Search

The column is the most important structural element were strengthening of columns became a demanding issue. In this paper, the effectiveness of strengthening reinforced concrete (R.C) columns with carbon fiber reinforced polymers (CFRP) wraps has been improved by increasing the contact area between the column’s surface area and CFRP. A new strengthening technique was hired for the purpose of enhancing the efficiency of CFRP jackets in improving the load capacity of R.C columns, especially columns with rectangular sections. The method is based on increasing the contact area between the CFRP jacket and the column's surface area. This was done by adjusting the profile of the col's cross-section to almost ellipsoidal. The experimental program in this research includes testing 13 columns to include all test parameters, the shape of the cross-section, and the cross-section profile. The results include axial stresses and corresponding axial strains, and lateral strains at the mid-height and quarter height of tested specimens. And also, the cracking load and maximum load with crack patterns are determined. The comparison involved the study of the effect of the traditional CFRP jacket wrapping of R.C columns with square, and rectangular sections and the newly developed strengthening technique. A theoretical study was also conducted. Where the capacity of the square and rectangular confined columns with different radius of curvature, R, of the ellipsoidal profile is determined by the predicted and design equations. The study revealed that the strengthening technique is expected to effectively enhance the efficiency of the CFRP strengthening technique, especially for columns with square and rectangular sections as the area of the well-known dead zone of these columns is reduced using the proposed technique. Also, the results proved that the efficiency of strengthening tested columns by CFRP jacket has been enhanced using the strengthening technique by about 80% of original RC columns, which exceeds the traditional method (Jacket) CFRP wrap by 60%.

Strengthening of existing isolated footings using concrete jacketing is a traditional method to increase the load-carrying capacity and to enhance the performance of isolated footings. This paper presents a parametric study and a numerical validation for full-scale square footings strengthened with concrete jacketing, using either dowels and bonding agent or bonding agent only, to connect the existing and new concrete surfaces. A nonlinear finite element program “ABAQUS” was used for the numerical validation and the parametric investigation for various parameter's effect on the load-carrying capacity and contact stress redistribution underneath the strengthened footings. The parameters used in the parametric analysis include the ratio of the concrete jacket depth to the concrete footing depth, concrete compressive strength, spacing between dowels, and the ratio of the concrete jacket width to the concrete footing width. The effect of dowels on load carrying capacity of footings strengthened using a full concrete jacket is insignificant for jacket width smaller than the footing width. In footing strengthened using a full concrete jacket, the load carrying capacity increases by 9% compared to the non-strengthened footing.

The contact pressure distribution below, reinforced concrete footing, does not solely depend on the type of soil, but also on the change of the footing stiffness after cracking. This paper presents a numerical simulation and validation for full-scale square reinforced concrete footing rested on sand soil using a nonlinear finite element program “ABAQUS 6.14” to investigate the effect of concrete damage plasticity on contact stress distribution beneath the footing. It was found that, as long as the foundation stiffness decreases during the loading cycle for the footing, the percentage of the contact stresses at the footing edges to the contact stresses under the column center are reduced. A parametric study is conducted on square concrete footings with various reinforcement ratios resting on sand soil to investigate the effect of increasing reinforcement ratio on the failure load, and the shape of the contact stress below the footing before and after cracking. The results determine the impact of increasing the steel reinforcement ratio from 0.15 % to 0.30 % on the footing performance, and the corresponding increases in the ratio between central to edge contact stress. The findings further indicate that contact stress distribution below square footing was not consistent with the theoretical assumption.