Experimental performance of RC moment frame beams with rectangular openings

A large-scale experimental case study was carried out to investigate the cyclic behavior of T-shaped, moment-resisting frame (MRF) beams with openings. The beams are located in an existing structure in the western U.S., which was designed according to ACI 31-95 and UBC97. Limited availability of test data in current literature and lack of guidance in existing design standards motivated the construction of four replica cantilever test specimens with lengths of 3.8-5.3 m. All other specimen dimensions were scaled to 80%, resulting in cross-sections of 0.61 in width and 0.98 m in height. Three beam specimens had openings with dimensions of 0.98 m × 0.37 m; the control specimen did not have openings. Each beam replica was instrumented with internal and external instrumentation consisting of strain gauges, linear voltage differential transducers (LVDTs) and string potentiometers, and tested to complete structural failure under quasi-static symmetric displacement reversals. The cyclic performance of all beams was evaluated in terms of failure progression and plastic hinge development, strength and stiffness degradation, and energy dissipation capacity. In addition, the contribution of shear and flexural deformations to the overall displacement profile was studied. Simple monotonic strut and tie modeling was utilized to estimate and compare the beams' capacities in the elastic range. A discussion of deficient and successful test results highlights the suitability of introducing openings in moment frame beams.