STRENGHT AND BEHAVIOR OF REINFORCED CONCRETE RING DEEP BEAMS

Abstract

ABSTRACT The main goal of this study is to investigate the behavior of reinforced concrete ring deep beams based on the STM of ACI 318M-14. This research includes casting and testing program for eight reinforced concrete ring deep beam specimens divided into four groups. The sectional width of all specimens is 100mm with a diameter of 1000mm c/c. All specimens are subjected to single concentrated load at mid of each span and supported on three supports except one of them. The variables that have been considered are as follows: secondary reinforcement, main reinforcement, height of ring deep beam, and number of supports. The first group comprises removing horizontal secondary reinforcement, removing vertical secondary reinforcement, and removing both of them together. The second group comprises decreasing quantity of main reinforcement by about 61% and 100%. The third group comprises reducing the height from 350 mm to 300 mm, i.e., 14%. The fourth group had increased in the number of supports from 3 to 4. The experimental ultimate capacity, load-deflection response, deflection at first crack, crack type and propagation, in addition to crack characteristics were all investigated and discussed. Besides to failure conditions, strain values in steel bars and average strain values in concrete surfaces are also investigated. Abstract vi The experimental results show that the load-midspan deflection responses obtained for the tested specimens are roughly linear for the majority of the loading process, then bend slightly, except when vertical shear reinforcement is omitted or no secondary reinforcement is provided, in addition to the case of no main reinforcement. This illustrates the most common shear deformation behavior, which leads to brittle failure. The experimental results also show the efficacy of the ACI 318 STM, although it is conservative by 37-41%. The lateral displacement at the load application point is also measured. Until the appearance of the first crack, the dependence of the torsional moments and lateral displacement is nearly linear. After cracking, the lateral displacement significantly increased. Load capacity decreased by about 12.5%, 38.5%, and 55%, when removing horizontal secondary reinforcement, removing vertical secondary reinforcement, and removing both of them together respectively. While the midspan deflection decreased by about 15% when removing horizontal secondary reinforcement, removing vertical secondary reinforcement and removing both of them together led to increase deflection by 0.5%, and 32.8% respectively. The load capacity and midspan deflection were not affected when the main reinforcement ratio decreased by about 61%, because the failure was a strut shear failure. As for when the main reinforcement was completely removed, the failure shifted from the strut to the tie, and the load capacity and midspan deflection decreased by about 36% and 23.5%, respectively. Reducing the height from 350 mm to 300 mm, i.e., 14%, led to decrease the load capacity by about 15%, while the midspan deflection increased by about 32.8%. The increase in the number of supports from 3 to 4 led to increase load capacity by about 63%, while midspan deflection decreased by about 48%.