Shear Behavior of Concrete Beams Externally Prestressed with Parafil ropes (original) (raw)
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Influence of Flexural Reinforcement on Shear Strength of Prestressed Concrete Beams DISCUSSION
Aci Structural Journal, 2009
The paper presents the experimental results of a series of nine prestressed concrete beams without stirrups failing in flexure and in shear. Some theoretical considerations are also proposed on the basis of a theory previously developed by the authors with respect to shear strength in reinforced concrete members (Tureyen and Frosch 2003). The innovative design of the tests as well as the well-documented data presented by the authors have allowed the discussers to investigate a number of aspects with respect to shear strength in prestressed members. A series of independent conclusions and interpretations derived from this analysis may complete those proposed by the authors.
Journal of Structural and Construction Engineering (Transactions of AIJ), 2010
Seven half-scale post-tensioned precast concrete beams were tested under anti-symmetrical flexure. The experimental parameters were shear span ratio and shear reinforcement ratio. Multi-strands and high strength shear reinforcement with nominal yield strength of 785 MPa were used as post-tensioning steel and shear reinforcement, respectively. Yielding of shear reinforcement was not observed in any of the specimens. The flexural capacity evaluated by the ACI rectangular concrete stress block with plane section assumption agreed well to the experimental results. The shear capacity was estimated by the design equation 71.2a in the AIJ Standard for Structural Design and Construction of Prestressed Concrete Structures. The experimental results collected by literature survey to past research revealed that shear failure modes could be related to each of the experimental parameters (shear span ratio, shear reinforcement strength and shear reinforcement ratio).
Influence of flexural reinforcement on shear strength of prestressed concrete beams
The paper presents the experimental results of a series of nine prestressed concrete beams without stirrups failing in flexure and in shear. Some theoretical considerations are also proposed on the basis of a theory previously developed by the authors with respect to shear strength in reinforced concrete members (Tureyen and Frosch 2003). The innovative design of the tests as well as the well-documented data presented by the authors have allowed the discussers to investigate a number of aspects with respect to shear strength in prestressed members. A series of independent conclusions and interpretations derived from this analysis may complete those proposed by the authors.
Ductility of Externally Prestressed Continuous Concrete Beams
Ductility is a desirable structural property that allows stress redistribution and provides warning of impending failure. Factors affect the ductility of beams prestressed with external FRP tendons are different than those affect the ductility of ordinary bonded prestressed concrete beams due to lack of bond and linear stress-strain relationship of FRP tendons. This paper investigated the effect of several variables on the ductility of continuous concrete beams, externally strengthened using Parafil ropes. The test variables included external prestressing force value, depth of external prestressing tendons, loading pattern, tendon profile and location of deviators. Test results show that the ductility of the externally prestressed concrete beams significantly reduced due to prestressing. Also, the eccentricity of the prestressing force and the tendon profile had the main influence on ductility of the externally prestressed beams, while the variation in prestressing force value, loading pattern and location of deviators had a less effect.
Shear Behavior of Steel Fiber Reinforced Prestressed Concrete Beams
2020
Prestressed concrete girders are the main superstructure elements in many bridge structures. Shear failures in these girders are undesirable due to brittle failure and little warning time. To prevent shear controlled brittle failure, it is normal practice to increase the amount of transverse reinforcement in flexural members. However, past studies have revealed that even higher transverse reinforcement ratios (i.e. > 4%) may not be able to eliminate shear failure in some cases. Moreover, the increased reinforcement makes it more difficult to place and consolidate the concrete. This research program aimed to investigate the feasibility of replacing traditional shear reinforcement in prestressed concrete beams with steel fibers. A total of 14 rectangular and 8 I-shaped prestressed concrete beams were investigated after subjecting them to two-point loading test. The beams were casted with steel fiber ratios ranging from 0.75% to 2.00%. Experimental results revealed that the inclusio...
Shear Carrying Capacity of Segmental Prestressed Concrete Beams
Doboku Gakkai Ronbunshuu E, 2009
This paper describes the results of an experimental study and nonlinear finite element method in order to examine the shear failure mechanism of segmental prestressed concrete beams by varying the length of segment, prestressing force and loading position. It is observed that after the opening of the segmental joints, the stiffness of such beams considerably decreases and the tendon stress is caused to increase significantly. The simplified truss model and other existing prediction methods for shear carrying capacity have been applied in this study in order to examine their applicability and accuracy. The simplified truss model can provide reasonable accuracy under the limitation of applied prestressing force.
Shear Strength of Reinforced Concrete Beam Strengthened by Transverse External Post-tension
Problem statement: Shear failure of concrete beam is brittle manner without warning so inadequate design for shear of beam and/or material deterioration lead to the possibility of sudden failure of beam. The change of functional use and future increased load of structure lead to the need for strengthening of concrete structure. Approach: This research focuses on behaviors under static loading of reinforced concrete beam, with shear strengthening by transverse external prestressing force. Post-tension high strength steel is vertically applied in shear span. Total eight beam specimens are divided into two groups each having shear span to depth ratios 2 and 1.5. Each beam, possessing the same reinforcing steels, is intentionally designed to be failing in shear. One of the beams from each group is used as reference, without shear strengthening. The other three specimens from each group are applied different amounts of external prestressing force. Results: The experimental result shows t...
An Investigation on Shear Behavior of Prestressed Concrete Beams Cast by Fiber Reinforced Concrete
Arabian Journal for Science and Engineering, 2018
Failure due to shear is brittle in nature, and inherent lesser concrete tensile strength is a main contributing factor. During loading before the shear reinforcement could start functioning, cracking in concrete starts. Use of fibers in concrete had proven improved impact on tensile strength of concrete. Active reinforcement role initiates after concrete cracking starts. This paper investigates into the shear behavior of fiber reinforced, pretensioned concrete I-section beam specimens. A total of six beam specimens were cast. Two types of fibers, steel fibers and polypropylene fibers were used in five different proportions. For comparison, one control specimen was also cast without inclusions of fibers in concrete. Concrete mix ratio, prestress force, shear span-to-depth ratio and shear and flexural reinforcement details were kept constant in all specimens. Specimens were subjected to four-point loading to ensure that all specimens fail due to excessive shear force. During tests, deflections and strains were also measured. It was concluded that shear strength of beams was improved using steel fiber reinforced concrete (SFRC) as compared to polypropylene fiber reinforced concrete (PPFRC). SFRC beam containing 0.65% fiber depicted 50.71% improvement in ultimate failure load, 67% improvement in first cracking load and 36% improvement in ultimate deflection as compared to control beam.
Shear Design and Assessment of Reinforced and Prestressed Concrete Beams Based on a Mechanical Model
Journal of Structural Engineering, 2016
Safe and economical design and assessment of reinforced (RC) and prestressed concrete (PC) beams requires the availability of accurate but simple formulations which adequately capture the structural response. In this paper, a mechanical model for the prediction of the shear-flexural strength of PC and RC members with rectangular, I or T sections, with and without shear reinforcement, is presented. The model is based on the principles of concrete mechanics and on assumptions supported by the observed experimental behavior and by the results of refined numerical models. Compact, simple and accurate expressions are derived for design and verification of the shear strength, which incorporate the most relevant shear transfer actions. Excellent agreement between the predictions of the model and the results of the recently published ACI-DAfStb databases, including more than 1287 tests on RC and PC beams with and without stirrups, has been observed. The theory behind the model provides consistent explanations for many aspects related to the shear response that are not clearly explained by current code formulations, making it a very helpful tool for daily engineering practice.
Retrofitting of reinforced concrete beams in shear using external prestressing technique
Retrofitting of existing concrete structures has become an important issue nowadays in the construction industry. There are many causes for repair and/or strengthening, but normally change of use, increased demands on the structure, errors in the design or/and construction phase or accidents are governing. Many methods to repair and/or strengthen concrete structures exist such as concrete overlays, shotcrete, external prestressed using cables and so on. This research presents laboratory tests of nine reinforced concrete beams with 2 m span strengthened in shear with external prestressing technique. In addition to a non-strengthened reference beam. the present work studied in three groups to examine beams strengthening using different configuration of prestressing details in shear domain, the effect of repairing beams cracked in shear with different damage levels, and the strengthening of beams using carbon fibre reinforced polymer plates in flexure and prestressing in shear. The tests results showed that prestressing is a very effective strengthening method to increase the shear load-carrying capacity of existing concrete beams. The external post-tensioning method can reduce the effect of the existing crack and increase the member capacity up to 95% of the original capacity. The failure of beam strengthened with external carbon fibre reinforced polymer laminate in flexure and using external post-tensioning technique in shear failed owing to peeling of the carbon fibre reinforced polymer laminate. In addition, a numerical model was presented and verified with the experimental result and showed good agreement.