An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.

Considerable amount of research was carried out into the properties and structural performance of high strength concrete for more than few decades. Whilst this research has produced relevant and useful results, there are several properties of high strength concrete like compressive and tensile strengths, stiffness, durability etc. that need to be evaluated and investigated to determine an accurate representation for the determination of different structural properties of beams made of high strength concrete. For this purpose, an investigation into the behaviour of beams made of higher concrete strengths has been carried out and conclusions drawn for the design of high strength concrete beams in flexure. Experimental data from previous research was considered for the study to establish some understanding of flexural behavior of HSC beams. A number of spreadsheets in Excel were developed using available data and various graphs were plotted to determine the accuracy of the code provisions for calculating the ultimate moment capacity of beams. A study on flexural ductility of beams has been carried out using a computer program FRMPHI which generates moment-curvature curves for the beams. Ductility has been studied using ductility factors. The influence of ductility on the value of the depth of neutral axis has been analysed and discussed. A chapter on the short-term deflection of simply supported high strength concrete beams under instantaneous deflections is presented. This chapter includes analysis of the available formula to calculate deflection to determine if these can be adopted for high strength concrete. Extensive ongoing research on the shear strength of beams by several researchers since many years has lead to the generation of a large body of knowledge. Although each author has analysed the data comparing them with existing relationships, the whole body of information has not been analysed to establish a statistical significance. In this study, regression analysis on experimental data collected from published research is carried a relationship between the different parameters affecting the shear strength of beams. The level of significance of the association between parameters influencing shear strength is also discussed.

Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von K??rm??n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.

Simple but still realistic physical models suitable for structural design of flat concrete plates and column footings with respect to punching are presented. Punching of a flat plate is assumed to occur when the concrete compression strain at the column edge due to the bending moment in the slab reaches a critical value that is considerably lower than the generally accepted ultimate compression strain 0.0035 for one-way structures loaded in bending. In compact slabs such as column footings the compression strength of the inclined strut from the load to the column is governing instead. Both the strain limit and the inclined stress limit display a size-effect, i.e. the limit values decrease with increasing depth of the compression zone in the slab. Due respect is also paid to increasing concrete brittleness with increasing compression strength. The influence of the bending moment means that flat plates with rectangular panels display a lower punching capacity than flat plates with square panels – a case that is not recognized by current design codes. As a consequence, punching shall be checked for each of the two reinforcement directions separately if the bending moments differ. Since the theory can predict the punching load as well as the ultimate deflection of test specimens with good precision, it can also treat the case where a bending moment, so called unbalanced moment, is transferred from the slab to the column. This opens up for a safer design than with the prevailing method. It is proposed that the column rotation in relation to the slab shall be checked instead of the unbalanced moment for both gravity loading and imposed story drift due to lateral loads. However, the risk for punching failure is a great disadvantage with flat plates. The failure is brittle and occurs without warning in the form of extensive concrete cracking and increased deflection. Punching at one column may even initiate punching at adjacent columns as well, which would cause progressive collapse of the total structure. A novel reinforcement concept is therefore presented that gives flat plates a very ductile behaviour, which eliminates the risk for punching failure. The performance is verified by tests with monotonic as well as cyclic loading. / QC 20100929

