Joseph Robert Yost

Effective Moment of Inertia for Glass Fiber-Reinforced Polymer-Reinforced Concrete Beams

This paper investigates deflection behavior of concrete flexural members reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars. It is recognized that serviceability plays a major role in the design of GFRP-reinforced concrete beams. Therefore, accurate modeling of flexural stiffness is critical and the effect of influencing parameters must be considered. This study accounts for variations in concrete strength, reinforcement density, and shear span-depth ratio. Experimental results from 48 simply supported concrete beams reinforced with GFRP are compared with ACI Committee 440s published deflection model. The ACI 440.1R model is found to overestimate the effective moment of inertia, and an appropriate modification is presented.

Flexural Behavior of Concrete Beams Strengthened with Near-Surface-Mounted CFRP Strips

Engineers have proposed relocating externally bonded strengthening fiber reinforced polymer (FRP) material from the unprotected exterior of the concrete to the protected interior. This technology is known as near-surface mounted (NSM) strengthening. In NSM reinforcement, the FRP is surrounded by concrete on three sides so the bond and damage problems associated with externally bonded FRP strengthening systems are reduced or eliminated. This paper presents experimental results from 12 full-scale concrete beams strengthened with NSM carbon FRP (CFRP) strips. Three companion unstrengthened specimens were also tested to serve as a control. Experimental variables include three different ratios of steel reinforcement and two different ratios of CFRP reinforcement. Yield and ultimate strengths, flexural failure modes, and ductility are discussed based on measured load, deflection, and strain data. Test results show measurable increases in yield and ultimate strengths in all beams strengthened with CFRP as well as predictable nominal strengths and failure modes. Force transfer between the CFRP, epoxy grout, and surrounding concrete was able to develop the full tensile strength of the CFRP strips. Energy and deflection ductilities were reduced for CFRP strengthened beams. Future research needs are addressed.

SHEAR STRENGTH OF NORMAL AND HIGH STRENGTH CONCRETE BEAMS REINFORCED WITH GFRP BARS

This paper evaluates the shear strength for normal and high strength concrete beams reinforced with longitudinal glass fiber reinforced polymer (GFRP) reinforcing bars and no web reinforcement. The effect of reinforcement ratio is examined, and experimental data is compared with values predicted by FRP shear strength expressions found in the literature, including the new design expression recommended by ACI Committee 440 (2001).

FLEXURAL DESIGN METHODOLOGY FOR CONCRETE BEAMS REINFORCED WITH FIBER-REINFORCED POLYMERS

This paper evaluates safety in fiber-reinforced polymer (FRP) reinforced flexural members with respect to energy consumption and reserve. It is proposed that service stresses in FRP reinforced flexural members be limited such that a minimum energy reserve at service relative to the ultimate limit-state is ensured. The minimum energy reserve is determined as per existing code-mandated stress limits established for steel reinforcement. The result is a rational justification for allowable stress limits in FRP reinforced members and a guaranteed minimum level of energy reserve equivalent to that provided by existing steel-design methodology. The feasibility of the method is demonstrated through a worked bridge deck design example.

TIME-DEPENDENT BEHAVIOR OF NORMAL AND HIGH STRENGTH CONCRETE BEAMS REINFORCED WITH GFRP BARS UNDER SUSTAINED LOADS

This paper presents results of a study in which time-dependent strains and deflections were monitored for normal and high strength concrete beams reinforced with glass fiber reinforced polymers. Sustained load behavior was observed to be similar to that of steel reinforced beams. The effect of additional flexural cracking over time was found to be significant.

Material Properties of Structurally Viable Alkali-Activated Fly Ash Concrete

AbstractAs the concern for the environment and need for sustainable construction practices continues to grow, development of portland cement–free binders is gaining wide interest in the concrete research and engineering community responsible for design and construction of civil infrastructure. In this work, microstructural (as determined by quantitative X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy techniques) and material properties of alkali-activated fly ash concrete were evaluated to verify the material’s performance and structural viability. Results show that the heat-cured products of reaction of fly ash in an aqueous alkaline solution form a concrete binder with adequate design properties and promising durability aspects.

