Reinforcement Rate Research Articles

Analysis of the Seismic Performance of Rectangular Recycled Aggregate Concrete Columns with Different Parameters

The influence of various seismic parameters on the seismic performance of rectangular reinforced recycled concrete columns was comprehensively revealed through collecting and screening experimental data from 53 rectangular recycled aggregate concrete columns. The research results showed that the bearing capacity of the specimens decreased and the ductility performance increased, which were attributed to the following factors. a. The increase in the replacement ratio and slenderness ratio of recycled coarse aggregate, and b. the reduction in the axial compression ratio and the strength of recycled aggregate concrete. The seismic design limitations and boundary conditions of this study are γ ∈ [0, 100%], n0 ∈ [0, 0.9], λ0 ∈ [5.06, 18.479], λ ∈ [1.09, 3.93], ρsl ∈ [1.01%, 2.45%], ρsv ∈ [1.4%, 5.33%], and f ∈ [C30, C50]. Thus, it is recommended that for the seismic design value of rectangular recycled aggregate concrete columns, the optimal longitudinal reinforcement rate be set at 1.59%.

Research on the resilience model of a new prefabricated shear wall structure

Based on high-strength bolts, steel plates and other components to achieve the advantages of prefabricated shear wall assembly connection “dry connection” operation advantages, a new type of assembled shear wall with friction energy consumption function was proposed. Using a combination of model tests and numerical simulations, three shear wall specimens with a scaling ratio of 1:1.54 were designed and the corresponding seismic performance tests were carried out. The effects of axial compression ratio and longitudinal reinforcement rate of edge members on the damage mode, hysteresis performance, load carrying capacity, deformation performance, stiffness degradation and energy dissipation capacity of specimens are systematically analyzed. The test results showed that the final failure modes of the three specimens were similar, which was the bending-shear failure from the development of the oblique cracks in the wall to the concrete spalling in the compression zone; The reduction of the axial compression ratio or the reinforcement rate of the longitudinal reinforcement of the edge members will lead to the reduction of the bearing capacity of the shear wall and the increase of the ultimate displacement has a negative impact on the seismic performance of the new assembled shear wall, which is manifested by the weakening of the hysteresis performance and the reduction of the ultimate bearing capacity. Combined with the finite element simulation results, the five-fold skeleton model and restoring force model of the new assembled shear wall were established, and then the calculation formulae of unloading stiffness and loading stiffness of the hysteresis curve were obtained by regression fitting. The restoring force model proposed in this paper is in good agreement with the test results, which can provide a reference for the elastic–plastic seismic response analysis of the new fabricated shear wall structure.

Coordinated and individual responding in pairs of rats under variable interval schedules

The coordination of responses in pairs of rats was investigated by parametrically manipulating the duration of variable-interval (VI) schedule mean inter-reinforcer intervals (IRIs). Two conditions required coordination for a group of three pairs of rats (VI 5 s, 10 s, 20 s, 40 s, 80 s, 120 s, 160 s, 60 s, and 243 s) and individual responding for another group of three pairs of rats (VI 5, 10 s, 20 s, 40 s and 80 s). An inverted U-shaped function related responding measures and reinforcement rates: Overall response rates, coordinated episode rates and percentage of coordination increased with increasing reinforcement rates, and decreased at the highest rates of reinforcement in both groups. Rats exposed to VI schedules that required coordination generally showed higher rates and higher percentages of coordinated responses when compared to rats that responded under the individual schedules. Local rates of coordinated episodes showed that coordination occurred at a steady rate across the VI IRIs for the Coordination Group. The results extend previous research on the patterns of coordinated responses maintained by intermittent schedules of reinforcement.

On-line monitoring the corrosion rate of reinforcing steel in concrete under natural conditions using bimetallic batch sensors along the coast of Khanh Hoa (Vietnam)

