Dynamic response of a reinforced concrete slab reinforced with FRP materials under the effect of blast load using the finite element method

Dissertation for receiving a master's degree in Civil Engineering (M.Sc)

Structural

Abstract:

The strengthening of important government buildings, infrastructure facilities and vital arteries due to the increase in terrorist attacks around the world and the possibility of bombings near buildings and urban places is one of the most important discussions in civil engineering science, especially in our country. One of the most widely used materials for strengthening structures is the use of carbon polymer fibers known as (FRP).

In this thesis, various methods of reinforcing reinforced concrete slabs against blast loading have been investigated. In this regard, with the aim of achieving a suitable and optimal geometry of materials (FRP) to improve the performance of reinforced concrete slabs against impact loads, simple and yet effective solutions for installing and implementing different layers of composite (FRP) have been presented. By conducting a series of parametric studies by creating more than 100 finite element models with the help of Abaqus software (version 6.10.1) and considering various parameters such as different arrangements of FRP sheets, the number of layers, the extension of fibers in one layer, and also using a wide range of slabs with different dimensions, the behavior of these members has been investigated. The results show that the arrangement of FRP layers has a great effect on the performance of slabs under explosive load. By examining various geometries of porcelain layer (FRP) for strengthening, it was found that the best performance is related to the use of porcelain layer with an angle of 20 degrees to the longitudinal axis of the slab. Also, the porcelain layer longitudinally and transversely, i.e. 0 and 90 degrees, will also have good results. The analysis showed that by increasing the number of layers from 1 to 2 and from 2 to 3 layers, we can see a decrease in displacement by 50% and 23%, respectively. But after 3 layers, increasing the number of layers is not very effective. Also, the extension of the fibers in the strip (FRP) has a great effect on the response of the slabs. It is better to extend the fibers in the direction of the load of the slab.

Key words: strengthening, reinforced concrete slab, blast load, composite (FRP), maximum displacement

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Chapter 1:

Research overview

1 Introduction

In order to strengthen the building against explosion, it is necessary to use high-performance building materials such as reinforced fibers polymer (FRP) to provide sufficient displacement and resistance. In order for modified building materials to be effective, it is necessary to accurately evaluate the design based on the dynamic responses of materials under blast loads [17]. Generally, concrete is considered as a building material with high resistance to blast loading compared to other materials. Despite this, concrete structures are designed for operating loads with normal strain, which requires special modification to increase the resistance of structures against blast loading. The method of strengthening the building in the form of connecting structural components or many supports to increase resistance to explosion is undesirable due to the increase in cost and the loss of usable space. Also, this usually does not increase the overall resistance of the structure against the blast load. Therefore, reinforced polymer sheets and plates, which are cheaper and more suitable, are used as surface connections to modify special areas of structural implementation. Surface connections significantly increase the resistance of the structure against the blast load without destroying the usable space and without requiring a long time for construction, which, as a result, saves money. It is important to modify concrete structures for resistance to explosion type selection (FRP). The selected FRP should improve the stiffness, strength and deformation of the modified structure in order to provide the required reliable resistance against explosion and absorb the explosion energy, whereby the failure mode of the structure is changed and instead of breaking the structure, it deforms [17]. In order to analyze and design structures reinforced with FRP under explosion loads, both laboratory studies and numerical studies are necessary, recently in order to improve analytical methods. Simplified, studies in the field of accurate explosion analysis methods follow the correctness of analysis results with the help of correct material models and finite element models to estimate the behavior of concrete structures [29]. If the analysis is valid, it can be used as an alternative to costly structural blast tests.. Moreover, even when special testing facilities and related resources are available, some conditions and statistics are more easily obtained through such practical tests. For these reasons, it is necessary to create effective analysis tools for modified and newly constructed concrete structures under blast loading to predict structural behaviors, select optimal modified materials and ensure optimal rupture mechanisms [29].

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-2 Explosion-resistant structures

Concrete structures are usually used as protective buildings, one of the important discussions in concrete structures. There is, the impact of blast waves on these structures, the volume of their destruction due to the explosion and the amount of penetration of the blast wave in the structure.

Buildings and structures are destroyed and collapsed in different ways against an explosion. This depends on the loading characteristics, the most important of which are: a) the intensity and power of the explosion b) the distance of the explosion to the target. These two characteristics largely determine the form of collapse and destruction of the structure for the designer of the safe building. These two destruction mechanisms weaken the part and the joint area between the hole and the hole collapses easily. The ability of different materials and materials against perforation or the state of collapse, and finally penetration determines the thickness required to maintain the integrity of that element. Usually, the type and shape of the behavior of materials and materials determines the method and state of deformation and, as a result, the mode of collapse. Some materials and materials are very weak in terms of tensile strength and will break when exposed to strong tensile force that exceeds its capacity. An example of this material, which is widely used in construction, is concrete material. The tensile strength of concrete is much lower than their compressive strength, and to solve this problem and increase the resistance of concrete against explosion, reinforcement is used in concrete. Steel reinforcements increase the shear strength and tensile strength of concrete. Now, if the amount and strength of the explosion exceeds the strength of the reinforced concrete member, then rupture will occur.

Designing a part to resist the effects of local and severe explosions may not always be reasonable, especially when the exact location of the explosion is not known. In this way, the concept of limited and local destruction should be considered.

Strengthening using reinforced polymer fibers (FRP)

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The use of (FRP) in strengthening concrete structures has been developed a lot in the last few years. Reinforcement is done for various purposes, including tensile strengthening, shear strengthening, increasing containment, repairing damage caused by corrosion, and the like using these materials. (FRP) has largely replaced steel, which has many problems such as weight, difficulty of implementation, and corrosion, due to its light weight, ease of implementation, and high tensile strength against harsh environmental conditions. In reinforcing reinforced concrete slabs, FRP is mostly used to strengthen the frame. This reinforcement is done by gluing (FRP) to the tensile face of the slab in the area with maximum anchorage, which causes a significant increase in the energy absorption capacity of the slab. But the use of (FRP) in shear strengthening of slabs has received less attention and has been limited to limited research. Today, the use of (FRP) to increase the resistance capacity of structures has received much attention and research continues on it. Considering the limitations and problems related to conducting laboratory studies, including the limitations related to the dimensions of the samples, installation and implementation problems, high cost and time, etc., by performing accurate numerical analysis, it is possible to generalize the laboratory results to a correct range of structures for which practical testing is not possible. Therefore, in this final paper, an attempt will be made to evaluate the effect of FRP on the bending behavior of slabs with different geometric dimensions by conducting numerical parametric studies using finite element models and by providing solutions to improve the performance of these composites, to obtain more extensive information than what has been obtained from the experiments conducted so far. By using different porcelain layers and checking the condition of the structure under explosive loading, finally, a suitable geometry for using these sheets is suggested.