Analysis and Design of Prestressed Precast Hollow Core Slabs Using Strut and Tie Method

Abstract

Strut-and-tie model (STM) is increasingly being used for analysis and design of concrete structures with D-regions, a disturbed region in which the basic assumptions of flexural theory are not applicable such as regions near force discontinuities or near geometric discontinuities. The strut-and-tie approach has also been recently incorporated in the ACI Building Code as an alternative design method. The main advantage of the strut-and-tie model is its transparency and adaptability to prestressed and reinforced concrete members with arbitrary geometry and loading configuration. The internal stresses due to applied loading in the concrete structural elements are transferred through an assumed plane or space truss mechanism to the supports. Precast hollow core slabs are being extensively used in modern commercial and residential buildings. These simply supported slabs are prestressed concrete members with tensile prestressing steel without any web reinforcement, and can be critical in shear for certain loading configuration and thicker slabs. A new strut-and-tie model is proposed to predict the ultimate load-carrying capacity, failure mode and design of prestressed precast hollow core slabs (PPHC slabs). In the proposed model for PPHC slabs without web reinforcement, the compression forces are resisted by concrete compression struts, the tension forces are resisted by prestressing tendons (tension tie) and the tensile forces in the web are resisted by concrete tension elements (concrete ties). The results obtained from the proposed STM model using the software CAST (computer-aided strut and tie) is compared with those obtained from full-scale loading tests conducted on 15 PPHC slabs of different shear span to depth ratio. The proposed strut-and-tie model provides a good correlation with the experimental results and the method can be easily used for analysis and design of hollow core slabs.