Strengthening/ retrofitting of coupling beams using advanced cement based materials

In this paper the effectiveness has been assessed of an upgrading/retrofitting system for coupling beams (span-to-depth ratio equal to 1.5) not designed to resist earthquake actions. The proposed retrofitting technology employs either High Performance Fiber Reinforced Cementitious Composites (HPFRCCs) or Textile Rein-forced Cementitious Composites (TRCCs). 14 mock-ups of coupling beam units, scale 1:2, have been casted and subjected to either monotonic or cyclic loading tests. The different resisting mechanisms in conventional plain and reinforced concrete coupling beams have been first of all investigated (tensile strength of concrete in plain concrete coupling beam; strut-and-tie mechanisms in coupling beams reinforced with only longitudinal bars; enhancement of the aforementioned mechanism due to stirrups). The influence of the boundary condi-tions due to the shear wall shafts on the coupling beam spanning between, has been investigated. Longitudinal and transverse reinforcement have been designed to comply only with EC2 minimum requirements for non-seismic design situations. In a second stage the effectiveness of the upgrading/retrofitting techniques has been checked testing non- and pre-damaged coupling beams. In the latter case two different drift levels have been selected for pre-damage, namely 1% and 2%, respectively meant as representative of ductility demand for SLS and ULS. Results highlight the effectiveness of the proposed upgrading/retrofitting techniques, which, also in view of their ease of execution and reduced invasiveness, can stand as a reliable alternative to other more commonly employed ones.