Prestressing Steel Reinforcement Research Articles

Numerical investigation of prestressed concrete sleepers reinforced with high-performance macro synthetic fibres

As modern railway tracks are exposed to heavier loads and higher operational speeds, the excessive cracking and premature failure of prestressed concrete sleepers are becoming more and more critical. Towards addressing these issues, this study focuses on the numerical integration of macro synthetic (polypropylene) fibres in prestressed concrete sleepers to improve the structural behaviours (i.e. residual capacity, cracking resistance & ductility) and assess the damage evolution. Moreover, the numerical investigation performed using Abaqus attempted to validate experimental results and optimised the sleeper design by partially reducing the number of prestressing wires. The analysis reveals good agreement with the experiment at critical cross-sections (i.e. rail seat & centre) and analytically allowed a ∼ 15 % reduction in prestressing steel reinforcement for the macro synthetic fibre reinforced concrete (MSFRC) sleeper. Accordingly, the optimised MSFRC sleeper performed adequately with minimum ultimate capacity reduction that meets the permissible specifications and future demands.

Effects of unbonded prestressing steel tendons and slit dampers on the seismic behavior of precast concrete beam-column joints

This article proposes a novel precast concrete (PC) beam–column joint that uses prestressing steel reinforcement tendons and external steel slit dampers (SSDs) to provide self-centering and energy dissipation capabilities. The SSDs are steel plates cut to a desired shape installed under the beam ends to control their yield through energy dissipation. Three exterior beam–column joint specimens were investigated through quasi-static reversed cyclic loading tests. The specimens included a PC beam–column joint with only an SSD and two PC beam–column joint specimens using unbonded prestressing steel tendons (two in one specimen and four in the other) and an SSD. A fiber-based model using the software Ruaumoko and a code-based design were developed and validated against the experimental results. The test results showed that without the tendon, the specimen was significantly damaged, whereas using unbonded prestressing steel tendons with an SSD endowed the beam–column joint with a higher lateral load capacity of up to 40%. In addition, the ductility improved significantly up to 1.88 times. The developed model and the code-based design were in excellent agreement with the experimental results. Overall, this innovative connection type offers an alternative for seismic-resistant PC structures, and its design enables easy repair after an earthquake.

Topology Optimization of Continuous Precast Prestressed Concrete Bridge Girders Using Shape Memory Alloys

Despite the growing interest in the concept of topology optimization, its acceptance in civil structures, especially in prestressed concrete structures, is still faced with practical obstacles primarily due to the geometric complexities of optimized structures. Quite often, complex concrete topology yields a complex distribution of tensile zones, which are hard to be effectively prestressed with continuous steel reinforcement. Shape memory alloys (SMAs), with their ability to apply localized prestressing force only at target tensile regions, can offer solutions to the issues facing conventional prestressing steel reinforcement in topology-optimized concrete structures. This paper investigates the topology optimization of prestressed concrete bridge girders using locally prestressed SMAs. A prototype continuous concrete bridge is selected to be optimized under the AASHTO loading conditions. To prove the feasibility of the optimized design, a detailed 3D finite element analysis is performed. The performance of the optimized girder is compared with that of two commonly used conventional designs. The results show that the optimized design can effectively satisfy the AASHTO limit state with less material than the conventional cases.

The bond and flexural strengthening of reinforced concrete elements strengthened with near surface mounted prestressing steel (PS) bars

The main objective of this work is to study the performance of prestressing steel (PS) bars as reinforcements in the reinforced concrete (RC) elements strengthened by the near-surface mounted method (NSM). The work includes two parts. In the first part, direct pull-out tests are performed in order to study the bond performance between PS reinforcement and concrete. The influences of groove sizes and PS surface conditions (smooth and sand coated) are evaluated. The results show that the sand coated PS (PS-Sc) reinforcement has the best adhesion behavior compared with the smooth bar, and its pull-out force is increased by 48%. For this reason, the PS-Sc bars are used in the second part of this work as NSM reinforcement to strengthen RC beams subjected to bending forces. Then, four-point bending tests are carried out to understand the flexural behavior of strengthened RC beams with PS-Sc reinforcements of different lengths and ratios. The obtained results demonstrate that the use of NSM-PS-Sc bars strengthening technique leads to important enhancement in the load carrying capacity of the RC beams. The first crack load and ultimate load of the strengthened RC beams attain 71.41 and 65.67%, respectively, which are higher than those of the control beam. Furthermore, the experimental values show a good agreement with the analytical values in both the ultimate deflection and the ultimate load. This proves that the NSM-PS-Sc bars studied in this work are promising reinforcement of the RC beams.

