بررسي آزمايشگاهي اثر خاموت‌هاي ابداعي دست‌ساز ساخته‌شده از FRP در مقايسه با خاموت‌هاي فلزي در اتصالات بتن مسلح، تحت اثر بارگذاري چرخه‌يي

Experimental Investigation on Cyclic Behavior of RC Joints using Novel Manually Made FRP Shear Reinforcement Compared To Conventional Steel Stirrups

استفاده از الياف پليمري FRP يكي از كارآمدترين روش‌هاي كاهش اثرات خوردگي بر سازهاست. از آنجايي كه تاثير خوردگي بر خاموت‌هاي فلزي به علت قطر پايين آنها و همچنين نزديكي آنها به سطح بيش از ميلگردهاي طولي است، در اين نوشتار، يك پژوهش آزمايشگاهي بر روي اثر جايگزيني خاموت‌هاي ساخته‌شده از الياف FRP به جاي خاموت‌هاي فلزي تحت بارگذاري چرخه‌يي صورت گرفته است. به اين منظور، سه اتصال بتني ساخته و آزمون شد. از 3 اتصال ساخته‌شده، يك اتصال به عنوان اتصال مرجع داراي ميلگرد طولي و خاموت فلزي بود. ميلگردهاي طولي كليه‌ي نمونه‌ها، فلزي و خاموت‌هاي دو نمونه‌ي باقي‌مانده از جنس FRP ساخته‌شده در محل بودند. سه نمونه‌ي اتصال تحت بارگذاري چرخه‌يي قرار گرفتند. مطابق نتايج به‌دست‌آمده ملاحظه شد كه خاموت‌هاي FRP داراي عملكرد مناسبي در مقايسه با خاموت‌هاي فلزي بودند.

One of the most important defects occurring in reinforced concrete structures is the corrosion of reinforcements under undesirable environmental conditions. Various innovative methods have been studied by different researchers to prevent corrosion. If a typical concrete structure, reinforced by steel rods, encounters corrosive environments like salts, acids and chlorides for a length of time, it will lose strength to some extent. In addition, the corrosion of the steel, which is located inside the concrete, might expand and damage it. Longitudinal rods have larger diameters compared to stirrups and, therefore, they demonstrate lower corrosion effects and are a better alternative. Stirrups with lower diameters and more proximity to the environment are subject to corrosion and, therefore, it is better to use FRP stirrups, which are resistant to corrosion. Precast stirrups have a special manufacturing process and are also expensive and rare. So, using them in small scale projects is not economic. Hence, it seems necessary to find a new method for manufacturing FRP stirrups that is economically viable as well as showing a good performance under external forces. The present research experimentally investigates replacing steel stirrups with stirrups made by FRP filaments under cyclic loads. So, three concrete connections were made and tested. A longitudinal reinforcement with steel stirrups was designed as the reference connection. Steel longitudinal reinforcements were used in all three connections. One specimen of FRP stirrup connections is exactly similar to the reference. As with the other two FRP stirrup connections, the space between the stirrups is twice that of the reference specimen. The stirrups in the last two specimens were made of FRP filaments, in the laboratory. The diagrams of moment-drift, moment-curvature and moment-strain have been obtained for steel and FRP stirrups. Energy absorption and hardness changes have been calculated for all three specimens. All three stirrups went under cyclic loads, and FRP stirrups showed a better performance compared to steel stirrups.