Seismic assessment and retrofit design of a multi-storey heritage reinforced concrete building with tapered columns and lap-splice failures

Abstract

The conservation and restoration of reinforced concrete (RC) heritage buildings has become a subject of increasing interest and has rightfully gained the attention of not only the engineering community, but also of the public in general. This is mainly attributed to the great architectural and cultural significance of these structures. Given the fact that heritage concrete structures were constructed in the absence of any building codes and under poor workmanship methods, which compromised the overall capacity and quality of these buildings, there is an imminent need for developing suitable assessment methodologies, which can be adopted today to extend the life cycle of historic concrete buildings. The challenge that must be surpassed does not relate only to the ability of these structures to withstand vertical loading, but – in seismic-prone regions, like Cyprus – to also withstand the dynamic loading generated by earthquakes. The correct selection of an analysis method that will lead to trustworthy results which will define the structural capacity in terms of displacement or ductility, is therefore indispensable. The case-study building of this dissertation, i.e., the Alexandros Demetriou Tower in Nicosia, was constructed at the end of 1950s. This RC structure is symmetrical in elevation, but its load bearing system consists of frames with tapered sections. The required knowledge for the simulation of the structural geometry, detailing and for the material properties for the case-study building, was attained through in-situ testing and measurements. This dissertation compares different linear and nonlinear analysis methods in accordance with Eurocode 8 - Part 3 – focusing primarily on the nonlinear static ‘pushover’ and the nonlinear time history analysis – aiming to define the pros and cons of each method and their applicability in the seismic assessment of the case-study building. The repair technique of FRP confinement is also examined to overcome the local lap-splice failures developed at the column bases. Finally, this research presents a methodology for the assessment and strengthening of reinforced concrete heritage structures, that can be elaborated in order to minimize the strengthening requirements in such structures.