پديد آورندگان :
مودي، ياسر دانشگاه سيستان و بلوچستان , موسوي، روح الله دانشگاه سيستان و بلوچستان - گروه مهندسي عمران , اصفهاني، محمدرضا دانشگاه فردوسي مشهد - گروه مهندسي عمران
كليدواژه :
بتن آرمه , مقاوم سازي , محصوركننده NSM-GFRP , NSM-Steel , CFRP
چكيده فارسي :
روش نصب در نزديك سطح (NSM)، يك روش بسيار مفيد در به كارگيري ميلگردها و نوارهاي FRP در مقاوم سازي ستون هاي بتن مسلح است. مطالعات انجام شده در اين زمينه نشان مي دهد كه اين ميلگردها ظرفيت باربري خمشي ستون ها را افزايش مي دهد. عليرغم افزايش ظرفيت خمشي توسط ميلگردهاي NSM-GFRP، اين روش تقويت باعث كاهش شكل پذيري و ظرفيت اتلاف انرژي ستون ها مي شود. علاوه بر مشكلات ذكر شده ي اين روش، عدم استفاده كامل از ظرفيت تحمل بار ميلگردهاي GFRP، يكي ديگر از عيب هاي روش مذكور مي باشد كه اين نقص با استفاده از تركيب اين روش با محصوركننده ي CFRP از بين مي رود. نتايج مطالعات نشان مي دهد كه استفاده از تركيب اين دو باعث افزايش توام مقاومت فشاري و خمشي ستون هاي بتن آرمه مي شود. در اين مطالعه به بررسي آزمايشگاهي دو روش تركيبي NSM-GFRP با محصوركننده ي CFRP و NSM-GFRP با NSM-Steel براي تقويت ستون هاي بتن آرمه تحت بارگذاري محوري ثابت و جانبي چرخه اي پرداخته شده است. با توجه به نتايج بدست آمده، نشان داده شد كه استفاده از اين دو روش تقويت تركيبي باعث افزايش ظرفيت تحمل بار، شكل پذيري، ظرفيت اتلاف انرژي و سختي اوليه ستون ها نسبت به ستون كنترلي و ستون تقويت شده با استفاده از روش NSM-GFRP مي شود. در همه ي اين پارامترها نتايج نشان مي دهد تقويت ستون هاي بتن آرمه به روش تركيبي NSM-GFRP با NSM-Steel (با نسبت NSM-Steel به NSM-GFRP بالاتر) نسبت به روش تركيبي NSM-GFRP با محصوركننده ي CFRP بهبود بيشتر مي دهد، اما با توجه به مباحث خوردگي ميلگردهاي فولادي روش تقويت تركيبي NSM-GFRP با محصوركننده ي CFRP به عنوان بهترين روش انتخاب مي شود.
چكيده لاتين :
In recent years, Fiber-reinforced polymer (FRP) materials are increasingly used for strengthening and retrofitting reinforced concrete structures. Fiber-reinforced polymers in the form of jackets with the fibers typically in the columns’ circumferential direction, are quite effective in carrying shear and in providing confinement. In addition, previous studies show that FRP jacket can greatly enhance the energy dissipation capacity and ductility of reinforced concrete columns. However, FRP jackets are not effective for strengthening columns in flexure. To overcome difficulties associated with FRP jacketing, recent research efforts have focused on the use of near surface mounted (NSM) FRP or stainless steel reinforcement through a combination of externally bonded (EBR) FRP sheets and anchors for the flexural strengthening of columns. NSM strengthening technique consists of FRP rods embedded in grooves made on the surface of the concrete and bonded in place with epoxy. The NSM technique is not effective in terms of enhancing the energy dissipation capacity of RC columns. Therefore, by combining NSM technique with FRP confinement sheets, a high effective technique (hybrid FRP-based strengthening technique) can be obtained. FRP and steel bars have been used for reinforcing the concrete beams in previous studies. However, the combination of both materials for strengthening of reinforced concrete columns is not common. The present paper experimentally investigates the effects of combined NSM-GFRP bars with the CFRP confinement sheets and also NSM-GFRP bars with NSM-Steel rods on strengthening of reinforced concrete columns. It should be noted that in combinatory method of NSM-GFRP with NSM-Steel, NSM-Steel to NSM-GFRP ratio is different.
The experimental program includes five square columns with a cross section of 250*250 mm and the length of 1200 mm. The columns were loaded up to failure by applying simultaneous constant axial compressive and increasing cyclic lateral loading. According to the results, it is indicated that using these two combinatory reinforcing methods cause an increase in load-bearing capacity, ductility, dissipated energy and initial stiffness of columns in comparison with the control column and also columns reinforced by using NSM-GFRP bars. Furthermore, NSM-GFRP technique increases the load capacity by 43 percent in comparison with the control specimen. In the case of combined retrofitting methods, load capacity increased up to 60 percent. Also, using NSM-GFRP reinforcement causes 7 percent increase in ductility and 6 percent decrease in energy dissipation capacity. In contrast, in the specimens reinforced by the combinatory methods, the ductility parameter and dissipation capacity increased by 3 to 150 percent and 24 to 133 percent, respectively. In addition, hysteretic diagrams corresponding to specimens strengthened by combinatory methods has less pinching effect than those of the control specimen. Experimental results indicate that the reinforced concrete column strengthened by combinatory method of NSM-GFRP with NSM-Steel is a viable solution toward enhancing the behavior of RC columns subjected to simultaneous axial and seismic loads. This is especially the case when the retrofitting scheme contains higher NSM-Steel to NSM-GFRP ratio. Finally, due to corrosion of steel reinforcement, NSM-GFRP bars combined with CFRP confining sheets is selected as the best choice of strengthening.
