Thesis (M.S.)--Rochester Institute of Technology, 2007. / Typescript. Includes bibliographical references (leaves 67-68).

A study has been made of glass fibre reinforced plastic beams in three-point bending. In recent years, the importance of flexural loading in composites has manifested itself in the form of composite leaf springs, helicopter rotors, and other applications. This study is directed at the initiation, growth, characterization and measurement of damage in unidirectional and cross-ply composite beams. Beams were tested in three-point static and cyclic bending. Following damage initiation, either by a machined notch or by repeated cycling, damage growth has been characterized by two damage parameters: a damage depth encompassing a number of broken fibres on the tensile surface at the central load point, and a damage length or delamination parallel to the beam longitudinal axis. A model was developed to predict the compliance, or deflection under applied load, as a function of beam properties and damage dimensions. The model is able to predict the compliance of damaged beams with reasonable accuracy. From fracture mechanics concepts it is shown that the two damage dimensions, depth and length, are related. It is concluded that the increase in compliance, a result of the growing damage dimensions, is related to the growth of the damage depth; the damage length follows from the relation between damage parameters and the compliance follows from the compliance model. The damage state can thus be determined by compliance measurements if the relevant material properties and loading conditions are known. However, in service, compliance measurements may not be practical. Therefore a section of this study is devoted to an alternative damage measurement technique, namely acoustic emission monitoring. Damage initiation, compliance, damage length and damage depth were measured with AE monitoring techniques. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / Ph.D.

When a structural element is acted upon by axial compressive force simultaneously with bending, the design must consider the effect of combined bending and compression. Hence, the structure should be designed with the consideration of bending moment in order to provide the enough design strength to the member. The main objective of this thesis is to compare the effect of interaction of flexural moment and axial compressive force on the regular column of the steel moment frame with the same column when cantilever section is introduced into the frame as the loading is kept constant in all three cases. In this work, STAAD is used to determine the required variables such as axial forces, bending moments and deformations in all the cases, and those values are used in approximate second order analysis for the further analysis of special steel moment frame. The calculated values are then plugged into the design interaction equation for combined flexure and compression as given by AISC Steel Construction Manual (2011) to check the criticality of the moment frame. The result of the analysis indicates that the regular frame model has higher demand of capacity ratio in design of columns than the one with cantilever projection.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 66-68). Also available in print.

The stress-strain characteristics of concrete developed in flexure is very important for flexural strength design of reinforced concrete (RC) members. In current RC design codes, the stress-strain curve of concrete developed in flexure is obtained by scaling down the uni-axial stress-strain curve to account for the strain gradient effect. Therefore, the maximum concrete stress that can be developed under flexure is smaller than its uni-axial strength, and the use of which always underestimates the flexural strength of RC beams and columns even though the safety factors for materials are taken as unity. Furthermore, the value of strength underestimation was different for RC beams and columns, which indicates that the extent of strain gradient will affect the maximum concrete stress and stress-strain curve developed under flexure. To investigate the maximum concrete stress, 29 column specimens were fabricated and tested in this study. They were divided into 9 groups, each of which was poured from the same batch of concrete and contained specimens with identical cross-section properties. In each group, one specimen was tested under concentric load while the rest was/were subjected to eccentric or horizontal load. To study the strain gradient effects, the ratio of the maximum concrete compressive stress developed in the eccentrically/horizontally loaded specimens to the maximum uni-axial compressive stress developed in the counterpart concentrically loaded specimens, denoted by k3, is determined based on axial force and moment equilibriums. Subsequently, the concrete stress block parameters and the equivalent rectangular concrete stress block parameters are determined. It is found that the ratios of the maximum and equivalent concrete stress to uni-axial cylinder strength, denoted respectively by k3 and , depend significantly on strain gradient, while that of the depth of stress block to neutral axis depth, denoted by , remains relatively constant with strain gradient. Design equations are proposed to relate and  with strain gradient for strength calculation, whose applicability is verified by comparing the strengths of RC beams and columns tested by various researchers with their theoretical strengths predicted by the proposed parameters and those evaluated based on provisions of RC codes. Based on the test results, the stress-strain curve of normal-strength concrete (NSC) developed under strain gradient is derived using least-square method by minimising the errors between the theoretical axial load and moment and the respective measured values. Two formulas are developed to derive the flexural stress-strain curve, whose applicability is verified by comparing the predicted strength with those measured by other researchers. Lastly, the application of the proposed stress-block parameters and stress-strain curve of NSC will be illustrated by developing some charts for flexural strength design of NSC beams and columns. The application will further be extended to develop strength-ductility charts for NSC beams and columns, which enable simultaneous design of strength and ductility. By adopting the proposed design charts, the flexural strength design, as well as that of the plastic hinge forming mechanism during extreme events, will be more accurate. The resulting design will be safer, more environmentally friendly and cost effective. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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Ultra-high performance concrete (UHPC) is a new type of concrete developed by selecting the particle sizes and gradation in the nano- and micro-scales targeting the highest possible packing. The resulting concrete with very high density is called UHPC. UHPC has very low permeability and hence it is very highly durable compared to traditional or high performance concrete (HPC). Micro reinforcement of UHPC by random distributed steel-synthetic fibers results in superior mechanical properties such as very high compressive and tensile strengths, high ductility, and high fatigue resistance. The material selection and early age curing processes, use of fiber reinforcement, and very high quality in production resulted in a very high initial cost of UHPC structures. In order to enable the mass production and cost effective use of the material, performance based design and optimization of UHPC structural members are required. This study is part of an NRC Canada research project to develop innovative, cost effective, and sustainable bridge structural systems using UHPC and other innovative materials. In this study, the estimation of shear and flexural capacities using the available approaches of international design guidelines of UHPC structures are comprehensively compared to a proposed truss models, linear and nonlinear finite element models. Several design trials intended to allow for an optimized use of the materials and a maximum load capacity was conducted for simply supported beams with one or two external loads, and having rectangular or I cross sections. Linear and non-linear finite element models are developed and their results were compared to the available international design recommendations. Truss models are proposed to simplify the stress analysis in the shear zone of the prestressed UHPC beams. It is found that prestressed UHPC I-beam section gives the highest possible load capacity with minimum use of materials. The study shows that for the case of no stirrups, massive flexure and shear cracks initiate and propagate suddenly where a diagonal shear crack is fully developed and sudden collapse may expected. The proposed truss model gives very good match to nonlinear finite element analysis results for almost all the truss members. The results are significantly improved when additional struts are considered for both cases of beams with or without shear reinforcement. The study shows the importance of future experimental investigatinons to calibrate the proposed models.