Effect of Peripheral Wall Openings in Basement and Number of Basement Floors on the Base level of Braced Framed Tube System
For seismic design, the base is defined as the level at which the seismic ground motion is considered to be transferred on to the structure. Although there are many factors affecting the base level, for a typical building without a basement, the base is generally considered near the ground level. This study aims to examine the influence of both, peripheral wall openings in the basement and the number of basement floors, on the base level under near-field earthquakes, taking into account the effect of soil–structure interaction. To this end, five 2D metal-braced frame models with different number of floors and the soil around them were subjected to near-field earthquakes. The basement beams and columns were assumed to be buried within the peripheral basement wall. The results showed that where the opening was greater than 50%, the base level had to be considered one story lower than the ground level, thus, disregarding the effect of openings in high-rise structures could lead to non-conservative results. Moreover, it was concluded that in case the basement beams and columns were buried in the peripheral basement wall so as to provide sufficient stiffness, increasing the number of basement floors from 3 to 6 had little effect on the base level of the studied soil–structure system.