السلوك الإنشائي للأعمدة الخرسانية المسلحة المتضررة عالية القوة التي تم إعادة تأهيلها بواسطة CFRP تحت التحميل اللامركزي

Rp_Structural Behaviour of Damaged High Strength Reinforced Concrete Short Columns Rehabilitated by CFRP Under Eccentric Loading.pdf

The strengthening process for any structural member, such as columns, has become one of the most standard solutions for building restoration in the world, which might be carried out for several reasons, including: change in use, failure in steel, over loads and/or cruel weather conditions. This research aims to investigate experimentally and numerically the structural ‎behaviour of partially loaded high strength short concrete columns strengthened with CFRP strips‎. In this study, Nine columns with a square cross-section (100×100) mm and height of 800 mm with two corbel heads were prepared and tested under eccentric load with an eccentricity of 50 mm from the center (e/h=0.5). One column, which is designated by CC, was tested to failure and considered as a control column. In contrast, the other eight columns were divided into two groups of four identical columns. The first group of columns was loaded by 25% of their ultimate design loads, while the second group was loaded by 50%. Then, all the partially loaded specimens in the two groups were strengthened with various schemes of CFRP based on the initial loading ratios, which is represented as follows: full by direction longitudinal wrapping with CFRP in all sides of the column, full longitudinal wrapping with CFRP for tension side only, full by direction horizontal wrapping with CFRP for clear column height and partial horizontal wrapping with CFRP for 250 mm length at column mid-height.
The experimental results for specimens strengthened with a full by longitudinal direction wrapping on all sides and for the tension side only of the columns in group one recorded the ultimate load capacity increases by 65.55% and 44.82 %, respectively, compared to CC. In addition, the ultimate load capacity for the strengthened columns in the second group With the same strengthened schemes increased by 44.83%, 37.93 %, respectively, compared to CC. Further, the ultimate load capacity for the specimens strengthened with full or partial horizontal encapsulation increased of the two groups by 24.14, 20.69, 13.79, and 10.34 %, respectively.
The finite element method (ABAQUS) was used to verify the structural behaviour of partially loaded high strength short square columns strengthened with CFRP strips, which were experimentally tested earlier. Results showed a good agreement between the experimental and numerical results regarding the ultimate load capacity and load-horizontal and vertical deflection curves. The mean difference in the ultimate load capacity and maximum deflection horizontal and vertical were (6.28%, 7.38%, 6.24 %), respectively, which ensure the accuracy of the numerical solution.
Additional parameters were suggested to be investigated numerically by the ‎verified model: the effect of increasing CFRP layers, the impact of different load eccentricities (e/h), the effect of various initial loading rates, ‎and the effect of increasing the width for CFRP. The numerical ‎results illustrated that Increasing the number of CFRP layers to two or three layers, presented in full longitudinal wrapping with CFRP for all column faces increased significantly the ultimate load capacity by 83.08% and 109.45%, respectively, compared with CC. Furthermore, decreasing in the deflection for eccentricity load (e/h) from (0.5 to 0.35) led ‎to obtained high ultimate load by 54.62% for specimens fully longitudinal strengthened. On the other hand, ‎increasing the percentage of initial loading from 50% to 80% caused a slight reduction in the ‎ultimate load by 9.23% and 11.92%, respectively, for control column and specimens fully longitudinal strengthened with CFRP sheets. Moreover, increasing the width for CFRP sheets for partial horizontal wrapping caused a slight increase in the ultimate ‎load