الفهرس 
Historical overview
Material properties and constitutive modelsOnly 14 pages are availabe for public view
 |  | from | 207 |  |  |
| | | from | 207 | | |
Abstract
Most of the new Reinforced Concrete (RC) structures which are built nowadays have a high safety level. Nevertheless, we cannot claim the same for structures built in the past. It seems that many old structures have reached the end of their service life and, in many cases, were designed to carry loads significantly lower than the
current needs specify. Therefore, the structural evaluation are considered necessary, so they can meet the same requirements as the structures which are built today. Existing techniques for the strengthening of RC structures present crucial parameter which are mainly related to the ease of application, the high cost, and the time it takes to be applied. Research is now focused on new techniques which combine strength, cost effectiveness and ease of application. The superior mechanical properties of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) compared to conventional concrete, together with the ease of preparation and application of the material, make the application of UHPFRC in the field of strengthening of RC structures attractive.
In this study, behavior of UHPFRC columns under eccentric loading was investigated with two different micro models using Abaqus\standard package. The analysis included 2D model using plane stress element, and 3D model using solid element. Moreover, the 2D model using shell element was extended to investigate the behavior of RC columns strengthened with UHPFRC jacket under eccentric loading. To allow for the debonding mode of failure, node-to-node interaction method using Cartesian elastic-plastic connector element in the 2D analysis model was adopted. The FE model results are validated by comparing them with the experimental results in the literature.
It is shown that the proposed finite element (FE) model can predict the
modes of failure due to debonding and could simulate the behavior of both UHPFRC columns and RC columns strengthened with UHPFRC jacket.
Additionally, using 2D plane stress model, two key parameters on the behavior of UHPFRC columns such as effect of using UHPFRC on over all the behavior of columns, and influence of cross section geometry b/h are investigated. Moreover, several parameters on the behavior of strengthened columns with UHPFRC jacket including interfacial shear stress, adhesive fracture energy, number of shear connectors, spacing of jacket stirrups, jacket thickness, the concrete strength in the jacket, and the longitudinal reinforcement ratio at the jacket are investigated.
FE results indicated that the monolithic behavior of RC columns strengthened with UHPFRC jacket can be achieved by increasing the substrate roughness surface, and using sufficient number of shear connectors or using closely spaced stirrups reinforcement in UHPFRC jacket with well roughened interface. In comparison with normal strength concrete (NSC) and high strength concrete (HSC) jackets, the UHPFRC jacket provides the best performance of the section in terms of strength and ductility for both the compression and the bending actions.
A comparison among the finite element model, the proposed analytical models, and experimental results available in the literature indicated that the proposed analytical models suggested in this research are capable of predicting the load and moment capacities of UHPFRC and UHPFRC-NSC columns.