Numerical study on the flexural performance of precast segmental concrete beams with unbonded internal steel tendons

This study presents a numerical investigation of the flexural performance of precast segmental concrete beams (PSBs) with unbonded internal steel tendons. Numerical models developed in this study using Abaqus software capture well the responses of the PSBs reported in previous studies. This is the first time a three-dimensional numerical model is built and successfully validated against experimental results of PSBs in literature. Based on the verified numerical model, intensive simulations of performances of segmental beams with different parameters and various conditions, i.e. tension-controlled, compression-controlled and balanced sections, are carried out. Based on the numerical results, the flexural behaviour of PSBs under four-point loading is extensively discussed regarding the failure modes, joint opening, stress increment in the tendon and the stress transfer mechanism. A parametric study is also conducted and the results show that the effective prestress, prestressing steel reinforcement ratio, and span length-to-tendon depth ratio strongly affect the load-carrying capacity, ductility, tendon stress increment, joint opening and failure modes of PSBs with unbonded tendons, while the loading type, concrete strength and the number of joints show insignificant effects on the flexural performance of the structure.

Statistical Distributions for the Corrosion Rates of Conventional and Prestressing Steel Reinforcement Embedded in Chloride Contaminated Mortar

Many concrete structures are built using plain mild (PM) and cold-twisted deformed (CTD) steel rebars. Also, quenched and self-tempered (QST) and prestressing (PS) steels are extensively used in today’s construction. For estimating the corrosion propagation period (tp) of concrete structures, the current practice is to assume that the corrosion rate (icorr) of different steels are equal to that of PM steel—leading to erroneous estimation of tp. This paper provides icorr data from a 33-month experiment on PM, CTD, QST, and PS steels embedded in chloride contaminated mortar. Linear polarization resistance test was adopted for icorr measurement. A total of 100 specimens were tested. It was found that the CTD and QST steels exhibit higher icorr than the PM and PS steels. The paper also provides statistical distributions for icorr of these four steels. For PM, CTD, QST, and PS steel embedded in chloride contaminated mortar, and exposed to wet-dry conditions, these are found to be ∼Weibull (2.5, 20.7, 0) μA/cm2, ∼Lognormal (0.45, 3.2, 0) μA/cm2, ∼Gamma (6.8, 3.5, 0) μA/cm2, and ∼Weibull 3P (1.3, 6.5, −0.02) μA/cm2, respectively. Similar distributions for dry condition are also presented. These statistical tools would help engineers in estimating residual service life and scheduling repair activities.

Non-destructive measurement toolkit for corrosion monitoring and fracture detection of bridge tendons

One of the most considerable challenges of building management is to ensure the integrity and the functionality of prestressed members during service life. But particularly corrosive and mechanical influences on the prestressing steel reinforcement strongly impair the long-term performance and durability of interior as well as of exterior tendons in concrete bridges and of other prestressed structures. The durability state and degradation of tendons can be assessed primarily on the basis of the tendon's force, the corrosion state and the existence of steel fractures. For the determination of these parameters, this paper will briefly report on the application and practical verification of a measurement toolkit, which is used for monitoring, inspecting and testing of prestressed concrete elements, with main consideration of prestressed tendons in bridges. This toolbox comprises conventional inspection and several innovative measurement and monitoring techniques, which have been developed, tested and optimised by the authors in the last decade.

중공 프리스트레스트 콘크리트 교각의 P-M 상관도 매개변수 분석

이 연구는 중공 프리스트레스트 콘크리트 교각의 P-M 상관도에 대한 매개변수 분석을 수행한 결과를 제시하고 있다. 다수의 매개변수 중에 콘크리트 압축강도, PS 강재량, 유효프리스트레스, <TEX>$D_s/D_o$</TEX>, 그리고 <TEX>$D_i/D_o$</TEX>를 선택하여 P-M 상관도에 미치는 영향을 중점적으로 다루었다. 준정적 실험을 통해서 중공 프리스트레스트 콘크리트 교각 실험체의 강도와 연성도를 평가하였다. 실험 및 해석결과와 각 코드를 기준으로 비교한 P-M상관도의 결과는 서로 다른 차이를 나타내었으며 AASHTO-LRFD는 근접한 값을 보여주었다. 무차 원화한 P-M 상관도를 중공 프리스트레스트 콘크리트 교각의 저항능력을 예측하기 위하여 제시하였다. This study presents the results of parametric studies of the P-M interaction diagram of hollow prestressed concrete bridge columns. Among the numerous parameters, this study concentrates on concrete compressive strength, prestressing steel reinforcement ratio, effective prestress, the Ds/Do ratio, and the Di/Do ratio. The strength and ductility of hollow prestressed concrete bridge columns were evaluated through quasistatic tests. The P-M interaction diagrams from the codes were different from that of the results, which were in good agreement with AASHTO-LRFD. Nondimensionalized P-M interaction diagrams were developed to predict the design resistance of hollow prestressed concrete bridge columns.

