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Behavior of Reinforced Concrete Beams with Large-Diameter High-Strength Tension-Spliced Bars
Design codes such as ACI 318-19 and AASHTO LRFD permit the use of high-strength steel in specific provisions. Particularly, reinforcing bars with yield strength of 100 ksi (689 MPa) and size as large as No. 11 (No. 36) are permitted for use in tension lap splices. However, the test data using larger-diameter bars, especially No. 11 high-strength bars, is limited. In this study, four large-scale reinforced concrete beams with No. 11 bars were tested in four-point bending. The beams were grouped in two groups: one used Grade 60 (420) steel while the other used Grade 100 (690) steel. Within each group, one beam had continuous bars, while the second beam had spliced bars. Test results showed that splicing No. 11 (No. 36) high-strength reinforcing bars had adequate load-carrying capacity; however, the crack width may not be adequate. Therefore, test results indicate that using No. 11 (No. 36) high-strength reinforcing bars in tension lap splice applications should be used with caution. Keywords: crack width; development length; high-strength reinforcing bar; large-scale tests; reinforced concrete (RC) beam; tension lap splice.
Journal Article
Electrochemical processes and corrosion in reinforced concrete
\"Some reinforced concrete structures prematurely corrode as they age, with significant financial implications, but it is not immediately clear why some are more durable than others. This book looks at the various mechanisms for corrosion and how what seemed to be a relatively simple matter has become more complex the further it is understood due to the properties of concrete, steel and the way reinforced concrete structures are constructed. The significance of electrochemical processes is identified with recent research using new technology discussed. Specialist contractors, consultants and owners of corrosion damaged structures will find this an extremely useful resource. It will also be a valuable reference for students at postgraduate level\"-- Provided by publisher.
BOOK
Effect of Staggering Distances on Splice Strength of New- Generation Glass Fiber-Reinforced Polymer Reinforcing Bars
This study addressed a critical knowledge gap by examining the influence of staggering on the bond strength of lapped glass fiber-reinforced polymer (GFRP) bars in concrete members. It involved a comprehensive investigation of new-generation GFRP bars with varying staggering configurations in nine large-scale GFRP-reinforced concrete (RC) beams with a rectangular cross section of 300 x 450 mm (11.8 x 17.7 in.) and a length of 5200 mm (204.7 in.). The tests investigated splice strength with three staggering distances: 0, 1.0, and 1.3 times the splice length ([l.sub.s]) from center-to-center of two adjacent splices, and three splice lengths of 28, 38, and 45 times the bar diameter ([d.sub.b]). Results revealed a slight improvement in ultimate load-carrying capacity (less than 10%) for partially and fully staggered splices compared to non-staggered ones, with the latter exhibiting a more ductile failure mode. The effect of staggering was consistent across different splice lengths, demonstrating that splice length was not a factor. Although staggering reduced flexural crack width, it increased the total number of cracks due to expanded splice regions. Bond strength improved with staggering, with gains of 4.0% and 8.0% for partially and fully staggered splices, respectively. ACI CODE-440.11-22 provides more accurate predictions of the bond strength of lap-spliced GFRP bars than the other design codes, showing an average test-to-prediction ratio of 1.03 for non-staggered splices. Nevertheless, it requires some reconsiderations when it comes to staggered splices. To address this, a proposed modification factor was introduced to account for staggering conditions when calculating bond strength and splice length in ACI CODE-440.11-22. Keywords: bond strength; concrete structures; design codes; development length; glass fiber-reinforced polymer (GFRP) reinforcing bars; lap splicing; splice length; splice strength; staggering effect.
Journal Article
Mechanical Properties of Reinforcing Steel Bars Corroded at Different Levels
Corrosion of reinforcing steel bars in concrete has always been one of the major causes of structural failure. This paper experimentally investigates the effect of corrosion on the mechanical properties of reinforcing bars. In the experiment, an anodic current is impressed at the specific current density to reinforcing bars of various diameters to attain different levels of corrosion. The correlation of actual mass loss with predicted mass loss, as per Faraday s law, and the equivalent section area loss are reported. Further, the uniaxial tensile test is performed on these corroded specimens to obtain load-displacement relations. Based on the test results, stresses and strains are evaluated for all the specimens, and their responses to induced corrosion are reported. Statistical models are developed for predicting yield stress, ultimate stress, and percentage elongation in reinforcing bars that are exposed to different levels of corrosion. Keywords: anodic current; corrosion; experimentation; levels of corrosion; mechanical properties; reinforcing bar; tensile test.
Journal Article
Statistical Distributions for Chloride Thresholds of Reinforcing Bars
Reliability-based durability design of reinforced concrete structures requires a probabilistic service life modeling approach. Probabilistic service life modeling of chloride-induced corrosion should consider the statistical distributions of key parameters that influence corrosion initiation and subsequent damage. For typical reinforced concrete structures (such as bridge decks), these are chloride exposure, chloride penetration resistance of the concrete, chloride-induced corrosion threshold, depth of concrete cover, and corrosion propagation time. Assessing the impact of the use of corrosion-resistant reinforcement, such as epoxy-coated reinforcing bars (ECR), is typically performed through a selection of the chloride threshold and/or propagation time. This paper provides recommendations for statistical distributions for the chloride threshold to be used in service life modeling for structures containing carbon steel and ECR based on both experimental work reported in the literature and field investigations of existing structures conducted by the authors. Keywords: carbon steel reinforcing bars; chloride threshold; corrosion; critical chloride content; durability; epoxy-coated reinforcing bars (ECR); probabilistic; service life; supplementary cementitious materials.
