Shear Performance of RC Beams Strengthened with Mortar-Based Composites

Most of the existing concrete buildings and bridges present deficiencies mainly related to old type construction practices and ageing of materials due to environmental aggressive conditions. In the last years, externally bonded composites are used extensively in alleviating deficiencies and extending the service life of existing construction. Fibre Reinforced Polymers (FRPs) has been widely used in several strengthening applications. However, the use of organic binders is related to various drawbacks the more significant ones being the poor behaviour to fire conditions, the relatively high cost of epoxy resins and the lack of vapour permeability with adverse effects on reinforced concrete structures. Replacing organic (resin) binders with inorganic (mortar) ones seems to be an efficient solution, since all the advantages of FRP restraints are preserved. This paper investigates experimentally the efficiency of various mortar-based composite jackets, such as Steel-Reinforced Grout (SRG), Textile-Reinforced Mortar (TRM) and Ultra High-Performance Fibre Reinforced Concretes (UHPFRC) jackets, in strengthening shear critical reinforced concrete (RC) beams. All tested beams have the same geometry and are subjected to monotonic asymmetric three-point loading using a stiff steel reaction frame. Key parameters of this study are the number of textile layers and the strengthening configuration of the jackets (U-shaped and fully wrapped). Experimental evidence demonstrates that all strengthening systems can improve the shear strength, especially the fully wrapped SRG jackets which modify the failure mode from brittle to ductile. The knowledge gained from this experimental study makes mortar-based jackets a very promising strengthening method of shear critical RC beams

Modelling load-transmission mechanisms in axially loaded RC columns retrofitted with steel jackets

The use of steel jacketing technique is a common practice for retrofitting existing reinforced concrete (RC) columns, as it allows increasing load-carrying capacity and ductility of the member. When the external jacket has no-end connections – i.e. the jacket is indirectly loaded- the load sustained by the column is transferred from the inner RC core to the external jacket through shear stresses along the contact surface. The assessment of this mechanism is quite complex, due to the marked non-linear behaviour of constituent materials and to the calibration of a proper shear stress-relative slip constitutive law of the concrete-to-steel interface. In this paper, a step-by-step analytical approach is proposed to assess the load transfer mechanisms in steel jacketed RC columns loaded in compression. The model is able to predict slip and shear stresses along the core-to-jacket contact interface and then the load-carrying capacity of strengthened members. Shear stress-slip constitutive law on the interface is initially assumed linear and a suitable stress-strain constitutive model of confined concrete is considered. Yielding of steel angles is also taken into account into the process by assuming an bilinear law with strain hardening. The progressive damage of concrete is also considered by dividing the examined member in portions and splitting governing equations. Finally, comparisons are performed in order to validate the proposed procedure against experimental results available in the literature, showing good agreement

Pushover Analysis of GFRP Pultruded Frames

Results of a pushover analysis of GFRP pultruded frames aimed at the evaluation of their overall ductility are presented. It is assumed that the dissipation capacity of the frame structures is concentrated in joints due to their nonlinear behavior induced by progressive damage, while a brittle-elastic behavior is assumed for frame members. A two-storey one-bay GFRP pultruded frame is considered for a case study in which the column-base and beam-column joints are modeled with nonlinear rotational springs with different moment-rotation laws derived from experimental results available in the literature. For comparison, frames with hinged connections and moment-resisting frames are also analyzed. Finally, the results obtained are compared with those for a similar steel frame. The final results bear witness, in particular, to the absence of a significant ductility of pultruded frames and the relevant influence of the characteristics of bracings on their structural response