EFFECTS OF SPAN LENGTH AND BUILDING HEIGHT ON THE SEISMIC VERTICAL RESPONSE OF NSCS IN RC BUILDINGS

This study investigates the effects of building height and span length on the vertical seismic response of the floors in reinforced concrete moment-resisting frame buildings. Symmetrical 3-and 6-storey three-span regular code-compliant buildings were subjected to sixty-five vertical time history records from historic near-field strong earthquakes. Spans of 5.0 m, 7.0 m and 9.0 m were considered for each building height to compute the normalized vertical peak floor acceleration (PFA_V) and the vertical floor spectral acceleration (FSA_V). Values were computed at all floor elevations along the height and at different locations within the plan, including the centre of the slab bays and the middle of the interior beams of the buildings under study. Linearly increasing PFA_V from the base to the first floor was observed, followed by constant amplification up to the rooftop for all considered span lengths of both buildings. Likewise, an almost constant amplification of FSA_V along the height of the buildings was also noted. Moreover, the amplification of PFA_V and FSA_V is higher in the case of the 3-storey buildings, in comparison to the 6-storey buildings with the same plan dimensions and geometry. In addition, it was noted that the amount of acceleration amplification increased as the span length decreased, which is more evident in the 3-storey building. In this regard, the obtained median normalized PFA_V value at the centre of the interior slab in the 3-storey building with 5.0 m spans was 2.84 times the value obtained with 9.0 m spans, while only a 34% corresponding increase was measured in the 6-storey building. To conclude, this research highlights the importance of considering the vertical component of earthquakes in the design of restraints for NSCs in low-rise buildings with short spans.