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Due to the important role of high strength concrete in the structural systems, present work focuses on the use of this material as a strengthening technique incorporating with the normal strength concrete in flat slab system. Eight simply supported flat slab models with (1,000 × 1,000 × 120 mm) dimensions are investigated based on three groups including normal strength concrete and high strength concrete. The first group represents models containing of two flat slabs fully with one type of concrete; NSC and HSC as control flat slab. The second and third groups consist of six flat slabs as hybrid flat slabs of two layer of concrete with different thicknesses. Concrete mixture HSC was used in tension zone in three hybrid flat slabs (second group) with three thicknesses (30, 60 and 90 mm), while the remaining three hybrid flat slabs (third group) was used the HSC in compression zone with the same previous thicknesses. The experimental results shown that the ultimate load increased about (19.4%) when HSC was used fully (hH / h = 1) instead of using NSC in the control flat slab (NSC slab). The hybrid flat slabs with use HSC in compression zone showed higher in cracking and ultimate flexural loads compared with those of the hybrid flat slabs with use HSC in tension zone and also were stiffer in load-defl ection curve with the hybrid flat slabs with HSC in tension zone, also the hybrid flat slabs showed an improvement in the cracking load and ultimate flexural load when increasing the thickness of the HSC layer (hH / h) in both tension and compression zone as compared to control flat slab (NSC slab).

This paper presents an experimental study of structural behavior of self compacting reinforced concrete beams strengthened in shear by vertical CFRP strips. The experimental work consists of casting and testing of eleven simply supported reinforced concrete beams. One of the tested beam was un-strengthened to be considered as beams, while the remaining beams were tested after being strengthened using vertical CFRP strips. In this study, three parameters were considered, the configuration of CFRP sheets wrapping system, i.e. two sides, U-shape and full wrapped, effect of horizontal strap of CFRP strips to enhance the vertical CFRP strips and CFRP amount. The results showed that the presence of horizontal strap of CFRP strips on the vertical strips increases the shear capacity of the beams ranged between (3-27)% for beams with the same properties, while the increase in the ultimate loads ranged between (20-26)% and (39.5-46)% by comparison of wrapping system (two side with U-shape) and (two side with full wrapped) of CFRP strips, respectively.

In this paper, the experimental work of this research included the test of seven concrete beams with dimensions (0.24 * 0.15 * 1.7) m. The mixing ratio is (1:2:3) and the water ratio(w/c) is 0.5. The first control beam has new aggregates and without strengthen with carbon fiber polymer sheet. The next three beams have the different ratio of recycled aggregate of (25%, 50%, 75%), and the last three beams have the different ratio of recycled aggregate of (25%, 50%, 75%) and with strengthen with carbon fiber polymer sheet. The experimental results showed that the ultimate load in the control beam (NC) became approximately (4,9,14) % respectively higher than the group of the recycle aggregate (B2. B3. B4) beams. When strengthening the beams by carbon fiber polymer sheet. The author notice the ultimate load in the control beam (NC) became approximately (20,16,0) % respectively lesser than the group of recycle aggregate (B5.B6.B7) strengthening beams.

The experimental work of this research included the test of seven columns, with dimensions of 900mm length, and cross section (150*150), a series of tests were carried out on control specimens (cylinder and prisms) for each mix for the purpose of studying the mechanical properties of reactive powder concrete such as compressive strength, splitting tensile strength, modulus of rupture and modulus of elasticity.The experimental results showed the increasing in steel fibers ratio by 2% led to the increase in the compressive strength by 22.3% and increased splitting tensile strength by 329.7%, modulus of rupture by 234.44% and modulus of elasticity by 20.80%. The experimental results of the tests of slender columns indicated that increasing the steel fiber ratio from 0% led decreasing the ultimate load by 36.454 % compared to the control columns, to 2% led increasing the ultimate load by 21.685 % compared to the control columns. The results showed that of diameter steel reinforcement ratio of short columns from Ø10 led to decreasing the ultimate load by 1.859% compared to the control columns, to Ø16 led to increasing the ultimate load by 32.901% compared to the control columns. And the results showed that of spacing between of stirrups (200mm) led to decreasing the ultimate load by 4.778% compared to the control columns, to (100mm) led to increasing the ultimate load by 12.924% compared to the control columns.In the second part of this research, the ANSYS program was used as a numerical method to investigate the behavior of these columns using nonlinear analysis (Finite element). When comparing the results of experimental with theoretical side ,the theoretical results showed a