Journal of Constructional Steel Research 67 (2011) 1042–1049 Contents lists available at ScienceDirect Journal of Constructional Steel Research journal homepage: www.elsevier.com/locate/jcsr Seismic rehabilitation of semi-rigid steel framed buildings—A case study H. Shakib a,∗ , S. Dardaei Joghan a , M. Pirizadeh a , A. Moghaddasi Musavi b a Department of Civil Engineering, Tarbiat Modares University, Tehran, Iran b Retrofitting Division, Natural Disaster Institute, Tehran, Iran article info Article history: Received 7 February 2010 Accepted 3 January 2011 Keywords: Vulnerability assessment Rehabilitation Semi-rigid Steel buildings abstract This paper presents the seismic vulnerability and rehabilitation of a steel building with semi-rigid connections in Tehran. This 19-storey building with an asymmetric plan was constructed 30 years ago in three blocks. The qualitative vulnerability of the building was evaluated in the first step of the study, indicating its high seismic vulnerability. In the next step of the study, the quantitative vulnerability of the structure was investigated. The results show that the building was strong enough to resist gravity loads but the strength was not adequate for seismic loads. Finally, three seismic retrofitting methods consisting of concrete shear wall, steel shear wall, and steel bracing were proposed. The comparison of the three retrofitting alternatives in terms of architecture, implementation, and seismic performance showed the superiority of using the concrete shear walls over the two other alternatives. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The use of steel buildings with a kind of semi-rigid connection called Khorjini has been very common in Iran in the past 50 years. In the construction of these steel buildings, a pair of continuous beams cross the two opposite sides of the columns and each beam is connected to the columns by top and bottom angles. The be- haviour of steel buildings with this connection type in different earthquakes such as, Manjil, 1990, and Bam, 2003, revealed the fail- ure of the connections before the failure of the beams and columns. In 1991, some tests on the physical model of Khorjini connection by Moghaddam and Karami [1] showed that this kind of connection is semi-rigid and it lacks the required ductile behaviour. In 1993, Tehranizadeh et al. [2] and also Barkhordari et al. [3] studied the de- gree of rigidity of this kind of connection. In 2000, Mirghaderi and Mazrouei [4] proposed a method to rehabilitate Khorjini connec- tions by adding top and bottom flanges and triangle plates. In their suggested method, a considerable increase in the degree of rigidity of these connections was observed. The present paper investigates the seismic vulnerability and rehabilitation of a steel building with such semi-rigid connections located in the mega city of Tehran. 2. The building The building investigated was designed and built between 1973 and 1978. As illustrated in Fig. 1, the building had 3 rather similar ∗ Corresponding author. Tel.: +98 21 88823382; fax: +98 21 88005040. E-mail addresses: shakib@modares.ac.ir (H. Shakib), dardaei@modares.ac.ir (S. Dardaei Joghan), pirizadeh@modares.ac.ir (M. Pirizadeh), ammtmu@yahoo.com (A. Moghaddasi Musavi). blocks. There was a distance of about 21 cm between the blocks. The blocks consisted of 19 stories: 3 underground stories, the ground floor and 15 stories on the ground. The area of each storey was approximately 1950 m 2 . The three underground stories were used as car parking areas and the upper floors, being offices for roughly 2000 people, had an administrative usage. The typical storey height was 3.2 m. The southern view of the building is shown in Fig. 2. 3. Qualitative evaluation of the building vulnerability In evaluating the qualitative vulnerability of the building, var- ious construction parameters such as site slope, soil type, build- ing height, opening dimensions, plan shape, load resisting system, floor diaphragm type and construction quality were considered. The results showed that the building may suffer substantial dam- age at VII intensity and it may collapse at VIII intensity in the MSK scale [5]. 4. Quantitative evaluation of the building vulnerability The following steps were taken in the quantitative vulnerability evaluation of the building: primarily, the structural performance level was selected and the data collection requirements were specified. Then the building configuration, material properties and site characteristics were identified and the seismic hazard was studied to obtain the necessary information. Finally, the building was modelled and analysed. These steps are described in more details below. 0143-974X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcsr.2011.01.002