A bimetallic batch sensor was proposed to assess the corrosion rate of steel reinforcement in concrete in the presence of chlorides under laboratory and marine conditions. The prepared sensor could generate an electric current independently, indicating the corrosion process's intensity. Moreover, this sensor did not require any external polarization, resulting in reducing the device's cost and power consumption. These advantages are very important when using sensors for autonomous monitoring systems away from energy sources. Laboratory tests in an aqueous extract of concrete have shown the possibility of a sensor to detect the transition from a passive state to corrosion with an increase in the concentration of chlorides. Activation was received when 0.010 < CCl ≤ 0.10 mol·dm−3. The boundary between the passive state and corrosion was obtained at a current density of 8.6 ± 0.5 μA·cm−2. The measurement results on the sensor coincided with the data of the anode polarization curves and the polarization resistance method. In addition, the monitoring system based on sensors was tested in the field conditions of Khanh Hoa (Vietnam) for four exposure conditions for nine months. The correspondence of the measured current for sensors with standard monitoring methods was obtained: the half-cell potential and the electrical resistivity. The most intense corrosion occurred for the samples placed in the splash zone or immersed to a depth of 1 m. The coefficient of conversion of the current on the sensor and the corrosion rate by the polarization resistance method for concrete samples was set to 69.9. Therefore, it is possible to use the current value on the sensor to predict the time to structural failure using well-known models based on data on the corrosion rate of reinforcement. The sensors could retain their functionality and integrity after 9 months of field tests. The current findings suggest a continuous monitoring system of the corrosion rate of steel reinforcement in marine conditions for practical applications.

Examining resurgence in rats following expanded-operant treatments.

Resurgence of previously reinforced behavior represents a challenge to otherwise successful interventions based on differential reinforcement of alternative behavior (DRA). Expanded-operant treatments seek to increase the number of functional alternative behaviors through DRA, thereby potentially mitigating resurgence. However, the few studies that have directly examined these methods as a tool for resurgence mitigation have provided limited and unclear results. Thus, the present experiments were designed to investigate the effect of expanded-operant DRA methods on resurgence of previously reinforced behavior using rat subjects. In two experiments, following a baseline phase in which a target response was trained, groups of rats experienced concurrent (i.e., five simultaneous alternative responses), serial (i.e., five sequentially available alternative responses), or single DRA interventions arranging similar rates of alternative reinforcement in order to examine potential differences in resurgence. Both experiments showed that neither serial nor concurrent DRA expanded-operant treatments reduced resurgence compared with single DRA regardless of whether stimuli associated with previously reinforced alternative responses were removed (Experiment 1) or remained present (Experiment 2) for the serial-DRA group. Further, a primacy effect in resurgence was obtained for the serial-DRA group in both experiments. Overall, these results suggest that expanded-operant treatments may not help to reduce resurgence.

Inhibition and paradoxical choice

The present study evaluated the role of inhibition in paradoxical choice in pigeons. In a paradoxical choice procedure, pigeons receive a choice between two alternatives. Choosing the “suboptimal” alternative is followed 20% of the time by one cue (the S+) that is always reinforced, and 80% of the time by another cue (S-) that is never reinforced. Thus, this alternative leads to an overall reinforcement rate of 20%. Choosing the “optimal” alternative, however, is followed by one of two cues (S3 or S4), each reinforced 50% of the time. Thus, this alternative leads to an overall reinforcement rate of 50%. González and Blaisdell (2021) reported that development of paradoxical choice was positively correlated to the development of inhibition to the S- (signal that no food will be delivered on that trial) post-choice stimulus. The current experiment tested the hypothesis that inhibition to a post-choice stimulus is causally related to suboptimal preference. Following acquisition of suboptimal preference, pigeons received two manipulations: in one condition one of the cues in the optimal alternative (S4) was extinguished and, in another condition, the S- cue was partially reinforced. When tested on the choice task afterward, both manipulations resulted in a decrement in suboptimal preference. This result is paradoxical given that both manipulations made the suboptimal alternative the richer option. We discuss the implications of our results, arguing that inhibition of a post-choice cue increases attraction to or value of that choice.

Evidence for Different Roles of Inhibitory and Prospective Intolerance of Uncertainty During Threat Discrimination Learning

Uncertainty is a core component of threat and associated learning processes. One methodological factor impacting uncertainty in threat learning paradigms is the threat reinforcement rate, which refers to the proportion of times a cue is reinforced with an aversive stimulus. This study tested the effect of partial vs continuous threat reinforcement on threat / safety discrimination learning, as indexed by skin conductance response (SCR). Using a within-participants design, fifty-nine participants completed a task in which three colored shapes were paired with electric shock at reinforcement schedules of 100% (CS+), 50% (CS+) and 0% (CS-). In addition, the study examined the relationship between the Intolerance of Uncertainty scale (IU) and two subscales – inhibitory and prospective IU – with threat discrimination learning. The data show heightened SCR in the continuous vs partial reinforcement condition to all stimuli, but limited evidence of enhanced discrimination learning. Furthermore, no association was observed between total IU score and threat-safety discrimination. However, using a two-factor model of IU, findings showed higher inhibitory IU and higher prospective IU were associated with diminished and heightened threat discrimination, respectively. These results contribute to a fast-growing literature exploring how the uncertainty inherent to predictors of threat, individual differences in sensitivity to uncertainty, and interactions between these two factors, can shape the acquisition of threat memory.

