Reinforced concrete columns are essential elements that are responsible for overall strength and stability of structures. Loss of a column within a frame can cause progressive collapse. While some research has been conducted on blast performance of reinforced columns, primarily under far-field explosions, very limited work exists on the effects of close-in explosions. Dynamic response of concrete columns, in multi storey building, was investigated under close-in blast loads numerically, using FEM software LS-DYNA. A six-storey reinforced concrete building was selected for this purpose. Different standoff distance/charge mass combinations were used to investigate the failure modes of external building columns. Three different charge masses were used; i) backpack bomb having 22.67 kg (50 lbs) of TNT, ii) compact sedan car bomb with 227 kg (500 lbs) of TNT and iii) sedan car bomb with 454 kg (1000 lbs) of TNT. The explosives were placed at different distances relatively close to the structure, triggering different failure modes. Effects of transverse reinforcement and column location (edge versus corner column) were studied under different combinations of charge weight and standoff distance. Column response under dynamic blast load was identified as either local or global. The results show that the failure mode with backpack bombs located at small standoff distance is either local breaching or concrete scabbing. Direct shear failure occurred at column supports when higher charge masses were detonated at close distances. As the standoff distance increased the response changed from breaching or direct shear to diagonal tension and flexure. The column transverse reinforcement played a major role in controlling diagonal shear cracks and promoting flexural response. Hence, the amount and spacing of transverse reinforcement were observed to be important design parameters.

Thesis (M.E.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

The behavior of concrete members reinforced with fiber reinforced polymer (FRP) bars has been the focus of many studies in recent years. Nowadays, several codes and design guidelines are available for the design of concrete structures reinforced with FRP bars under flexural and shear loads. Meanwhile, limited research work has been conducted to examine the axial behavior of reinforced concrete (RC) columns with FRP bars. Due to a lack of research investigating the axial behavior of FRP reinforced concrete columns, North American codes and design guidelines do not recommend using FRP bars as longitudinal reinforcement in columns to resist compressive stresses. This dissertation aims at evaluating the axial performance of RC compression members reinforced with glass FRP (GFRP) and carbon FRP (CFRP) bars and stirrups through experimental and analytical investigations. A total of twenty seven full scale circular RC specimens were fabricated and tested experimentally under concentric axial load. The 300 mm diameter columns were designed according to CAN/CSA S806-12 code requirements. The specimens were divided to three series; series I contains three reference columns; one plain concrete and 2 specimens reinforced with steel reinforcement. Series II contains 12 specimens internally reinforced with GFRP longitudinal bars and transverse GFRP stirrups, while series III includes specimens totally reinforced with CFRP reinforcement. The experimental tests were performed at the structural laboratory, Faculty of Engineering, University of Sherbrooke. The main objective of testing these specimens is to investigate the behavior of circular concrete columns reinforced with GFRP or CFRP longitudinal bars and transverse hoops or spirals reinforcement. Several parameters have been studied; type of reinforcement, longitudinal reinforcement ratio, the volumetric ratios, diameters, and spacing of spiral reinforcement, confinement configuration (spirals versus hoops), and lap length of hoops. The test results of the tested columns were presented and discussed in terms of axial load capacity, mode of failure, concrete, longitudinal, and transverse strains, ductility, load/stress-strain response, and concrete confinement strength through four journal papers presented in this dissertation. Based on the findings of experimental investigation, the GFRP and CFRP RC columns behaved similar to the columns reinforced with steel. It was found that, FRP bars were effective in resisting compression until after crushing of concrete, and contributed on average 8% and 13% of column capacity for GFRP and CFRP RC specimens, respectively. Also, the use of GFRP and CFRP spirals or hoops according to the provisions of CSA S806-12 yielded sufficient restraint against the buckling of the longitudinal FRP bars and provided good confinement of the concrete core in the post-peak stages. The axial deformability (ductility) and confinement efficiency can be better improved by using small FRP spirals with closer spacing rather than larger diameters with greater spacing. It was found that, ignoring the contribution of FRP longitudinal bars in the CAN/CSA S806-12 design equation underestimated the maximum capacity of the tested specimens. Based on this finding, the design equation is modified to accurately predict the ultimate load capacities of FRP RC columns. New factors ?[indice inférieur g] and ?[indice inférieur c] were introduced in the modified equation to account for the GFRP and CFRP bars compressive strength properties as a function in their ultimate tensile strength. On the other hand, proposed equations and confinement model were presented to predict the axial stress-strain behavior of FRP RC columns confined by FRP spirals or hoops. The model takes into account the effect of many parameters such as; type of reinforcement, longitudinal reinforcement ratio; transverse reinforcement configuration; and the volumetric ratio. The proposed model can be used to evaluate the confining pressure, confined concrete core stress, corresponding concrete strain, and stress-strain relationship. The results of analysis using the proposed confinement model were compared with experimental database of twenty four full-scale circular FRP RC columns. A good agreement has been obtained between the analytical and experimental results. Proposed equations to predict both strength and stress-strain behavior of confined columns by FRP reinforcements demonstrate good correlation with test data obtained from full-scale specimens.

