Lightweight Concrete Modification Factor for Shear Friction

2013PDFTech ReportNUTC R276 / R317Project #00034650 / 00040840DTRT06-G-0014Lightweight concreteShear propertiesBridge superstructuresPrecast concreteCoefficient of frictionFriction factorStructural connectionResearch HubLightweight concreteShear propertiesFriction factorMissouriUnited StatesMissouri University of Science and Technology. Center for Transportation Infrastructure and SafetySneed, Lesley H.Shaw, Dane M.Missouri University of Science and Technology. Center for Transportation Infrastructure and SafetyUnited States. Dept. of Transportation. Research and Innovative Technology AdministrationUS Transportation CollectionThis report describes the results of a study initiated to examine the influence of concrete unit weight on the direct shear transfer across an interface of concretes cast at different times. This type of interface is common with structural precast concrete connections, such as corbels, for which shear friction design provisions are commonly used. Increasing use of lightweight aggregate concretes prompted this investigation to determine the appropriateness of current shear friction design provisions with respect to all-lightweight and sand-lightweight concrete. The experimental investigation included thirty-six push-off test specimens, each of which was constructed with a cold-joint at the interface shear plane. Test variables included unit weight of concrete (108, 120, and 145 pcf), target compressive strength of concrete (5000 and 8000 psi), and interface condition (smooth or roughened). A constant amount of reinforcing steel was provided across the shear plane. Results suggest that concrete unit weight did not play a significant role in the interface shear strength for the cold-joint specimens in this study. Results were also compared with shear friction design provisions in both the ACI 318 code and the PCI Design Handbook. Shear strengths computed using the coefficient of friction approach was conservative for the sand-lightweight and all-lightweight cold-joint specimens in this study. The value of the effective coefficient of friction e computed using the PCI Design Handbook approach was found to be conservative for both roughened and smooth non-monolithic interfaces for each concrete type. Finally, the use of the lightweight concrete modification factor in the calculation for the effective coefficient of friction ?e was found to be conservative for the sand-lightweight and all-lightweight cold-joint specimens in this study. This study is sponsored by the Precast/Prestressed Concrete Institute Daniel P. Jenny Fellowship Program and the National University Transportation Center at the Missouri University of Science and Technology in Rolla, Missouri