Seismic response of a non-ductile RC frame building subjected to shake-table excitations

This article presents the results of shake-table experiments of a 2/5 scale 3-storey reinforced concrete (RC) frame building designed with non-ductile detailing and no capacity-design considerations, tested with and without column lap-splices in the upper two storeys in two experimental series comprising different input motions. The specimen consisted of two 2-span frames in parallel jointed together by transverse beams and floor slabs. It included a set of "older" detailing comprising of: (1) plain round bars, (2) 180 degrees end hooks in beam longitudinal reinforcement, (3) no transverse reinforcement in the joints, and (4) lap splices in potential plastic hinge zones (first test series only), which, alongside a strong-beam and weak-column mechanism, create a very fragile fuse in the panel zone region of the exterior/corner beam-column joints. In the first experimental series, the structure experienced predominantly elastic responses during the first two tests, and a top-storey rocking mechanism due to column lap-splices failure during the third test. In the second experimental series, the modified specimen with welded lap-splices experienced minor damage during the first test whereas it suffered severe shear failures in the corner beam-column joints of the first storey during the second test, associated to inter-storey drift ratios and joint rotations of up to 3.8% and 0.035 rad, respectively. The large global and local demands suffered by the specimen during this last test were associated to resonant effects, as found with the Short-Time Fourier Transform (STFT) spectrogram analysis of the building response and of the input motion.