Abstract:

In order to investigate the changing rule of shear force transfer mechanism in reinforced concrete beams without stirrups, 9 rectangular shaped and 27 T-shaped reinforced concrete beams without stirrups were designed and fabricated, and shear damage tests were carried out on them. Digital Image Correlation (DIC), displacement meters and strain gauges were used to record the data on displacement, strains and crack kinematic diagrams of critical shear cracks were plotted. Ultimately, the shear resistance contributions of the four shear force transfer mechanisms (aggregate interlock, dowel action, residual tensile stress across cracks, and uncracked compression zone) in the whole process of loading were calculated, and the changes of various shear force transfer mechanisms during the loading process were analyzed. Results show that the number, development level and height of shear cracks have complex coupled effects on the four shear mechanisms; the aggregate interlock basically reaches its maximum at 0.9P_u (P_u is the peak load), and its shear resistance value changes little with the shear span-to-depth ratio, but its contribution proportion gradually decreases as the shear span-to-depth ratio decreases; the dowel action is more stable during the whole loading process, but its proportion also shows a certain decrease with the increase in overall shear capacity; the contribution of the residual tensile stress across cracks is mainly observed in the early loading period, and at the maximum load, this mechanism no longer provides shear resistance due to the full development of cracks; the shear resistance of the uncracked compression zone is influenced by many factors, among which the shear span-to-depth ratio has the most significant effect; the shear resistance of the compression zone in beams with small shear-span-to-depth ratios can exceed twice that of beams with large shear span-to-depth ratios. At the peak load, the aggregate interlock is the most important mechanism in beams with larger shear span ratios, but with the decrease of shear span ratio, the shear capacity of the uncracked compression zone increases rapidly and becomes the most important mechanism.

Key words: reinforced concrete beams without stirrups, shear failure, aggregate interlock, dowel action, residual tensile stress across cracks, uncracked compression zone