Reward maximization assessed using a sequential patch depletion task in a large sample of heterogeneous stock rats

Choice behavior requires animals to evaluate both short- and long-term advantages and disadvantages of all potential alternatives. Impulsive choice is traditionally measured in laboratory tasks by utilizing delay discounting (DD), a paradigm that offers a choice between a smaller immediate reward, or a larger more delayed reward. This study tested a large sample of Heterogeneous Stock (HS) male (n = 896) and female (n = 898) rats, part of a larger genetic study, to investigate whether measures of reward maximization overlapped with traditional models of delay discounting via the patch depletion model using a Sequential Patch Depletion procedure. In this task, rats were offered a concurrent choice between two water “patches” and could elect to “stay” in the current patch or “leave” for an alternative patch. Staying in the current patch resulted in decreasing subsequent reward magnitudes, whereas the choice to leave a patch was followed by a delay and a resetting to the maximum reward magnitude. Based on the delay in a given session, different visit durations were necessary to obtain the maximum number of rewards. Visit duration may be analogous to an indifference point in traditional DD tasks. Males and females did not significantly differ on traditional measures of DD (e.g. delay gradient; AUC). When examining measures of patch utilization, females made fewer patch changes at all delays and spent more time in the patch before leaving for the alternative patch compared to males. Consistent with this, there was some evidence that females deviated from reward maximization more than males. However, when controlling for body weight, females had a higher normalized rate of reinforcement than males. Measures of reward maximization were only weakly associated with traditional DD measures and may represent distinctive underlying processes. Taken together, females performance differed from males with regard to reward maximization that were not observed utilizing traditional measures of DD, suggesting that the patch depletion model was more sensitive to modest sex differences when compared to traditional DD measures in a large sample of HS rats.

Corrosion mechanism of recycled mortar prepared from CO2-treated hardened cement paste powder

CO2-treated recycled powder improves the mechanical properties of concrete. However, its corrosion mechanisms are not thoroughly understood. This study focused on the carbonation-induced corrosion mechanism of recycled mortar prepared from CO2-treated hardened cement paste powder (CCPP). First, the corrosion behavior of the steel reinforcement in a CCPP mortar (CCPPM) was evaluated using electrochemical and corrosion mass loss tests. Furthermore, the carbonation resistance of the CCPPM was quantified by testing the carbonation coefficient, and a corrosion model was established to predict corrosion. Finally, the microproperties of CCPPM and CCPP were investigated to reveal the corrosion mechanism. The results show that the corrosion rate of the steel reinforcement in the CCPPM is controlled by the combined effect of the concentration of OH– ions around the steel reinforcement and mortar porosity; the former plays a more critical role than the latter. Moreover, the variation in the w/c ratio of the CCPP base material had a slight effect on the compressive strength and carbonation resistance of the CCPPM and the corrosion rate of the steel reinforcement. The low concentration of OH– ions in the CCPPM increases the corrosion current density of the steel reinforcement by 15.91%–26.79%, consistent with the 10.96%–18.67% higher corrosion mass loss of the steel reinforcement embedded in the CCPPM cured for 540 days relative to that of the hardened cement paste powder mortar. Although incorporating CCPP increases the steel corrosion risk, the corrosion model developed herein demonstrates that CCPP can be used to guarantee a service life of 50 years for mortars when its replacement ratio is less than 20%.

Further evaluation of prompt density, rate of reinforcement, and the persistence of manding

AbstractPrevious research has evaluated the effects of prompt rates on the rate of communicative behavior. More recent research has suggested that dense prompting can result in communicative behavior that is more resistant to change. However, existing research has not considered the impact that higher response rates had on reinforcement rate, a variable known to impact response persistence. The current study systematically replicated previous research by evaluating communicative responding in contexts associated with dense‐ and lean‐prompt schedules and extended existing research by (a) holding reinforcement rates similar across the two prompting schedules (lean and dense), and (b) evaluating the persistence of communicative responding in the contexts associated with each prompting schedule. The results for Experiment 1 clearly replicated and extended previous research. The results for Experiment 2 were equivocal and suggested that previous reinforcement history and response class size impacted outcomes.

