Design Against Cracking at Openings in Prestressed Concrete Beams Hany Abdalla, Ph.D. Post-Doctoral Fellow Department of Civil and Environmental Engineering University of Windsor Windsor, Ontario, Canada Web openings in beams occur quite often in practice to provide convenient passage of electrical and mechanical conduits. In this paper, the analysis and design against cracking of simply supported prestressed concrete beams with rectangular openings are presented. Several design parameters are varied, including opening width and depth, horizontal and vertical locations of the opening, type of cross section, and amount and arrangement of reinforcement around the opening. The results from a finite element analysis are substantiated by test results. A simple design method for estimating the cracking load for the different crack patterns is proposed and two illustrative design examples are presented. L John B. Kennedy D.Sc., Ph.D, P.Eng. University Distinguished Professor Department of Civil and Environmental Engineering University of Windsor Windsor, Ontario, Canada I n modern building construction, openings through beams and gird ers are required for the passage of utility ducts. Passing these ducts through openings in the webs of the floor beams eliminates a significant amount of dead space and results in a more compact and, often, more eco nomical design. However, the pres ence of openings gives rise to exces sive stresses that may be detrimental unless properly assessed and designed. Practical and experimental experi ences have shown that, quite fre quently, horizontal cracks develop at openings at the transfer stage and in clined cracks develop at the corners of openings at the working stage. Such cracks can seriously reduce the load carrying capacity of the beam. Several investigations have been carried out on reinforced concrete beams with openings (Mansur et al.” 2 ). Comparatively little attention has been directed toward the behavior of pre stressed beams with openings. Barney et al. 3 suggested that the shear force at an opening in a pretensioned pre stressed beam be distributed to the bottom and top chords of the opening in proportion to their uncracked mo ments of inertia until cracking occurs. After cracking, the shear distribution between the opening chords was based on the extent of cracking in the tension chord. Dinakaran and Sastry 4 proposed that this force be distributed in propor tion to the cross-sectional areas in post-tensioned prestressed concrete T beams with openings. 60 PCI JOURNAL