## 1 Background  
Non-ductile concrete moment-resisting frame (MRF) buildings are known to be susceptible to earthquake damage. As such, many buildings designed and erected under previous code recommendations are retrofitted to meet current seismic demands and to accommodate additional movement considered in today's building codes. A five-year-long seismic upgrade program aimed at enhancing the strength and ductility of a 12-story reinforced concrete (RC) MRF building located in downtown Los Angeles, California, was developed to derive a creative, structural, and economical retrofit solution for a variety of structural and nonstructural components in the building. The retrofit implementation was completed in December 2021, allowing for subsequent dissemination of research insights. The construction of the building (Figure 1) was completed in September 1998. The building's structural design was based on code requirements of the 1996 City of Los Angeles Building Code (LABC) for an \"essential facility\" (i.e., importance factor I = 1.25). The superstructure holds 12 above-ground levels consisting of cast-in-place concrete special moment-resisting frames (SMRF) with precast concrete gravity frames, overlain by a cast-in-place concrete floor. The building's concrete moment frames generally consist of beams with cross-sectional dimensions of 1.22 m (48 in) in depth and 0.76 m (30 in) in width and typical spans of 9.14 m (30\({}^{\prime}\)-0\({}^{\prime\prime}\)) or 9.75 m (32\({}^{\prime}\)-0\({}^{\prime\prime}\)) c.c. Only a few days have shorter spans of 6.1 m (20\({}^{\prime}\)-0\({}^{\prime\prime}\)) or 13 m (42\({}^{\prime}\)-8\({}^{\prime\prime}\)) c.c. The foundation consists of isolated spread footings and perimeter wall footings. Following multiple repairs associated with shear cracking in several RC MRF beams between 2008-2010, a seismic structural evaluation of the lateral force-resisting system was conducted in 2011 by an external consulting engineering firm to assess potential structural deficiencies of the MRF design. The performance assessment was based on code-based structural checks and a 3D linear dynamic analysis model (i.e., response spectrum) considering two different seismic occupancy scenarios: the original essential-facility (I = 1.25) design criteria using codes and design parameters applicable at the time of design (1996 Los Angeles Building Code (LABC), 1995 California Building Code (CBC), and ACI 318-89 [1]) and a reduced occupancy category as an ordinary occupancy building (I = 1.0) using applicable code requirements in 2011 (i.e., International Building Code (IBC) 2006, ASCE 7-10 [2], and ACI 318-05 [3]) and modified seismicity. The basic performance objective for the building lateral force-resisting system (LFRS) required both Life Safety (LS) performance under the design basis earthquake (DBE) hazard level and Collapse Prevention (CP) performance under the maximum considered earthquake (MCE) hazard level. To note, an RC MRF building designed and detailed under the 1996 LABC is expected to behave in a ductile manner. However, the investigation revealed that the LFRS in this building was non-ductile and unable to achieve its intended seismic performance. Specifically, some of the MRF beams had insufficient shear capacity at the end-yielding regions (with a predicted overstress of up to 30%) and at sections with large rectangular web penetrations for passage of ductwork and pipes (with probable design shear demands ranging between two to four times larger than the available shear capacity). These shear deficiencies were attributed to a combination of inadequate detailing of the transverse reinforcement, with some of the MRF beams having only single hoops without intermediate crossties and/or noncompliant tie spacing around the openings, as well as an oversimplified estimation of the probable design shear demand, with the compression flange and compression reinforcement not being accounted for in the original design.