ON THE REDUCTION OF PRESTRESSING FORCE NEAR SUPPORTS IN PARTIALLY PRESTRESSED CONCRETE FLEXURAL MEMBERS

2018 ◽  
Vol 5 (2) ◽  
Author(s):  
Nazar Oukaili
Keyword(s):  
Prestressed Concrete ◽  
Load Capacity ◽  
Compression Zone ◽  
Flexural Members ◽  
Tensile Stresses ◽  
Prestressing Force ◽  
Service Load ◽  
Bending Stresses ◽  
The Moment ◽  
Concrete Section

Straight tendons in pretensioned members can cause high-tensile stresses in the concrete extreme fibers at end sections because of the absence of the bending stresses due to self-weight and superimposed loads and the dominance of the moment due to prestressing force alone. Accordingly, the concrete tensile stresses at the ends of a member prestressed with straight tendons may limit the service load capacity of the member. It is therefore important to establish limiting zone in the concrete section within which the prestressing force can be applied without causing tension in the extreme concrete fibers. Two practical methods are available to reduce the stresses at the end sections due to the prestressing force. The first method based on changing the eccentricity of some tendons by raising them towards the end zone. The second method is based on bond prevention by encasing some of the tendons in plastic sheathing, effectively moving the point of application of prestressing force inward toward midspan for part of tendons. The present study focuses on a proposed third method to reduce the effect of the prestressing force near end supports by using straight strands with limited initial prestressing value in compression zone. New equations were suggested for the cracking moment and the prestressing force which consider the prestressed tendons in compression zone.

The Effect of Higher Prestress on Concrete Railroad Tie Behavior

2015 ◽  
Author(s):  
N. D. Catella ◽  
R. A. Mayville
Keyword(s):  
Stress State ◽  
Prestressed Concrete ◽  
Three Dimensional ◽  
Negative Consequences ◽  
Premature Failure ◽  
Model Interaction ◽  
Tensile Stresses ◽  
Prestressing Force ◽  
Consistent Performance ◽  
Three Dimensional Finite Element

Prestressed concrete crossties are used extensively by North American railroads because they offer improved service life and consistent performance. Recent industry trends have encouraged manufacturers to effectively increase concrete ties’ prestressing force to improve their structural performance in flexure and shear. This paper presents the results of linear and nonlinear three-dimensional finite element analyses of typical concrete crossties to study the stress state of crossties at prestress transfer and to identify potential negative consequences of increasing effective prestressing force. The analyses utilize finite-sliding contact with Coulomb friction to model interaction between prestressing strands and adjacent concrete. Variation of several parameters that affect stress state at prestress transfer are considered, including magnitude of prestressing force, stiffness of concrete, crosstie geometry, and strand configuration. The analyses indicate that tensile stresses develop near the ends of the crossties at prestress transfer and their magnitudes increase with decreasing transfer length and increasing prestress force. These tensile stresses may account for widespread longitudinal cracking that has been observed in premature failure of concrete crossties in the last ten years.

scholarly journals Long-term Deflections in Balanced Cantilever Prestressed Concrete Bridges

2009 ◽  
Vol 4 (1) ◽  
pp. 22
Author(s):  
Eltayeb Hassan Onsa ◽  
Elsafi Mohamed Adam ◽  
Abdalla Khogali Ahmed ◽  
Mohamed Elmontasir Elbagir
Keyword(s):  
Prestressed Concrete ◽  
Concrete Bridges ◽  
Live Load ◽  
Prestressed Concrete Bridges ◽  
Prestressing Force ◽  
Load Tests ◽  
The Moment ◽  
Aashto Lrfd ◽  
Made In

Long-term deflections in balanced cantilever prestressed concrete bridges are reviewed. Burri and Shambat Bridges are taken as cases study to calculate long-term deflection. The two bridges were constructed at Khartoum State in the years 1972 and 1962, respectively. Due to the shortage of the basic data regarding the two bridges the AASHTO-LRFD is used to estimate and calculate the missing data in the two bridges. The Moment Area method is used to calculate the long-term deflections due to the dead load, live load and prestressing force. The calculated long-term deflections are compared with measured live load deflections obtained from load tests made by a Chinese contractor requested to evaluate the two bridges. Remarkable differences between theoretical and measured deflection at the end of cantilevers are encountered. The differences are probably due to the basic assumptions made in the formulations of deflection calculations. Some adjustments in the long-term deflection formulae are suggested to bring the calculated deflections in compatibility with measured ones.

scholarly journals Studi Analisis Batasan Persentase Prategang Parsial pada Struktur Balok Prategang (Hal. 48-59)

