بررسي عوامل موثر بر افزايش مقاومت برش پانچ در اتصالات دال تخت مقاوم سازي شده با FRP

Assessment the Effective Parameters on Punching Shear in Slab-Column Connections and Strengthening Them with FRP

در سالهاي اخير تقويت سازههاي بتن آرمه با استفاده از كامپوزيت هاي - FRP مورد توجه زيادي قررار گرفتره كره در ايرن ميران تقويت دالهاي دوطرفه براي افزايش مقاومت پانچ كمتر مورد مطالعه قرار گرفته است. مزاياي دالهاي دوطرفه به ويژه دالهراي تخرت سرب كاربرد زياد اين نوع سازه شده است؛ ولي اين سيستمها با مشكلاتي مانند خيز زياد و برش پانچ روبرو است. در اين پژوهش تقويت دالهراي تخت با استفاده از صفحات FRP براي تقويت ظرفيت برش پانچ مورد مطالعه قرار گرفت. براي اين منظور ابتدا مدل اجزا محدود دال در نرر افزار ABAQUS توسرعه داده شرد و ويژگي هاي غيرخطي مصالح منظور شد. پر از كراليبره كرردن نرر افرزار، مطالعراتي پارامتريرو روي اتصال دال به ستون انجا شد و تاثير نسبت آرماتور دال، مقاومت فشاري بتن و وجود آرماتور در ناحيه فشراري مرورد بررسري قررار گرفرت . نتايج اين بررسي نشان داد كه مقدار آرماتور اتصال در تعيين مد شكست اتصال نقش اساسي بازي ميكند. همچنين با افزايش مقاومت فشراري بتن، ظرفيت باربري و تغييرمكان نهايي اتصال افزايش خواهد يافت. سپ دالهاي تخت بتن مسلح با الياف پليمرري مقراو سرازي شرد. تراثير جن الياف، تعداد نوارها و تعداد لايههاي FRP و همچنين دو نوع الگوي متفاوت مقاو سازي مورد بررسي قرار گرفت. نترايج ايرن بررسري نشان داد كه صفحات FRP در دالهاي تخت، علاوه بر افزايش ظرفيت برش پانچ، افزايش سختي نمونه و كاهش انرريي جرذ شرده را بره همراه داشت.

Many flat slab -column frame structures have been built in many parts of the world, since the beginning of the century. The absence of beams makes the formwork simple, increase the clear story height, and decreases total building height. However brittle punching failure is a problem that unnecessarily limits the widespread use of flat plates in active earthquake zones. Many slab -column connections in flat plate structures were damaged and failed in punching shear after the 1985 Mexico City earthquake, the 1989 Loma Prieta earthquake, and the 1994 Northridge earthquake. These shows that slab –column connections are prone to punching shear failure when lateral forces, due to earthquake loadings, cause substantial unbalanced moments to be transferred from the slab to the column. Slabs with low or medium reinforcement ratios tend to fail in flexure rather than in punching shear. For slabs that have reinforcement ratios of 1% and more, the mode of failure tends to be the punching shear type of failure. Fiber-Reinforced Polymers (FRPs) have gained increasing popularity in retrofit of reinforced concrete members in the last two decades. Using FRP materials to enhance slabs in flexure is very desirable from the application point of view due to the ease of handling and installing. FRP material, unlike steel, are not subject to either corrosion or rust in the long term. There is limited amount of research available on srengthening of slab -column connections. These studies include investigations where the slabs were strengthened using FRP laminates around a central stub column or bonded over the entire width of the slab. with regard to flexural strengthening, externally bonded FRP strips have been used for the strengthening of one way slabs as well as two way slabs. The determination of the structural behavior of FRP–strengthened concrete slabs requires extensive experimental and/or advanced numerical methods. as far as theoretical methods are concerned, Reitman and Yankelevsky have developed a nonlinear finite element grid analysis based on the yield line theory. Other researchers have employed finite element packages to investigate the structural behavior of both unstrengthened as well as FRP–strengthened slabs. In all of these simulations, a full bond between the concrete and the adjacent strengthening FRP materials was assumed. Recently, Binici and Bayrak reported the test results of a strengthening method using carbon fiber reinforced polymers (CFRPs) as shear reinforcement. Previous studies concentrated on enhancing shear capacity of slab-column connections for new construction. Stirrups, bent -up bars, and shear studs were used as shear reinforcement in previous studies. This study investigates the application of different methods of strengtheing of flat slabs. At first, slabs were model in ABAQUS in order to study the parameters that influences punching shear capacity. Analytical result indicate that increasing concrete compressive strength improves punching shear capacity. Based on this result, steel reinforcement ratios determines the mode of failure. Then, FEM models of slab were strengthend, and type of strengthening, type of FRP materials, number of strip and layer were investigated. The results show that using FRP strip increases punching shear capacity and reduces energy absorption.