Development Length Assessment of Bonded Post-Tensioning Slabs with Bulb-Shaped Dead end Anchorage

The bond between prestressing strands and concrete within the dead-end zone of a post-tensioned concrete member significantly influences the effectiveness of the strand-concrete system. However, the existing code equations for determining development length rely on studies conducted on pretensioned concrete members rather than post-tensioned ones. As a result, the implementation of development length for prestressing strands with bulb-shaped dead end anchorage in post-tensioning slabs relies on common practice and former experience. Unfortunately, this can sometimes lead to concrete cracks or strand slippage at the dead end zone due to insufficient development length. This paper presents an experimental study on post-tensioning slab segments representing the dead end zone. The aim of this study is to assess the development length of prestressing strands with bulb-shaped dead end that shall guarantee full bond with concrete throughout the member’s service life. The Specimens were divided according to three different concrete compressive strengths 34 MPa, 48 MPa and 70 MPa. The parameters considered included slab thicknesses of 160 mm and 250 mm, as well as strand embedment lengths of 700 mm and 850 mm. Based on the test results, the sufficient development length was determined. Furthermore, a verification was carried out to assess the validity of applying predicted equations from an adopted bond model to determine the bond strength of strand with bulb-shaped dead end anchorage in concrete slabs.