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<p class="Normal1">Earthquakes are natural events, caused mainly due to the relative movement between tectonic plates (interplate earthquakes) and in faults between rocky blocks (intra-plate earthquakes), or induced by human activity. It is possible to observe a relation between the regions located in areas with greater seismicity and the areas that are close to several intraplate failures and shale gas reserves in Brazil. According to NBR 15421/2006, this condition results in a map of seismic accelerations characteristic of the design. Such accelerations can be used to estimate equivalent horizontal loads. However, it is not usual to consider these effects in the design of reinforced concrete buildings. Therefore, this work aims to evaluate the global stability of reinforced concrete buildings with different bracing systems, subject to seismic accelerations provided for in NBR 15421/2006. Initially, the global stability was verified considering the wind and vertical actions by the γz coefficient. Therefore, all the frames analysed in this paper behaved as non-sway structures (γz ≤ 1,10). Then the wind actions were replaced by seismic ones since it is improbable that both phenomena occur simultaneously. Finally, global stability was re-evaluated by means of the γz coefficient. Therewith, it was observed that all the buildings analysed started to behave as structures of mobile nodes (γz &gt; 1,10), that is, susceptible to the second-order global effects.</p>

Structural accidents of high-rise buildings due to instability has occurred with some frequency in Brazil. Generally, building instability implies in a series of pathologies in structural and non-structural elements. The Brazilian code regulation suggests two simplified procedures, named as instability parameter α and γz coefficient. In terms of design, the main difference between such simplified procedures is that, differently from the instability parameter α, the γz coefficient can be used to estimate the second order effects and it is applied to buildings that do not present double symmetry. In the light of the foregoing, this paper addresses to the evolution process of pathological manifestations due to structural instability in an actual high-rise building. As soon as the building was occupied, cracks nucleated and propagated in few days. The observed cracking pattern indicated that the building could break in two pieces as a way to compensate the second order effects. Thereby, the structural instability and its consequences were evaluated by means of a commercial design computer software