Push-out tests for shear connections between UHPFRC slabs and FRP girder Hai Nguyen a,⇑ , Hiroshi Mutsuyoshi b , Wael Zatar c a Rahall Transportation Institute, 907 Third Avenue, Huntington, WV 25701, United States b Department of Civil and Environmental Engineering, Saitama University, Shimo-Okubo 255, Sakura-ku, Saitama-shi 338-8570, Japan c College of Information Technology and Engineering, Marshall University, 112 Gullickson Hall, One John Marshall Drive, Huntington, WV 25755, United States article info Article history: Available online 15 August 2014 Keywords: Composite girders Carbon/glass Fiber-Reinforced Polymer Ultra-High Performance Fiber-Reinforced Concrete Shear connectors Ultimate resistance Empirical equation abstract This paper presents an experimental investigation on the shear connections between carbon/glass Fiber- Reinforced Polymer I-girder and Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs. Effects of straight/inclined bolt shear connectors and effective embedment depth-to-bolt diameter (h ef / d) ratios were investigated. Fourteen push-out tests were conducted to evaluate the load–slip behavior and the ultimate resistance of the bolt shear connectors. With the use of the UHPFRC, the h ef /d ratio needed for obtaining a shear connector failure mode was 2.7 times lower than that obtained from 43 push-out tests in the literature for normal weight and lightweight concrete slabs. The inclined bolt shear connectors showed a more ductile behavior than the straight bolt shear connectors. The experimentally obtained ultimate resistance of the bolt shear connectors was compared against the equations provided by ACI 318-11, AISC 2011, AASHTO LRFD 2010, PCI 2004, and EC-4 2004. An empirical equation to predict the ultimate shear connector resistance was proposed and validated by the experimental data. Idealized load–slip models and equations to predict the load versus slip relationship for all push-out tested spec- imens were proposed. Curve fitting was performed to find fitting parameters for all tested specimens and the results showed a very good correlation with the experiments. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Fiber-Reinforced Polymer (FRP) materials have been widely used in civil infrastructure applications due to their excellent mechanical properties such as lightweight, high strength-to- weight ratio, good fatigue strength/durability, and corrosion resis- tance. Hybrid FRP (HFRP) I-girders consisting of carbon FRP (CFRP) and glass FRP (GFRP) laminae were developed for bridge applica- tions [1]. Lightweight and good corrosion resistance of the HFRP I-girders can provide an excellent solution for structures exposed to hostile and aggressive environments. These girders also provide an acceptable alternative for accelerated bridge construction. The HFRP I-girders were successfully applied to a pedestrian bridge construction in Kure city, Hiroshima prefecture, Japan in 2011 (Fig. 1). The bridge consisted of two HFRP I-girders topped with a GFRP gratings bridge deck and was built to replace a deficient steel bridge. It was simply supported with a total length of 12 m and an effective width of 0.75 m. The HFRP I-girders subjected to four-point flexural loading were tested and analyzed [1]. The results indicated that the design of the HFRP I-girders was governed by deflection rather than strength limitations. This was due to the low elastic modulus of the FRP materials compared with the steel girder alternative. To improve the strength and stiffness of the HFRP I-girders, they were com- bined with the Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs to form HFRP–UHPFRC composite girders. The effectiveness of the HFRP–UHPFRC composite girder system has been proved by experimental investigations presented elsewhere [2–6]. An important consideration when designing composite girders is the shear interaction between the girder and the slab. Headed studs have been widely used in steel–concrete composite girders to transmit horizontal shear force from the slab to the girder. Stud resistance and load–slip behavior of stud connections have been experimentally and numerically evaluated by various researchers. Viest [7] performed push-out tests of round headed steel studs to determine the behavior and load carrying capacity of stud shear connectors. He proposed one of the first empirical equations for determining the relationship between the shear connector strength and the compressive strength of concrete. Driscoll and http://dx.doi.org/10.1016/j.compstruct.2014.08.003 0263-8223/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 (304) 942 2295; fax: +1 (304) 696 5454. E-mail address: hai.nguyen.2004@gmail.com (H. Nguyen). Composite Structures 118 (2014) 528–547 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct