This research concentrates on evaluating the effect of using two new techniques for strengthening steel beams with carbon fiber–reinforced polymer (CFRP) strips on the structural behavior of these beams at service and ultimate load stages by using a confining steel plate in two different configurations. Five steel beams with lengths of 1,500 mm were tested under a single concentrated load at midspan: the first (nonstrengthened) beam was used as a reference beam, the second beam was strengthened by only a CFRP strip located at the bottom flange (tension face), and the third beam was strengthened by only a steel plate, which is also located at the bottom flange. The first technique is represented in the fourth beam, which was strengthened by a CFRP strip confined by a steel plate welded at its ends, whereas the second technique is obtained by an amendment done on the first technique and is represented by the fifth beam, which was strengthened by a CFRP strip with the confining steel plate (welded at its ends) and glued with the CFRP strip by a suitable epoxy adhesive. Test results have shown that the first technique has led to less deflection, less tensile strain, and a higher yield load at the service load stage (i.e., elastic region), whereas the second modified technique has led to a further decrease in deflection and tensile strain and an additional increase in yield and ultimate loads, and both of those outcomes were higher than the algebraic sum of the increases resulting from beams strengthened by a “steel plate” and “CFRP strip” individually.
Seven simply supported steel beams were tested to examine the effects, in terms of strengthening, of external prestressing of strands on the shear behaviour of steel beams. All beams had the same steel section and clear span length and strengthening was implemented using two external prestressing strands. The tested beams were divided into two groups based on the presence of the external prestressing strands: the first group thus consisted of just one steel beam, as a reference, while, the second group had six steel beams strengthened by external prestressing strands divided according to the eccentricity location of a prestressing strand with jacking stress fpj = 1120.061 MPa. During the tests, it was found that the shear load strain curves for the tested beams were slightly stiffer than for the reference beams and that the percentage of stiffening increased with any increase in the eccentricity of strand locations from the shear points; the maximum shear load increased by 0.521%, 29.565%, 38.26%, 61.739%, 24.347% and 86.956% with an increases in the eccentricity location from (0 to 165) mm compared to the reference beam. The maximum shear strain increased by 9.664%, 3.553%, 8.121%, 62.436%, 37.563% and 13.451% with an increase s in the eccentricity location from (0 to 165) mm respectively as compared with the reference beam.
In this research, an attempt has been made to study the effect of replacing all normal-weight aggregate “NWA” by lightweight aggregate “LWA” (having a volume equal to 60% of the volume of normal-weight aggregate) on the behaviour of layered steel fibrous self-compacting reinforced concrete slabs with various volume fractions of steel fiber under uniform area load using fine sand technique. The experimental work consists of two groups “NWA” and “LWA,” each group consists of three slab specimens (having an aspect ratio equal to the golden ratio, i.e., 1.618), the thickness of each slab is divided into two equal layers, the top layer is free from steel fibers, while the steel fibers exist only in the bottom layer with three volume fractions (0%, 0.4%, and 0.8%). Ultimate uniform load of the slabs decreases with the increase in steel fiber content, while the percentage of decrease in the bulk density remains rather constant. It was also found that the ultimate uniform load of the slabs in each group is significantly improved with increasing steel fiber content, and the percentage of this improvement is higher in lightweight concrete “LWC” than in normal-weight concrete “NWC” Finally, it was noticed that when steel fiber increased, the flexural strength of slabs increased higher than shear strength; therefore, the mode of failure has been changed from bending to shear mode for slabs of both groups “NWC” and “LWC.”
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