength, FRP anchors, CFRP vs GFRP sheets, and various wrapping configurations. The experimental results showed that CFRP/GFRP sheets increased the shear resistance of UPC beams by 4–26%, which was much lower than that in RC beams. In comparison with the UPC beams with straight tendons, those with harped tendons exhibited a reduction in the shear contribution of CFRP/GFRP sheets (approximately 40%) and showed a more ductile failure mode with an improvement of the beam deformation (up to 2.3 times). FRP anchorage systems significantly enhanced the FRP shear contribution and energy absorption increased by 88% and 42% regarding those without anchors, respectively. Besides, it was observed from the test data that the widely-used method to determine the experimental shear contribution of FRP sheets in PC beams based on the difference between the shear resistance of strengthened and unstrengthened beams was inappropriate because it failed to consider the interactions between FPR sheets and other shear components, i.e. concrete and stirrups. Meanwhile, the experimental shear contribution of FRP sheets is recommended to be determined from the actual strain data of the FRP sheets across the main shear crack.

Secondary transfer length and residual prestress of fractured strand in post-tensioned concrete beams

Secondary transfer length and residual prestress of fractured strand in post-tensioned concrete beams

Influence of various design parameters of the grouted duct on mono-strand bond behavior in post tensioned members

There are many factors that may affect the concrete-strand and concrete-duct bond behavior in post-tensioned (PT) concrete slabs and beams. The importance of bond strength is to ensure a proper transfer of stresses from strands and ducts to the surrounding concrete. This research focused on bonded post-tensioned (PT) concrete elements, which includes the use of grout and ducts to provide the link between the strand and the concrete. The strength of the grout, the type and geometry of the ducts, and the embedment length of both strands and ducts were investigated through an experimental testing program to disclose the average interface shear stress within the embedded length of PT elements. This work helped in a better understanding of the bond behavior and the corresponding related parameters involved in the design process.

An application of physics: simply supported bridges made of post-tensioned concrete and structural steel beams

Bridges represent an important application of physics capable of solving real transportation problems. Knowledge of convenience of different mechanical solutions when analyzing and designing bridge is needed. For these reasons, this work is focused on the study of convenience of using two types of bridges. Simply supported short-medium span bridges (30 m to 45 m) are usually excessively long when choosing reinforced concrete solutions and usually short for other types of structures such as cable-stayed or cantilever bridges. The suitability of simply supported bridges leads to the need of studying their cost benefit ratios. This work studies the cost benefit ratio for post-tensioned concrete beams and structural steel girders in simply supported straight bridges. Eight models built of type I sections were used in both cases to analyze the bridges using a software based on the stiffness method. Span of each bridge was set to 30 m, 35 m, 40 m, and 45 m. The convenience of each type of bridge was done comparing the total and the cost per linear meter of each solution (post-tensioned and structural steel). Comparison was done using material consumption, labor, and construction processes costs only. Also, allowable vertical displacement given by current bridge design standards was verified.

Break even analysis & response of longer span frames with or without post-tensioned beams in multipurpose hall

In this paper analyzed the RC a nd PT Beam against variation in the clear span length of the beam. This work includes the design and estimate of Cost/Beam from 5m span up to 15m span length of the beam. Also, The response of the frame following two variation in its modelling. Initially, The primary model consists of a conventional RCC frame with all beams and columns as RCC. The secondarily model considers peripheral beams as RCC and interior beams with PT. Such as ETABS software used to designed RC beam element and ADAPT-PTRC used to designed PT beam element. However it has been note that variation of cost with respect to the span of beam where the break-even point between RCC and PT technique is approx 7m Span. Also the control on deflection of beam by restrict the depth of beam by using unbonded Post-tensioned prestress concrete beam method. There is very good understand all aspects PT beam better than as compared with to RC beam in deflection against longer span length of beams. This paper gives suggestion about to reach a decidedly conclusion regarding which technique is superior over one another.

A new empirical model for residual flexural capacity of corroded post-tensioned prestressed concrete beams

In this paper, a total of 70 experimental flexural tests of corroded post-tensioned prestressed concrete (PC) beams were gathered from the published literatures. Using the experimental data, a comprehensive databank of flexural capacity of the corroded PC beams was established. Meanwhile, four existing empirical models for calculating the residual flexural strength of the corroded PC beams were also gleaned and contrasted with each other based on the databank. It turns out that three of the four existing empirical models underestimate the flexural capacity. To deeply analyze the factors affecting the flexural capacity, numerous factors were discussed, e.g., the corrosion ratio, beam width, effective height of the beam section, concrete compressive strength, and the ratio of strength between the tensile reinforcement (including prestressed and non-prestressed reinforcement) and concrete. It is found that the corroded post-tensioned PC beams’ residual flexural capacity is affected most by the corrosion ratio. In the end, a better empirical model is proposed for computing the residual flexural capacity of corroded PC beams, which provides accurate and effective predictions in a wide range of corrosion ratio for engineering practice.

