Strength Effect of Cutting off Tension Bars in Concrete BEAMS

摘要

Sixty-four concrete beams reinforced with no. 8 or no. 11 bars (largely A432) were tested as simple beams. Most of these had bars cut off at the minimum point for moment or at 12D or 15D beyond such points. Some, for comparison, contained full length bars or bars bent up. The majority of the beams with bars cut off were designed to be balanced at ultimate in flexural strength, shear strength, and bond strength. The addition of extra stirrups improved the weak beams, but stirrup effectiveness in replacing strength was only about half the normal rfy evaluation. Design recommendations based on the use of the ACI Building Code allowables for bond and shear stresses are made for beams with bars cut off. Designs should be based on a typical 30 percent loss of shear strength where bars cut off, a 20 percent loss where heavy stirrups are already provided (rfy greater than or equal to 130 psi), and a 10 percent loss for slabs 12 inches or less in thickness. If remedial stirrups are used, they should provide an rfy adequate to care for twice the indicated shear deficiency and in no case less than 100 psi. (BPR Abstract)