Flexural behavior of reinforced concrete beams with high performance fiber reinforced cementitious composites

This article presents an experimental study on the flexural performance of reinforced concrete(RC)beams with fiber reinforced cementitious composites(FRCC)and hybrid fiber reinforced cementitious composites(HFRCC)in the hinge portion.Beam specimens with moderate confinement were used in the study and tested under monotonic loading.Seven diverse types of FRCC including hybrid composites using fibers in different profiles and in different volumes are employed in this study.Companion specimens such as cylindrical specimens and prism specimens are also used to study the physical properties of composites employed.The moment?curvature,stiffness behavior,ductility,crack pattern and modified flexural damage ratio are the main factors considered in this study to observe the efficacy of the employed hybrid composites.The experimental outputs demonstrate the improved post yield behavior with less rate of stiffness degradation and better damage tolerance capacity than conventional technique.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Lateral load-carrying capacity analyses of composite shear walls with double steel plates and filled concrete with binding bars

A method is developed to predict the lateral load-carrying capacity of composite shear walls with double steel plates and filled concrete with binding bars(SCBs). Nonlinear finite element models of SCBs were established by using the finite element tool, Abaqus. Tie constraints were used to connect the binding bars and the steel plates. Surface-to-surface contact provided by the Abaqus was used to simulate the interaction between the steel plate and the core concrete. The established models could predict the lateral load-carrying capacity of SCBs with a reasonable degree of accuracy. A calculation method was developed by superposition principle to predict the lateral load-carrying capacity of SCBs for the engineering application. The concrete confined by steel plates and binding bars is under multi-axial compression; therefore, its shear strength was calculated by using the Guo-Wang concrete failure criterion. The shear strength of the steel plates of SCBs was calculated by using the von Mises yielding criterion without considering buckling. Results of the developed method are in good agreement with the testing and finite element results.

Fatigue properties of special kind of reinforced concrete composite beams

The special reinforced concrete composite beam consists of a steel fiber reinforced self-stressing concrete composite layer and a reinforced concrete T-beam, and constructional bars are set up at their bonding interface. Fatigue properties of the composite beam under the action of negative moment were experimentally studied. Through inverted loading mode the load-beating state of a composite beam was simulated under the action of negative moment. With the ratios of constructional bars being 0, 0.082% and 0.164% respectively as parameters, the effects of constructional bars on the properties of composite beam, such as fatigue life, crack propagation, rigidity loss as well as damage behavior of bonding interface, were studied. The mechanism of the constructional bars on the fatigue properties of the composite beams and the restriction mechanism of crack widths and rigidity loss were analyzed. The test results show that the constructional bars can enhance the shear resistance of the bonding interface between composite layer and old concrete beam and restrict expanding of steel fiber reinforced self-stressing concrete, which are beneficial to synergistic action of composite layer and old concrete beam, to reducing the stress amplitude of bars and the crack width of composite layer, and to increasing the durability and fatigue life of the composite beam.

Behaviour of GFRP R.C. Slabs in Flexure in Localenvironment An Experimental Study

A variety of new materials in the field of concrete technology have been developed during the past three decades with the ongoing demand of construction industry to meet the functional, strength, economical and durability requirements. Though reinforced concrete has high strength and is most widely used construction material it suffers from disadvantages like corrosion of steel, susceptibility to chemical and environmental attack. In order to overcome the above deficiencies of reinforced concrete new materials （special concrete composites） have been developed over the past three decades. Glass Fibre Reinforced Polymer （GFRP） is one such material with wide range of applications. Based on the preliminary investigations on GFRP bars, an optimum fiber/resin ratio of 7：3 was arrived. The tensile strength of GFRP bars is comparable to that of the mild steel as per the tests carried out, but the modulus of elasticity is about 25-30 percentage of that of steel bars. This paper deals with the experimental investigations carried out on small slab panels supported on all four edges with effective spans of 0.9 m ~ 0.45 m, which is a part of large research problem undertaken with different ratios of 10ng span to short span with different support conditions. The test results are compared with similar slab panels reinforced with conventional mild steel bars.