Determination of the structural efficiency of short bridges according to their physical and economic characteristics

Bridges are structures designed and built to overcome natural and artificial obstacles. The analysis and design of bridges is carried out following principles of physics applied to engineering. The aim is to estimate the structural efficiency of short bridges according to their physical and economic characteristics through equations that measure the cost tendency, identifying which ones have the highest structural efficiency for a given length between supports. The design of short bridges was carried out by means of a mathematical modeling in a software based on finite elements. A comparative cost analysis was carried out for various types of short vehicular bridges designed with reinforced concrete decks supported by reinforced concrete beams; post-tensioned concrete beams; and structural steel beams. It was determined that the bridge with a reinforced concrete deck is the alternative with the best structural efficiency according to its physical and economic characteristics with spans of 12 meters and 18 meters. According to the estimated cost equations, it is concluded that, from 18.49 meters post-tensioned concrete bridges are the most efficient physically and economically. Structural steel bridges are the least structurally efficient for short bridges. Therefore, the construction of short vehicular bridges with structural steel is not feasible.

Isogeometric analysis-based design of post-tensioned concrete beam towards construction-oriented topology optimization

Isogeometric analysis-based design of post-tensioned concrete beam towards construction-oriented topology optimization

Experimental investigation on shear behavior of FRP post-tensioned concrete beams without stirrups

To investigate the shear behavior of post-tensioned concrete beams with longitudinal fiber-reinforced polymer (FRP) reinforcements and without stirrups, seven large-scale beams, with a shear span-to-effective depth ratio of approximately 3.0, were tested. The test variables included the prestressing level, type of flexural reinforcement, and tendon profile. The shear crack width and slip were tracked using digital image correlation technique. It was found that the post-tensioned concrete beams failed in shear-compression or shear-tension, while the nonprestressed concrete beam failed in diagonal tension. The post-tensioned beams designed to have approximately the same longitudinal reinforcement stiffness, exhibited similar shear strength. Draping FRP tendons resulted in an increase of 8.8% in shear cracking strength, while it had slight effect on the maximum shear strength. In this study, it was demonstrated that arching action played a major role in the shear resistance of FRP post-tensioned beams, while the contribution of aggregate interlock was negligible.

Determination of the Stress Increase of the Unbonded Tendon in a Continuous Concrete Beam at Ultimate Capacity Using Nonlinear Analysis

Abstract Predicting the stress increase of an unbonded tendon in a post-tensioned continuous concrete beam at ultimate capacity is more difficult than when bonded tendons are used. The failure mechanisms of the continuous beam are also different to that of the simple-span beam. The loading type, ductility of the support area and moment redistribution influence the behaviour of the continuous structures. In this research, the simplified nonlinear analysis was used for predicting the unbonded tendon stress increase at ultimate capacity in continuous two-span beams. The model is based on the moment-curvature relationships of the reinforced concrete cross-sections under different compressive forces and deformations of the continuous beam under loading. The results have been compared with the experimental results of recent studies found in the literature. In addition, 92 unbonded post-tensioned two-span beams with different reinforcements have been examined by using the model and compared to the results obtained from empirical equations from the literature. The results from the nonlinear analysis correspond well to the results from the other models up to the reinforcement ratio of 0.35. The calculated values of the maximum moment capacity at the centre support were close to the results from the test beams.

Shear Behavior of Post-Tensioned Concrete Beams with Draped FRP Tendons and without Transverse Reinforcement

To investigate the shear behavior of post-tensioned concrete beams with fiber-reinforced polymer (FRP) reinforcements, six large-scale post-tensioned beams without transverse reinforcement and with a shear span-to-effective depth ratio of approximately 3.0 were tested to failure. All beams were longitudinally reinforced with draped prestressed carbon FRP tendons and non-prestressed glass FRP bars. The test variables included the amount of flexural reinforcement and the prestressing level. With the aid of full-field measurement on the beam surface using digital image correlation, the kinematics of the critical shear crack of each beam were tracked. Two shear failure modes, including shear compression and shear tension, were observed in the tested beams. Generally, when the amount of flexural reinforcement increased, there was a corresponding increase in the maximum shear force. When the total prestressing force was increased from 360 to 440 kN, the shear cracking strength and the maximum shear strength increased by 6.9% and 10.0%, respectively. It was demonstrated that an arch mechanism formed in the tested FRP post-tensioned beams, although the contribution of aggregate interlock to the shear capacity was negligible. The predictions of the shear capacity calculated from various shear design models showed that the American and Japanese recommendations were highly conservative, whereas the Canadian recommendations were more consistent with the experimental results.

