بررسي آزمايشگاهي پيوستگي بين آرماتورهاي پليمري مسلح به الياف شيشه (GFRP) و بتن در نمونه‌هاي تيري وصله‌دار

An experimental study on bond strength between concrete and GFRP bars for lap-spliced concrete beams

نتايج آزمايشگاهي گذشته در مورد پيوستگي بين بتن و آرماتور در نمونه‌هاي تيري وصله‌دار مسلح به آرماتورهاي پليمري اليافي (FRPR) كافي به نظر نمي‌رسد. علاوه‌ بر اين، تحقيقات كمي در رابطه با اثر آرماتور جانبي اطراف وصله در رفتار پيوستگي بين آرماتورهاي FRP و بتن صورت گرفته است. در اين نوشتار، 15 نمونه‌ي تيري وصله‌دار مسلح به آرماتورهاي پليمري مسلح به الياف شيشه (GFRP) ساخته و آزمايش شدند. به كمك نتايج آزمايش اثر آرماتور جانبي وصله و مشخصات سطح ظاهري آرماتور در پيوستگي بين آرماتورهاي GFRP و بتن بررسي شد. نتايج نشان مي‌دهند كه اثر آرماتور جانبي وصله در پيوستگي بين بتن و آرماتور بسته به مشخصات سطح ظاهري آرماتور متفاوت است. علاوه بر اين، به كمك نتايج نمونه‌هاي آزمايشي اين پژوهش و نتايج آزمايش‌هاي موجود در ساير مراجع، ضوابط آيين‌نامه‌هاي CAN/CSA-S806-02 و ACI 440.1R-06 براي تعيين مقاومت پيوستگي مورد ارزيابي قرار گرفتند.

Steel reinforcing bars have not performed well in applications where members have been subjected to corrosive environments. To reduce the risk of reinforcement corrosion, several techniques have been employed. However, none of these methods have proven to serve as long-term solutions. Fiber-Reinforced Polymer (FRP) bars can be used as a reinforcing material by nature corrosion resistant. FRP reinforcing bars are available in different grades of tensile strength and modulus of elasticity. The behavior of concrete beams reinforced with FRP bars is different from that of steel reinforced concrete beams. FRP bars have high tensile strength and appropriate durability but are not ductile. In addition, the bond between concrete and FRP bars is different from steel bars because of the difference in their surface geometries and mechanical characteristics. In this experimental study, fifteen Lap-spliced concrete beams reinforced with GFRP bars were manufactured and tested. The parameters of concrete compressive strength, amount of transverse reinforcement along the splice length, the surface conditions and the diameter of longitudinal bars were selected as the variables for the beam specimens. There are ten specimens reinforced with ribbed GFRP bars and five specimens reinforced with sand coated GFRP bars. Laboratory specimens were designed so that bond failure occurs. The cracks of the specimens were mapped and test observation was recorded during loading steps and at the time of failure. Also, the relationships of force versus mid-span displacement were obtained by means of a Load Cell, a LVDT (Linear Variable Displacement Transducer), a Data Logger and a computer system. Then the bond strength and ductility of specimens were analyzed. Based on the experimental results, the effects of transverse reinforcement along the splice length, concrete compressive strength and bar diameter on bond strength are evaluated. The experimental results show that the effect of transverse reinforcement along the splice length on bond strength of GFRP bars is largely dependent on the surface conditions of the bars. Bond strength increases with increase in the amount of transverse reinforcement. The concrete beams reinforced with sand coated GFRP bars are more ductile than ribbed GFRP reinforced concrete beams. The results of forty three beam specimens tested by other researchers are used in the study. The experimental bond strengths are compared with the values obtained using CAN/CSA-S806-02 and ACI 440.1R-06 Code provisions. The comparison shows that the bond strengths calculated with the code provisions are higher than the experimental values especially in the specimens with no transverse reinforcement along the splice length. Therefore, the code provisions should be modified to consider the effect of transverse reinforcement on bond strength.