## 1 Background
As part of this investigation, large-scale component testing of selected shear-deficient MRF beams was deemed necessary to assess the actual beam performance and aid in designing appropriate retrofit solutions. The testing program, sponsored by the building owner and conducted at the structural testing facility of the University of California, Irvine (SETH), was divided into two phases: Phase 1 focused on the performance assessment of representative, as-built, unstrengthened MRF beams with large rectangular web openings. Four 4/5-scale flanged beam (T-beam) specimens were tested in this phase. These tests were executed between March and June 2013 and published by [PERSON] et al. [4]. Phase 2 focused on the design and evaluation of retrofit schemes for the shear-deficient MRF beamsat the end and opening regions using externally bonded (EB) fiber-reinforced polymer (FRP) and FRP anchors. Phase 2 consisted of three 4/5-scale FRP-strengthened T-beam specimens evaluated sequentially between Juny 2014 and November 2015. The retrofit schemes were designed collaboratively by the consulting engineer and the FRP specialists and tested at the Structural Laboratory at UC Irvine. The first two specimens, S1A and S1B, represented exact replicas of the unstrengthened specimen S1 from Phase 1. S1 was the only specimen to fail in shear at the opening region. Specimens S1A and S1B were externally strengthened with FRP at both the opening and the end-yielding regions and used to verify and optimize a retrofit concept around the web openings, as well as to relocate the plastic hinge to the beam ends by keeping the opening area elastic and damage-free. Results and discussions focusing on the beam openings are part of a previous publication by the authors [5] and won't be repeated hereafter. A second objective for specimens S1A and S1B was to evaluate two low-effort and commonly used shear-strengthening schemes for the end-yielding region next to the support, where the shear overstress was estimated to be around 10%. The strengthening schemes consisted of a one-layer carbon FRP (CFRP) sheet U-wrap with no mechanical anchorage, applied to specimen S1A, and a similar CFRP U-wrap with embedded glass FRP (GFRP) anchors at the ends, installed on S1B. However, both tests revealed detailing issues of the FRP reinforcement at the beam ends, as discussed later in this paper. Specifically, complete detachment of a strip of the CFRP U-wrap occurred similarly for both S1A and S1B at 3% drift, accompanied by anchor pull-out at the location of the dominant flexural crack (S1B), followed by the sudden fracture of an adjacent CFRP strip and an abrupt loss in load-carrying capacity. In addition, both S1A and S1B exhibited wide cracks along the flange/web cold joint, indicative of horizontal shear transfer issues, as well as buckling of the top longitudinal reinforcement at large displacement levels. This can be attributed to the lack of intermediate vertical crossties, a detailing deficiency affecting multiple MRF beams in the building. Findings from specimens S1A and S1B pertaining to the beam end region were utilized to develop a third retrofit concept applied to another replica specimen, S5, tested several months after specimens S1A and S1B. The retrofit scheme for S5 consisted of fully closed external CFRP hoops supplemented with intermediate crack-control joints. Complete continuity of the shear-strengthening FRP wrap around the perimeter of the beam was achieved with continuous FRP splice anchors through the flanges and over the slab. Figure 1: A 12-story reinforced concrete building in downtown Los Angeles. This case history documents the experimental research, design, and implementation of the full-wrap shear-strengthening concept that was experimentally tested on specimen S5 under fully reversed cyclic loading. A broader discussion on this retrofit project can be found in [6]. FRP design calculations and test results for specimens S1A, S1B, and S5 as they concern to the end-yielding regions are presented and discussed hereafter.