Description
Existing Reinforced Concrete (RC) building stock often have exhibited a significant vulnerability under seismic shaking after the most recent earthquakes worldwide. They were often designed without capacity design principles, even where seismic hazard is very high, such as in Italy. Two-third of Italian existing RC buildings have been designed to sustain gravity loads only (GLD). Almost all of them lack stirrups in beam-column joints and have a minimum amount of transverse reinforcement in columns. These features make such buildings extremely prone to shear failures under seismic actions. Additionally, the same physical phenomenon, i.e., the shear failure of beams/columns or joints, is assessed differently worldwide, with the result that the same building has (even great) different seismic capacity depending on the code adopted for its assessment. The main aim of this work is quantifying such a difference with reference to RC GLD Italian case-study buildings with different number of stories located in sites with different seismic hazard, based on nonlinear static analyses. Code-based safety checks according to European (Eurocode 8-part 3, 2005; Italian D.M. 2018) or American (ASCE-SEI 41, 2017) approaches are carried out. The results show that capacity at Severe Damage (SD) Limit State (LS) is always limited by joints failures. Nevertheless, European codes strongly limit the building capacity due to the first shear cracking (tensile failure) of beam-column joint. On the contrary, ASCE-SEI 41 (2017), considering just a compressive shear failure for joints, lead to significantly higher capacity at SD LS for the shortest buildings. Relevant design of seismic strengthening, thus, strongly depend on the adopted code approach, leading to generally higher strengthening costs when joints failures are (very conservatively) detected by means of the current European approach.
