Torsion behavior of strengthened reinforced concrete box girders with openings: Analytical and experimental investigation

The objectives of the current work are to investigate the influence of pure torsion on the attitude of RCBGs with and without openings and the effect of applying different strengthening systems, such as CFRP sheets or steel plates, on their performance. The strengthening materials were wrapped throughout the span and around the opening region. An experimental test program used eleven RCBGs with dimensions of 1300 mm in length, 350 x 350 mm in cross-section, and 200 x 200 mm in the inner cross-section. Numerical models were employed, and the findings were compared to the outcomes of experiments to validate the FE. After verification, various factors were examined, including the impact of the opening's location, size, quantity, area, and changes in the amount of longitudinal and transverse steel. The comparison investigation showed that the most significant variables determining the torsional moment are the number of apertures and their diameters. Additionally, the torsional strength lost due to the strengthening around it makes up for the aperture.