Many studies have been conducted on the behaviour of reinforced concrete (RC) to determine the effects of different fibre types on the mechanical properties of concrete. Tests such as flexural and shear tests are used to evaluate the behaviour of RC. Most previous studies have focused on reinforcement of the entire cross-section with one fibre type, but the use of double-type reinforcement is growing and the lower cost of polypropylene (PP) fibres can be a significant factor in the use of double-type reinforcement. Therefore, in this work, experimental tests and numerical simulations were carried out to study reinforcement of the cross-section with steel fibres, PP fibres or both, in two separate layers. Beams were reinforced using 0 . 5%, 1% and 2% fibre volume fractions of steel and PP fibres. The beams with a reinforced cross-section with one or two fibre types were evaluated under flexural loading. The results showed that reinforcement of the entire cross-section with steel fibres led to a higher load-carrying capacity than reinforcement of the cross-section with two fibre types in two separate layers.

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Nowadays, using fibrous materials is used widely in strengthening applications such as cross-section enlargement and using functionally graded reinforced concrete. Functionally graded reinforced concrete is used as multireinforced concrete layers that can be reinforced by different fiber types. The objective of this research was to address the structural benefits of functionally graded concrete materials by performing analytical simulations. In order to achieve this purpose, in the first stage of this study, three functionally graded reinforced concretes by steel and polypropylene (PP) were experimentally tested under flexural loading. Inverse analysis was applied to obtain the used material properties of reinforced concrete by FEMIX software. After obtaining the material properties, to assess the performance of proposed slabs, some other cases were proposed and numerically evaluated under flexural and shear loading. The results showed that increasing steel fiber in reinforced entire cross section led to achieve better shear and flexural performance while the best performance of reinforced functionally graded slabs was achieved for slab at 1% fiber content. In the second stage, nineteen reinforced functionally graded RC slabs with steel bars were simulated and assessed and some other cases were considered which were not experimentally tested.

In this research, in addition to ensuring the accuracy of the numerical simulations, a 3D reinforced concrete column is numerically modeled in three conditions, including a non-retrofitted state, as well as two states retrofitted with steel plates and CFRP. The coupled temperature-displacement analysis of these columns is conducted under cyclic lateral loading in various heat levels, and the effects of both the retrofits and heat on the cyclic lateral behavior of the columns are studied and compared. According to the results of the study, with temperature rise, both lateral forces and energies increase in the non-retrofitted column, the column retrofitted with steel plates, and the column retrofitted with FRP. This is even more significant at 500°C, particularly in retrofitted columns with steel plates. Besides, retrofitting the columns with steel plates (compared to FRP plates) causes a more substantial increase in the heat sensitivity of the column during cyclic lateral loading.