Influence Of Steel Fiber On The Flexural And Shear Behavior Of High Performance Self-consolidating Concrete Elements

Symmetric inclation beam is a new test method used to investigate the stress state of tunnel segment. It is developed by German scientist and is widely adopted in the investigation of TBM tunnels. Tunnel segment is the main bearing structure for TBM tunnels, thus the cracking resistance, the security and durability is highly desired. While due to the large weight, brittle characteristics and low tensile strength of concrete, traditional RC tunnel segments are prone to crack or damaged during production, transportation, installation and service periods. The poor workability of fresh concrete may reduce the effective bond between matrix and reinforcement and the thickness of concrete cover at high dense reinforcement region with increasing reinforcement ratio and local reinforcement. Cracks often appear in tunnel lining under complex loading conditions, which may damage the integrity of lining structure. The security, permeability, serviceability and durability of the tunnel are strongly influenced by such macro cracks.Fiber reinforced high performance self-consolidating concrete (FRHPSCC) has great potential significance of the high workability of high performance self-consolidating concrete (HPSCC) and high toughness of fiber reinforced concrete (FRC). The macro fiber could improve the tensile and flexural behavior of concrete, replace the steel reinforcement partially, enhance the bar spacing and ensure the ductility of concrete structure. At present the investigation on the workability and mechanical behavior of FRHPSCC is still insufficient, and the experimental study on the application of FRHPSCC in tunnel segment is limited. Therefore, the workability of FRHPSCC, flexural behavior and shear behavior of FRHPSCC beams are firstly investigated in this study. Furthermore, symmetric inclination beam is used to investigate the load-carrying capacity and the toughness of tunnel segment. On this basis and funded by the National Natural Science Foundation-The influence of hybrid fibers on the crack and mechanical behavior of tunnel segment (NO.51078058), the mechanical behavior of FRHPSCC tunnel segment is investigated. The details of the investigation in this dissertation are introduced as follows:(1) The workability of fresh concrete mixture is studied using the wildly used methods in the world, slump flow test and J-ring test. Through the workability test and compressive strength test, the proposed mix design produces the concrete that meet satisfactorily the requirement for workability and strength of SFRSCC.(2) According to RILEM recommendation, flexural behavior of SFRSCC is studied. The influence of fiber size and dosage on flexural behavior and toughness is compared. According to the test results, prediction equation for critical fiber contents to achieve deflection hardening behavior in bending is proposed. Based on the load-deflection curves of notched beam, the a-w relationships of SFRSCC with different fiber contents are derived by inverse analysis method. A model based on σ-w relationship and simple principles of mechanics is proposed to predict the load-deflection behavior. The model is shown to be in good agreement with experimental results.(3) In order to eliminate the influence of wall effect of steel fiber on flexural toughness, a new kind of notched panel with a sectional dimension of600mm×100mm is adopted. Reference to Rilem TC162-TDF, the influence of fiber on the flexural toughness of panels are evaluated. Compared with notched beam, the difference of panel and beam test results is analyzed.(4) The influences of concrete strength, fiber content, fiber type, span and load method on the relationship of central span deflection and CMOD are studied. The results indicate that the deflection-CMOD curves have a linear relationship. The concrete strength, fiber content, fiber type do not show an obvious influence on the relationship between CMOD and central deflection for SFRC member with fiber content less than50kg/m3. The span and load method show clear influence on the gradient of CMOD and central deflection relationship. A relationship for modeling of the central span deflection and CMOD relationship has been proposed, the experimental data of panel test agree well with the suggested model.(5) Shear behavior of simply support SFRSCC beams is studied. The influences of steel fibers on load-deflection curve, load-bearing capacity, crack pattern and failure mode are investigated. Shear ductility indexed are defined and the influence of steel fiber on shear ductility is analyzed quantitatively. The results show that steel fiber can reduce the crack width and space in shear span, and enhance the shear capacity, energy absorption capacity and toughness. The addition of50kg/m3steel fiber can change the failure mode of the beam reinforced with constructive reinforced stirrups from brittle shear to ductile flexure. Stirrups cannot totally replaced by steel fiber. The combination of steel fiber and stirrups shows obvious positive hybrid effect, and the amount of stirrups can be reduced by the addition of steel fiber.(6) The influence of steel fibers on the crack pattern, load-deflection relationship and load-tensile reinforcement strain relationship of symmetric inclination beam is investigated. The main parameters are fiber content, stirrup ratio, tensile reinforcement ratio and shear span ratio. The results show that the failure modes of symmetric inclination beams are similar with their simply supported beam counterparts. The axial force of symmetric inclination beam can enhance the load-bearing capacity and decrease the longitudinal reinforcement strain. Inclusion of steel fiber can restrict mid-span deflection and steel strain, improves the energy absorption capacity and tends to change failure mode to more ductile one. The longitudinal reinforcement ratio show obvious influence on load bearing capacity and energy absorption capacity, according to fiber content and stirrup ratio. The constructive reinforced stirrups can be replaced by steel fibers in symmetric inclination beam.(7) An empirical equation is proposed to predict the shear strength of RC beams and steel fiber reinforced RC beams based on the shear transfer mechanisms and the published experimental data of142beams failed in shear mode. The main variables considered are the compressive strength of concrete, longitudinal reinforcement ratio, shear span to depth ratio and fiber factor. A correction factor to account for the effect of axial force on the beam action and arch action of symmetric inclination beam is included in the equation for predicting the shear strength of symmetric inclination beam. It is shown that the equation predicts with adequate accuracy shear strength of symmetric inclination beams.