Research on Corrosion Rate Model of Reinforcement in Concrete under Chloride Ion Environments

In a chloride environment, taking reinforced concrete structures as the research object, the corrosion rate of reinforcement determines its corrosion expansion because multiple coupling parameters will affect the corrosion rate of reinforcement, which is extremely difficult to effectively predict. In this paper, 144 sets of experimental data were collected and sorted out by reading the relevant literature, and six empirical models for predicting the corrosion rate of steel bars were compared and analyzed based on these experimental data. Based on the investigations, a new empirical model is proposed for predicting the corrosion rate of reinforcement, and the relevant influencing factors are considered in the new model. By comparing the 144 sets of experimental data and 90 experimental data for this paper, the new prediction model can well predict the corrosion rate of reinforcement. Furthermore, the time variability of the new prediction model is verified. The probability distribution characteristics of seven prediction models are obtained through model error analysis, which provides a theoretical basis for the next step of concrete cover cracking and reliability analysis.

Prediction equations for corrosion rate of reinforcing steel in cement-fly ash concrete

ABSTRACT This study is to incorporate the time-dependent development of microstructures of cement-fly ash concrete into the evaluation of corrosion severity for newly constructed structures and existing structures. The electrical resistivity, corrosion potential, and corrosion rate were determined for twelve series of concrete mixtures prepared with various water-to-binder ratios, fly ash contents, and chloride contents. The time-dependent developments of cement-fly ash paste, including hydration degree, pozzolanic reaction degree, and capillary porosity, are adopted based on previous models. The correlation between the corrosion rate and the time-dependent developments was considered for the proposed equations. The experimental results indicate that low water-to-binder ratio concrete and fly ash concrete show a low corrosion rate of reinforcement. Because the microstructure of concrete became denser, represented by a high degree of hydration and low porosity. This phenomenon increases the corrosion resistance of concrete. Besides, the chloride ions can accelerate the corrosion rate of reinforcement. Its effects of corrosion acceleration are found to be different in fly ash concrete because the fly ash can capture free chloride ions.

Focused-attention mindfulness increases sensitivity to current schedules of reinforcement.

Four experiments explored the impact of focused-attention mindfulness training on human performance on free-operant schedules of reinforcement. In each experiment, human participants responded on a multiple random ratio (RR), random interval (RI) schedule. In all experiments, responding was higher on RR than RI schedules, despite equated rates of reinforcement. A 10-min focused-attention mindfulness intervention (focused attention) produced greater differentiation between schedules than relaxation training (Experiments 1, 2, and 4), or no intervention (Experiment 3). Focused-attention mindfulness improved learning when the schedules associated with components of the multiple schedule were reversed. This occurred irrespective of whether the focused-attention mindfulness was before (Experiment 2) or after (Experiments 3 and 4) initial training, or whether compared to relaxation (Experiments 2 and 4) or no intervention (Experiment 3). In Experiment 4, following multiple RR, RI training, focused-attention mindfulness increased sensitivity to contingency reversal and did not interfere with previous training in a group that did not receive a contingency reversal. In contrast, relaxation training did not facilitate reversal learning and interfered with previous learning. The results suggest that focused-attention mindfulness improves awareness of operative contingencies by focusing participants on the present, rather than reducing interference from previous learning. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Experimental and numerical study for the bending behaviour of UHPC beams with waste foundry sand

Waste foundry sand (WFS) is a waste material inevitably generated during the casting process, the resourceful recycling of which has received much attention in recent years. WFS has been tried for various concrete preparations without involving ultra-high performance concrete. In this study, the bending behaviour of ultra-high performance concrete beams with WFS as an aggregate replacement (i.e., FUHPC) was investigated. Firstly, the bending tests for 6 FUHPC beams with the variable of WFS substitution rate (0%, 10%, 20% and 30%) and water-binder ratio (0.16, 0.18 and 0.20) were carried out, and the effects of the two were discussed based on the failure mode, load–deflection response and load–strain response of the beams. Then, finite element simulation was used to further explore the bending behaviour of FUHPC beams. Finally, the applicability of the equation in the code for calculating the bending capacity of FUHPC beams was evaluated. The results showed that the bending performance of FUHPC beams first improved and then decreased as the WFS substitution rate and water-binder ratio increased. The best bending performance of FUHPC beams was achieved when the two were 20% and 0.18, respectively. In this case, the cracking load, yield load and ultimate load of FUHPC beam were 1.26, 1.23 and 1.12 times higher than those of the beam without WFS, respectively, and the ultimate strain was also elevated. When the WFS substitution rate was too large (30%), the damage of FUHPC beams showed certain brittle characteristic. The plastic damage of FUHPC beams was mainly concentrated in the pure bending section. Tensile reinforcement strength, reinforcement rate and especially the beam height have obvious positive effects on the bending performance of FUHPC beams. The theoretical equation of bending capacity suggested by the code CECS 38:2004 is applicable for FUHPC beams.

