No description available.

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 12, 2008) Includes bibliographical references.

This study developed a reinforced steel rod bending machine for rods with diameters of up to 8 mm and annealed wire cutter for up to 5 kg for replacing manual intervention required to bend rods in reinforced concrete columns. This study aims to reduce the physical effort that could lead to occupational diseases, such as tenosynovitis, bursitis, muscle disorders. Clamp manufacturing possesses great risk for workers, who are exposed to injuries while using different cutting devices, such as grinders and electric saws. They also face potential problems such as muscular fatigue due to the nonergonomic and repetitive work positions. The proposed machine features a mechanical dragging and bending systems and manual shears. Additionally, the proposed machine has been designed theoretically and its effectiveness has been assessed through simulations conducted using the SolidWorks CAD software. A bending machine prototype for producing clamps is developed and its machine productivity is measured. Using this machine, approximately 300 clamps can be bent per hour without possessing any risk to the worker.

Alkali silica reaction (ASR) and delayed ettringite formation (DEF) are two causes of concrete deterioration. Both mechanisms cause expansion of concrete and thus extensive cracking. Most previous research on ASR and DEF focused on understanding the material science of the mechanisms. This dissertation adds to the smaller body of knowledge about ASR/DEF’s effect on the structural behavior of reinforced concrete columns. It compares the structural performance of ASR/DEF affected concrete columns to mechanically cracked columns, evaluates the relative performance of four different concrete repair methods for strengthening damaged columns, and describes how to model pre-existing cracks in the finite element program ATENA. Previous research on scaled columns used mechanically cracked concrete as an approximation of ASR/DEF cracking damage. These earlier column tests, by Kapitan, were compared to two columns affected by ASR/DEF. Due to a deficiency in original design of the actual columns modeled, all of these scaled column specimens failed in bearing during testing under biaxial bending. The ASR/DEF affected columns exhibited nearly identical performance (including bearing capacity) as Kapitan’s control specimen. Thus, with over one percent expansion due to ASR/DEF, there was no reduction in bearing capacity for these columns. Based on the bearing failure observed in these scaled column specimens, concrete repairs were designed to increase confinement of the column capital to address the bearing capacity deficiency. A series of bearing specimens was constructed, externally reinforced using four different strengthening schemes, and load tested. From this bearing specimen series, both an external post-tensioned repair and a concrete jacketing repair performed well beyond their designed capacities and are recommended for bearing zone confinement repair of similar ASR/DEF affected concrete columns. Further, this dissertation presents how Kapitan’s scaled column results were modeled using ATENA (a reinforced concrete finite element program). A technique for modeling the mechanical cracking was developed for ATENA. Once calibrated, a parametric study used the model to find that a 0.17-inch wide through-section crack in the scaled columnd (5/8 inches in the field) was the threshold that reduced capacity of the scaled column to the factored design load. / text