프리스트레스트 경량 콘크리트 보의 휨 거동에 대한 부분 프리스트레싱비와 유효 프리스트레스의 영향

이 연구에서는 상부 2점 집중하중을 받는 프리텐션 경량 콘크리트 보의 휨 거동을 부분 프리스트레싱 비와 긴장재의 유효 프리스트레스에 따라 평가하였다. 절건비중 1,770 kg/㎥의 경량 콘크리트 설계강도는 35 MPa이었으며, 항복강도 383 MPa의 일반 이형철근과 인장강도 2,040 MPa의 3연선을 각각 주 인장철근과 프리스트레싱 긴장재로 사용하였다. 실험 결과, 프리텐션 경량 콘크리트 보의 휨 내력은 부분 프리스트레싱 비의 증가와 함께 증가하지만 긴장재의 유효 프리스트레스에는 거의 영향을 받지 않았다. 동일 휨 보강지수에서 프리텐션 경량 콘크리트 보의 무차원 휨 내력은 Harajli and Naaman 및 Bennet에 의해 실험된 프리텐션 보통중량 콘크리트 보와 비슷한 수준이었다. 한편 프리텐션 경량 콘크리트 보의 변위 연성비는 부분 프리스트레싱 비의 감소와 함께 그리고 유효 프리스트레스의 증가와 함께 증가하였다. 프리텐션 경량 콘크리트 보의 하중-변위 관계는 비선형 2차원 해석모델에 의해 적절하게 평가될 수 있었다. 또한 프리텐션 경량 콘크리트 보의 휨 균열 내력 및 최대 휨 내력은 각각 탄성이론 및 ACI 318-08의 등가응력블록과 긴장재의 응력평가 식을 이용하여 안전측에서 예측될 수 있었다.

외부 프리스트레싱으로 보강된 프리스트레스트 콘크리트 보에서 프리스트레싱 강재의 극한응력

This study deals with literature review, developing a predicting equation for the ultimate stress of internal and external prestressing steel, and an experimental test with the parameters affecting the ultimate stress of prestressing steel in prestressed concrete beams strengthened by external prestressing tendons. The proposed predicting equation takes rationally the effect of internal and external prestressing steels into consideration as a function of prestressing steel depth to neutral depth ratio. In the experimental study, prestressed concrete beams strengthened using external steel tendons are tested with the test parameters having a large effect on the ultimate stress of internal and external prestressing steel. The test parameters include internal and external prestressing steel reinforcement ratio and span to depth ratio. The test results are analyzed to confirm the rationality and applicability of the proposed equation for predicting the ultimate stress of internal and external prestressing steel. This research shows that the results obtained by the proposed equation for predicting the ultimate stress agreed very well with the test results.

외부 프리스트레싱으로 보강된 R.C 보에서 강재량 및 텐던깊이에 따른 프리스트레싱 강재의 극한응력

This study deals with literature review, developing a predicting equation for the ultimate stress of prestressing steel, and experimental test with the parameters affecting the ultimate stress of prestressing steel in reinforced concrete beams strengthened by external prestressing. The ACI predicting equation for the ultimate stress of unbonded prestressing steel is analyzed to develop a new integrated predicting equation. The proposed predicting equation takes rationally the effect of internal reinforcing bars into consideration as a function of prestressing steel depth to neutral depth ratio. In the experimental study, steel reinforced concrete beams strengthened using external prestressing steel are tested with the test parameters having a large effect on the ultimate stress of prestressing steel. The test parameters includes reinforcing bar and external prestressing steel reinforcement ratios, and span to depth ratio. The test results are analyzed to confirm the rationality and applicability of the proposed equation for predicting the ultimate stress of external prestressing steel.

Spannungsrißkorrosion von Spannstahl - Vorstellung einer neuen Untersuchungsmethode / Stress corrosion of prestressing steel reinforcement - Presentation of a new test method

Abstract The origin of the susceptiblility of prestressing steel reinforcement with respect to stress corrosion and the observed failure mechanisms can be described 'in detail. So far, however, no precise method exists to determine the sensitivity of prestressing reinforcement or to distinguish different types of steel with respect to their susceptiblility for stress corrosion. This fact leads not only to prejudices in practice but also to additional safety measures (f.e. robust reinforcement), which implies economical consequences. The aim of a cooperation project between the Institute of Concrete Structures and Building Materials Technology at Leipzig University and the Institute for Materials Technology and Testing at Otto-von-Guericke- University Magdeburrg is to develop a general acceptable test method which provides us quickly with meaningful results. It turned out that the observation of electrochemical noise is a promising method to study stress corrosion of prestressing steel reinforcement. This method can be applied both in laboratory testing and under site conditions and can therefore also serve as a basis for corrosion monitoring.

Structural Safety of Post-Tensioned Concrete Slab Bridges With Unbonded Tendons

The authors examine the structural safety of simply supported post-tensioned concrete slab bridges with unbonded tendons. Slab designs are in accordance with the American Association of State Highway and Transportation Officials (AASHTO) load factor design specifications, and service stresses and ultimate strength are both considered in the design. Probabilistic resistance models that consider variabilities in material properties and section dimensions are developed using simulation methods. Reliability for flexural capacity at ultimate limit state is measured in terms of the reliability index. Sensitivity analysis is conducted to study the effects of changes in span length and prestressing steel reinforcement ratio on stress in unbonded tendons, bending moment capacity, and reliability index. Results of the analysis revealed that statistical properties of bending moment capacity at ultimate are a function of the amount of prestressing steel. Furthermore, designs based on current AASHTO specifications result in considerable nonuniform safety for bridges having different span lengths and reinforcement indexes.