Innovative method for strengthening dapped-end beams using an external prestressing technique

Dapped-end beams are precast members of concrete structures that are widely used in buildings and bridges. At the end of dapped-end beams, the discontinuities caused by the abrupt changes in cross-sectional dimensions, as well as the concentrated applied load, characterize this as a disturbed region. Improper dimensioning and distribution of reinforcing steel lead to undesirable cracking and failure mechanisms that must be predicted to apply proper strengthening systems. This article presents an experimental program for eight reinforced concrete beams with dapped ends. Seven specimens were strengthened using different shapes of external prestressing technique directions: horizontal, vertical and inclined. A non-strengthened specimen was investigated as a reference beam. The test results showed that vertical external prestressing techniques are a very effective strengthening method to increase the capacity of dapped-end beams up to 82 % compared to the control specimen. A new failure mode according to the strengthening technique using horizontal external prestressing appeared and led to compression failure. Additionally, a comparative study was conducted to evaluate the efficiency of various strengthening techniques. A strut-and-tie model was utilized in the analysis of such discontinuity in the D-region. A comparison between the present strengthening techniques and other previous work was conducted to provide a reasonable estimation of the efficiency of the results.