SEISMIC BEHAVIOUR OF THE I-EXOS SYSTEM DESIGNED BY IH-MADE STRONG MIDDLE SECTIONS

Many countries in the world located in high seismicity zones have old, reinforced concrete (r/c) building stocks with poor seismic performance. The i-EXOS system has been proposed as an effective retrofitting solution; it consist of a steel exoskeleton, connected externally at the building floors and designed to remain elastic during the earthquake (even for the major event) to prevent the building from the formation of the soft-storey collapse mechanism. Within this design objective for i-EXOS, novel Strong-middle Circular Hollow Sections (Sm-CHS) made through the Induction Heat treatment technology appears to be an efficient solution to secure the elastic response of the i-EXOS system. This study performs a computational analysis on the seismic behaviour of a five-storey i-EXOS designed with Sm-CHS and assesses its structural performance under earthquake loads. First, a non-linear finite element model is developed of the steel i-EXOS in the commercial software ABAQUS. Then, the most demanding earthquake displacement time-histories are extracted from a sibling simplified dynamic model developed in OpenSEES and induced in the ABAQUS i-EXOS model to assess the seismic response of two design solutions for i-EXOS: (1) use of conventional steel CHS and (2) use of novel Sm-CHS. For the conventional design, it was found that a few conventional steel members of i-EXOS fail suddenly by buckling although the design has passed the average capacity checks according to Eurocode 8 provisions. This indicates the need to further increase the section dimensions to ensure stability of the system. On the contrary, the results showed that the design of the i-EXOS using the novel Sm-CHSs can remain almost elastic without experiencing any severe damage under major earthquake events, thus meeting the design criteria with lighter steel sections.