Confinement of normal and high-strength concrete columns.

A comprehensive research project was conducted to investigate the behaviour and design of earthquake resistant normal-strength and high-strength concrete columns. The project included three essential components; testing of full size columns, development of an analytical model, and development of a design procedure. The experimental program consisted of material research and structural testing. The first phase was designed to study mechanical properties of high-strength concrete, which involved testing of a large number of concrete cylinders. The second phase was designed to investigate performance of confined normal and high-strength concrete columns under concentric compression. The experimental program included tests of 46 full size square and circular columns, with concrete strength ranging between 60 MPa and 124 MPa. The parameters considered included; cross-sectional shape (circular and square), volumetric ratio and spacing of transverse reinforcement, distribution of longitudinal reinforcement and resulting tie arrangement, yield strength of transverse reinforcement, concrete compressive strength, influence of longitudinal reinforcement in circular columns, and type of circular reinforcement (continuous spiral and circular hoops). The analytical component of the research program involved development of a mathematical model to represent stress-strain relationship of confined concrete. This was done in two steps. The first step included formulation of the relationship for normal strength concrete, for which extensive test data was available. The second step involved modification of the model for high-strength concrete. An extensive literature survey was first conducted, followed by evaluation of previous test data. This information was used, along with the results of the experimental phase of this investigation to develop a generalized cofinement model for normal-strength and high-strength concrete columns. The analytical and experimental research was used in developing a design procedure for confinement of earthquake resistant concrete columns. The procedure includes all the relevant parameters of confinement that have been observed to be important in column tests, and relates the design variables to deformation capacities. A displacement based design methodology was developed, where the lateral drift demand is a design parameter. This approach leads to different confinement steel requirements for columns with different deformability demands, an approach currently lacking in practice. Furthermore, the reinforcement arrangement is recognized as a design parameter, allowing lower volumetric ratio of confinement reinforcement for efficient arrangements. This may result in significant savings in steel, eliminating the common problem of steel congestion in earthquake resistant columns. (Abstract shortened by UMI.