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Abstract
The main purpose of this thesis was to study the behavior of lap splice of deformed steel reinforcement in tension zones in reinforced concrete beams. The effect of different variables affecting the behavior of flexural members with lap splice in tension was studied. An experimental program was conducted on twelve simply supported reinforced concrete beams. All tested beams have the same dimensions of (150 x 160 x 2600 mm), concrete strength (f,,,=36 N/mm 2 ), and the same longitudinal reinforcement ratio (V=0.86%). All beams were tested using four points loading, till failure occurred. The variables studied were:
1. Cut-off ratio at definite section, which is the ratio between spliced bar’s area at this, section and the total bars area at the same section. The values of cut off ratio were 0.0%, 25%, and 100% of tensile reinforcement area.
2. Lap splices length. Values of 27, 54, and 75 times the bar diameter were used.
3. The type of transverse reinforcement in the splice zone. In this study different types of transverse reinforcement were used, they were vertical stirrups, vertical stirrups with additional legs in the splice zone, rectangular confinement reinforcement in the splice zone, continuous rectangular confinement reinforcement in the splice zone, and spiral confinement reinforcement in the splice zone.
4. Spacing of vertical stirrups; the values of spacing were 120mm, 90mm, and 60mm (three, four, and five stirrups in the splice zone, respectively).
The test results are illustrated with tables and figures, and discussed briefly. Some of the outcome conclusions which the results illustrate may be summarized as follow:
1. For the same value of the lap splice length recommended by Egyptian Code (54 db), without the use of transverse reinforcement at the spliced zone, the change of the cut off ratio from 25% to 100% resulted in a reduction in ductility and changed the mode of failure from ductile flexural failure to splitting one.
2. Spliced beams with splice length of 27 times the bar diameter, 100% cut off ratio, and provided with transverse reinforcement as confinement for the spliced zone showed higher values of ultimate loads when these beams were compared with the un-spliced beam. The gain in the ultimate strength ranged between 3 to 10%, depending on the type of the transverse reinforcement which was used. The maximum increase in strength was obtained for the beam with two interlocking spiral confinement. Also, there was a drastic increase in ductility of beams when transverse reinforcement, in form of vertical stirrups, two interlocking spiral confinement, and continuous rectangular confinement was used in the spliced zone. The ratio of A „/ A y was about 2.7 times larger than that of the un-spliced.
3. Splitting cracks at the bottom of the spliced beam did not occur for beams provided with transverse reinforcement with 60 mm spacing. However, for beams with transverse reinforcement in form of vertical stirrups with greater spacing (90 mm, and 120mm), these splitting cracks appeared just before failure. The failure of these beams was ductile flexural failure and the presence of transverse reinforcement prevent the occurrence of the brittle failure as happened in the beam with the same cut off ratio (100%) , and splice length (27 db).
4. The behavior of the ordinary beam without splice can be achieved in spliced beams with 100% cut off ratio when the lap splice length equal to or greater than 54 times the bar diameter without using any transverse reinforcement, or when the lap splice length equals 27 times the bar diameter using transverse reinforcement having spacing equal to or less than 120mm (i.e. Three stirrups at the lap splice zone) for the dimensions and reinforcement used in the present study.