Fatigue behavior of GFRP and steel reinforced bridge decks designed using traditional and empirical methodologies

In this research study, experimental behavior of two full-scale bridge decks, one each reinforced with steel and GFRP, and subjected to fatigue loading is investigated. Reinforcement is provided as required by traditional (TR) and empirical (EM) design methodologies on each transverse half of each deck. The decks are subjected to load cases corresponding to an HS25 truck axle positioned for critical positive and negative bending. Measured response before, during and after the two million cycles of fatigue loading per load case is used to evaluate compliance with serviceability limits on crack-width, deflection and material stress. For the GFRP reinforced deck, results show both TR and EM are compliant with allowable limits, and that the EM load-sensor slope response is measurably less than the TR for like load cases. Similar results were found for the steel reinforced deck. Importantly, the study validates the EM design methodology for use with GFRP reinforced concrete bridge decks.

Strength and Ductility Trends for Concrete Members Strengthened in Flexure with Carbon Fiber-Reinforced Polymer Reinforcement

For reinforced concrete (RC) beams and slabs under-reinforced with steel and strengthened in flexure with carbon fiber-reinforced polymers (CFRPs), the yield plateau is eliminated and post-yield flexural capacity increases linearly by elastic straining in the CFRP. At the ultimate flexural limit state, failure occurs by either concrete crushing or CFRP rupture. The consequence is an increase in strength and decrease in ductility. In this study, a parametric analysis is presented where strength and energy ratios are investigated as a function of existing steel and strengthening CFRP reinforcements. Both normal-strength and high-strength concretes are considered. A graphical representation showing the controlling strength limit state is developed. Strength and energy ratios for various service, yield, and ultimate limit state combinations show that strength increase and ductility loss are significantly affected by the amounts of steel and CFRP reinforcements. The ultimate-to-yield strength ratio increases rapidly with decreasing steel and CFRP reinforcements; consequently, the service strength approaches the yield strength. Ductility loss is nonlinear and inversely related to the amounts of steel and CFRP reinforcements. For the parameters considered, ductility relative to the unstrengthened condition was reduced between 35 and 93%.

Investigation of alternative technologies for cast-in-place concrete bridge decks

Concrete bridge decks are designed using traditional methodology (TM) or empirical methodology (EM). TM models the deck as a continuous beam in flexure, and EM recognizes the compressive membrane action that aids in distributing wheel loads. An extension of membrane behavior is complete removal of reinforcement from within the deck; this is referred to as steel free deck (SF). In this research study three full-scale bridge decks are investigated, one reinforced with steel, a second is reinforced with glass fiber reinforced polymer (GFRP), and a third is SF. For each the steel and GFRP reinforced decks, the south and north sides are reinforced as required by the TM and EM, respectively. The SF deck is based on research done in Canada. Each deck is subjected to four load cases, corresponding to an AASHTO truck axle positioned for critical positive and critical negative bending on each the north and south sides. Measured response for crack width, deflection, and concrete strain is used to evaluate behavior at the service limit state.

Experimental evaluation of GFRP bars as reinforcement for concrete bridge decks: Negative bending low cycle fatigue study

Bridge deck durability is often compromised due to corrosion of the steel reinforcement. The use of glass fiber reinforced polymer (GFRP) bars as a substitute for steel is a possible solution to this problematic condition. GFRP is an elastic brittle material with a high tensile strength, and modulus of elasticity that is approximately 20% that of steel reinforcement. Considering these material properties, meaningful data is required to demonstrate compliance with imposed design limits at all relevant limit states. Experimental evaluation of GFRP bars as structural reinforcement for highway bridge decks must recognize and duplicate the load and support conditions specific to this application. Laboratory testing should consider load magnitudes associated with AASHTO service, strength and fatigue limit states, indeterminacy of the deck in the transverse direction, two-way distribution of wheel loads, and load application and deck support conditions as affected by truck tire contact area and girder flange stiffness, respectively. In this research study 2-span continuous concrete beams doubly reinforced with GFRP bars are tested under load and support conditions designed to simulate performance of the GFRP reinforcement in a highway bridge deck environment. Monotonic, cyclic, and low cycle fatigue loading are applied to establish behavior of the experimental deck as related to an actual bridge deck load condition. Test results related to strength, deflection, and crack width are presented.