TECHNICAL PAPER Pryout capacity of headed stud anchor groups with stiff base plate: 3D finite element analysis Khalil Jebara 1 | Joško Ožbolt 2 | Akanshu Sharma 2 1 Institut für Werkstoffe im Bauwesen, Befestigungs- und Verstärkungsmethoden, Universität Stuttgart, Ronse, Belgium 2 Institut für Werkstoffe im Bauwesen, Befestigungs- und Verstärkungsmethoden, Universität Stuttgart, Stuttgart, Germany Correspondence Khalil Jebara, Institut für Werkstoffe im Bauwesen, Befestigungs- und Verstärkungsmethoden, Universität Stuttgart, Hemelberg 36, Ronse 9600, Belgium. Email: khalil.jebara@hotmail.de Abstract Concrete pryout failure mode of a group of relatively shallow embedded anchors welded to a steel base plate has not been extensively investigated in the past. Therefore, the failure mechanism and resistance of such anchor groups needs to be clarified. In this paper a three-dimensional (3D) finite ele- ment parametric study for quadruple (2 × 2) anchor groups loaded in shear with no influence of edges is carried out. In the study, embedment depth of anchors and anchor spacing in both directions are varied. The results show that the increase of anchor spacing perpendicular to the shear load direction has no major influence on the concrete pryout capacity, whereas the increase in anchor spacing parallel to the loading direction significantly increases the pryout capacity. For anchor spacing greater than a particular threshold value, the pryout resistance of a group of anchors is approximately equal to the resis- tance of a single anchor multiplied by the number of anchors. Based on the results of the study, a design formula for anchor group failing in pryout is pro- posed and compared with the current design code recommendations. KEYWORDS anchor group, CC design method, FE analysis, headed stud, pryout failure mechanism, pryout resistance, shear load 1 | INTRODUCTION Group of headed stud anchors welded to a steel base plate, embedded in concrete, and loaded in shear are fre- quently used in engineering practice for various type of anchors. For anchor groups located away from the edge and having relatively shallow embedment depths often result in pryout failure which is associated with a con- crete breakout behind the anchors opposite to the loading direction. 1 Tests focusing on pryout failure of anchor groups have been performed by Hawkins, 2 Zhao and Eligehausen, 3 and more recently by Anderson and Meinheit. 4 A comprehensive database including push-off tests was reevaluated to account for the influence of the anchor spacing S x parallel to the loading direction. 4 Nev- ertheless, the influence of anchor spacing perpendicular to the loading direction S y for anchor groups with multi- ple rows was hardly studied in the past. According to the work by Viest, 5 steel stud failure occurred with a mini- mum S y -spacing of four anchor diameters (4d) or greater, which was adopted in the ACI provisions. Closer spacing was shown to reduce the capacity due to invoked con- crete failure. It is desirable to understand the pryout fail- ure mechanism of multiple rows of headed stud anchors in the form of a mechanical model. Currently EN1992-4/ Discussion on this paper must be submitted within two months of the print publication. The discussion will then be published in print, along with the authors’ closure, if any, approximately nine months after the print publication. Received: 21 June 2019 Revised: 6 November 2019 Accepted: 9 November 2019 DOI: 10.1002/suco.201900241 Structural Concrete. 2019;1–12. wileyonlinelibrary.com/journal/suco © 2019 International Federation for Structural Concrete 1