Optimum installation arrangement of FRP materials in shear reinforcement of reinforced concrete beams with embedding method near the surface

Dissertation for receiving a master's degree

Civil engineering field, structural orientation

March 2013

Abstract

The scope of using FRP materials for shear strengthening of reinforced concrete beams is increasing in recent years. In addition to the common method of using FRP sheets that are glued on the concrete surface; Recently, a lot of research has been done on near surface mounting (NSM) method. In a part of this thesis, experiments were carried out on reinforced concrete beams in shear by NSM method and with GFRP rebar. The beams were evaluated in terms of bearing capacity and deformation. The results of the tests showed that with the same amount of GFRP and the same installation distance, the use of GFRP rebars with an angle of 60 degrees is more effective than 90 degrees. It was also found that with the same amount of GFRP and the same installation angle, the use of rebar with a smaller diameter and with a shorter distance has a greater effect on the final bearing capacity of the reinforced beam. In the other part of this thesis, reinforced concrete beams Reinforced in cutting with GFRP material and numerically modeled by NSM method and the modeling results were evaluated. In conventional modeling methods, the adhesion behavior between concrete and steel as well as the cracking behavior of concrete are modeled with simplified assumptions. It was observed that in the shear strengthening of reinforced concrete beam by NSM method with the same number and the same installation distance of GFRP rods, the arrangement of rods with an angle of 45 degrees has the greatest effect compared to the angles of 60 and 90 degrees. It was also found that with the same amount of GFRP and the same installation distance, the arrangement of GFRP rebars with an angle of 60 degrees is more effective than 90 degrees. The investigation showed that in the shear strengthening of the reinforced concrete beam using the NSM method with the same installation angle of the GFRP rod, the use of a rod with smaller dimensions and with a shorter distance has a greater effect on the performance of the reinforced beam. Key words: shear strengthening, reinforced concrete beam, embedding method near the surface, GFRP

Chapter One

Introduction

1-1 Introduction

In engineering applications, it is often necessary to combine material properties. For example, in the aerospace industry, underwater applications, transportation, and the like, it is not possible to use one type of material that provides all the desired properties. For example, in the aerospace industry, there is a need for materials that, while having high strength, are light, and have good abrasion resistance. Since it is not possible to find a material that has all the desired properties, composite materials were invented. Composites are multi-component materials whose properties are better than each of the components as a whole. At the same time, different components improve each other's efficiency. Although natural, metal, and ceramic composites are also included in this discussion, here we focus more on polymer composites. The composite materials used in civil engineering are polymers reinforced with FRP [1] fibers.

FRP are light, durable and resistant materials that are easily available to engineers today. FRP materials are insulated in magnetic environments and do not have corrosion problems, so by using these materials, the corrosion problem of concrete structures can be avoided. Also, these materials have superior characteristics such as high tensile strength, which makes their use as reinforcement of concrete structures suitable. It should be noted that like any material, FRP‌ They have weaknesses such as sensitivity to fire and weakness in bearing compressive stresses, as well as a high price. 1-2 History Composites or multi-structure materials or straws of the new age are a class of advanced materials in which the combination of simple materials is used to create new materials with superior mechanical and physical properties. is Constituent components retain their characteristics, do not dissolve in each other and do not mix with each other. The use of these materials has been common throughout history. Among the first composites or man-made multi-structures, we can mention mud straw and mud bricks in which straw reinforcement is used.When these two are mixed together, a product is obtained that is much more durable and resistant than both primary materials, i.e. mud and straw. The boats that the Redskins made with bitumen and bamboo and the ovens that were made of mud, glass powder and goat wool and found in different regions of our country are also among the first composites. The oldest example of composites was related to adding straw to mud to strengthen mud and making resistant bricks for use in buildings. This work dates back to 4000 years before Christ. In this case, the straw plays the role of reinforcement and the flower plays the role of the background or matrix. Bam citadel, which is a masterpiece of Iranian architecture, has been a clear example of the use of composite technology in the past centuries. Another example is the reinforcement of concrete by steel bars. In reinforced or reinforced concrete, metal rods create the necessary tensile strength in concrete, because concrete is a brittle material and has little resistance to tensile loads. In this way, concrete is responsible for bearing compressive loads and steel bars are responsible for bearing tensile loads. Many industrial needs, such as space, reactor, electronics, construction, transportation, cannot be met using conventional materials and require extensive changes in properties. Therefore, the use of composites has solved many problems. The history of polymer materials reinforced with fibers goes back to the 1940s in the defense industry and especially aerospace applications. For example, in 1945, more than 7 million pounds of fiberglass were used specifically for the military industry. Later, according to their advantages, they entered the general industries. Polymer based composites are the most important category of composites. A wide range of industries, such as high-end industries, such as the production of aircraft parts, to low-end industries, such as the production of sinks, are produced from polymer-based composites, and for this reason, they are considered the largest subset of composite materials. Strict design, during the last two decades, there has been a lot of emphasis on the repair and strengthening of structures all over the world. On the other hand, seismic improvement of structures, especially in earthquake areas. Rise has become very important. In the meantime, the techniques of using FRP composite materials as reinforcement. Because of its unique characteristics, including high resistance, lightness, chemical resistance and ease of implementation, externalizers have gained special importance in building resistance and revitalizing structures. On the other hand, these techniques have been particularly attractive due to their quick implementation and low costs. FRP composite materials were initially used as bending-resistant materials for reinforced concrete bridges and also as enclosures in reinforced concrete columns. But following the initial research efforts, since the mid-1980s, a lot of development has been observed in the field of using FRP materials in the construction of various structures. The number of applications of FRP materials in strengthening, repairing or improving structures has increased from a few cases 10 years ago to thousands at present. Various structural components including beams, slabs, columns, shear walls, joints, chimneys, arches, domes and trusses have been strengthened by FRP materials. FRP systems are used to improve a damaged structural member or to make a healthy member resistant or to fix defects in construction. Now, a large number of researchers and researchers of the structural industry around the world are investigating, studying and conducting tests to strengthen structures with FRP composites. Concrete structures are not limited and are used for all kinds of masonry, wooden and steel structures. During this period, many researchers in these three continents have paid attention to the development of the use of FRP materials, and the result of their efforts is the compilation of various regulations.