Behavior of high-strength concrete interior slab-column connections with openings under seismic loading Ahmed M. Yousef a , Salah E. El-Metwally a , Hamed H. Askar a , Mahmoud A. El-Mandouh b,⇑ a Faculty of Engineering, Mansoura University, Mansoura 35516, Egypt b Civil Engineering Department, Beni-Suef University, Beni-Suef, Egypt highlights  Seismic behavior of HSC slab-column connections is similar to that of NSC.  The size of openings have significant effect on the punching shear strength.  The ultimate punching shear strength equations of ACI 318-2014 are safe for HSC.  Opening size of one-seventh the width of column strip is still on the safe side.  The proposed numerical model gives accurate predictions for the punching strength. article info Article history: Received 7 November 2018 Received in revised form 13 February 2019 Accepted 17 April 2019 Keywords: Interior slab-column connection Opening High-strength concrete Punching shear strength Finite element model abstract Nine full-scale reinforced High-Strength Concrete (HSC) and Normal-Strength Concrete (NSC) interior slab-column connections with openings have been tested under seismic loading. The applicability of the punching shear design provisions of ACI 318-2014 building code, the Egyptian code (ECP 203- 2017) and the code of the Japan Society of Civil Engineering (JSCE-2007) when applied to HSC interior slab-column connections have been examined. The main studied parameters is the concrete strength (NSC with f c ‘ = 25 MPa and HSC with f c ‘ = 75 MPa) and the openings location and size. A numerical model for predicting the seismic behavior of interior slab-column connections has been proposed using three dimensional finite element computer program. The results show that the punching shear strength calcu- lated using the equations of the ACI 318-2014 are conservative for NSC and HSC specimens, while for ECP 203-2017 the calculated values are conservative for NSC specimens and just safe for HSC specimens. Ó 2019 Published by Elsevier Ltd. 1. Introduction During a ground motion, the large horizontal inertia forces and lateral displacements in buildings are induced by the horizontal movement of the ground. The moments in the exterior slab- column connections are produced by the inter-story drifts and rotation of slab-column connections. The moments and gravity loads increase the punching shear stresses in a concrete slab around the column region, especially for the cases of openings. Subsequently, flat slab buildings may suffer collapse during earth- quakes. Ninety-one waffle slab structures collapsed and forty-four experienced damage in Mexico city due to an earthquake in 1985, in addition, four stories reinforced concrete flat slab buildings were damaged in Northridge by earthquake in 1994 [1]. In the past three decades, several experimental and analytical investigations on the behavior of Normal-Strength Concrete (NSC) slab-column connec- tions with and without openings have been reported [1–12], while very small number of tests has been conducted on the behavior of slab-column connections with and without openings constructed from High-Strength Concrete (HSC) [13–16]. Recently, compressive strengths approaching 138 MPa have been used in cast-in-place tall buildings [17]. So, many questions have been raised about the seismic behavior of HSC interior slab-column connections with and without openings. On the other hand, there are considerable variations in the provisions used to estimate the punching shear strength of reinforced concrete interior slab-column connections in the current international codes. In the united states, the code of the American Concrete Institute (ACI 318-2014) [18], the Inter- national Building Code (IBC-2018) [19], in Europe, the Eurocode 2 (EC-2) [20], in Egypt, the Egyptian code (ECP 203-2007) [21], and https://doi.org/10.1016/j.conbuildmat.2019.04.143 0950-0618/Ó 2019 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail addresses: ahmyousef@mans.edu.eg (A.M. Yousef), mahmoudaziz_2008@ yahoo.com (M.A. El-Mandouh). Construction and Building Materials 214 (2019) 619–630 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat