UC Irvine

Large scale cyclic testing was carried out to study the nonlinear behavior of T-shaped, moment resisting frame beams (MRF) with openings. The beams are located in an existing structure in the western U.S., and were designed according to ACI 31-95 and UBC97. Four test specimens were constructed as half-length replicas and scaled by 80% in all cross-sectional dimensions compared to their in-situ counterparts. Cross sections had geometries of 38.4 in. x 24.0 in., and beam lengths varied from 12.4 ft. to 17.5 ft. Three experimental specimens had openings with dimensions of 38.4 in. x 14.4 in.; 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, cyclic load 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. A nonlinear strut and tie model procedure was applied to predict the cyclic envelope and the load versus displacement relationship of the beam specimens. One monotonic and two cyclic strut and tie model arrangements were developed. Additionally, the cyclic truss models were compared using two different steel material models.