Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Effect of shear span-to-depth ratio on shear strength components of RC beams Biao Hu a,1 , Yu-Fei Wu b, ⁎ a Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University, Shenzhen 518060, China b School of Engineering, RMIT University, Australia ARTICLE INFO Keywords: Reinforced concrete beams Shear strength Contribution of concrete Contribution of transverse reinforcement Test ABSTRACT The additive model of shear strength of reinforced concrete (RC) members, i.e. shear strength (V) is equal to the sum of the contribution from concrete (V c ) and that from transverse reinforcement (V s ), has been widely ac- cepted in the literature and engineering practice. Shear span-to-depth ratio (a/d) is known to be a significant factor affecting V of RC members. However, very few quantitative studies on the influence of a/d on V c and V s have been reported in the literature. Another issue is related to the controversial relationship between the shear force at first diagonal cracking (V cr ) and V c , for which different guidelines are given in ACI, AASHTO LRFD and CSA codes. Through direct measurement of V c and V s from 11 RC beam tests, this work provides experimental evidence for these issues. The experimental results show that V c can be very different from V cr . At small shear span-to-depth ratio (a/d), V c is much larger than V cr , while it is the opposite for beams with a large a/d value. Not all stirrups crossing the critical shear crack yield at ultimate shear strength, and V c as well as V s are not constant under increasing member deformation. Although design codes give a conservative prediction of V, they predict an un-conservative value of V c at large a/d. 1. Introduction The understanding of shear failure and shear resistance in re- inforced concrete (RC) beams has been considered as one of the most critical issues that has not been fundamentally and conclusively re- solved. This problem has attracted intensive interest of the research community, especially after the failure of beams in two Air Force warehouses in 1955 [1]. Due to the great efforts made by the research community in this area, a large number of test results are available in the literature which forms a comprehensive test database [2–5]. These experimental studies have laid a solid foundation for understanding the mechanisms of shear transfer and the development of theories, models and design codes provisions. The well-established theories include the traditional truss model [6,7], compression field theory (CFT) [8] as well as modified com- pression field theory (MCFT) [9,10], plasticity approach [11], strut- and-tie model (STM) [12,13], tooth model [14,15], rotating- and fixed- angle softened-truss models [16–18], critical shear crack theory (CSCT) [19,20] and the mechanical models [21–24]. Other typical truss-related analogies and models are well documented in ACI-ASCE Committee 455 [25]. For slender RC beams, a consensus has been reached that the shear strength (V) is taken as the sum of the shear strength of concrete (V c ) and that of transverse reinforcement (V s ). This additive model is widely adopted by existing design codes [26–30] and in the literature [20,31–33] with the exception of the new edition of EC2 [34] that adopts a variable-angle truss method. For RC deep beams, in which case a significant portion of shear is transferred directly from the loading point to supports via diagonal compression struts, STM is more ap- propriate than sectional approaches [29,30]. Mihaylov et al. [35] de- veloped kinematic models for RC deep beams while others suggest improvement of STM [36–39]. Despite the extensive efforts made by the research community, very few reliable information is available in the literature in terms of how the total shear resistance (V) is distributed between the concrete (V c ) and stirrups (V s ) during the loading process. The authors have recently developed an innovative experimental method, with which the varia- tions of V c and V s against member deflection during the whole loading process can be captured [40,41]. It was found that V c is related to member deformation (or crack width), which is generally consistent with the assumption made by Priestley et al. [33] and Ruiz and Muttoni [20]. For V s , the authors found that not all stirrups intersecting critical https://doi.org/10.1016/j.engstruct.2018.05.017 Received 3 January 2018; Received in revised form 3 April 2018; Accepted 7 May 2018 ⁎ Corresponding author. 1 Formerly, Dept. of Architecture and Civil Engineering, City Univ. of Hong Kong, Hong Kong Special Administrative Region. E-mail address: yufei.wu@rmit.edu.au (Y.-F. Wu). Engineering Structures 168 (2018) 770–783 0141-0296/ © 2018 Elsevier Ltd. All rights reserved. T