The effects of concrete strength, coarse aggregate quantity and type, and reinforcing bar geometry on splice strength are evaluated. Results for 64 splice specimens with reinforcing bars with relative rib areas (ratio of projected rib area normal to bar axis to the product of the nominal bar perimeter and the center-to-center rib spacing) ranging from 0.069 to 0.141, concrete strengths ranging from 4,250 psi to 15,650 psi (29-108 MPa), and quantities of limestone and basalt coarse aggregate ranging from 1,586 lb/cu yd to 1,908 lb/cu yd (941-1,132 kg/cu m) are reported. The results are combined with the American Concrete Institute (ACI) Committee 408 database to develop design equations for development and splice length, which are then compared with the design criteria in ACI 318-99. For splices not confined by transverse reinforcement, the 1/4 power of compressive strength (f'c) best characterizes the effect of concrete strength on splice strength. f'c (3/4 power) characterizes the effect of concrete strength on the additional splice strength provided by transverse reinforcement. The splice strength of bars confined by transverse reinforcement increases with an increase in relative rib area and bar diameter. The use of stronger coarse aggregate results in an increase in splice strength for bars both with and without confining reinforcement. For splices confined by transverse reinforcement, the higher the quantity of coarse aggregate, the greater the contribution of transverse reinforcement to splice strength. The expressions characterizing the splice strength of reinforcing bars accurately represent the development/splice strength of bottom-cast uncoated bars as a function of member geometry, concrete strength, relative rib area, bar size, and confinement, provided by both concrete and transverse reinforcement. The new design expressions are superior to the design criteria in ACI 318-99 in terms of both safety and economy. The criteria in ACI 318-99 for developed bars and Class A splices are unconservative for No. 6 (No. 19) and smaller bars.

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Splice Strength of Conventional and High Relative Rib Area Bars in Normal and High-Strength Concrete

Flexural design for concrete members reinforced with fiber‐rein‐forced‐plastic (FRP) composites may be conducted using both the ultimate‐strength method and the working‐stress method. Since FRP reinforcement does not yield, there should be the explicit provision that failure be controlled by concrete crushing as opposed to reinforcement rupture. Deflection control may become as important as flexural strength for the design of FRP‐reinforced concrete structures. The paper contends that, at this stage of development, the working‐stress method is better suited to FRP‐reinforced concrete. The primary reasons are that the predicted ultimate moment capacity represents a highly variable state only attainable at a high level of deformation and crack opening and that it depends strictly on concrete ultimate strain. FRP reinforcement is better suited to pre‐ and posttensioned‐type concrete members; however, it cannot be ruled out that FRP should become the reinforcement of choice in special nonprestressed applicati...

Flexural Behavior and Design of RC Members Using FRP Reinforcement

The basic mechanical and chemical properties of fly-ash-based inorganic polymer concretes (IPC) have been studied widely, but, key engineering and structural properties of the material for instance modulus of elasticity, compressive, tensile, flexural strengths and bonding strength of the material to reinforcement have received little attention. Structural applications of reinforced IPC depend on the bond performance of the material to the reinforcement. Due to their difference with ordinary Portland cement (OPC) based concrete in terms of chemical reaction and matrix formation it is not known whether IPC exhibit different bonding performance with the reinforcement. Simply relying on compressive strength of the material and extrapolating models and equations meant for OPC based concrete may lead to unsafe design of structural members. To that end, 27 beam-end specimens, 58 cubic direct pullout type specimens and number of laboratory test specimens were tested to evaluate bonding performance of IPC with reinforcement. The results of beam-end specimens and direct pullout type specimens correlate favourably, although the results of direct pullout tests are in general more conservative than those of beam-end specimens. Overall, it can be concluded that bond performance of IPC mixes are comparable to OPC based concrete and therefore IPC and steel can be used as a composite material to resist tension in addition to compression.

Bond performance of reinforcing bars in inorganic polymer concrete (IPC)

The details are described of a study of the effect of deformation pattern on bond strength usign 1 inch diameter machined bars with deformation heights of 0.05, 0.075, and 0.10 inch and deformation spacings ranging from 0.26 to 2.2 inch. The study found that the bond force-slip response of reinforcing bars is a function of the relative rib area of the bars, independent of the specific combination of rib height and rib spacing. Under all conditions of bar confinement, the inititial stiffness of load-slip curves increases with an increase in the relative rib area. Under conditions of relatively low confinement, in which bond strength is governed by splitting of the concrete, bond strngth is independent of deformation pattern. Under conditions in which additional bar confinement is provided by transverse reinforcement or higher cover, bond strength increases, compared to the bond strength of bars with less confinement. The magnitude of the increase in bond strength increases with an increase in the relative rib area.