Journal Article
Cyclic Loading Test for Walls of Aspect Ratio 1.0 and 0.5 with Grade 550 MPa (80 ksi) Shear Reinforcing Bars
In the shear design of massive walls in nuclear power plants, high-strength reinforcing bars need to be employed to enhance the constructibility and economy of the walls. In the present study, walls with aspect ratios of 1.0 and 0.5 were tested under cyclic lateral loading to investigate the effect of 550 MPa (80 ksi) reinforcing bars on the shear strength of squat walls. The test parameters included the grade of shear reinforcement, the failure mode, and the presence of boundary hoops. The ratios of the test shear strength to ACI 349 prediction (that is, safety margins) were 1.54 to 1.90 and 1.11 to 1.38 for the general and seismic provisions, respectively. The test results of walls with 550 MPa (80 ksi) reinforcing bars were comparable to those of walls with 420 MPa (60 ksi) reinforcing bars for all three evaluations: failure mode, safety margin, and average crack width. Keywords: cyclic loading; high-strength reinforcing bars; reinforcing bar ratio; shear strength; squat shear walls.
Journal Article
Hysteretic Model of Coupler Box Assembly for Seismic Retrofitting of Severely Damaged Reinforced Concrete Buildings
Cyclic tests are conducted on interlinked reinforcing bar coupler-box assemblies, adopted to retrofit buckled reinforcing bars at the plastic hinge locations of columns in multi-storied reinforced concrete building frames. The efficacy of the proposed retrofitting technique is evaluated by comparing the hysteresis behavior, computed parameters of performance index, and failure mechanism of the reconstructed frame with the original frame. An energy-based strength deterioration hysteresis model is developed on the basis of cyclic test results for analytically computing the post-yield behavior of retrofitted reinforced concrete (RC) frame with the proposed coupler-box assembly. The experimental test results manifest that the coupler-box assembly can be a promising futuristic approach for seismic retrofitting of severely damaged reinforced concrete buildings, where buckling of longitudinal reinforcing bars at the plastic hinge location of columns is inevitable, and the process of restoration is challenging under existing gravity loads. The suggested retrofitting mechanism restrains the section from any movement against rotation and helps in shifting the yield location of reinforcing bars. The main advantage of adopting the coupler-box is that there is no observed slip of reinforcing bar from the sleeve, and the entire retrofitted section remains intact even after a lateral storey drift of 6%, which is larger than the collapse prevention drift level of 4% as per Federal Emergency Management Agency guidelines. Keywords: coupler-box assembly; deterioration strength hysteresis model; energy dissipation; hysteresis behavior; reinforcing bar coupler sleeve; seismic retrofitting.
Journal Article
Pullout Strength of Embed Plates with Welded Anchor Bars in Concrete
Embedded plates are used to support external attachments such as heavy piping, brackets, sprinkler systems, or other equipment in concrete structures. The plates are typically welded with deformed reinforcing bars or deformed wires, which are embedded in reinforced concrete walls. The ACI Codes (ACI 318-19 and ACI 349-13) provide design equations to calculate the pullout strength of anchors in concrete under tension loading. However, these empirical equations are based on experiments conducted on headed studs, hooked bars, headed bolts, and adhesive anchors. With the lack of experimental data and resulting Code provisions on straight deformed reinforcing bars or deformed wires used as anchors, it is believed that anchoring bars with the embedment length as per the Code-prescribed development length will provide sufficient strength to transfer tensile forces to the concrete, ignoring other failure modes such as concrete breakout and pullout. The applicability of the concrete-governed adhesive bond model of ACI 318-19 for bonded anchors is evaluated to estimate the strength and failure modes of these connections. The current ACI adhesive bond model does not capture the correct failure mode and the influence of anchor spacing and bond strength on the capacity. The issue is addressed by incorporating the correction factor ([psi]g,N). This paper presents eight large-scale group-anchor test results to evaluate their concrete breakout strength and the applicability of the ACI 318-19 adhesive anchor/bond model to estimate connection capacities and failure modes. The mean average back-calculated effective k value is 33.3 for deformed reinforcing bar anchors (DRAs) and 36.5 for deformed wire anchors (DWAs). Single-anchor tests were also performed to evaluate the bond behavior per the ACI 318-19 uniform bond model. The experimental study confirms that the axial tension capacity of embedded plates anchored to concrete using deformed reinforcing bars or deformed wires can be limited by concrete breakout strength. The ACI bond model with the correction factor appropriately estimates the failure mode and strength of such connections. Keywords: concrete breakout; deformed reinforcing bars; deformed wire anchors; embedded plates; pullout strength.
Journal Article
Simplification of Buckled Bar Tension Test through Fiber Modeling
Buckled reinforcing bars exhibit bending strains across the bar section. The bending strain threshold that triggers brittle bar fracture in tension, referred to as the critical bending strain, can be obtained with the buckled bar tension (BBT) test. However, the BBT test requires three-dimensional (3-D) position measurement systems that are not widely available. To make the BBT test more accessible, this paper uses fiber-based models to develop empirical equations for curvature, neutral axis depth, and bending strains in buckled reinforcement. These equations may be employed in the BBT test without the need for advanced instrumentation systems. This study shows that bending strains calculated from fiber models of buckled reinforcing bars have a 95% probability of having less than 20% variation compared with experimental measurements. Furthermore, the determination of the bending strains for the BBT test is simplified to equations with three input parameters: bar fixed length, bar diameter, and bar axial displacement. Keywords: buckling; critical bending strain; fiber models; fracture; reinforcing bar.
Journal Article