2018 ◽  
Vol 4 (3) ◽  
pp. 48
Author(s):  
Devy Yolanda ◽  
Priyanto Saelan
Keyword(s):  
Tensile Strength ◽  
Tensile Stress ◽  
Prestressed Concrete ◽  
Crack Width ◽  
Analytical Study ◽  
Reinforcing Steel ◽  
Prestressing Force ◽  
Concrete Section

ABSTRAKPengurangan gaya prategang yang diperlukan pada suatu penampang beton prategang penuh (full prestressed) menyebabkan diperlukannya baja tulangan, dan beton prategang berperilaku menjadi beton prategang parsial. Pengurangan gaya prategang akan menimbulkan tegangan tarik yang bilamana tegangan tarik yang terjadi melampaui kuat tarik lentur beton maka akan terjadi retak. SNI 03-2847-2002 membolehkan penggunaan beton prategang parsial namun belum mensyaratkan batasan persentase prategang yang harus digunakan. Oleh karena itu dilakukan studi analisis untuk mengetahui persentase prategang minimal yang dapat digunakan. Studi kasus dilakukan pada persentase prategang 50, 60, 70, 80, dan 90. Dari hasil studi kasus didapatkan bahwa persentase prategang yang semakin kecil akan berakibat tegangan tarik dan lebar retak yang terjadi semakin besar. Persentase prategang harus dipilih sedemikian rupa sehingga lebar retak yang terjadi tidak melampaui lebar retak yang diizinkan. Pada kelima variabel penelitian, batasan minimal persentase prategang yang lebar retaknya tidak melebihi lebar retak yang diizinkan adalah 60%.Kata kunci:  beton prategang parsial, persentase prategang, tegangan tarik, lebar retak ABSTRACTReducing the required prestressing force on a full prestressed concrete section requires the need for reinforcing steel, and prestressing concrete behaves to partial prestressed concrete. Reduction of the prestressing force will cause tensile stress when the tensile stress that goes beyond the tensile strength of the concrete will result in cracking. SNI 03-2847-2002 allows the use of partial prestressed concrete but does not require the limitation of the prestress percentage to be used. Therefore, an analytical study was conducted to determine the minimum prestressed percentage that can be used. The case study was carried out at 50, 60, 70, 80, and 90 prestressed percentages. From the case study it was found that the smaller the prestress percentage would result in greater tensile stress and crack width. The percentage of prestress shall be chosen so that the crack width does not exceed the allowable crack width. In the five research variables, the minimum limit of prestressing percentage whose crack width does not exceed the allowable crack width is 60%.Keywords: partial prestressed concrete, prestress percentage, tensile stress, crack width

Design for Torsion and Shear in Prestressed Concrete Flexural Members

PCI Journal ◽  
2004 ◽  
Vol 49 (3) ◽  
pp. 34-42 ◽  
Author(s):  
Paul Zia ◽  
Thomas T. C. Hsu
Keyword(s):  
Prestressed Concrete ◽  
Flexural Members

scholarly journals Smart Sensing of PSC Girders Using a PC Strand with a Built-in Optical Fiber Sensor

2021 ◽  
Vol 11 (1) ◽  
pp. 359
Author(s):  
Sung Tae Kim ◽  
Hyejin Yoon ◽  
Young-Hwan Park ◽  
Seung-Seop Jin ◽  
Soobong Shin ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Prestressed Concrete ◽  
Steel Wire ◽  
Optical Fiber Sensor ◽  
Fiber Reinforced Polymer ◽  
Bridge Structure ◽  
Fbg Sensor ◽  
Prestressing Force ◽  
Reinforced Polymer ◽  
Loading Tests

This paper presents a multi-functional strand capable of introducing prestressing force in prestressed concrete (PSC) girders and sensing their static and dynamic behavior as well. This innovative strand is developed by replacing the core steel wire of the strand used in PSC structures with a carbon fiber-reinforced polymer (CFRP) wire with a built-in optical Fiber Bragg Grating (FBG) sensor. A full-scale girder specimen was fabricated by applying this multi-function strand to check the possibility of tracking the change of prestressing force at each construction stage. Moreover, dynamic data could be secured during dynamic loading tests without installing accelerometers and made it possible to obtain the natural frequencies of the structure. The results verified the capability to effectively manage the prestressing force in the PSC bridge structure by applying the PC strand with a built-in optical sensor known for its outstanding practicability and durability.

