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The study presents the results of an experimental and analytical investigation aimed at examining the lateral stability of rectangular reinforced concrete slender beams. In the experimental part of the investigation, a total of eleven reinforced concrete beams having a depth to width ratio between 10.20 and 12.45 and a length to width ratio between 96 and 156 were tested. Beam thickness, depth and unbraced length were 1.5 to 3.0 in., 18 to 44 in., and 12 to 39.75 ft, respectively. Each beam was subjected to a single concentrated load applied at midspan by means of a gravity load simulator that allowed the load to always remain vertical when the section displaces out of plane. The loading mechanism minimized the lateral translational and rotational restraints at the load application point to simulate the nature of gravity load. Each beam was simply-supported in and out of plane at the ends. The supports allowed warping deformations, yet prevented twisting rotations at the beam ends. In the analytical part of the study, a formula was developed for determining the critical loads of lateral torsional buckling of rectangular reinforced concrete beams free from initial geometric imperfections. The influences of shrinkage cracking and inelastic stress-strain properties of concrete and the contribution of longitudinal reinforcement to the lateral stability are accounted for in the critical load formula. The experiments showed that the limit load of a concrete beam with initial geometric imperfections can be significantly lower than the critical load corresponding to its geometrically perfect configuration. Accordingly, a second formula was developed for the estimation of limit loads of reinforced concrete beams with initial lateral imperfections, by introducing the destabilizing effect of sweep to the critical load formula. The experimental results were compared to the proposed analytical solution and to various lateral torsional buckling solutions in the literature. The formulation proposed in the present study was found to agree well with the experimental results. The incorporation of the geometric and material nonlinearities into the formula makes the proposed solution superior to the previous lateral torsional buckling solutions for rectangular reinforced concrete beams.

Recent research has shown that a significant number of the falls from elevation occur when laborers are working on unfinished structures. Workers walking on wood I-joists on roofs and floors are prone to fall hazards. Wood I-joists have been replacing dimension lumber for many floor systems and a substantial number of roof systems in light-frame construction. Wood I-joists are designed to resist axial stresses on the flanges and shear stresses on the web while minimizing material used. However, wood I-joists have poor resistance to applied lateral and torsional loads and are susceptible to lateral-torsional buckling instability. Workers walking on unbraced or partially braced wood I-joists can induce axial and lateral forces as well as twist. Experimental testing demonstrated that workers cause lateral-torsional buckling instability in wood I-joists. However, no research was found related to the lateral-torsional buckling instability induced by individuals walking on the wood I-joists. Furthermore, no research was found considering the effects of the supported end conditions and partial bracing in the lateral-torsional buckling instability of wood I-joists. The goal of this research was to derive mathematical models to predict the dynamic lateral-torsional buckling instability of wood composite I-joists loaded by individuals walking considering different supported end conditions and bracing system configurations. The dynamic lateral-torsional buckling instability was analyzed by linearly combining the static lateral-torsional buckling instability with the lateral bending motion of the wood I-joists. Mathematical models were derived to calculate the static critical loads for the simply supported end condition and four wood I-joist hanger supported end conditions. Additionally, mathematical models were derived to calculate the dynamic maximum lateral displacements and positions of the individual walking on the wood I-joists for the same five different supported end conditions. Three different lean-on bracing systems were investigated, non-bracing, one-bracing, and two-bracing systems. Mathematical models were derived to calculate the amount of constraint due to the lean-on bracing system. The derived mathematical models were validated by comparison to data from testing for all supported end conditions and bracing systems The predicted critical loads using the static buckling theoretical models for the non-bracing system and the static buckling theoretical models combined with the bracing theoretical models for the simply and hanger supported end conditions agreed well with the critical loads obtained from testing for the two wood I-joist sizes investigated. The predicted maximum lateral displacements and individual positions using the bending motion theoretical models for the simply and hanger supported end conditions agreed well with the corresponding maximum lateral displacements and individual positions obtained from testing for both wood I-joist sizes. Results showed that; a) the supported end condition influenced the critical loads, maximum lateral displacements and individual positions, b) the bracing system increased the critical loads and reduced the maximum lateral displacements, c) the critical load increased as the load position displaced away from the wood I-joist mid-span, d) the critical load reduced as the initial lateral displacement of the wood I-joist increased and e) the wood I-joist mid-span was the critical point in the dynamic lateral-torsional buckling instability. / Ph. D.