Longitudinal joints are one of the critical factors that cause premature pavement failure. Poor-quality joints are characterized by a low density and high permeability; which generates surface distresses such as ravelling or longitudinal cracking. Density has been traditionally considered as the primary performance indicator of joint construction. Density measurements consist of taking cores in the field and determining their density in the laboratory. Although this technique provides the most accurate measure of joint density, it is destructive and time consuming. Nuclear and non-nuclear gauges have been used to evaluate the condition of longitudinal joint non-destructively, but did not show good correlation with core density tests. Consequently, agencies are searching for other non-destructive testing (NDT) options for longitudinal joints evaluation. NDT methods have significantly advanced for the evaluation of pavement structural capacity during the past decade. These methods are based either on deflection or wave velocity measurements. The light weight deflectometer (LWD) is increasingly being used in quality control/quality assurance to provide a rapid determination of the surface modulus. Corresponding backcalculation programs are able to determine the moduli of the different pavement layers; these moduli are input parameters for mechanistic-empirical pavement design. In addition, ultrasonic wave-based methods have been studied for pavement condition evaluation but not developed to the point of practical implementation. The multi-channel analysis of surface waves (MASW) consists of using ultrasonic transducers to measure surface wave velocities in pavements and invert for the moduli of the different layers. In this study, both LWD and MASW were used in the laboratory and in the field to assess the condition of longitudinal joints. LWD tests were performed in the field at different distances from the centreline in order to identify variations of the surface modulus. MASW measurements were conducted across the joint to evaluate its effect on wave velocities, frequency content and attenuation parameters. Improved signal processing techniques were used to analyze the data, such as Fourier Transform, windowing, or discrete wavelet transform. Dispersion curves were computed to determine surface wave velocities and identify the nature of the wave modes propagating through the asphalt pavement. Parameters such as peak-to-peak amplitude or the area of the frequency spectrum were used to compute attenuation curves. A self calibrating technique, called Fourier transmission coefficient (FTC), was used to assess the condition of longitudinal joints while eliminating the variability introduced by the source, receivers and coupling system. A critical component of this project consisted of preparing an asphalt slab with a joint in the middle that would be used for testing in the laboratory. The compaction method was calibrated by preparing fourteen asphalt samples. An exponential correlation was determined between the air void content and the compaction effort applied to the mixture. Using this relationship, an asphalt slab was prepared in two stages to create a joint of medium quality. Nuclear density measurements were performed at different locations on the slab and showed a good agreement with the predicted density gradient across the joint. MASW tests were performed on the asphalt slabs using different coupling systems and receivers. The FTC coefficients showed good consistency from one configuration to another. This result indicates that the undesired variability due to the receivers and the coupling system was reduced by the FTC technique. Therefore, the coefficients were representative of the hot mix asphalt (HMA) condition. A comparison of theoretical and experimental dispersion curves indicated that mainly Lamb waves were generated in the asphalt layer. This new result is in contradiction with the common assumption that the response is governed by surface waves. This result is of critical importance for the analysis of the data since MASW tests have been focusing on the analysis of Rayleigh waves. Deflection measurements in the field with the LWD showed that the surface modulus was mostly affected by the base and subgrade moduli, and could not be used to evaluate the condition of the surface course that contains the longitudinal joints. The LWDmod software should be used to differentiate the pavement layers and backcalculate the modulus of the asphalt layer. Testing should be performed using different plate sizes and dropping heights in order to generate different stress levels at the pavement surface and optimize the accuracy of the backcalculation. Finally, master curves were computed using a predictive equation based on mix design specifications. Moduli measured at different frequencies of excitation with the two NDT techniques were shifted to a design frequency of 25 Hz. Design moduli measured in the field and in the laboratory with the seismic method were in good agreement (less than 0.2% difference). Moreover, a relatively good agreement was found between the moduli measured with the LWD and the MASW method after shifting to the design frequency. In conclusion, LWD and MASW measurements were representative of HMA condition. However, the condition assessment of medium to good quality joints requires better control of the critical parameters, such as the measurement depth for the LWD, or the frequency content generated by the ultrasonic source and the coupling between the receivers and the asphalt surface for the MASW method.

The development of the Surface Albedo Treatment System (SATS) onboard a spacecraft mission to the near earth asteroid (NEA) Apophis in 2012 is an innovative concept of deflecting NEAs from possible impact with the Earth through altering the Yarkovsky effect, a non-secular force in the solar system due to uneven surface thermal emission most profoundly affecting small rotating bodies subjected to sunlight. Though this force is small, its magnitude can be dramatic if extended over a period of time and if it uses the close approach of an asteroid near Earth to magnify the perturbation. The payload dispenses colored powder called albedo changing particles (ACPs) onto the surface changing its albedo and indirectly the surface temperature which changes the Yarkovsky effect. This study gives an in-depth description of both computational and experimental parts of the design of this system with primary focus on initial ground test setup. The initial experiments proposed to design the SATS is outlined in detail and justified by the mission criterion of interest as well as modeling the actual dispersal on the surface.

