No description available.

No description available.

No description available.

UHPC (ultra-high performance concrete) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish UHPC from conventional reinforced concrete are the improved compressive strength, the tensile strength, the addition of steel fibers, and the resistance to corrosion and degradation. The mechanical properties of UHPC allow for smaller, thinner, lighter sections to be designed while strength is maintained or improved. The use of UHPC has been limited to a few structural applications due to the high cost of the materials and the lack of established design guidelines. A proposed material model based on material and finite element models has served as the foundation of this research effort. The model was used to minimize the dimension of an optimum section in order to limit the material usage and maximize the performance. In the model, the top flange served as the riding surface and contained no reinforcing steel to resist shear. The lack of steel reinforcement allowed for the possibility of a punching shear failure to occur from the application of a point load such as a wheel tire patch load. The model and optimized section served as the foundation for this research, the characterization of punching shear capacity of thin UHPC plates. A total of 12 UHPC slabs were tested to failure to determine the boundary between a flexural failure and a punching shear failure. The variables considered were the slab thickness and loading plate dimensions. The results of the testing were compared to existing models for punching shears and other failure modes, with varying success. The test results aided in the development of a design equation for the prediction of punching shear in UHPC slabs. After evaluation of the test results, recommendations are made as to which model predicts the punching shear capacity of UHPC slabs and the minimum slab thickness required to prevent a punching shear failure. / Master of Science

In this study the properties of ferro-cement are investigated. Ferro-cement is a kind of reinforced concrete differing from normal reinforced concrete in that cement mortar and fine steel reinforcement are used rather than aggregate concrete and bar reinforcement. Concrete consistency and three kinds of reinforcement are taken as the parameters which affect the properties of the ferro-cement, Tests are carried out on beams subjected to bending while varying these parameters. A comparative analysis of the experimental results is made and some analytical explanations are included. It was found that mortar with high cement content and fine mesh reinforcement delayed the crack formations and increased the ultimate load carrying capacities of the beams. / Master of Science

Reinforced concrete (RC) shear wall buildings constitute a significant portion of the building inventory in many earthquake-prone regions. A similar type of structural system is fully-grouted reinforced masonry (RM) shear wall structures. The accurate determination of the nonlinear response of reinforced concrete and reinforced masonry (RC/RM) walls subjected to lateral loading is of uttermost importance for ensuring the safety of the built environment. Analytical models provide a cost efficient and comprehensive tool to study the nonlinear response of RC/RM structures, as compared to experimental tests. Predictive models should capture nonlinear material behavior as well as the geometrically nonlinear response of RC/RM shear wall structures during major seismic events. This thesis outlines the formulation and validation of a nonlinear shell element for the simulation of RC/RM structures. The proposed shell element enhances an existing formulation of a four-node Discrete Kirchhoff shell element through the inclusion of a corotational approach to account for geometric nonlinearities and of nonlinear material models to capture the effect of cracking and crushing in concrete or masonry and the nonlinear hysteretic behavior of reinforcing steel. The analytical results obtained from multiple linear and nonlinear analyses are compared against theoretical solutions and experimental test data. These comparative validation studies show the enhanced shell element can satisfactorily capture the salient features of the response of nonlinear reinforced concrete/masonry shear wall structures including axial-shear-flexure interaction, damage patterns, and in-plane and out-of-plane loading. / Master of Science

Post-earthquake fires can negatively affect the safety and collapse probability of Reinforced Concrete (RC) structures. At present, there has been no systematic effort to assess the performance of RC structures for combined earthquake and fire effects. Developing appropriate guidelines for this scenario requires simulation tools that can accurately capture material behavior during cyclic loading and at elevated temperatures. Ideally, simulation tools must also be conceptually simple and computationally efficient to allow extensive parametric analyses. The goal of the present study is to enhance a previously established modeling approach so that it can describe the performance of RC structures for both cyclic loading and changes in material behavior due to elevated temperatures. The modeling approach is based on the nonlinear truss analogy and has been extensively validated for cyclic loading of RC shear walls and columns. The constitutive models for concrete and reinforcing steel are enhanced with the capability to account for the effect of elevated temperatures. The enhanced material models are validated using experimental data for concrete and steel at elevated temperatures. The capability of the proposed model to analyze structural-level behavior is verified and compared with experimental testing. The method is also endowed with the capability to describe the time-dependent heat conduction in a fire simulation. The use of the enhanced nonlinear truss model is more advantageous than refined finite element models because of its computational efficiency and conceptual simplicity. / Master of Science

Reinforced concrete (RC) moment frames comprise a significant portion of the built environment in areas with seismic hazards. The beam-to-column joints of these frames are key components that have a significant impact on the structure's behavior. Modern detailing provides sufficient strength within these joints to transfer the forces between the beams and the columns during a seismic event, but existing structures built with poor detailing are still quite prevalent. Identifying the need and extent of retrofits to ensure public safety through nondestructive means is of primary importance. Existing models used to analyze the performance of RC beam-to-column joints have either been developed for modern, well-detailed joints or are simplified so that they do not capture a broad range of phenomena. The present study is aimed to extend a modeling technique based on the nonlinear truss analogy to the analysis of RC beam-to-column joints under cyclic loads. Steel and concrete elements were arranged into a lattice truss structure with zero-length bond-slip springs connecting them. A new steel model was implemented to more accurately capture the constitutive behavior of reinforcing bars. The joint modeling approach captured well the shear response of the joint. It also provided a good indication of the distribution of forces within the joint. The model was validated against three recently tested beam-column subassemblies. These tests represented the detailing practice of poorly-detailed RC moment frames. The analytical results were in good agreement with the experimental data in terms of initial stiffness, strength and damage pattern through the joint. / Master of Science

Master of Science

Corrosion in reinforced concrete bridge decks has always been a concern amongst engineers. However, as structures continue to increase in size and in the amount of reinforcement present, consideration must be given to parameters such as the clear spacing arrangements between bars, the presence and absence of stay-in-place (SIP) forms, and differences in the cathode bar to anode bar ratios. Limited research has been performed to determine the effects of the parameters (Shiessel, P. 1986). Research has been conducted on the effects of macrocell corrosion compared to microcell corrosion. Previous studies have shown that the measured microcell corrosion is not augmented greatly by the macrocell current (Andrade et al. 1991). In this study, twenty-seven specimens were cast with reinforcing steel to represent reinforcing mats at the top and bottom of each specimen. Top and bottom spacing arrangements were approximately 51, 76, 102 mm (2, 3, and 4-inches), cathode-to-anode bar (C/A) ratios were 2 and 1, and the presence and absence of SIP were considered. Macrocell currents, resistivity measurements, half-cell potential measurements, and corrosion current densities were recorded over a 273 day time period to compare the differences that existed amongst the three different parameters. Based upon the data that was collected, no significant differences were recorded when comparisons were made between the spacing arrangements, the absence and presence of SIP, and differences in C/A ratios. The formation of the passive layer was confirmed by the corrosion current densities and half-cell potentials. The rate of the formation of the passive layer occurred in two distinct periods, a rapid rate from casting to about 105 days and a significantly slower rate beyond 105 days after casting. There was no detected influence of the macrocell activity on the formation of the passive layer throughout the 273 day study period. / Master of Science