Improving the shear behavior of RC dapped-end beams using precast strain-hardening cementitious composite (P-SHCC) plates

Abstract

Dapped-end beams (DEBs) are frequently used in precast concrete structures in order to facilitate the construction procedures. However, premature failure is most likely to happen at their re-entrant corner owing to the immense shearing stresses in this region. To mitigate such a problem, a new strengthening system making use of Strain-Hardening Cementitious Composites (SHCC) material was utilized in this paper. For this purpose, an experimental study on ten DEBs specimens, including one defected un-strengthened specimen (BC), was prepared and tested under a monotonic 4-point loading protocol to assess the efficiency of the adopted strengthening system. The traditional reinforcement at the re-entrant corner was substituted by precast SHCC (P-SHCC) plates to upgrade the shear strength and serviceability of the tested DEBs. The P-SHCC plates were pre-cured for about 4 weeks before being used to mitigate any volumetric change issues related to SHCC. A slight amount of reinforcement was provided inside the P-SHCC plates to enhance their cracking behavior and avoid strain localization. The studied parameters were the scheme of P-SHCC plates at the re-entrant corner (continuous or intermittent/discontinuous), the orientation of P-SHCC plates (vertical or 45°-inclined), as well as their position with regard to the beam's cross-section (external or internal). The thickness of each external P-SHCC plate was kept constant at 20 mm so as to be easily incorporated into the concrete cover, whereas the internal P-SHCC plates had varied thicknesses (40, 55, or 70 mm). The test results revealed that providing DEBs with P-SHCC plates could significantly improve both shear capacity and the developed ductility. The gain in the ultimate load reached up to 91 % relative to the un-strengthened specimen (BC). Furthermore, a great reduction in the developed major shear crack width for all strengthened DEBs was attained. At the service load level, all strengthened DEBs showed a decreased crack width, with an average value of about 77 % compared to the specimen BC. Finally, two equations considering the contribution of P-SHCC plates were proposed to predict both the shear strength and the average crack width of the strengthened DEBs. The proposed equations showed good agreement with the experimental results.