Experimental study on slender reinforced concrete columns wrapped with CFRP

By axial compression tests on 6 reinforced concrete slender columns wrapped with carbon fiber-reinforced plastic (CFRP),with slenderness ratio(SR) from 4.5 to 17.5,the results show that when SR increases the retrofitting effect declines. In the case of same SR,the stability coefficient (SC) for the reinforced concrete(RC) columns with CFRP is much less than that without CFRP. There is 20% increase of stable bearing capacity to the former as compared with the latter when the SR in less than 17.5. The study summarized the simplified formula for SC,which provides a reference for engineering designers.

Numerical Analysis of the Composite Connection of Steel Joist Embedded in Concrete Girder

So far, numerous numerical studies have been conducted on the behavior of Composite Reinforced Concrete-Steel （RCS） beam-to-column connections. However, the lack of studies regarding the steel joist-concrete girder connection has yet to be addressed through comprehensive finite element methods to get an understanding of influential parameters. Hence, in this paper, composite connection of embedded steel joist in concrete girder is investigated with an appropriate finite element software, namely, ABAQUS. The validity of the proposed model is examined by the comparison made with the test data in literature. Results indicate that maximum bending capacity of the connection is achieved when embedment ratio is 1.78. Moreover, double web angles in the embedment region significantly reduce the embedment length required to achieve the maximum bending capacity. Finally, damage analyses show that bending capacity of concrete girder is slightly reduced in the connection zone.

Strengthening of Pultruded Glass FRP Section Combined with Concrete Slab Using CFRP Plates

This paper demonstrates the possibility of combining both glass and carbon FRP （Fibre Reinforced Polymer） composite materials with a low-cost construction material （i.e. concrete） in a hybrid system that brings higher performance levels to the design of lightweight, corrosion resistant, yet inexpensive beams providing acceptable structural properties. The objective of the research is to investigate the behaviour of a hybrid composite section under flexure. The hybrid section consists of a top concrete slab, Glass Fibre Reinforced Polymer （GFRP） beam section and Carbon Fibre Reinforced Polymer （CFRP） laminate on the extreme underside. This maximizes the benefits of each material, that is： high tensile strength of CFRP, compressive strength and low cost of concrete, light weight and lower cost of GFRP, and high corrosion resistance of all components. Three beam samples were manufactured and tested to failure while monitoring deflections and strains. By adding CFRP layers under the concrete-GFRP composite beam increases the bending strength and reduces the deflection. The most important factor in the proposed strengthening technique of GFRP-concrete composite beams by using CFRP is the adhesive material that bonds the CFRP to the GFRP. Any weakness in CFRP-GFRP bond may cause brittle failure of the beam. The study results indicate the benefits of using hybrid FRP-concrete beams to increase flexural load carrying capacity and beam stiffness and provide a numerical model that can be further developed to model more advanced material arrangements in the future. The outcome of this research provides information for both designers and researchers in the field of FRP composites.

Strengthening an in-service reinforcement concrete bridge with prestressed CFRP bars

Carbon fiber reinforced polymer (CFRP) bars were prestressed for the structural strengthening of 8 T-shaped rein-forced concrete (RC) beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes of strengthening with CFRP bars-including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons-were introduced in detail. In order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed strengthening technology is feasible and effective.

Seismic behavior of precast concrete coupled shear walls with engineered cementitious composite (ECC) in the critical cast-in-place regions

The seismic performance of precast reinforced concrete （RC） coupled shear walls is significantly influenced by coupling beams and the beam-to-wall joints during large deformations into plastic ranges. This study investigated the use of engineered cementitious composite （ECC） in the cast-in-place beam-to-wall joints and the upper regions of the composite coupling beams as an innovative method to improve the seismic performance ofprecast RQ coupled shear walls. Two 1/2-scale precast coupled shear walls were tested under reversed cyclic loading and seismic behavior in terms of failure characteristic, mechanical characteristic value, load-displacement hysteresis curves, load-displacement envelope relationship, stiffness degradation, ductility and energy dissipation capacity were evaluated. Research results show that the substitution of concrete with ECC in the critical cast-in-place regions proved to be an effective method to improve the seismic performance of the two-story spatial of precast RC coupled shear walls.