Analysis of Tensile Stresses in Transfer Zone of Prestressed Concrete U-Beams

2005 ◽  
Vol 1928 (1) ◽  
pp. 134-141 ◽  
Author(s):  
Dongzhou Huang ◽  
Mohsen Shahawy
Keyword(s):  
Prestressed Concrete ◽  
Practical Method ◽  
Tensile Stresses ◽  
Prestressed Girders ◽  
Plate Elements ◽  
Mechanical Models ◽  
Concentrated Forces ◽  
Shell Plate ◽  
Finite Shell ◽  
Transfer Zone

Prestressed U-beam bridges compare favorably in cost and appearance to traditional concrete I-beam bridges. Consequently, U-beam bridges are gaining in popularity and usage, especially when aesthetic issues are deemed important. U-beam bridges first appeared in Florida in 2000; however, during construction, cracks developed in the webs of the U-beams. This paper presents results of an analysis of representative cracking of U-beams and proposes a practical method for the transfer zone stirrup design. For the purpose of the analysis, the U-beam is divided into a series of finite shell-plate elements, and the prestressing tendons are simulated as a number of concentrated forces. Two different mechanical models of the U-beams are developed on the basis of the stages of construction. Analytical results show that high tensile stresses occur in the end zone of the U-beam because of the prestressing tendons and that these tensile stress must be properly considered in bridge design. The research results are applicable to the design of prestressed U-beams and similar types of prestressed girders.

scholarly journals Long-Term Characteristics of Prestressing Force in Post-Tensioned Structures Measured Using Smart Strands

2020 ◽  
Vol 10 (12) ◽  
pp. 4084 ◽  
Author(s):  
Sang-Hyun Kim ◽  
Sung Yong Park ◽  
Se-Jin Jeon
Keyword(s):  
Prestressed Concrete ◽  
Mechanical Strain ◽  
Prestress Losses ◽  
Prestressing Force ◽  
Eurocode 2 ◽  
Study Results ◽  
Girder Bridge ◽  
Creep And Shrinkage ◽  
Term Monitoring

The proper distribution of prestressing force (PF) is the basis for the design of prestressed concrete (PSC) structures. However, the PF distribution obtained by predictive equations of prestress losses has not been sufficiently validated by comparison with measured data due to the poor reliability and durability of conventional sensing technologies. Therefore, the Smart Strand with embedded fiber optic sensors was developed and applied to PSC structures to investigate the long-term characteristics of PF distribution as affected by concrete creep and shrinkage. The data measured in a 20 m-long full-scale specimen and a 60 m-long PSC girder bridge were analyzed by comparing them with the theoretical estimation obtained from several design equations. Although the long-term decreasing trend of the PF distribution was similar in the measurement and theory, the equation of Eurocode 2 for estimating the long-term prestress losses showed better agreement with the measurement than ACI 209R and ACI 423.10R did. This can be attributed to the more refined form of the predictive equation of Eurocode 2 in dealing with the time-dependency of the PF. The study results also confirmed the need to compensate for the temperature variation in the long-term monitoring to derive the actual mechanical strain related to the PF. We expect our developed Smart Strand to be applied practically in PF measurement for the reasonable safety assessment and maintenance of PSC structures by improving several of the existing drawbacks of conventional sensors.

Design method for checking tensile stresses under service loads in cracked prestressed concrete members with 2,400‐MPa strands

2019 ◽  
Vol 29 (1) ◽  
Author(s):  
Hyo‐Eun Joo ◽  
Sun‐Jin Han ◽  
Deuckhang Lee ◽  
Hyunjin Ju ◽  
Soo‐Yeon Seo ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
Design Method ◽  
Tensile Stresses ◽  
Concrete Members

Flexural Behavior of Void Reinforced Concrete Slab with CFRP Reinforcing Bars

2012 ◽  
Vol 184-185 ◽  
pp. 988-991
Author(s):  
Seung Hun Kim
Keyword(s):  
Concrete Slab ◽  
Flexural Behavior ◽  
Test Results ◽  
Compression Zone ◽  
Reinforcing Bars ◽  
Flexural Capacity ◽  
Reinforced Concrete Slab ◽  
Bending Tests ◽  
Bending Performance ◽  
Flexural Members

Use of hollow material in slab can reduce self-weight and deflection than solid slab with CFRP reinforcement. This study was intended to evaluate the bending performance of void flexural members with CFRP reinforcements by bending tests. Test results showed that specimens with void and solid section had the similar failure mode by concrete crushing at the compression zone, and that there was a big flexural capacity difference between the two section. Flexural capacity of solid section with CFRP bars was increased by 55% for void section. Thus, for the design of flexural members with CFRP bars by concrete crushing failure, it is important to calculate the exact distribution of strains and stresses, and to consider the reduction of flexural strength of void section.

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