No description available.

Concrete filled steel tubular (CFST) columns are widely used in building and infrastructure projects throughout the world.Compared with other form of construction CFST columns offer superior structural performance and speed and ease of construction.Design procedures and recommendations provided in most of the design codes are often tedious and complex. There have been attempts to simplify the design procedure by providing a simplified expression to predict the capacity of a CFST under a general loading condition.In this thesis a rigorous analysis procedure was presented for the analysis of CFST beam-columns under general loading conditions.All the analytical results were verified by comparisons with the available test results and current ACI, AISC AND Eurocode 4 design codes. The comparisons demonstrated that the proposed numerical equations are accurate, and slightly conservative. Based on the numerical analysis, a simple and easy to follow calculation procedure was proposed for design of CFST columns under either uniaxial or biaxial bending moment and axial load. / Doctor of Philosophy (PhD)

This thesis is concerned with the effects of lateral confining reinforcement on the ductile behaviour of reinforced concrete columns. The contents of the chapters are summarized as follows. In Chapter one, the general problems in seismic design are discussed and earthquake design methods based on the ductile design approach are described. Japanese, New Zealand and United States design codes are compared. Finally, the scope of this research project is outlined. In Chapter two, after reviewing previous research on confined concrete, the factors which affect the effectiveness of lateral confinement are discussed. Especially the effects of the yield strength of transverse reinforcement, the compressive strength of plain concrete and the strain gradient in the column section due to bending are discussed based on tests which were conducted by the author et al at Kyoto University and Akashi Technological College, Japan. In the axial compression tests on spirally reinforced concrete cylinders (150 mm in diameter by 300 mm in height), the yield strength of transverse reinforcement and the compressive strength of plain concrete were varied from 161 MPa to 1352 MPa and from 17 MPa to 60 MPa, respectively, as experimental parameters. It is found that, when high strength spirals are used as confining reinforcement, the strength and ductility of the confined core concrete are remarkably enhanced but need to be estimated assuming several failure modes which could occur. These are based on the observations that concrete cylinders with high strength spirals suddenly failed at a concrete compressive strain of 2 to 3.5 % due to explosive crushing of the core concrete between the spiral bars or due to bearing failure of the core concrete immediately beneath the spiral bars, while the concrete cylinders with ordinary strength spirals failed in a gentle manner normally observed. In addition, eccentric loading tests were conducted on concrete columns with 200 mm square section confined by square spirals. It is found that the effectiveness of confining reinforcement is reduced by the presence of the strain gradient along the transverse section of column. In Chapter three, the effectiveness of transverse reinforcement with various types of anchorage details which simplify the fabrication of reinforcing cages are investigated. Eight reinforced concrete columns, with either 400 mm or 550 mm square cross sections, were tested subjected to axial compression loading and cyclic lateral loading which simulated a severe earthquake. The transverse reinforcement consisted of arrangements of square perimeter hoops with 135° end hooks, cross ties with 90° and 135° or 180° end hooks, and 'U' and 'J' shaped cross ties and perimeter hoops with tension splices. Conclusions are reached with regard to the effectiveness of the tested anchorage details in the plastic hinge regions of columns designed for earthquake resistance. In Chapter four, the effectiveness of interlocking spirals as transverse reinforcement is studied. Firstly, the general aspects and the related problems of interlocking spirals to provide adequate ductility in the potential plastic hinge region of columns are