Hiroshi Mutsuyoshi

Shear Strengthening of Reinforced Concrete Beams Using Fiber-Reinforced Polymer Sheets with Bonded Anchorage

This paper presents results of a study into shear strengthening of reinforced concrete (RC) beams using externally bonded fiber-reinforced polymer (FRP) sheets. The study focused on the effect of extending the length of sheet on the top surface of the beam to delay or prevent sheet debonding. Test variables were the kinds of fibers, the wrapping layouts, and the length of bonded anchorage. From the experiments, it was confirmed that FRP with bonded anchorage is much more effective than the U-wrap scheme. Extending the sheets on a top surface of the beam resulted in a decrease in interface bond stresses and an increase in FRP strain at failure. Four different models for estimating the contribution of FRP sheets to the shear capacity V-sub-f of beams were investigated. Two new equations to calculate V-sub-f are given: when failure occurs due to sheet debonding and when the beams are provided with bonded anchorage at the top face of beams.

Shear strengthening of reinforced concrete beams using steel plates bonded on beam web: experiments and analysis

Abstract Experiments for shear strengthening of reinforced concrete beams using epoxy-bonded continuous horizontal steel plates were carried out. Two control beams and 10 beams with steel plates bonded to their webs were tested. A two-dimensional non-linear finite element analysis is also described. From the experiments and analysis, it was confirmed that continuous steel plates bonded externally to beam webs are effective for the shear strengthening of RC beams. It was observed that the shear strength increases with increasing plate thickness and plate depth. A maximum 84% increase in ultimate shear strength was observed over that of the control beam without steel plates. In the case of relatively thin plates bonded to the beam web, the present numerical analysis accurately predicts the ultimate shear strength as well as overall shear and flexural behaviour.

Flexural Behavior of Two-Span Continuous Prestressed Concrete Girders with Highly Eccentric External Tendons

[Abstract]: It is generally known that the flexural strength of beams prestressed with external tendons is comparatively lower than that of members with internal bonded tendons. One possible method of enhancing the flexural strength of such beams is to place the tendons at high eccentricity. To obtain an insight into the flexural behavior of beams with highly eccentric tendons, an experimental investigation is conducted on single-span and two-span continuous beams. The test variables include external tendon profile, loading pattern on each span, casting method, and confinement reinforcements. It is found that continuous girders with linearly transformed tendon profiles exhibit the same flexural behavior irrespective of tendon layout. The presence of confinement reinforcement enhances the ductility behavior but does not increase the ultimate flexural strength. The degree of moment redistribution is affected by the tendon layout and the loading pattern on each span. The results of the experimental investigation are discussed in this paper.

SEISMIC PERFORMANCE OF REINFORCED CONCRETE PIERS WITH BOND-CONTROLLED REINFORCEMENTS

New seismic design codes for reinforced concrete (RC) bridges in Japan have resulted in difficulties in placing and compacting the concrete, which may cause construction defects in the concrete. Thus, it becomes important to find alternative methods of improving shear capacity and ductility to avoid relying primarily on shear reinforcements. This article reports on a study undertaken to examine how controlling the bond of the longitudinal reinforcements can improve seismic performance factors, such as shear strength and ductility, of reinforced concrete (RC) structures. The experiment employed fifteen, 300 x 300 mm square RC columns tested under reversed cyclic loading. The columns were of six different bond conditions, varying from perfect bond, with the use of ordinary deformed bars, to perfect unbond. The other test variables included the shear span-depth ratio, shear to flexural strength ratio, and the length of unbonded region. Results showed that the failure mode at the ultimate state could be changed from shear to flexure by reducing the bond strength of the longitudinal bars. Complete unbonding of the reinforcing bars in the column leads to a smaller amount of hysteretic energy absorption as compared with ordinary columns. This is due to the occurrence of wide flexural cracks in the column-footing joint. The test results also showed that RC columns reinforced with bond-controlled bars had significantly better shear strength and ductility than RC columns reinforced with ordinary bars.

