ارائه اتصال مكانيكي جديد براي مقاوم سازي ستون هاي بتن مسلح با مواد كامپوزيتي

new mechanical connection for retrofitting concrete piers of bridges with composite materials

تحقيقات انجام شده بر روي پلهاي بتن مسلح آسيب ديده در زلزله هاي گذشته، مويد اين مطلب است كه اصلي‌ترين دليل فروپاشي اين نوع سازه‌ها خرابي در ستونهاي ضعيف بوده است. با اينكه مقاوم‌سازي ستونهاي بتني مسلح با الياف FRP در تقويت برشي و محوري ستونها نقش بسزايي دارد با اين حال در بالا بردن ظرفيت خمشي اين اعضا تاثير زيادي نداشته است. يا اين وجود با ادامه تحقيقات تا كنون روشهاي مختلفي جهت بالا بردن ظرفيت خمشي ستونهاي بتني با الياف FRP پيشنهاد شده است. بر اساس بررسي‌هاي انجام گرفته، روشهاي ارائه شده داراي مشكلات مختلفي مي‌باشند كه از جمله آنها ميتوان به دشواري اجرا، هزينه بالا، سرعت پايين عمليات اجرايي و عدم اطمينان از عملكرد اشاره نمود. در اين تحقيق يك اتصال جديد مكانيكي براي افزايش ظرفيت خمشي ستونهاي بتني مسلح مقاوم سازي شده با الياف FRP پيشنهاد گرديده است. اتصال مكانيكي ارائه شده ضمن سهولت اجرا و هزينه كم، در زماني كوتاه قابل اجرا مي‌باشد. به منظور ارزيابي رفتار اتصال پيشنهادي ابتدا با استفاده از نتايج آزمايشگاه، يك مدل ستون بتن مسلح در نرم‌افزار اجزاء محدود ABAQUS مدلسازي شده و صحت‌سنجي گرديده است. سپس دو حالت مختلف متداول نصب لايه‌هاي طولي CFRP در مقايسه با اتصال مكانيكي پيشنهادي مورد مطالعه قرار گرفته است. بر اساس نتايج بدست آمده اتصال مكانيكي پيشنهادي موجب بهبود ظرفيت خمشي ستون مي‌گردد. علاوه بر آن كاربرد مواد كامپوزيتي همراه با اتصال ارائه شده، رفتار كلي المان تقويت شده را ارتقاء داده و موجب ايجاد خرابي نرم در ستون بتني مسلح مي‌شود.

Studies on reinforced concrete bridges damaged in the last earthquakes, confirm that weak piers are the main reason for the collapse of these structures. Retrofitting concrete piers with FRP plays an important role in enhancing axial and shear strength. However, it will have an insignificant effect on raising the flexural capacity of the members. To increase the bending capacity of reinforced concrete piers, various methods have been suggested by researchers. However, each method has different shortcomings such as difficulty in implementation, high cost, low operation speed, and uncertainty of performance. Considering the problems of the existing techniques and after comprehensive studies, a new mechanical connection to enhance the bending strength of reinforced concrete piers using FRP was proposed in this study. The proposed detail is easy to perform and is cost effective. Meanwhile, it can be applied in a short time. In addition, suggested mechanical connection eliminates detachment of FRP layer from the surface of concrete and develops proper connection between FRP layer and the surface of the concrete column. So, the detail can be used to improve the flexural capacity of the column. To assess the proposed mechanical connection, a reinforced concrete column was modeled in Abaqus software. The concrete column was built in 2007 and was tested at IIEES. To validate the model, calculated results were compared with experimental results and the accuracy of the model is ensured. Using the validated model, the other models were simulated. The models consisted of a reinforced concrete column retrofitted with longitudinal FRP layers, a concrete column retrofitted with longitudinal FRP layers and transverse FRP layers in flexural plastic hinge location and the other model is a reinforced concrete column retrofitted with longitudinal FRP layers and proposed mechanical connection. So, in order to evaluate and study the detail, four finite element models were created in Abaqus software. The performance of the concrete columns under vertical and lateral loading was studied using forcedeformation curves. According to the results, flexural capacities of concrete columns retrofitted with longitudinal FRP layers were increased. By comparison of the results obtained from forcedeformation curves of the models, wrapping columns in the plastic hinge locations partially raises flexural capacity. However, Due to the linear elastic behavior of FRP material, damage mode is sudden in both second and third models. Based on the results, the general behavior of the concrete columns retrofitted with longitudinal FRP layers with or without transverse FRPlayers in flexural plastic hinge location did not improve and failure damages occurred immediately. Based on the observation, the best behavior has been shown by the concrete column retrofitted with longitudinal FRP layers and proposed mechanical connection. Using the proposed detail, the flexural strength of the reinforced concrete column was increased. As forcedeformation curves show, the proposed mechanical connection can inhibit efficiency of the longitudinal FRP layers and enhance the flexural capacity of the reinforced concrete column. Moreover, the detail improves the overall performance of the concrete column retrofitted by FRP layers and prevents instantaneous failure damages.Keywords: Rinforced Concrete, Bridge Piers, Flexural Rehabitation, FRP Layers, Mechanical Fasteners.