No description available.

The purpose of this study was to observe and analyze the factors that lead to a child's increase in responding to a previously neutral stimulus after observing another child's behavior and consequences in the same setting. The effects of five video presentations on rate of button-pressing responses were observed across four students. Rates of button-pressing behavior on an FR3 schedule of reinforcement were collected for each student using a computer and a metal apparatus with two flat push buttons. Each student completed two baseline phases to establish neutrality of stimuli, and viewed a total of five video presentations. Each video segment contained a model engaging in button pressing and receiving tokens under various social and nonsocial conditions, which would potentially serve as reinforcers. Rates of responding were recorded immediately after each video presentation. Three of the four students' rates of responding increased and surpassed their levels of responding during baseline sessions. From these results, it was concluded that neutral stimuli can acquire reinforcing properties for children through an observational learning procedure. It is suggested that observational learning (the presentation of a model engaging in a specific behavior) might be considered and establishing operation to temporarily increase the value of a reinforcer.

In this investigation, the elasto-plastic behavior and the seismic performance of concrete reinforced frame structures reinforced are evaluated by applying the Pushover method. This evaluation is done on several cases: with high ductility steel (Grade 40), conventional steel (Grade 60) and high strength steel (Grade 75). For the previous, the capacity curve graph obtained from the displacement coefficient method was used to measure the capacity of the structure. In addition, the performance of the structure for different levels of seismic design are evaluated with the resulting values of ductility and rigidity of each case. The results showed that reinforcing a structure with a Grade 40 reinforcing steel increases the energy dissipation capacity, and if reinforced with a Grade 75 reinforcing steel increases the strength capacity in the structure. Finally, the comparative result of the various cases are presented to demonstrate the influence of reinforcing steel on the plastic behavior of concrete reinforced frame structures.

No description available.

No / Paper accepted for conference.

No description available.

Aluminum alloys are presently used extensively as a conductor material for overhead transmission wires. Their lack of strength must be compensated by using a reinforcing agent, namely steel. The aim of this thesis was to investigate the possibility of deforming Al-Fe and Al-Ni alloys in order to produce high strength, high conductivity wire product. The main goal was to produce a two phase Al alloy wire with adequate strength so that the wire would be self supporting as an overhead electrical power transmission line. The Al-Fe and Al-Ni two phase alloy rods were Ohno cast to provide directional solidification. In both alloys, wire drawing was unsuccessful due to fiber fracture and damage accumulation during drawing. The Al-Fe alloy was subjected to hydrostatic extrusion in an attempt to induce co-deformation of the matrix material and the brittle intermetallic second phase, Al6Fe. Hydrostatic extrusion proved to be successful in inducing some deformation of the Al6Fe and provided valuable initial insight into the investigation of the deformation of Al6Fe. The final stage in the development of an aluminum alloy for use as a self supporting overhead transmission wire was the development of a “macrocomposite”. This macrocomposite was a combination of an Fe rod 4 mm in diameter and a tube of aluminum 8 mm in diameter. This macrocomposite was successfully cold worked to achieve an overall yield strength of 395 MPa. / Thesis / Master of Engineering (MEngr)

After 17 years in service, a 3 ft by 3 ft closure pour section of an Interstate 81 (I-81) bridge deck failed by punching through near Marion, Virginia. Visual inspection noted that there was considerable corrosion on some of the reinforcing bars in the vicinity of the construction joint, while other failure bars had little or no corrosion. Sections of the bridge deck were cut and delivered to Virginia Tech for further investigation. It was clear from an initial investigation that shrinkage of the deck concrete had caused the construction joints to open and thereby allow water and chlorides to enter the joint. In addition, it was observed that several bars across the closure pour construction joints had suffered significant section loss due to corrosion, but it was not clear if fatigue and strength failure of the reinforcing bars were also contributing factor in the closure pour failure. To study the problem four fatigue tests and five strength tests performed. The specimens included six slab strips cut from the I-81 bridge deck, with the 3-ft closure pour included, and three additional specimens that were cast in the laboratory to represent a base line for performance. A three-point loading setup was used for both fatigue and strength tests. However, for the final strength and fatigue tests, a jacking system was designed and implemented in an effort to open the closure pour construction joints to simulate the open joints of the I-81 bridge. The objectives of this research program are to provide a better understanding of the closure pour failure mechanism, develop inspection procedures for Virginia Department of Transportation (VDOT) to assess its bridge inventory containing similar construction joints, and to develop recommendations for future construction of similar construction joints. / Master of Science

In order to predict the future needs of existing bridges, Bridge Management Systems use models to predict the time when damage will reach a level to cause repair, rehabilitation, or replacement of the structure. One such model is the deterioration model, which has three distinct phases. The second phase of the model, the corrosion phase, is the focus of this study. During the corrosion phase, chloride ion concentration reaches a threshold level at the depth of the reinforcing steel which initiates corrosion. The corrosion continues until sufficient pressure is exerted on the surrounding concrete to cause cracking. This study is a continuation of a study implemented in the Materials Division at Va Tech. The study includes the monitoring of the corrosion rate of steel reinforcing bars placed in simulated bridge decks. The corrosion rates were varied by placing between 0 - 9.6 Ibs/yd³ of chloride ions in the concrete to produce six different series. Also, the depth of concrete cover, bar spacing, bar size, and exposure conditions were varied. The specimens were monitored until the time that the cracking of the concrete was observed. At that time, samples of the steel reinforcing bars were removed and the actual amount of corrosion which had occurred was determined as the weight loss of the steel. The actual weight loss of the steel reinforcing bars was then compared to the predicted weight loss from the corrosion rate measurement devices. The time to cracking and the mode of cracking was compared to Bazant's equations for cracking which are the basis for the corrosion phase of the deterioration model. Although only one series cracked during the study, corrections in the use of Bazant's equations were proposed. / Master of Science

Reinforced Concrete (RC) structures are common in earthquake-prone areas. During an earthquake, the steel reinforcement is subjected to cyclic strain histories which lead to inelastic response. In the case of rare, strong earthquakes, inelastic buckling and even rupture due to low-cycle fatigue can also occur. The understanding and characterization of the performance of RC structures under earthquake hazards requires the accurate simulation of the inelastic hysteretic behavior of steel reinforcement by means of appropriate constitutive models. Several uniaxial material models have been developed for reinforcing steel. Existing material models sacrifice efficiency for accuracy or vice versa. Conceptually simple and numerically efficient models do not accurately capture the hysteretic response and ignore rupture or buckling. On the other hand, more refined material models are characterized by iterative stress update procedures which can significantly increase the computational cost of an analysis. Additionally, experience suggests that refined models attempting for the effect of inelastic buckling tend to lead to numerical convergence problems in the stress update procedure. The goal of the present study is the formulation and implementation of an accurate and computationally efficient constitutive model for steel reinforcement under cyclic loading. A previously developed model, capable of capturing the inelastic hysteretic response of reinforcing steel in the absence of buckling and rupture, is used as a starting point in this study. The model is enhanced by replacing its original, iterative stress update procedure with an equally accurate, non-iterative one. Additionally, the model is enhanced to capture the effects of inelastic buckling and of rupture. The accuracy of the model and the efficiency of the non-iterative stress update algorithm are demonstrated by means of validation analyses. / Master of Science