M.S.

Eight reinforced concrete beams with two different concrete strengths and four different schemes of reinforcing were tested to failure in pure torsion. SR⁻⁴ strain gages were used to measure the concrete strains at the surface of the test beams. A review of analytical and experimental studies in the literature is presented and briefly discussed. The test results were then compared with the theoretical predictions developed by Cowan, Ernst and Gesund. In general the failure surface of the test beams agreed with those previously predicted. The test ultimate torque varied considerably from the predicted ultimate torque of Cowan and Gesund. Ernst’s basic equation was modified to compensate for less than the minimum longitudinal reinforcement in four of the beams. With this modification Ernst’s theoretical predictions were very close to the test results. A study of the test results also shows that one of the presented theories is valid for one particular case, but that none of the theories is valid for every case. Consequently, there is a need for further research in this subject in order to develop a more exact theory for use in design. / Master of Science

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

The purpose of this study is to investigate the effects of tension stiffening and softening of concrete in reinforced concrete beams and beam-columns. Analytical models of beams and beam-columns are prepared and the results compared to experimental results previously conducted by Berwanger et al. (1960) A layered model of the beams is developed and strains and stresses at various layers are computed. Moment-curvature relationships are then obtained from these. The stress-strain curves adopted are from El-Metwally and Chen (1989). The effects of tension stiffening and softening are included by adopting realistic stress-strain curves in both compression and tension. / 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

Master of Science

Results are presented on tests of reinforced concrete T-beams with a flange 20 inches wide by two inches thick setting on a stem five inches deep and four inches wide. These beams were loaded at the quarter points of an eight-foot span and also at the end of cantilever sections of two feet. The beams were loaded until they collapsed. The reinforcing steel was varied at the support section, but remained constant at the center. Moment-curvature information is developed from the experimental results, and conclusions are drawn concerning present theory for deriving analytical moment-curvature relationships for reinforced concrete sections. Ultimate concrete strain in confined sections is reviewed in light of the experimental results. Discussed also are current theories for calculating ultimate loads for indeterminate reinforced concrete beams. / M.S.

The use of fiber reinforced plastics (FRP) in repairing and strengthening bridges has been researched in recent years. In particular, attaching unidirectional FRP to the tension face of reinforced concrete beams has provided an increase in stiffness and load capacity of the structure. However, due to the brittle nature of the unidirectional FRP, the ductility of the beam decreases. One possible solution to this problem is the use of cross-ply or off-axis FRP laminates. This thesis focuses on the investigation of the flexural behavior of reinforced concrete beams strengthened with one of two different FRP orientations (0°/90° and ±45°). More particularly, the change in strength and ductility of the beams as the number of FRP layers are altered is investigated. Seven under-reinforced concrete beams were constructed and tested to failure. With the exception of the control beam, each specimen was applied with two, three, or four layers of either 0°/90° and ±45° FRP orientations. To predict the flexural behavior of the specimens, a theoretical model was derived using basic concepts, past research, and the tested properties of the concrete, steel reinforcement, and FRP. Also, two methods were used to analyze the ductility of the tested beams. Along with the test details of each specimen; the moment, deflection, CFRP strain, crack patterns, and mode of failure are discussed. The results included an increase in load capacity with respect for the number of CFRP layers applied for both orientations. Also, the ductility of the beams were reduced by adding CFRP orientations. / Master of Science

No description available.

Submitted in fulfillment for the Master of Engineering, Department of Civil Engineering and Surveying, Durban University of Technology. Durban. South Africa, 2015. / Beam and block slab systems have become a preferred suspended flooring technology in South Africa. Their structural efficiency and relatively low cost makes them suitable for low to medium cost developments. Like all other structural components, they are required to demonstrate sound structural integrity. Concerns were raised by some manufacturers and users in Durban (South Africa) about (a) the lack of basic technical information which makes it difficult to identify methods of improving efficiency and effectiveness of these flooring systems in general, (b) the efficiency and effectiveness of concrete masonry rebated filler blocks - with respect to the load carrying capacity and protecting the structural topping from fire, (c) what constitutes acceptable quality of a deliberately roughened precast concrete surface, (d) interfacial tensile bond strength of special connections and (e) an alternative rib that can span 5 metres without temporary props. These issues were investigated by the student. Thus, this project aimed at improving the structural efficiency and effectiveness in designing, manufacturing and constructing beam and block slab systems was undertaken in Durban, South Africa, between 2012 and 2013. Pilot studies (involving questionnaires), interviews with manufacturers, site visits, and testing of non-structural and structural components were also undertaken. The first aim (in order to address concern (a)) was to provide users of beam and block slab systems with basic technical information about the possible ways to improve efficiency and effectiveness in the design, manufacturing and construction of beam and block slab systems by undertaking an exploratory (pilot) study to better understand users of these systems concerns. The second aim (to address concern (b)) was to investigate, by conducting a series of strength to weight ratio tests, how efficient or inefficient these filler blocks are, examine the structural integrity with respect to the integrity of the manufacturing methodologies and the product thereof, and formulate a method to quantify the fire-resistivity of concrete masonry rebated filler blocks to the structural topping with respect to confining fire. The third aim (to address concern (c)) was to determine what constituted acceptable quality of a deliberately roughened precast concrete surface through a literature review and by conducting a survey to learn about the construction methodologies used by manufacturers. Site visits were undertaken to validate information given by the contractors. The fourth aim (to address concern (d)) was to determine interfacial tensile bond strength through physical testing of deliberately roughened concrete ribs which are sometimes used in special connections. The fifth aim (to address the last concern (e)) was to make an assessment by undertaking a basic comparison study between one local beam and block slab system that uses a shallow rectangular precast pretensioned rib to beam and block slab systems used in the United Kingdom and propose an ideal section (precast pretensioned rib) that spans up to 5 metres without temporary props. With respect to the first aim, it was found that the lack of technical knowledge, including access to critical information about the design philosophy, manufacturing and construction standards of these flooring systems leads to reluctance in selecting them. The outcome of the second aim is that all concrete masonry rebated filler blocks tested were found to be effective because they supported more than the required construction load but some were shown to be inefficient as more materials, such as binders, are wasted in producing over-strength filler blocks and also, undertaking trial mix designs and the testing of samples prior to batch production will reduce costs. A method is formulated in the thesis that could also show that concrete masonry rebated filler blocks provide significant protection to the structural topping thereby preventing fire progression. With respect to the third aim, although a broom or brush is effective in providing a surface roughness (Rz) of 3 mm, it is not always efficient when considering factors like the variation in uniformity, appearance of laitance and roughening frequency, which are not addressed by the South African codes. The outcome of the fourth aim is that connections should be designed such that they do not rely purely on the tensile bond strength but through reinforcing bars (or ties) taking the full tension load causing delamination. With respect to the fifth aim, a basic comparison study indicates that T-section beams are more efficient than common rectangular ribs (±150 mm wide x ±60 mm deep) since they can eliminate completely the use of temporary props for spans of up to 4.51 m. Consequently, further research is underway to design an inverted T-section rib by using high strength precast pretensioned concrete that can span up to 5 m without using temporary props.