The present approach to the design of prestressed beams is antiquated and time consuming. Neither SLS or ULS requirements are satisfied directly. There is a need for a new approach using plastic principles to design the prestressing requirements at ULS considering a whole span at a time, with checks made for SLS requirements afterwards. For a plastic design, the designer would need to know the limits of the bending moment redistribution for the beam under consideration. An equation is therefore necessary to assist the designer in this regard. Such an equation should take into account the cross-section shape of the beam and the prestress to reinforcing steel ratios. Many examples would have to be investigated using a rigorous plastic analysis to formulate such an equation. A computer program has been written as part of this thesis to perform such a rigorous analysis. It's accuracy has been evaluated by comparison with laboratory test beam results. The comparison was favourable, although more results would have to be compared to establish the accuracy that could be expected. A few examples were investigated and the observations noted. Two extreme cases were examined, those of a T-beam and I-beam. The redistribution of bending moments was similar in both cases, but the percentage of the central moment capacity reached was considerably less for the T-beam. For both beams it was impossible to reach the ultimate capacity at the centre before the strain capacity at the supports was exhausted. It was concluded that a plastic design procedure should be introduced, based on the ULS capacity of a span at a time. SLS requirements could then be checked afterwards. This approach would provide a design procedure corresponding to those used for other forms of modern structural design and would be much quicker, safer, more accurate and less costly that the existing design procedures.

published_or_final_version / abstract / toc / Civil Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Civil Engineering / Doctoral / Doctor of Philosophy

There are two basic methods used to analyze and design reinforced concrete members for shear, the American Concrete Institute Code method (used in the United States) and the truss model method (used in different European Codes and in the Canadian Codes). The ACI Code method is a semi-empirical solution since it builds on fitting actual test results to the analytical mechanism method. Although it will lead to safe results, the ACI method lacks a physical model to represent the actual forces in the beam. For this reason, attention is increasingly being given to develop a mechanical-mathematical model to show the actual behavior of the beam failing in shear. The truss model theory provides a more promising way to treat shear since it can model the structural action in the beam. It was first proposed by Ritter and Marsh at the turn of the twentieth century. The concept has been extended by recent work of Lampert and Thürlimann (1971), Collins and Mitchell (1980), MacGregor (1988), and others. The purpose of this study is to compare the ACI method and the truss model method for the design of reinforced concrete slender and deep beams. The results of this study suggest that the truss model is better suited for the design of deep reinforced concrete beams because it models the dominant mechanism that happens in the beam which is the force transfer from load to reaction by the direct compression struts. For slender reinforced concrete beams, either method is suitable for design. / Master of Science

This thesis presents an investigation and derivation of the expression: fer bending moment, torsional moment, and shear at the ends and at any intermediate point along a circularly curved beam. The investigation includes both cantilever beams and fixed ends beams, loaded with a uniformly distributed load, concentrated loads or a combination of the two. The solutions of the equations have been presented in a graphical form for the case of the uniformly distributed load, and a tabulated form representing the ordinate of the influence lines for the case of the concentrated loads. The graphs and tables cover a series of beams whose arcs are subtending central angles of 50, 45, 60, 75, 90, 120, 135, 150, 165 and 180 degrees and whose stiffness ratio: (K) are 1.33, 2, 4, and 10.67. Special emphasis has been given to reinforced concrete curved beam design as based on the theories and experiments presented in the literature by Timoshenko and Gowan. The investigation shows that many questions still remain to be answered in the design of reinforced concrete beams subjected to bending moment, torsional moment and shear; and there is a need for the ACI Code to give some criteria for such designs in the near future. / Master of Science

Call number: LD2668 .T4 1985 T33 / Master of Science

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

The level of safety associated with the ACI Standard 318-83 design criteria for torsional reinforced concrete members is evaluated. Advanced first-order, second-moment reliability analysis is used to compute the reliability index. Reinforced concrete beams, subjected to both equilibrium and compatibility torsion, are analyzed. The uncertainties associated with the various torsion design parameters are included in the reliability-based formulation. For beams designed to carry equilibrium torsion, reliability indices ranging from 3.10 to 3.65 are obtained. The reliability indices for the compatibility torsion designs, analyzed in this study, vary from 1.88 to 2.09. For a given beam section, the reliability index is found to decrease with an increase in beam reinforcement. When the live load is reduced for members having a load influence area greater than 400 ft 2, the reliability index is found to increase with increase in basic live load to nominal dead load ratio. / M.S.