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Capacity Design and Fatigue Analysis of Confined Concrete Columns
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1998-07-14
[PDF-4.13 MB]
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TRIS Online Accession Number:1111142
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Abstract:The capacity design philosophy requires the identification of all potential failure mechanisms. A preferred failure mechanism is chosen and efforts are made, through design detailing, to suppress all other undesirable failure modes. For the seismic design of bridges, the preferred failure mechanism is ductile flexural hinging of the reinforced concrete columns in the substructure. The undesirable failure modes that must be suppressed by design are three: concrete failure due to lack of confinement; buckling of the longitudinal reinforcement; and shear failures both within and outside the plastic hinge zone. The principal subject of this report is an in-depth examination of these three primary failure modes and establishing a theoretical basis for suppressing their occurrence. First, based on energy balance requirements, the required amount of transverse confinement reinforcement to inhibit hoop fracture resulting from reversed cyclic (low cycle fatigue) loading is derived. Secondly, the required amount of transverse reinforcement to inhibit buckling of the longitudinal compression reinforcement is considered a new approach to the inelastic buckling problem based on plastic analysis is presented. The theory distinguishes between local buckling (between two levels of hoops) and global buckling (that occurs over several levels of hoops or spirals). This approach to bar stability analysis is validated against experimental results. The third undesirable failure mode that needs to be suppressed concerns shear resistance. Shear failures can occur both within and without the potential plastic hinge zone. Moreover, the level of shear resistance to be provided must be based on the maximum flexural overstrength demand. Therefore, following a review of present state-of-the-art and state-of-the-practice recommendations, a new rational method of shear resistance is proposed. This method independently considers the three principal components of shear resistance: steel truss action (Vs); concrete arch or strut action (VP); and concrete tension field action (Ve). The basis of apportioning each component of resistance is through a principal crack angle ( 8), which is derived from energy considerations. Finally, design recommendations are presented in the form of simple equations that require the determination of a volumetric ratio of transverse reinforcement ( p 0 ) based on three main parameters: longitudinal steel volume (pt), axial load intensity (PeffcAg) and the shear span aspect ratio ( M /VD).
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