Evaluation of vertical ground and floor accelerations and spectra in elastic RC frame buildings located in Eastern Canada

Abstract

Whilst significant structural damage to buildings has generally been rare as a result of recent moderate and severe earthquakes, destructive non-structural damage has been much more widespread and can lead to additional economic loss. In most codes and standards, only the effect of the horizontal component has been discussed in relation to seismic design and analysis. The effect of the vertical component has been less considered or completely neglected. However, the effect of vertical seismic acceleration can be more impressive in some cases and severely affect a building’s structural performance and, consequently, its nonstructural components (NSCs). The National Building code of Canada (NBC, 2015) is mainly limited to an empirical ratio of 2/3 in the relationship between vertical and horizontal acceleration. Also, in this code, the requirement to consider the vertical seismic component is limited only to structures with long spans, pre-stressed structures, and structures with highly stressed elements under gravity loads. In this project, the characteristic of the vertical component of ground motions for Site Class C in the Eastern Canada seismic region was investigated, and a relation was proposed to establish the vertical design spectral acceleration using the vertical-to-horizontal pseudo-spectral acceleration ratios (V/H PSA) obtained from the selected 248 records of 67 earthquakes of this region with a magnitude Mw ≥ 3.0 and an epicentral distance (Repi) <150 km. Due to the lack of enough records for very dense soil according to the mentioned criteria in this region, records from other soil types than very dense soil and soft rock were converted to the corresponding records on Site Class C using the software DEEPSOIL. The computed V/H PSA ratios were calibrated with those obtained from compatible Ground Motion Prediction Equations (GMPEs). The computed mean V/H PSA ratios exceeded the typical value of 2/3 recommended in NBC 2015, especially for short periods of up to 1.3 sec. A profile of vertical acceleration design spectra (ADSver) was proposed for Site Class C in Montreal and compared with those obtained by ASCE/SEI 7-16 (2017) and ASCE 41-17 (2017) provisions. In addition, the effect of building height and the flexibility of the slab on the vertical response of the floor system, including different locations within the floor and along the building height on the amplification of vertical peak floor accelerations and floor spectral accelerations was assessed. To this end, four 3-D elastic regular RC moment-resisting frame buildings with limited ductility for the location on Site Class C of Montreal. Therefore, 3-, 6-, 9- and 12- storey regular RC buildings with moderately ductile moment-resisting frame systems and three spans of 7.0 meters in each direction, designed in accordance with the National Building Code of Canada (NBC 2015), were selected for this research. Moreover, 65 sets of historical records relating to 31 severe earthquakes from across the world as input time history accelerations were used to analyze the linear behavior of these structures. The maximum amplification of vertical Peak Floor Acceleration (PFAV) was observed at the center of the buildings’ interior slab, with the maximum median normalized values ranging from 4.0 in the 3-storey building, to 1.24 in the 12-storey building. Moreover, the constant amplification of the vertical Floor Spectral Acceleration (FSAV) was observed along the building height. The significant impact of the vertical component of the earthquake was more visible at shorter periods since the maximum vertical acceleration resulted at periods of less than 0.35 sec. Finally, the estimated FSAV corresponding to the input vertical ground acceleration was proposed for the typical buildings. Therefore, this study indicates that the vertical earthquake motion should not be overlooked in the analysis and design process, especially in low-rise buildings.

Date	12 May 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Rola Assi (Supervisor)