Design of steel brace connection to an RC frame using Uniform Force Method Mahmoud R. Maheri ⁎, S. Yazdani Shiraz University, Iran abstract article info Article history: Received 15 May 2014 Received in revised form 30 March 2015 Accepted 12 September 2015 Available online xxxx Keywords: Steel bracing Reinforced concrete Brace connection Uniform Force Method Seismic design Seismic retrofitting Steel bracing is a viable alternative to a shear wall when designing or retrofitting reinforced concrete frames for seismic loads. Directly connecting the bracing system to the RC frame is the most cost effective method of joining the two systems together. In this paper, the design basis for such a connection is set out and controlled for accuracy and safety. To this end, numerical models of steel brace/RC frame connections are developed and verified against experimental results obtained from similar connections. The numerical models are then used to evaluate the efficiency of the analytical Uniform Force Method (UFM) used for connecting braces to steel frames and adopted here for connecting braces to RC frames. It is found that the UFM can be applied effectively and conservatively to design brace/RC frame connections. A detailed investigation on the level of overdesign is also carried out through parametric analyses of the main problem variables including the brace angle and dimensions of the gusset plate. It is found that, for most practical cases, the error in using the UFM analytical approach is less than 20%. Finally, necessary considerations for design of different components of the brace–frame connection are set out. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The idea of using steel bracings as lateral resisting elements in RC frames has received some attention in recent years. The earlier works concentrated either on external bracing of the RC frames [1,2] or on indirect internal bracing through intermediary steel frames [3,4]. Both methods have a number of shortcomings, particularly in terms of application and cost. In 1997, Maheri and Sahebi [5] proposed a direct connection between steel bracing and RC frame in a manner similar to that used in steel frames. Further experimental [6–9] and numerical [10,11] works carried out by Maheri and colleagues showed the efficien- cy of the directly connected steel brace/RC frame systems in resisting the seismic loads and improving the seismic performance of the system. In their works, they experimented with different bracing systems including X-bracing and Knee-bracing [6] and studied the efficiency of a new compression release device, placed in the compression brace [9]. Also, Maheri and Akbari [10] evaluated the seismic behaviour factor for the brace/RC frame system used in calculating seismic force and Maheri and Ghaffarzadeh [11] proposed design principles for steel bracing of RC frames. Other works carried out by Tasnimi and Massomi [12] and Abou-Elfath and Ghobarah [13] have also shown that by using the appropriate forms of direct internal bracing with appropriate con- nections, good seismic performance could be expected from the steel brace/RC frame systems. The efficiency of the directly connected brace–RC frame system depends on the ability of the connection between the two elements to successfully transfer the loads. This was highlighted in the results of the experiments reported by Maheri et al. [6]. To address this important issue an initial experimental investigation was conducted by Maheri and Hadjipour [7]. They carried out nonlinear static tests on full-scale models of three types of connections. They adopted the Uniform Force Method provisions for designing brace–steel frame connections to design their connection specimens. They showed that the connections and their elements were strong enough to withstand the forces and that the brace failure and rupture preceded the failure of the connection elements. However, they did not investigate the level of overdesign in the tested specimens and did not investigate the effects of design variables such as the size of the gusset plate and angle of the brace on the efficiency of the UFM for such connections. Further to the work reported by Maheri and Hadjipour [7], in the present paper the effects of design variables and the general efficiency of UFM are investigated in detail through experimental and numerical evaluations and a design basis is set out for individual elements within the connection. 1.1. Types of connection Although steel bracing of RC frames started as a measure for retrofitting existing buildings, it soon developed into a method for designing new buildings. Presently, therefore, different connections may be used depending on the type of application. A number of differ- ent connection types have been proposed [7]. In the present paper, Journal of Constructional Steel Research 116 (2016) 131–140 ⁎ Corresponding author. E-mail address: maheri@shirazu.ac.ir (M.R. Maheri). http://dx.doi.org/10.1016/j.jcsr.2015.09.010 0143-974X/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Journal of Constructional Steel Research