The need to satisfy aerospace industry's demand not met by traditional materials motivated researchers and scientists to look for new solutions. The answer was found in developing new material systems by combining together two or more constituents. Composites, also known as fiber reinforced polymers (FRP) consisting of a reinforcing phase (fibers) embedded into a matrix (polymer), offered several advantages with respect to conventional materials. High specific modulus and strength together with other beneficial properties, corrosion resistance and transparency to electrical and magnetic fields above all, made FRP also suitable for use as construction materials in structural engineering. In the early years of the twenty-first century, the publication by the American Concrete Institute (ACI) of design guidelines for the use of FRP as internal reinforcement and for external strengthening of concrete members accelerated their implementation for structural engineering applications. To date, FRP have gained full acceptance as advanced materials for construction and their use is poised to become as routine as the use of conventional structural materials such as masonry, wood, steel, and concrete. However, new concrete columns internally reinforced with FRP bars and FRP confinement for existing prismatic reinforced concrete (RC) columns have currently important unsolved issues, some of which are addressed in this dissertation defense. The dissertation is articulated on three studies. The first study (Study 1) focuses on RC columns internally reinforced with glass FRP (GFRP) bars; the second (Study 2) on RC prismatic columns externally confined by means of FRP laminates using glass and glass/basalt fibers; and the third (Study 3) is a theoretical attempt to interpret and capture the mechanics of the external FRP confinement of square RC columns. Study 1 describes an experimental campaign on full-scale GFRP RC columns under pure axial load undertaken using specimens with a 24 by 24 in. (0.61 by 0.61 m) square cross section. The study was conducted to investigate whether the compressive behavior of longitudinal GFRP bars impacts the column performance, and to understand the contribution of GFRP ties to the confinement of the concrete core, and to prevent instability of the longitudinal reinforcement. The results showed that the GFRP RC specimens behaved similarly to the steel RC counterpart, while the spacing of the ties strongly influenced the failure mode. Study 2 presents a pilot research that includes laboratory testing of full-scale square and rectangular RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated ACI 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects ultimate axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity. The discussion of the results includes a comparison with the values obtained using existing constitutive models. Study 3 proposes a new theoretical framework to interpret and capture the physics of the FRP confinement of square RC columns subjected to pure compressive loads. The geometrical, physical and mechanical parameters governing the problem are analyzed and discussed. A single-parameter methodology for predicting the axial stress - axial strain curve for FRP-confined square RC columns is described. Fundamentals, basic assumptions and limitations are discussed. A simple design example is also presented.

Slender structures are elegant aesthetically. The insufficiency in knowledge of the real resistance to buckling of very slender reinforced concrete columns leads to an exaggeration of the sizes of the columns. _The examples of concrete compression members cited and constructed in Industry on a global basis suggest that very slender columns have inherent safety both from the point of view of the ultimate strength and stability. The strengths of columns given. by the British codes would seem to be exceeded by many of the long slender reinforced concrete columns and struts which have been used Internationally. Both the theoretical and the experimental short term investigations have been carried out to establish the behaviour of hinged, very slender reinforced concrete columns at various stages'of axial loading. Forty three very slender reinforced concrete columns of two different square cross sections with two sizes of longitudinal reinforcements with lateral ties were cast. Slenderness rates, L A, were varied from 30 to 79. Special factors were obtained to relate the actual modulus of elasticity of concrete in columns at buckling failure to a knowledge of the initial modulus of elasticity of concrete in control cylinder specimens. Both theoretical and experimental graphs of load against moment, made dimensionless for critical sections of columns have been obtained. Dimensionless load-moment interaction diagrams using material failure as the criterion have been superimposed on these graphs to show considerable inherent material strength of the tested columns near buckling collapse failures. A theory using the fundamental approach has, been developed to predict the deflected shape and moments along the, heights of the columns at various stages of loading. The proposed theory predicts with good correlations the experimental deflections and moments of any loading stages of the columns. The theory has been used to obtain the required variables, to arrive at the initial predicted design loads of the investigated columns. Good correlations of the moments derived from observed strains have also been obtained. The developed theory predicts satisfactorily the buckling collapse loads of the columns. Although the theory has been derived for axially I loaded very slender reinforced concrete-columns, it seems to accept satisfactorily eccentricities of up to about 10 mm. This was confirmed after extensive comparisons of the theoretical buckling collapse loads with the applicable tests of other authors. Creep In the columns investigated was discovered to be one of the major factors for serious consideration. This was conclusively revealed from the observations on the last two very long term creep tests on columns. The actual safe sustained loads for these very slender columns of slenderness ratios, L/H, between 40 and 79 seem to be between 33% and 19% of the short term buckling collapse loads. The reduced modulus approach to predict the safe long term sustained loads seems to give reasonable values for L/H ratios of 40 and 50. The recommendations given for the proposed design of very slender reinforced concrete columns seem to be adequate and simple to use in practice. They are further simplified by the derivation of two equations for the reduction factors, R, for the slenderness ratios between 36 and 40 and between 40 and 79 respectively. The investigation has proved that very slender reinforced concrete columns are very dangerous structural members, as they tend to have violent buckling failures. Nevertheless, It must be prudent not to design against disaster at any cost. This Investigation seemed to have enhanced considerably knowledge of the design of very slender reinforced concrete columns.

Slender structures are elegant aesthetically. The insufficiency in knowledge of the real resistance to buckling of very slender reinforced concrete columns leads to an exaggeration of the sizes of the columns. _The examples of concrete compression members cited and constructed in Industry on a global basis suggest that very slender columns have inherent safety both from the point of view of the ultimate strength and stability. The strengths of columns given. by the British codes would seem to be exceeded by many of the long slender reinforced concrete columns and struts which have been used Internationally. Both the theoretical and the experimental short term investigations have been carried out to establish the behaviour of hinged, very slender reinforced concrete columns at various stages'of axial loading. Forty three very slender reinforced concrete columns of two different square cross sections with two sizes of longitudinal reinforcements with lateral ties were cast. Slenderness rates, L A, were varied from 30 to 79. Special factors were obtained to relate the actual modulus of elasticity of concrete in columns at buckling failure to a knowledge of the initial modulus of elasticity of concrete in control cylinder specimens. Both theoretical and experimental graphs of load against moment, made dimensionless for critical sections of columns have been obtained. Dimensionless load-moment interaction diagrams using material failure as the criterion have been superimposed on these graphs to show considerable inherent material strength of the tested columns near buckling collapse failures. A theory using the fundamental approach has, been developed to predict the deflected shape and moments along the, heights of the columns at various stages of loading. The proposed theory predicts with good correlations the experimental deflections and moments of any loading stages of the columns. The theory has been used to obtain the required variables, to arrive at the initial predicted design loads of the investigated columns. Good correlations of the moments derived from observed strains have also been obtained. The developed theory predicts satisfactorily the buckling collapse loads of the columns. Although the theory has been derived for axially I loaded very slender reinforced concrete-columns, it seems to accept satisfactorily eccentricities of up to about 10 mm. This was confirmed after extensive comparisons of the theoretical buckling collapse loads with the applicable tests of other authors. Creep In the columns investigated was discovered to be one of the major factors for serious consideration. This was conclusively revealed from the observations on the last two very long term creep tests on columns. The actual safe sustained loads for these very slender columns of slenderness ratios, L/H, between 40 and 79 seem to be between 33% and 19% of the short term buckling collapse loads. The reduced modulus approach to predict the safe long term sustained loads seems to give reasonable values for L/H ratios of 40 and 50. The recommendations given for the proposed design of very slender reinforced concrete columns seem to be adequate and simple to use in practice. They are further simplified by the derivation of two equations for the reduction factors, R, for the slenderness ratios between 36 and 40 and between 40 and 79 respectively. The investigation has proved that very slender reinforced concrete columns are very dangerous structural members, as they tend to have violent buckling failures. Nevertheless, It must be prudent not to design against disaster at any cost. This Investigation seemed to have enhanced considerably knowledge of the design of very slender reinforced concrete columns. / Scientific Research Council

[pt] Neste trabalho é feito o estudo da influência do cobrimento da armadura longitudinal e dos grampos suplementares na resistência de pilares de concreto submetidos à compressão excêntrica. Para este fim foram ensaiados pilares curtos, com armadura longitudinal contínua e pilares com emenda na armadura. Foi elaborado um modelo para o cálculo da distribuição da tensão normal e da tensão de aderência nas barras de emendas comprimidas que reproduziu bem o verificado experimentalmente. Mostra-se a importância da tensão de ponta na transmissão de forças na emenda. Se alerta sobre como a técnica normalmente empregada no reparo dos pilares onde as armaduras apresentam corrosão, que consiste na retirada parcial ou total do que restou do cobrimento para o tratamento e/ou substituição da armadura, e posterior reposição da camada de cobrimento, pode levar a ruptura do elemento por perda de aderência. Mostra-se como não colocar os grampos suplementares pode levar a perda da estabilidade do elemento. / [en] In this work, the influence of the longitudinal reinforcement cover and supplementary transversal reinforcement on the ultimate strength of the concrete columns under eccentric compression is studied. For this purpose, tests on short columns with continuum and lapped spliced bars were carried out. A theoretical model for the calculation of the stress and bond distributions on the splice length is proposed and tested with the experimental data of this work, showing a good agreement. The relevance of the end bearing effect on the transmission of the forces in the splice is shown. An alert again the usual technique used to repair the corroded bars inside the column, i.e., to remove partially or totally the remaining concrete cover to treat or substitute the damaged reinforcement bars, and lately to put back the concrete cover. This technique may provide the element failure by the lost of bond between the remaining concrete surface and reinforcement bars. It is shown how the absence of supplementary transversal reinforcement can lead to the instability of column.

Este trabalho tem o objetivo de transmitir aos Engenheiros de Estruturas o conhecimento teórico necessário para o dimensionamento e detalhamento de pilares usuais de edifícios em concreto armado. A definição das posições dos pilares em uma estrutura, bem como uma estimativa da seção transversal dos mesmos são abordadas neste trabalho. O estudo da estabilidade global, realizado no Capítulo 3, nos permite avaliar se os deslocamentos ocorridos na estrutura em função das ações horizontais e verticais, geram esforços de segunda ordem consideráveis ou não. A instabilidade de pilares será comentada no Capítulo 5, bem como os Métodos desenvolvidos para avaliar se um determinado pilar é estável ou instável. O detalhamento de pilares segundo as prescrições do Texto Base para a revisão da NBR - 6118/78, bem como o desenvolvimento de exemplos de dimensionamento de pilares estão contidos neste trabalho nos Capítulos 7 e 8, respectivamente. / The objective of this work is to transrnit to the structural engineers the necessary theoretical knowledge for the design and detail of usual columns in reinforced concrete buildings. The definition of the columns positions in the structure, as well as an estimate of their cross section will be explained in this work. The global stability study, described in chapter 3, allows us to evaluate whether the deformations ocurred in the structure due to horizontal and vertical actions, cause considerable second order strength or not. The columns instability will be commented in chapter 5, as well as the methods developed to evaluate whether a specific column is stable or instable. The columns detail as prescribed in the Basic Text for the Revision of NBR - 6118/78, and also the development of examples for columns design are in chapter 7 and 8, respectively.

Este trabalho tem o objetivo de transmitir aos Engenheiros de Estruturas o conhecimento teórico necessário para o dimensionamento e detalhamento de pilares usuais de edifícios em concreto armado. A definição das posições dos pilares em uma estrutura, bem como uma estimativa da seção transversal dos mesmos são abordadas neste trabalho. O estudo da estabilidade global, realizado no Capítulo 3, nos permite avaliar se os deslocamentos ocorridos na estrutura em função das ações horizontais e verticais, geram esforços de segunda ordem consideráveis ou não. A instabilidade de pilares será comentada no Capítulo 5, bem como os Métodos desenvolvidos para avaliar se um determinado pilar é estável ou instável. O detalhamento de pilares segundo as prescrições do Texto Base para a revisão da NBR - 6118/78, bem como o desenvolvimento de exemplos de dimensionamento de pilares estão contidos neste trabalho nos Capítulos 7 e 8, respectivamente. / The objective of this work is to transrnit to the structural engineers the necessary theoretical knowledge for the design and detail of usual columns in reinforced concrete buildings. The definition of the columns positions in the structure, as well as an estimate of their cross section will be explained in this work. The global stability study, described in chapter 3, allows us to evaluate whether the deformations ocurred in the structure due to horizontal and vertical actions, cause considerable second order strength or not. The columns instability will be commented in chapter 5, as well as the methods developed to evaluate whether a specific column is stable or instable. The columns detail as prescribed in the Basic Text for the Revision of NBR - 6118/78, and also the development of examples for columns design are in chapter 7 and 8, respectively.