Seismic rehabilitation of existing RC school buildings with under-designed joints by means of reinforced jacketing of high performance fiber reinforced cementitious composite (HP-FRCC)

Abstract

The existing Reinforced Concrete (RC) School buildings are often characterized by low-rise height, very long beams, and relatively large-valued uniformly distributed loads. Beams present a large amount of longitudinal reinforcement so that they exert huge shear stresses, on the joint panels into which they frame, during a seismic event. For this reason, the main cause of seismic inadequacy of these buildings is often the premature shear failure of the joints. These latter can result either a) completely devoid of reinforcing stirrups, or b) not suitably reinforced, or c) under-dimensioned. In some cases, due to either the results of the feasibility study or to instructions given by the Contracting Authority, the seismic rehabilitation of such buildings must be obtained by local interventions. To rehabilitate an existing RC building with under-dimensioned joints, by means of local interventions, the availability of pourable and self-compacting High-Performance Fiber Reinforced Cementitious Composites (HP-FRCC) renders the RC jacketing the ideal solution. In cases in which an aggressive environment is concomitant with the susceptibility to earthquakes, an Engineered Cementitious Composite (ECC) designed ad hoc could be an even better option. The RC jacketing of the joint allows to enlarge it, thus making it work in uncracked regime. However, when the joint panel is enlarged, the appropriate hierarchy of resistances must be restored throughout the length of the column, to guarantee the activation of the desired global dissipative mechanism. In this article a calculation strategy to follow in these cases, in compliance with the Building Regulations, is proposed and described by referring to a case-study. Finally, a discussion is provided on some aspects, which are still susceptible to improvement, to refine the intervention technique.