Cyclic performance of precast coupling beams with bundled diagonal reinforcement Sang Whan Han a , Chang Seok Lee a , Myoungsu Shin b,⇑ , Kihak Lee c a Dept. of Architectural Engineering, Hanyang University, Seoul, Republic of Korea b School of Urban and Environment Engineering, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon-ri, Eonyang-eup, Ulju-gun, Ulsan 689-798, Republic of Korea c Dept. of Architectural Engineering, Sejong University, Seoul, Republic of Korea article info Article history: Received 8 March 2014 Revised 12 March 2015 Accepted 16 March 2015 Available online 30 March 2015 Keywords: Precast coupling beam Bundled diagonal reinforcement Ductility Energy dissipation abstract Diagonally reinforced coupling beams designed according to current codes are expected to endure significant inelastic deformations during earthquakes. However, it is very difficult to fabricate the cou- pling beams in a construction site due to the congestion of reinforcement and the complex arrangement of diagonal reinforcement. For resolving the problems, this study developed precast coupling beams with bundled diagonal reinforcement. To verify the effectiveness of the proposed design method, experimental tests were conducted on four 1/2-scale coupling beam specimens subjected to cyclic loading. The test results suggest that the precast coupling beams with bundled diagonal reinforcement exhibited good ductility and energy dissipation capacities similar to those having code-specified diagonal reinforcement. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction A coupled wall system that consists of separate structural walls linked together by coupling beams is effective to resist lateral forces in high-rise buildings [1,2]. Coupling beams designed according to current codes [3–6] are expected to endure significant inelastic deformations under design-level earthquakes. Thus, coupling beams should be provided with appropriate reinforcing details to execute sufficient seismic performance such as ductility and energy dissipation. Conventionally reinforced coupling beams, which have longitu- dinal bars parallel to the span of the beam, may suffer sliding shear failure at the beam ends [7]. Transverse reinforcement could not prevent sliding shear failure because vertical cracks propagated across the entire depth of the beam between stirrups [8]. A good example of the sliding shear failure of coupling beams can be found in the failure of coupling beams in Mount McKinley building in Anchorage, Alaska due to the 1964 Anchorage Earthquake [9]. Since then, many studies have been conducted to resolve this prob- lem. Historically, Paulay and Binney [10] first developed diagonal reinforcement for coupling beams. Diagonally reinforced coupling beams were proven to not suffer sliding shear failure and have superior ductility and energy dissipation capacities and stiffness retention than conventionally reinforced beams [10–12]. From the previous studies mentioned above, Section 21.9.7 of ACI 318 [3] specifies two confinement options for coupling beams with diagonal reinforcement, as shown in Fig. 1. In the first option in Fig. 1(a), each group of diagonal reinforcement comprises at least four longitudinal bars enclosed by transverse reinforcement. This confinement method requires very complex bar arrangement, especially near the mid-span of the beam where diagonal reinforcement groups cross each other. Also, according to Harries et al. [13], arranging diagonal bars enclosed by transverse reinforcement is practically difficult when the average shear stress in the beam is greater than 0:5 ffiffiffiffi f 0 c q (where f 0 c is the concrete compressive strength in MPa). Due to such shortcomings, the sec- ond confinement option in Fig. 1(b) is allowed in Section 21.9.7.4(d) of ACI 318 [3] that transverse reinforcement required for beams and columns of special moment frames should be provided for the entire cross section of the beam. Shui et al. [14] reported that diagonal reinforcement would generally be less effective in coupling beams with large length- to-depth ratios (l n /h) that cause the small angles of diagonal reinforcement [15,7]. For a similar reason, ACI 318-11 [3] allows to use conventional reinforcement layout in shallow coupling beams. As an example, for a coupling beam with l n /h larger than 2, diagonal reinforcement is not required by ACI 318 [3]. In efforts to resolve the difficulty of fabricating diagonal reinforcement in coupling beams, various reinforcing details have been proposed and tested to date [12,16,17]. Recently, steel and composite coupling beams have been developed [18,19]. In this http://dx.doi.org/10.1016/j.engstruct.2015.03.034 0141-0296/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +82 52 217 2814. E-mail address: msshin@unist.ac.kr (M. Shin). Engineering Structures 93 (2015) 142–151 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct