Experimental study on smooth and ribbed bars investigating adherence behaviour improvement using active confinement CAM® technology: pull-out laboratory test

In the period after the Second World War all the Europe has been involved in the reconstruction, and the most common, economic, technically affordable construction material was reinforced concrete. Italy, Albania, other European and non-European countries (for example Egypt), from their side, and in different ways, discovered the reinforced concrete technology, and developed it. But despite all the enthusiasm and the energy put in that reconstruction, today we can recognize several mistakes, errors and lack of construction details, which affected buildings of the period ranging from 1960 to 1990. Erroneous architectural design of the buildings, wrong details, errors in choosing material led to build constructions which cannot stand earthquakes like those that occurred frequently in the Mediterranean Area in recent years, as shown in Figure 1-1: Croatia (29.12.2020 – Mw 6.3), Greece (30.10.2020 – Mw 7.0), Durazzo (26.11.2019 – Mw 6.2), Norcia (30.10.2016 – Mw 6.5), Accumoli (24.08.2016 – Mw 6.0), L’Aquila (06.04.2009 – Mw 6.1), San Giuliano di Puglia (31.10.2002 – Mw 5.4). Good bond behaviour between concrete and steel bar is an essential requirement to guarantee structural RC beams performance and consequently building performance. Currently this issue is substantially overcome by using good technical practice, reinforced bars and thanks to high concrete prescription. At the same time all buildings with smooth bars, realized mainly before the 80’s, generally have bad bond behaviour. This critical issue, together with other several buildings’ problems due to their age (material degradation), poor concrete quality, load occurred during years, may determine low structures’ “safety values”. The purpose of this thesis is to investigate bond behaviour and its improvement with new CAM® technique (which is an active confinement) currently used mainly for masonry buildings. The target is to observe, with a simplified model and with some complex ones, how the adherence may increase and consequently positively affect the building performance. The thesis has been implemented as a sequence of analysis phases and more precisely:  Phase 1 – Seismic vulnerability assessment of existing concrete buildings with smooth and ribbed bars;  Phase 2 – Bond formulations and bond analysis;  Phase 3 – FEM analysis  Phase 4 – Pull out analysis - Laboratory tests with strain gauge;  Phase 5 – FEM and Laboratory tests - Pull out with CAM® technology;  Phase 6 – Conclusions - Results of test.