This dissertation is concerned with a type of energy absorption device made of thin-walled tubes. The tubes will undergo plastic deformation when subjected to an impact loading, and therefore absorb kinetic energy. It has been found that, if the surface of a tube is pre-folded according to an origami pattern, the failure mode of the tube can be altered, leading to a noticeable increase in energy absorption while at the same time, reducing the force needed to initiate plastic deformation within the tube. The main work is presented in four parts. First of all, an experimental study of a type of previously reported thin-walled square tube with pre-manufactured pyramid patterns on the surface has been conducted. Quasi-static axial crushing tests show that the octagonal mode, although numerically proven to be efficient in terms of energy absorption, cannot be consistently triggered. Secondly, a new type of thin-walled tubular energy absorption device, known as the origami tube, which has origami pattern pre-fabricated on the surface, has been studied. A family of origami patterns has been designed for tubes with different profiles. The performances of a series of origami tubes with various configurations subjected to quasi-static axial crushing have been investigated numerically. It is found that a new failure mode, referred to as the complete diamond mode, can be triggered, and both over 50% increase in the mean crushing force and about 30% reduction in the peak force can be achieved in a single tube design in comparison with those of a conventional square tube with identical surface area and wall thickness. A theoretical study of the axial crushing of square origami tubes has been conducted and a mathematical formula has been derived to calculate the mean crushing force. Comparison between theoretical prediction and numerical results shows a good agreement. Quasi-static axial crushing experiments on several square origami tube samples have been carried out. The results show that the complete diamond mode is formed in the samples and both peak force reduction and mean crushing force increase are attained. Thirdly, a new type of curved thin-walled beam with pre-manufactured origami pattern on the surface, known as the origami beam, has been designed and analyzed. A numerical study of a series of origami beams with a variety of configurations subjected to quasi-static lateral bending has been conducted. The results show that two new failure modes, namely, the longitudinal folding mode and the mixed mode, can be induced, and both reduced peak force and increased energy absorption are achieved. Finally, a number of automobile frontal bumpers, which have the origami tube and the origami beam as key components, have been designed and analyzed. Three impact tests have been conducted on each bumper. The numerical results show that both types of origami structures can perform well in realistic loading scenarios, leading to improved energy absorption of the bumpers.

Increasing vehicle performance requirements and virtualization of its development process require more understanding of physical background of tire behavior, especially in transient rolling conditions with combined slip. The focus of this research is physical description of transient generation of tire lateral force and aligning torque. Using acceleration measurement on the tire inner liner it was observed that the contact patch shape of the rolling tire changes nonlinearly with slip angle and becomes asymmetric. Optical measurement outside and inside the tire has clarified that carcass lateral bending features both shear and rotation angle of its cross-sections. A physical simulation model was developed, which considers the observed effects. A special iterative computing algorithm was proposed. The model was qualitatively validated using not only tire force and torque responses, but also deformation of the tire carcass. The model-based analysis explained which tire structural parameters are responsible for which criteria of tire performance. Contact patch shape change had a low impact on lateral force and aligning torque. Variation of carcass bending behavior perceptibly influenced aligning torque generation. As an example, the gained understanding was applied for feasibility analysis of a novel method to estimate the utilized friction potential rate of a rolling tire.:1 Introduction 1.1 Thesis structure 1.2 Motivation 1.3 State of the art 1.4 Mission statement 1.5 Main terms and hypotheses 1.6 Summary of chapter 1 2 Experimental investigation of tire deformation 2.1 Introduction to experimental research 2.2 Test samples 2.3 Experimental equipment 2.4 Contact patch pressure distribution 2.5 Contact patch geometry of the rolling tire 2.6 Tire carcass deformation 2.7 Tread block properties 2.8 Summary of chapter 2 3 Simulation method of tire deformation behavior 3.1 Concept development 3.2 Physical representation of the model 3.3 Model computing method 3.4 Model parameterization routine 3.5 Model validation 3.6 Summary of chapter 3 4 Model-based analysis 4.1 Understanding of the physical background 4.2 An example of application 4.3 Summary of chapter 4 5 Investigation summary and discussion 5.1 Key results 5.2 Discussion, critique and outlook References List of abbreviations List of symbols List of tables List of figures Appendix