وسيم حمزه مهدي الحداد

This study aims to improve the mechanical properties of waste aggregate concrete by using steel fibers and waterproof liquid admixture. The study shows that using waste rocks and glass aggregate improves mechanical properties comparing with reference mix, using steel fibers increase compressive strength, tensile strength and much higher values in the flexural strength. Using waterproof admixture enhance mechanical properties of steel fiber concrete and give higher strength concrete, compressive strength increased from 43.33 MPa for steel fiber concrete (with waste aggregates) to 57.82 MPa, tensile strength increased from 4.64 MPa to 5.83 MPa , flexural strength increased from 8.95 to 12.73 MPa and also the modulus of elasticity increased from 29801 MPa for steel fiber-waste aggregate concrete to 33879 MPa for waste aggregate-steel fiber concrete improved with waterproof admixture.

In this paper, shear behavior of reinforced hybrid concrete connection of corbel-column is experimentally investigated. Nine homogenous and hybrid concrete corbel-column connections subjected to vertical applied loads were constructed and tested within two test groups (A, B). The experimental program included the effect of several variables such as type of hybrid concrete;high strength concrete (HSC) or steel fiber reinforced concrete (SFRC), monolithic casting of hybrid concrete connection, and presence of construction joint at the interface of corbel-column. Experimental results showed significant effects of concrete hybridization on the structural behavior of connection specimens such as: ultimate strength, cracking loads, cracking patterns, and failure modes. Hybridization process in group (A) included hybrid connection of corbel-column with HSC or SFRC corbel instated of NSC. This process led to increase the capacity of connection by (26%, 38%) and shear cracking loads by (20%, 120%) respectively. Moreover, connections of hybrid concrete corbels cast monolithically improved the shear capacity of corbels by (19%, 42%) for HSC or SFRC respectively. In group (B), presence of construction joint at connection region reduced the shear capacity of connectionsby (10% to 22%) and cracking loads by (23%-62%) compared with connections cast monolithically.

Abstract: Rehabilitation, upgrading, or strengthening of structural members, especially columns, has become the target of many researchers because columns are the most important members in a building and the failure of columns causes direct collapse in the building. This study aims to get an assessment of the best pattern of steelframed jacket used for strengthening axially loaded concrete columns by numerically studying the behavior of the column for different cases of the same amount of steel jacket. The jacket consists of four angles and/or battens. lacings, or battens with lacings. The nonlinear analysis program designated as ARCC-SSJ (Analysis of Reinforced Concrete Columns (Strengthened by Steel Jacket) is used to compare different patterns with the same and different cross-sections of battens and single lacing, as well as battens and lacing with battens taken into account. It is found that lacing with battens is the best pattern for the same amount of steel jacket with different cross-sectional areas. It is observed that the load-carrying capacity of the column increased by approximately 1.8 and 1.15% over that of battens alone in the case of a lacing angle of 60.832 ∘ and 74.407∘ with the vertical axis of the column, respectively.

In this paper, shear and flexural behavior of reinforced hybrid concrete corbel-column system was experimentally investigated. Fourteen hybrid and homogeneous concrete corbel- columns systems subjected to un-symmetrical loading were constructed and tested within two test groups (A, B). The experimental program included several variables, such as: type of hybrid concrete; high strength concrete (HSC) or steel fiber reinforced concrete (SFRC), shear span to depth ratio (a/d), area of hybridization in corbel - column system.Experimental results showed significant effects of concrete hybridization on structural shear and flexural behavior, including: ultimate strength, cracking loads, cracking patterns, failure modes, and ductility. hybridization process ingroup (A) included casting the corbel with HSC or SFRC instated of normal strength concrete (NSC). In shear behavior, corbels (a/d= 0.37), this process led to increase the shear capacity of corbel by 26% (38%) and shear cracking loads by (20%, 120%), respectively. Furthermore, in flexural behavior, corbels (a/d= 0.74) shear capacity increased by (19%, 42%), flexural cracking loads increased by (29%, 143%) for HSC and SFRC corbels respectively. In group B, the hybridization process included increasing the hybrid area of corbelcolumn system in group (A) to represent a distributed region (D-region) or decreasing it to represent hybrid corbel. In both cases, shear capacity of corbel increased with a range of (10 to 41%) for specimens hybridized monolithically with HSC, while it increased with a range of (19 to 44%) for specimens hybridized monolithically with SFRC, compared with homogenous NSC specimens having same (a/d) ratio.