In this study, a laminated glass unit which consists of two glass sheets bonded together by PVB is analyzed as a curved beam and as a cylindrical shell. Laminated glass curved beams and shells are used in architecture, aerospace, automobile and aircraft industries. Curved beam and shell structures differ from straight structures because of their initial curvature. Because of mathematical complexity most of the studies are about linear behavior rather than nonlinear behavior of curved beam and shell units. Therefore it is necessary to develop a mathematical model considering large deflection theory to analyze the behavior of curved beams and shells. Mechanical behavior of laminated glass structures are complicated because they can easily perform large displacement since they are very thin and the materials with the elastic modulus have order difference. To be more precise modulus of elasticity of glass is about 7*104 times greater than the modulus of elasticity of PVB interlayer. Because of the nonlinearity, analysis of the laminated glass has to be performed by considering large deflection effects. The mathematical model is developed for curved beams and shells by applying both the variational and the minimum potential energy principles to obtain nonlinear governing differential equations. The iterative technique is employed to obtain the deflections. Computer programs are developed to analyze the behavior of cylindrical shell and curved beam. For the verification of the results obtained from the developed model, the results from finite element models and experiments are used. Results used for verification of the model and the explanation of the bahavior of the laminated glass curved beams and shells are presented in figures.

Theoretical formulations, analytical solutions, and finite element solutions for laminated composite plate and shell structures with smart material laminae are presented in the study. A unified third-order shear deformation theory is formulated and used to study vibration/deflection suppression characteristics of plate and shell structures. The von K??rm??n type geometric nonlinearity is included in the formulation. Third-order shear deformation theory based on Donnell and Sanders nonlinear shell theories is chosen for the shell formulation. The smart material used in this study to achieve damping of transverse deflection is the Terfenol-D magnetostrictive material. A negative velocity feedback control is used to control the structural system with the constant control gain. The Navier solutions of laminated composite plates and shells of rectangular planeform are obtained for the simply supported boundary conditions using the linear theories. Displacement finite element models that account for the geometric nonlinearity and dynamic response are developed. The conforming element which has eight degrees of freedom per node is used to develop the finite element model. Newmark's time integration scheme is used to reduce the ordinary differential equations in time to algebraic equations. Newton-Raphson iteration scheme is used to solve the resulting nonlinear finite element equations. A number of parametric studies are carried out to understand the damping characteristics of laminated composites with embedded smart material layers.

Title from PDF of title page. / Document formatted into pages; contains 29 pages. / Thesis (M.S.C.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Knowledge of structural stability theory is of paramount importance to the practicing structural engineer. In many instances, buckling is the primary consideration in the design of various structural configurations. The first chapter introduces a simplified treatment of the elastic stability of a battened column using classical methods without getting involved with lengthy and complicated mathematical operations. In chapter two, a treatment of the elastic stability of a frame is presented, including effects of elastic restraints. In this study, a theoretical treatment is given which although approximate, is believed to constitute a satisfactory solution of the structure. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

This thesis improves a previous kinematic analysis and develops the elastic portion of the analysis of a curved compliant beam. This analysis is used to develop a Pseudo-Rigid-Body Model for the curved compliant beam. The Pseudo-Rigid-Body Model consist of kinematic and elastic parameters which can be used to simplify the computation of the large deflections of the beam as it undergoes spherical motion. The kinematic parameters that are developed are the characteristic radius, Gamma*length, the parametric angle coefficient, c_theta, and the kinematic parametrization limit, Capital_theta_max(Gamma). The elastic parameters developed are the stiffness coefficient, K_theta, and the elastic parameterization limit, Capital_theta_max(K). Additionally, curve fit parameters are developed which enable the calculation of the stress in curved beam as it deflects.