An improved analytical model for two-step corbels in a precast concrete system

Corbels are a common element in the beam–column connections of precast concrete structures. This paper analyses the failure of a two-step corbels system using computational modeling. A finite element model is developed and calibrated using the test results for two-step corbels without secondary reinforcement but with steel fiber–reinforced concrete. A database is developed from the parametric analyses of two-step corbels, varying the a/d ratio (0.34–0.76), the rate of the main reinforcement (0.19–0.50%), the compressive strength of the concrete (30–70 MPa) and the amount of steel fibers (1.0% and 1.5%). An improved analytical model, using the developed database, is proposed to design the two-step corbels. The reliability of the proposed analytical model is evaluated using a second database, developed in this paper, and a strength reduction factor of 0.66 for failure by yielding of the main reinforcement and 0.56 for failure by crushing of the concrete strut, were obtained. Therefore, the improved analytical model obtained for the design of two-step corbels represents an advance, in terms of structural safety and economy, when compared to the previous analytical models recommended in the literature.

A quantitative analysis of resurgence following downshifts in alternative-reinforcer magnitude.

Resurgence is the increase in a previously reinforced and then extinguished target response due to changes in reinforcement conditions for an alternative response, including reductions in the rate or magnitude of reinforcement for the alternative response. Research with nonhumans suggests that reductions in both alternative-reinforcer rate and magnitude produce resurgence, but the present study was the first to examine effects of downshifts in alternative-reinforcer magnitude on humans' resurgence. Moreover, it was the first to evaluate whether the quantitative framework, resurgence as choice in context (RaC2 ), could account for those effects. Consistent with predictions of RaC2 , resurgence of a target button press occurred with reductions in point gain for an alternative response, with greater reductions producing higher levels of resurgence. However, the model consistently underpredicted and then overpredicted resurgence during tests with low-magnitude reinforcement and extinction. Systematic deviations in model predictions of alternative responding were also evident and consistent with previous fits of RaC2 to nonhuman data. Overall, our findings suggest that RaC2 could be a useful quantitative theoretical framework for understanding processes contributing to resurgence in humans, but further theoretical development is needed to account for the apparent divergent effects of extinction versus downshifts in reinforcer magnitude.

Experimental investigation and numerical modelling of the seismic performance of corroded T-shaped reinforced concrete shear walls

Six T-shaped reinforced concrete (RC) shear wall specimens were subjected to constant-current and drying-wetting cycle accelerated corrosion tests and pseudostatic loading tests in this paper. The corrosion appearance, failure mode, and mechanical properties of each specimen were compared, and the impact of the corrosion degree and axial compression ratio on the seismic performance of the T-shaped RC shear wall was analysed. The experimental outcomes illustrate that the seismic behaviour of the specimens under positive and negative loading was conspicuously different because of the asymmetric section of the specimens. Under positive loading, the bearing capacity of the specimens was higher, and the deformation capacity was poor, while the negative loading was the opposite. As the corrosion degree increased, the bearing capacity, deformability, stiffness degradation degree, cumulative energy dissipation capacity, and proportion of shear deformation in the total deformation of the specimens all showed a downwards trend. With increasing axial compression ratio, the bearing capacity of the specimen increased, the cumulative energy dissipation capacity, ultimate displacement and the proportion of shear deformation in the total deformation decreased, and the degradation rate of stiffness accelerated. Subsequently, considering the correction of corroded materials, a numerical model of the corroded T-shaped RC shear wall based on the ShellMITC4 multilayer shell element was established, and the exactitude of the numerical model was validated based on test data. Finally, based on the established numerical model, the effects of the concrete strength, boundary column longitudinal reinforcement ratio and vertical distribution reinforcement rate on the seismic behaviour of corroded T-shaped RC shear walls were studied. These research outcomes can offer supporting theories for numerical modelling analysis and seismic capacity assessment of existing RC shear wall structures in coastal environments.