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Effect of Deformation Height and Spacing on Bond Strength of Reinforcing Bars

Statistical analyses of 133 splice and development specimens in which the bars are not confined by transverse reinforcement and 166 specimens in which the bars are confined by transverse reinforcement are used to develop an expression for the bond force at failure as a function of concrete strength, cover, bar spacing, development/splice length, transverse reinforcement, and the geometric properties of the developed/spliced bars. Results are used to formulate design criteria that incorporate a reliability-based strength reduction factor that allows the calculation of a single value for both development and splice length for given material properties and member geometry. As with earlier studies, the analyses demonstrate that the relationship between bond force and development or splice length is linear but not proportional. The most accurate representation of the effect of transverse reinforcement on bond strength obtained in the current analysis includes parameters that account for the number of transverse reinforcing bars that cross the developed/spliced bar, the area of the transverse reinforcement, the number of bars developed or spliced at one location, the relative rib area of the developed/spliced bar, and the size of the developed/spliced bar. The yield strength of transverse reinforcement does not play a role in the effectiveness of the transverse reinforcement in improving development/splice strength. Depending on the design expression selected, for conventional and high relative rib area bars that are not confined by transverse reinforcement, development lengths average 2 to 14 percent higher and splice lengths 12 to 22 percent lower than those obtained using American Concrete Institute (ACI) 318-95. For conventional reinforcing bars confined by transverse reinforcement, development lengths average 5 percent lower to 16 percent higher than those obtained using ACI 318-95. For high relative rib area reinforcing bars confined by transverse reinforcement, development lengths average 3 to 17 percent lower than those obtained using ACI 318-95, while splice lengths average 25 to 36 percent lower than those obtained using ACI 318-95. When confined by transverse reinforcement, high relative rib area bars require development and splice lengths that are 13 to 16 percent lower than required by conventional bars.

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Development length criteria for conventional and high relative rib area reinforcing bars

The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests included beam end and splice specimen testing. The results are compared with the splice tests that were used to establish the epoxy coated bar provisions in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coating are found to reduce bond strength significantly, but the extent of the reduction is less than that used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Sepcifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern; bars with relatively larger rib-bearing areas with respect to the bar cross section are affected less by the coating than bars with smaller bearing areas.

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Bond of epoxy-coated reinforcement: bar parameters

The effects of concrete cover, casting position, concrete slump, and degree of consolidation on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end specimens containing No. 5, No. 6, No. 8, and No. 11 bars. Bottom-cast and top-cast bars with 1, 2, or 3 bar diameters of cover are evaluated. Concrete slump ranges from 2 1/4 to 8 inches. Some specimens containing high slump concrete are not vibrated. The results of the study are used to develop improved development length modification factors for epoxy-coated bars. The details of the study are described, and the results are presented and discussed.

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Bond of epoxy-coated reinforcement: cover, casting position, slump, and consolidation

The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No. 5, No. 6, No. 8, and No. 11 bars with average coating thicknesses ranging from 3 to 17 mils. Three deformation patterns are evaluated. All bars are bottom-cast. Beam-end specimens have covers of 2 bar diameters, while splice specimens have covers that depend on bar size and are less than 2 bar diameters. The results are compared with the splice tests that were used to establish the epoxy-coated bar provisions in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coatings are found to significantly reduce bond strength, but the extent of the reduction is less than used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Specifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars and smaller. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern: bars with relatively larger ribbearing areas are affected less by the coating than bars with smaller bearing areas. This is the first in a series of reports. Subsequent reports will address the effects of concrete cover, bar position, concrete strength, and transverse reinforcement.

Bond of Epoxy-Coated Reinforcement to Concrete: Bar Parameters

The results of a large-scale study to determine the effect of epoxy coating on bond strength is described. The study addresses the effects of coating thickness, deformation pattern, bar size, concrete cover, bar position, and transverse reinforcement. The results indicate that bond strength decreases with increasing coating thickness only for No. 5 bars and smaller. The deformation pattern plays an important role in determining the effect of epoxy coating, and the reduction obtained due to epoxy coating increases with bar size. Concrete cover increases the bond strength of both uncoated and coated reinforcement. Transverse reinforcement significantly increases the bond strength of both uncoated and coated bars, and also appears to negate the reduction in bond strength caused by epoxy coating compared to uncoated bars without transverse reinforcement.

Hossain Hadje-Ghaffari

Papers

Bond of epoxy-coated reinforcement: bar parameters

Bond of epoxy-coated reinforcement: cover, casting position, slump, and consolidation

Bond of Epoxy-Coated Reinforcement to Concrete: Bar Parameters

Bond Strength of Epoxy-Coated Reinforcement to Concrete—An Update

Effects of Epoxy-Coating on the Bond of Reinforcing Steel to Concrete