A stress-strain model for uniaxial and confined concrete under compression
- Authors: Samani, Ali Khajeh , Attard, Mario
- Date: 2012
- Type: Text , Journal article
- Relation: Engineering Structures Vol. 41, no. (2012), p. 335-349
- Full Text: false
- Reviewed:
- Description: Analytical models for the full stress-strain relationship of confined and unconfined concrete in compression are required for the numerical simulation of the structural behavior of reinforced concrete structural elements. There are many analytical models presented in the literature, which are generally empirical and are based on tests either on plain concrete specimens or reinforced concrete columns. This paper reviews some widely used analytical models calibrated using triaxial test results on plain concrete and compares their predictions with available test data on uniaxial and triaxial compression on specimens with different specimen height, width or diameter and concrete strength. The model prediction's for the peak stress and corresponding strain due to confinement are also compared. The residual stress level and the post-peak fracture energy under confinement are discussed. Estimates of the post-peak fracture energy per unit area are obtained from available experimental data showing that the post-peak fracture energy varies with confinement. The size effect on the softening behavior of uniaxial and triaxially loaded plain concrete specimens with different aspect ratios, heights and level of confinement, are also discussed. A new analytical model for unconfined and confined concrete is introduced which tries to address the limitations in previous models. The proposed model is capable of predicting the behavior of normal strength concrete, as well as high strength concrete and incorporates allowances for size effects dependent on specimen height and aspect ratio. Comparisons are made between the proposed new model, the models of others in the literature, and available compression triaxial and uniaxial test results. © 2012.
Ductility in concentrically loaded reinforced concrete columns
- Authors: Samani, Ali Khajeh , Attard, Mario , Foster, Stephen
- Date: 2015
- Type: Text , Journal article
- Relation: Australian Journal of Structural Engineering Vol. 16, no. 3 (2015), p. 237-250
- Full Text: false
- Reviewed:
- Description: In recent years, the use of high-strength concrete materials has been regulated into Australian design standards. The use of high-strength concrete is desirable in many cases. For instance, in reinforced concrete columns of high rise buildings, the columns can carry more load with a smaller cross section compared to reinforced concrete columns built of normal strength material. However, there are some disadvantages, one being the reduction of ductility. The Australian Concrete Standard AS3600 deals with this issue by changing the tie arrangement in reinforced columns for different concrete strength grades. This study reviews the ductility index used to measure the ductility of reinforced concrete columns and uses an analytical model to predict the ductility index of several practical example columns. These columns are designed and detailed using the requirements of the Australian Concrete Standard. The outcome of a parametric study shows that the columns designed and detailed using the rules in the Australian Concrete Standard may not necessarily have the ductility index which the code assumes. Another well-known deficiency observed in the behaviour of reinforced high-strength concrete columns is premature spalling of the cover concrete. The Australian Concrete Standard addresses premature cover spalling by modifying a reduction factor which is applied to the strength of the concrete when the squash load of a reinforced concrete column is calculated. This reduction factor accounts for many issues not only premature cover spalling. Using an analytical model, it is shown that the code formula for estimating the squash load is too conservative and needs adjustment for very large columns with small cover to core ratio. © 2015 Engineers Australia.