Shear-critical reinforced concrete structures such as older columns with insufficient transverse reinforcement details or short columns are found to be vulnerable to earthquake loading. Meanwhile, in the aggressive environment, RC structures tend to be more vulnerable to earthquake since corrosion of reinforcements will cause deterioration of the material properties. In the present study, a new framework is proposed for seismic fragility analysis of shear-critical structures with the consideration of corrosion effects. A new model for corroded concrete columns is proposed which can account for shear performance deterioration due to corrosion and the seismic flexure-shear interaction (FSI) behaviors. The modified Ibarra-Medina-Krawinkler deterioration model is adopted to simulate the shear response in order to capture shear strength and stiffness deterioration as well as pinching behavior of corroded shear-critical columns. The deteriorating material properties are determined based on corrosion modeling methods, and the corrosion level differences between transverse and longitudinal reinforcement are addressed. Furthermore, the proposed framework adopts time-variant structural capacities as obtained from the proposed numerical model in the fragility analysis. The developed framework is demonstrated with a shear-critical bridge column. The results clearly indicate the adverse effects of corrosion on seismic fragility of shear-critical columns, especially at severer damage states. Using flexure model and time-invariant capacity index will underestimate seismic fragility compared with the results obtained using the proposed method.
An analytical model, verified by the finite element method, is developed to study the effect of confining pressure on stress intensity factors for the cracked Brazilian disk. The closed-form expressions for stress intensity factors under both confining pressure and diametric forces are obtained based on the weight function method. The results show that the confining pressure has no effect on the mode II stress intensity factor; however, the mode I stress intensity factor decreases with the increase of confining pressure and the change may be above 100% for a large confining pressure. In addition, the effect of confining pressure on the loading condition of pure mode II crack is also investigated. It is shown that the critical loading angle for pure mode II crack decreases as the confining pressure increases. Depending on the magnitude of confining pressure, the failure problem of a disk may be no longer a pure fracture problem. These results have established the theoretical foundation to measure the fracture toughness of materials under confining pressure.
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