Title: Shear strength of cast-in connectors in ultra-thin, ultra-high-performance-concrete panels with polyoxymethylene fibers
Date Published: January - February 2026
Volume: 71
Issue: 1
Page Numbers: 25 - 46
Authors: Hoda Osman and Amir Fam
https://doi.org/10.15554/pcij71.1-01

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Abstract

The replacement of normal-strength concrete in precast concrete panels with ultra-high-performance concrete (UHPC) results in a significant reduction in panel thickness. This poses a challenge when connecting these very thin wall or floor panels to the frame of the building, for example, because of the small embedment of the connectors. This paper examines the behavior of cast-in-place connectors in ultra-thin UHPC panels under direct shear loading for a variety of connector types, including two threaded bolts (carriage bolt and L-shaped bolt) and two female headed inserts (zamac insert and flower-shaped insert). The connections were tested under shear loading in 104 panel tests with varying parameters for panel thickness, connector diameter, polyoxymethylene (POM) fiber content, support span length, and edge distance of the connector. The failure mode observed by most connector types was consistently a V-shaped concrete cone breakout. Cast-in connectors outperformed the postinstalled connectors by 110%. Connectors embedded in 38 mm (1.5 in.) thick panels showed up to a 120% increase in strength compared with 15 mm (0.6 in.) thick panels. In addition, a 45% to 65% increase in strength occurred when the cast-in-place connection was embedded at a 64 mm (2.5 in.) edge distance compared with a 25 mm (1 in.) distance. Existing shear strength equations for normal-strength concrete grossly overestimated connector strength. A design equation is proposed for cast-in connectors in thin UHPC panels with POM fibers by introducing a strength amplification factor to an existing equation for postinstalled connectors.