Interface Shear Transfer of Lightweight-Aggregate Concretes with Different Lightweight Aggregates

This report presents the results from the second phase of an ongoing investigation of the direct shear transfer across an interface of lightweight aggregate concretes. The lightweight concretes were made with different lightweight aggregate materials (expanded shale, expanded slate, and expanded clay). The second phase of the experimental investigation included 52 push-off specimens. Test variables included concrete type (normalweight, sand-lightweight, or alllightweight), lightweight aggregate materials, surface preparation of the shear interface, reinforcement ratio, and crack interface condition. Applied shear force-slip relations are presented and discussed. Peak shear strengths are also compared. Current shear-friction design provisions in the ACI 318 code and the PCI Design Handbook are examined. Shear strengths computed using the coefficient of friction μ-approach by the PCI Design Handbook (Equation 5-32a) and the ACI 318 code (Equation 22.9.4.2) and the effective coefficient of friction μe-approach in the PCI Design Handbook (Equation 5-32b) are found to be conservative for the sand-lightweight and alllightweight monolithic and cold joint specimens in this study. This report also presents a database of shear-friction test results collected from the literature that is analyzed for the effective coefficient of friction μe-approach used in the PCI Design Handbook (Equation 5-32b), and the coefficient of friction μ-approach used in the PCI Design Handbook (Equation 5-32a) and the ACI 318 code (Equation 22.9.4.2). The database is limited to pushoff specimens subjected to monotonic loading and without external normal forces. The data are categorized in terms of concrete type, interface condition, compressive strength of concrete, clamping stress, and area of shear interface to help identify gaps in the literature. It is envisioned that this database will be expanded in the future to further examine shear-friction models and design provisions in various codes/standards. Analysis of the current database shows that PCI Equation 5-32b is more accurate and has a lower coefficient of variation than both PCI Equation 5-32a and ACI Equation 22.9.4.2 for normalweight, sand-lightweight, and all-lightweight concrete with monolithic uncracked, monolithic pre-cracked, and cold joint roughened interface conditions. Based on the results of the experimental program conducted and analysis of the database developed, revisions to the PCI Design Handbook and ACI 318 code are proposed for shearfriction design provisions of a smooth interface condition. For the cold joint smooth interface condition, the authors recommend removing the term  in the coefficient of friction μ to provide more accurate and economical designs.

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