Post-tensioning of glass beams: Analytical determination of the allowable pre-load

The effectiveness of post-tensioning in enhancing the fracture resistance of glass beams depends on the level of compressive pre-stress introduced at the glass edge surface that will in service be exposed to tensile stresses induced by bending. Maximum pre-load that can be applied in a post-tensioned glass beam system, yielding maximum compressive pre-stress, is limited by various failure mechanisms which might occur during post-tensioning. In this paper, failure mechanisms are identified for a post-tensioned glass beam system with a flat stainless steel tendon adhesively bonded at the bottom glass edge, including the rupture of the tendon, glass failure in tension and adhesive/glass failure in the load introduction zone. Special attention is given to the load introduction failure given that the transparent nature of glass limits the use of vertical confinement usually applied in concrete. An analytical model for determination of the allowable pre-load in post-tensioned glass beams is proposed, based on the model applied for externally post-tensioned concrete beams. The model is verified with the results of a numerical model, showing good correlation, and applied in a parametric study to determine the influence of various beam parameters on the effectiveness of post-tensioning glass beams.

Indirect Determination of Residual Prestressing Force in Post-Tensioned Concrete Beam.

A diagnostic survey on the precast prestressed bridge Nižná confirmed significant deterioration due to environmental distress. Evidently, decisive failures of the structure have a similar character as in the previous precast prestressed bridge in Podbiel in the northern part of Slovakia. These failures result from the unsuitable concept of the first generation of precast prestressed concrete beams, which was used in the former Czechoslovakia in the second half of the 20th century. Subsequently, experimental verification using the proof-load test was also executed. This bridge was built in 1956, so at the time of testing, it was 60 years old. The paper presents the indirect determination of prestressing level in one precast post-tensioned concrete beam using the saw-cut method. Experimental measurement was executed during the bridge demolition. Subsequently, a 2D numerical model in ATENA 2D Software, with the assumption of nonlinear material behavior for verification of experimental results, was performed. Finally, the residual prestressing force was evaluated and compared with the expected state of prestressing according to Eurocodes after 60 years of service.

Distinguished bond behaviour of CFRP sheets in unbonded post-tensioned reinforced concrete beams versus single-lap shear tests

The interfacial bond relationship between carbon fiber reinforced polymer (CFRP) sheets and concrete beams was developed based on single-lap shear tests on concrete blocks, which has been popularly used in the literature. However, the interfacial bond behaviour between CFRP sheets and concrete beams is different from that in single-lap shear tests. This study experimentally investigates the difference in the interfacial bond behaviour between CFRP sheets and concrete blocks in single-lap shear tests vs CFRP sheets and concrete beams, i.e. unbonded post-tensioned concrete beams (UPC). The experimental investigation comprises of ten full-scale UPC T-beams, including eight uncracked/pre-cracked UPC T-beams strengthened with CFRP sheets and two unstrengthened beams. These strengthened beams had a different design, such as various CFRP ratios and with/without U-wraps CFRP anchors. Meanwhile, seven corresponding single-lap shear tests were also carried out to compare to those from the beams. The experimental results showed that the interfacial bond behaviour in the beams was very different from that in the single-lap shear tests in terms of the debonding strain and strain distribution of CFRP sheets. Strain of CFRP sheets in the UPC beams exhibited stress concentration at cracks and substantial non-uniformity, particularly at high load levels. The debonding strain of CFRP sheets in the strengthened UPC beams was significantly higher than that in single-lap shear tests by 250% for the beams without U-wraps anchors and up to 490% for the beams with U-wraps anchors. The use of CFRP U-wraps anchors considerably enhanced the debonding strain up to 127% regarding the beams without anchors. Also, the accuracy of some existing codes and models such as fib Bulletin 14 and CNR-DT 200/2004 in estimating the bond strength of CFRP-to-concrete joints in UPC beams was evaluated in this study.