Controlling shear behavior of strand debonded pretensioned bridge girders: An experimental study for Indian highway design practice

Abstract

Strand debonding is commonly used in pretensioned prestressed concrete bridge girders to control end-zone tensile stresses and improve flexural behavior. However, reducing effective prestress near the supports can lower web-shear resistance. Earlier editions of the Indian road congress (IRC) Code IRC 112 did not limit debonding, and several bridges designed on flexural criteria alone exhibited premature web-shear cracking. The 2020 revision of IRC 112, via SP 71 (2018), introduced limits on debonded strands (33 % overall), but these provisions lack experimental validation for Indian girder configurations and provide no guidance for end-zone reinforcement detailing found in international provisions such as the AASHTO LRFD Bridge Design Specifications (2024) and detailing guidance reported in NCHRP Research Report 849 (2017). This study reports shear-dominant static tests on four half-scale pretensioned I-girders representative of typical 25 m highway spans, with 0 %, 25 %, 50 %, and 75 % strand debonding. Increasing debonding resulted in reduced shear capacity, steeper diagonal crack inclination, and larger crack widths, indicating weakened compression field and end-zone shear transfer due to reduced precompression. The results provide practical, evidence-based recommendations for allowable strand debonding and end-zone detailing to improve long-term safety and performance of prestressed concrete bridge girders in India.