This study presents the experimental results of twenty three reinforced concrete beams with rectangular web openings externally strengthened with Fiber Reinforced Polymers (FRP) composites bonded around openings. All tested beams had the same geometry and reinforcement details. At openings locations, the stirrups intercepted the openings were cut during fabrication of reinforcement cage to simulate the condition of inclusion of an opening in an existing beam. Several design parameters are considered including the opening dimensions and location in the shear zone, the wrapping configurations, and the amount and the type of the FRP composites in the vicinity of the openings. The wrapping configurations of FRP included: sheets, strips, U-shape strips, and U-shape strips with bundles of FRP strands placed at the top and sides of the beam forming a fan under the strips to achieve closed wrapping. The effect of these parameters on the failure modes, the ultimate load, and the beam stiffness were investigated. The shear contribution of FRP on the shear capacity of tested beams with web openings was estimated according to ACI Committee 440-08, Canadian Standards S6-06, and Khalifa et al. model and examined against the test results. A modification factor to account for the dimensions of opening chords was applied to the predicted gain in the shear capacity according to ACI 440-08 and CSA S6-06 for bonded Glass Fiber Reinforced Polymers (GFRP) around openings. The analytical results after incorporating the modification factor into the codes guidelines showed good agreement with the test results.
The results of an experimental program conducted on seventeen simply supported concrete beams to study the effect of transverse reinforcement on the behavior of the lap splice of a steel reinforcement in tension zones in high-strength concrete beams are presented. The parameters included in the experimental program were the concrete compressive strength, the lap splice length, the amount of transverse reinforcement provided within the splice region, and the shape of the transverse reinforcement around the spliced bars. The experimental results showed that the displacement ductility increased and the mode of failure changed from a splitting bond failure to a flexural failure when the amount of the transverse reinforcement in the splice region increased, and the compressive strength increased up to 100 MPa. The presence of the transverse reinforcement around the spliced bars had a pronounced effect on increasing the ultimate load, the ultimate deflection, and the displacement ductility. The prediction of maximum steel stresses for spliced bars using the ACI 318-05 building code was compared with the experimental results. The comparison showed that the effect of the transverse reinforcement around spliced bars has to be considered into the design equations for lap splice length in high-strength concrete beams.
This research presents the experimental and analytical results for reinforced concrete (RC) beams with rectangular large web openings under pure torsion. Fifteen specimens were tested; one solid specimen without opening, six specimens without reinforcement around opening as if an opening is created in an existing beam; where the investigated parameters were opening width, opening height and opening eccentricity from the longitudinal beam axis, and eight specimens with reinforcement installed around the opening to reduce the effect of the opening on the torsional behavior; where the investigated parameters were the shapes and amounts of the reinforcement around the opening. The test results showed that installing stirrups and horizontal reinforcement bars in the chords above and below the openings efficiently increased the cracking and ultimate torque of the tested specimens; where using inclined stirrups by 45º to the longitudinal axis of the specimens increased the ultimate torque to be about 90% of that of the solid specimen. Installing closed stirrups around the opening had small effect on enhancing the torsional behavior of the tested specimen compared with using horizontal and vertical reinforcement bars. The analytical model based on Modified Variable Angle Truss Model (MVATM) used to obtain the torque-rotation curves for beams under pure torsion was modified to incorporate the beams with large web opening which have different arrangements of reinforcement around the opening. MATLAB program language was used to obtain the analytical torque-rotation curves for the specimens that have reinforcement around the opening which were in good agreement with the experimental results.
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