Computational Modelling Strategies for Nonlinear Response Prediction of Corroded Circular RC Bridge Piers
A numerical model is presented that enables simulation of the nonlinear flexural response of corroded reinforced concrete (RC) components. The model employs a force-based nonlinear fibre beam-column element. A new phenomenological uniaxial material model for corroded reinforcing steel is used. This model accounts for the impact of corrosion on buckling strength, postbuckling behaviour, and low-cycle fatigue degradation of vertical reinforcement under cyclic loading. The basic material model is validated through comparison of simulated and observed responses for uncorroded RC columns. The model is used to explore the impact of corrosion on the inelastic response of corroded RC columns.
DETAILING FOR REINFORCEMENT STABILITY IN RC MEMBERS
Instability of reinforcement in adequately detailed reinforced concrete (RC) structural elements is a symptom of excessive deformation in compression, and it typically marks the limit of usable ductility of the member. Because the supply of ductility (deformability) is a measure of the effectiveness of the confining reinforcement, detailing necessary for reinforcement stability is intimately related to that required for confinement. Existing design models consider the two problems independently, and associate the initiation of bar buckling with the occurrence of a critical milestone of material behavior under compression. The resulting requirements for lateral support of the reinforcement do not correlate well with those obtained from studies for confinement and rarely control in cases of earthquake design. The objective of this paper is to develop alternative requirements for reinforcement stability that recognize the interaction between displacement ductility demand in the critical section, tie effectiveness, limiting concrete strain, bar size, and tie spacing. To quantify this relationship an extensive database consisting of over 300 column tests was compiled from international literature. Tests considered in the database were conducted under repeated axial and flexural load reversals, simulating earthquake effects on specimens with a variety of confining and longitudinal steel arrangements. The database was systematically analyzed to identify from experimental evidence the critical condition for reinforcement stability and its relationship to the limiting average compressive strain and/or ductility demand in the plastic hinge zone, and to the confinement geometry and effectiveness. Recognizing the interdependence between critical buckling conditions and confinement presents an opportunity to relate detailing requirements for the stability of reinforcement to detailing for ductility, and to distinguish between designs intended to satisfy different levels of deformation demand required for construction in various zones of seismic risk.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.