Effect of Polypropylene Fibers on Swelling Potential and Shear Strength of Clay

Expansive clays can cause major problems for urban development (roads, railways, infrastructure, etc.); therefore, reducing the swelling potential of clays has always been a concern in the geotechnical field. The presented paper investigates the effect of polypropylene reinforcement fibers on the swelling potential and shear strength of clay. The samples studied were taken from the clayey region of Mila, located in the northern east of Algeria. The experimental procedure adopted in this research consists first of the assessment of the physical, mechanical, and mineralogical characteristics of the soil samples without reinforcement. Then, swelling pressure, swelling rate, and swelling index are used to assess the swelling potential of these samples. After the reinforcement using a variety of polypropylene fiber concentrations (2 to 6% of the weight of the dry clay), the free swelling is clearly reduced. The optimum reinforcement rate in this case is 4%, in which the swelling was reduced by 90.7%. Finally, to offer more insights regarding the impact of clay reinforcement using polypropylene fibers, the effect of this later on the mechanical properties of the studied clay was also analyzed through the tangential shear strength. It was found that the polypropylene fibers increased the tangential shear resistance of Mila’s clay. Doi: 10.28991/CEJ-2023-09-03-04 Full Text: PDF

Safety Analysis of Rebar Corrosion Depth at the Moment of Corrosion-Induced Cover Cracking

Concrete cover cracking induced by reinforcement corrosion is an important indication of the durability limit state for reinforced concrete (RC) structures and can be used to determine the structural service life. The process of rebar corrosion from the beginning of rusting to the occurrence of cover cracking due to corrosion expansion can be divided into two phases: the phase of the free expansion of the corrosion product and the phase of cover cracking. Based on the assumption of the uniform corrosion of the reinforcement, one model for predicting the reinforcement corrosion depth from corrosion initiation to cover cracking was established according to the cylindrical cavity expansion theory. The main factors affecting the reinforcement corrosion depth were analyzed. The main factors affecting the corrosion depth of reinforcement were analyzed. The quantitative sensitivity analysis of the factors influencing the calculation formula shows that the depth of reinforcement corrosion and the thickness of the concrete protective layer are approximately linearly increasing, with a growth rate of 0.2366 μm/mm; the diameter of the reinforcement is approximately linearly decreasing, with a decrease rate of 0.2122 μm/mm; the volume expansion rate of rust is approximately power function decreasing; the overall influence range of the yield criterion selection parameter is 0.15 μm; for the concrete strength grade, the overall influence range is 0.1 μm. The coefficient of determination R2 is 0.87, and the overall accuracy of the calculated formula is high, which can be used to predict the service life of reinforced concrete structures and guide the durability design in combination with the research results on the corrosion rate of reinforcement under different environments.

Impulsive choice in two different rat models of ADHD-Spontaneously hypertensive and Lphn3 knockout rats.

Impulsivity is a symptom of attention-deficit/hyperactivity disorder (ADHD) and variants in the Lphn3 (Adgrl3) gene (OMIM 616417) have been linked to ADHD. This project utilized a delay-discounting (DD) task to examine the impact of Lphn3 deletion in rats on impulsive choice. "Positive control" measures were also collected in spontaneously hypertensive rats (SHRs), another animal model of ADHD. For Experiment I, rats were given the option to press one lever for a delayed reward of 3 food pellets or the other lever for an immediate reward of 1 pellet. Impulsive choice was measured as the tendency to discount the larger, delayed reward. We hypothesized that impulsive choice would be greater in the SHR and Lphn3 knockout (KO) rats relative to their control strains - Wistar-Kyoto (WKY) and Lphn3 wildtype (WT) rats, respectively. The results did not completely support the hypothesis, as only the SHRs (but not the Lphn3 KO rats) demonstrated a decrease in the percent choice for the larger reward. Because subsequent trials did not begin until the end of the delay period regardless of which lever was selected, rats were required to wait for the next trial to start even if they picked the immediate lever. Experiment II examined whether the rate of reinforcement influenced impulsive choice by using a DD task that incorporated a 1 s inter-trial interval (ITI) immediately after delivery of either the immediate (1 pellet) or delayed (3 pellet) reinforcer. The results of Experiment II found no difference in the percent choice for the larger reward between Lphn3 KO and WT rats, demonstrating reinforcement rate did not influence impulsive choice in Lphn3 KO rats. Overall, there were impulsivity differences among the ADHD models, as SHRs exhibited deficits in impulsive choice, while the Lphn3 KO rats did not.