Numerical simulation of steel-plate strengthened concrete beam by a non-linear finite element method model

Abstract Strengthening with epoxy bonded steel plate is one of the most widely used techniques for flexural upgrading of reinforced concrete (RC) beams. However, debonding failure at the plate cut-off zone and or in the vicinity of flexure and shear cracks leads to catastrophic failure of the upgraded beams. This particular failure depends on several factors such as the distance of plate curtailment from the support, plate thickness and the provision of end anchors. Since the conventional beam theory cannot predict the debonding failure of such beams, a finite element model capable of predicting the overall behavior of strengthened beams including different failure modes accurately is developed. This paper presents the formulation of finite elements and material models and simulation results of some RC beams tested for flexural strengthening with epoxy bonded steel plates.

Shear Behavior of Reinforced High-Strength Concrete Beams

This paper describes the shear behavior of reinforced high-strength concrete (RHSC) beams without web reinforcement. The use of high-strength concrete (HSC) has led to some concerns about its shear strength because of its brittleness, smooth fracture surface, and high early-age shrinkage. Test results indicated that the ratio of uniaxial compressive strength to tensile strength (the ductility number) of the concrete relative to that of the aggregate governs the shear strength of HSC. When the ductility number of the concrete coincided with that of the aggregate, the shear strength remained constant, irrespective of concrete strength. When the ductility number of the concrete was higher than that of the aggregate, however, shear strength started to decrease due to the smooth fracture surface and brittleness. By introducing early-age shrinkage and a suitable aggregate size, the modified compression field theory was found to accurately predict the shear strength of RHSC beams.

Composite Behaviour of a Hybrid FRP Bridge Girder and Concrete Deck

This paper involves experimental investigation onto the composite behaviour of a hybrid FRP bridge girder with an overlying concrete deck. Two types of shear connections were investigated: epoxy resin adhesives alone and epoxy resin combined with steel u-bolts. The results showed that the steel u-bolts combined with epoxy resin provided a more effective connection; hence a full-size specimen was prepared based on this result. Four-point bending test was carried out to determine the behaviour of a full-scale composite hybrid FRP girder and concrete deck. The composite action resulted to a higher stiffness and strength with the hybrid FRP girder exhibiting higher tensile strain before final failure. There was a significant decrease in the compressive strain in the top flange of the FRP girder thereby preventing the sudden failure of the beam. The composite beam failed due to crushing of the concrete followed by shear failure in the top flange and web of the FRP girder.

Flexural Behavior of Hybrid Composite Beams

This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Experimental Investigation of HFRP Composite Beams

This paper presents the development of composite beams using hybrid CFRP/GFRP (HFRP) I-beam and Normal Strength Concrete (NSC) slab and precast Ultra-High Performance fiber reinforced Concrete (UHPFRC) slab. UHPFRC has high strength and high ductility allowing for a reduction in the cross-sectional area and self weight of the beam. A number of full-scale flexural beam tests were conducted using different dimensions of slab and with/without epoxy bonding between the slab and HFRP I-beam. The test results suggested that the flexural stiffness of composite beams with bolted and bonded shear connection is higher than that with bolted-only shear connection. Delamination failure was not observed in the compressive flange of the HFRP I-beam and the high tensile strength of CFRP in the bottom flange was effectively utilized with the addition of the UHPFRC slab on the top flange.

Hybrid Fiber-Reinforced Polymer Girders Topped with Segmental Precast Concrete Slabs for Accelerated Bridge Construction

The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, topped with precast ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs is presented in this paper. HFRP I-girders were manufactured under the pultrusion process in which unidirectional carbon fibers and bidirectional fiberglass fabric or continuous strand mat were used. Four large-scale composite girders were tested under four-point flexural loading. In the first composite girder, the HFRP I-girder was topped with a full-length precast UHPFRC slab. Twelve precast UHPFRC segments were used in each slab of the other three composite girders. Either epoxy or mortar connections were used to connect the precast UHPFRC segments. The test results showed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs was similar to that of the full-length precast composite girder. The mortar-connected girder exhibited more ductile behavior than the epoxy-connected girder. All the composite girders exhibited significant improvements in strength and stiffness compared with the HFRP I-girder without the UHPFRC slab. The HFRP–UHPFRC composite girders were shown to provide a promising and sustainable solution for accelerated bridge construction.