Awad Waryosh, Waleed, et al. “Torsional Behavior of Reinforced Concrete Hollow Core Beams”. Journal of Engineering and Sustainable Development, vol. 19, no. 2, Mar. 2015, pp. 72-88, https://jeasd.uomustansiriyah.edu.iq/index.php/jeasd/article/view/806.