discussed, referring to the provisions in the New Zealand code,the CALTRANS (California Transportation Authority) code and other related codes. Secondly, based on those discussions, a design method to securely interlock the spirals is proposed. Thirdly, the effectiveness of interlocking spirals is assessed based on column tests conducted as part of this study. Three columns with interlocking spirals and, for comparison, one rectangular column with rectangular hoopsandcross ties, were tested under cyclic horizontal loading which simulated a severe earthquake. The sections of those columns were 400 mm by 600 mm. In Chapter five, analytical models to investigate the buckling behaviour of longitudinal reinforcement restrained by cross ties with 90° and 135° end hooks and by peripheral hoops are proposed. The analyzed results using the proposed models compare well with the experimental observations described in Chapter three. Using those proposed models, a method to check the effectiveness of cross ties with 90° and 135° end hooks is proposed for practical design purposes. In Chapter six, a theory for the prediction of the ultimate longitudinal compressive concrete strain at the stage of first hoop fracture referred to as the "Energy Balance Theory", which has been developed by Mander, Priestley and Park at University of Canterbury, is introduced. After discussing the problems in the "Energy Balance Theory", a modified theory for the prediction of the ultimate longitudinal compressive concrete strain at the stage of first hoop fracture is proposed. The predictions from the modified theory are found to compare well with previous experimental results.

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.

Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002. / "June 2002" Includes bibliographical references (leaves 349-374).

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 334-340).

Recent attacks and accidental explosions have demonstrated the necessity of ensuring the blast resistance of critical buildings and infrastructure in Canada such as federal and provincial offices, military buildings and embassies. Of particular importance is the blast resistance of ground-story columns in buildings which must be properly detailed to provide the necessary strength and ductility to prevent progressive collapse. There exists a need to explore the use of innovative materials that can simultaneously improve the performance of such columns, while also allowing for a relaxation of required detailing to ease construction. Advancements in concrete material science have led to the development of ultra-high performance fiber reinforced concretes (UHPFRC) which show superior mechanical properties when compared to conventional concrete, such as increased compressive strength, tensile resistance and toughness. These enhanced properties make UHPFRC an attractive material for use in the blast design of reinforced concrete columns. This thesis presents the results of a research program examining the performance of UHPFRC columns under simulated blast loads. As part of the experimental program twelve half-scale UHPFRC specimens, six built with regular grade steel reinforcement and six built with steel high-strength steel reinforcement, are tested under blast loading using the University of Ottawa shock tube. The specimens were designed according to CSA A23.3 standard requirements for both seismic and non-seismic regions, using various fibre types, fibre amounts and longitudinal reinforcement ratios, allowing for an investigation of various design parameters on blast behaviour. The results demonstrate that the use of UHPFRC improves the blast performance of columns by reducing displacements, increasing resistance and enhancing damage tolerance. The results also indicate that fiber content, fiber properties, seismic detailing, longitudinal reinforcement ratio and longitudinal reinforcement strength are factors which can affect the behaviour and failure mode of UHPFRC columns. As part of the analytical study the response of the UHPFRC columns is predicted using dynamic inelastic analysis. The dynamic responses of the columns are predicted by generating dynamic load-deformation resistance functions for UHPFRC and conducting single-degree-of-freedom (SDOF) analysis using software RC-Blast.