International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 05 | May 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1842 Stiffness of Reinforced Concrete Beams after Retrofit with External Steel Reinforcement Method Novita Ike Triyuliani 1 , Sri Murni Dewi 2 , Lilya Susanti 3 1 PG Student, Department of Civil Engineering, Brawijaya University, Malang, Jawa Timur, Indonesia 2 Professor, Department of Civil Engineering, Brawijaya University, Malang, Jawa Timur, Indonesia 3 Lecturer, Department of Civil Engineering, Brawijaya University, Malang, Jawa Timur, Indonesia ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - How many inovations to retrofitting of building structures are important topics. Failure in structures such as beams dan columns due to time, refunctions of a building, even initial design errors that are weak or lack the safety factor of a building structure. External reinforced concrete beams are one of the beams currently being developed, concrete blocks with reinforcement of steel reinforcement on the outer (external) of beam. This study aims to determine the stiffness of RC beams before and after retrofit with external stell reinforcement, dimension of beams 15 x 15 x 100 cm repeat 12 pcs, with external reinforcement each 6 pcs 2Ø6 and 3Ø6. The results from this research are stiffness pre-crack and after crack. Where beams pre-crack in term of load P = 1000 kg, have an average decrease stiffness of 31.11%, 28.32%, 0.58%, and increase stiffness 17.09%. And after crack in term of load P = 3000 kg, have an average increase stiffness of 1.8%, 2.8%, while increase significant until 41.88% and 59.72%. Key Words: retrofit, external steel reinforcement, stiffness, pre-crack, after crack, 1.INTRODUCTION Reinforced concrete is a combination of concrete and reinforcing steel which functions as reinforcement in fibers/ tensile parts which are not owned by concrete. One of the structural elements in the building is concrete blocks [4]. Concrete beams as structural elements are designed to hold loads perpendicular to the axis [4]. Increasing the strength of building structures has become an important topic lately. Transfer of functions of a building, failure of structures such as beams and columns due to time serviceability, environment that affects the decrease in structural strength and even initial design errors that are weak or lacking or disaster such as earthquakes. In the research of Suhad Susanto, et al. "External Reinforced Concrete Beams" where Steel Lips Channel is used as reinforcement. The results showed that after being strengthened with steel Lips Channel there was an increase in strength. Kothandaraman et al (In Zhang., 2012) "Flexural Retrofitting of RC Beams Using External Bars at Soffit Level-An Experimental Study". The method of retrofitting RC beams with external reinforcement at the soffit level. This retrofit method is cost effective, and easy to apply. All specimens are under two-point loading until they collapse. Middle-range and quarter deflections are shown in Figure 2.2 and the tests are presented in Table 2.1. The results showed that external reinforcement retrofitting at the soffit level in this way significantly reduced crack width, deflection, and increased moment capacity compared to without retrofit. [1] Alanwar, A and Elbatal (2015) "A Smart Reinforced Steel Wire Mesh U-Shape Jacketing Technique in Strengthening and Retrofitting RC Beams". This method uses external steel reinforcement for reinforcement and is covered with U-shaped wiremesh. The difference in the number of variations of external steel reinforcement is used in the repair method. The results show that the reinforcement method significantly increases the flexural and shear strength and performance of reinforced concrete beams. With the addition of variations in the number of reinforcement from 2Ø8 to 5Ø8, it shows the results of increasing load carrying capacity from 108% to 136%. [2] Hamza Salim Mohammed Al Saadi, et al (2017) Research "An Experimental Study on Strengthening of Reinforced Concrete Flexural Members using Steel Wire Mesh". In this method, wiremesh is used to increase the flexural capacity of the beam, but the installation of wiremesh is only on the flexible side, so that when a lot of testing is done shear crack occurs. [3] n this research case is retrofit with external steel reoinforcement method and add confinement external reinforcement to hold the shear strength of beam. 2. EXPERIMENTAL PROCEDURES 2.1 Test Specimen The specimens for reinforced concrete beams dimension of 15 x 15 x 100 cm, while the beam of the specimen after retrofitting remains with a size of 15 x 15 x 100 add external steel reinforcement at the bottom and sides of the beam, with cross section right-left 6 pieces of confinement. The following is the detail of the test object to be made in the study, namely as follows: