In correspondence with each floor, a uniaxial, carbon fibre band running around the outside of the building was applied to counteract the tensile stresses in the kerb of each floor diaphragm and to counteract the onset of the mechanisms mentioned above.
To strengthen the floor-slabs, once all the various layers on the surface of the extrados of the SAP brick floor-slabs had been removed, their substrate was prepared for application of the structural screed by removing all loose material and roughening the surface with a power-scarifier to create a surface roughness of at least 5 mm. Lengths of B450C steel were then anchored in the outer walls with MAPEFIX EP 385 pure epoxy, resin-based chemical anchor.
After consolidating the substrates with PRIMER 3296, a 3 cm-thick layer of PLANITOP HPC FLOOR 46 was applied to form the structural screed.
The effectiveness of this solution was tested and validated by the University of Brescia (Northern Italy) by carrying out a series of in-situ load tests, through which it was possible to verify an absence of slip at the interface between the PLANITOP HPC FLOOR 46 structural screed and the extrados of the floor-slab and a three-fold increase in the slab’s flexural stiffness, against an increase in thickness of just 3 cm.
To form the strengthening wrapping for each floor, the first step was to remove the render from the walls. The sharp corners of the existing joists were then rounded off to a radius of 30 mm, the surfaces were levelled off and any damaged concrete was integrated with PLANITOP SMOOTH&REPAIR R4 after cleaning the surface of the exposed rebar and applying MAPEFER to prevent corrosion. The strengthening band was then formed using MAPEWRAP C UNI-AX 600 W uniaxial, high modulus, high tensile carbon fibre fabric, particularly recommended for seismic upgrading applications.
The fabric was applied using a special Mapei epoxy resin system, consisting of MAPEWRAP PRIMER 1 as a primer, MAPEWRAP 11 thixotropic epoxy putties for levelling, and MAPEWRAP 31 adhesive for impregnating and bonding.
The surface was then broadcast with dry QUARTZ 1.2 quartz sand while the resin was still wet to create a good rough surface for the skim coat. To make the strengthening system even more effective, special ties made from pieces of MAPEWRAP C FIOCCO carbon fibre cord impregnated with MAPEWRAP 21 super-fluid epoxy resin were applied transversally in correspondence with any areas where there were changes in direction, to the corners of the masonry and at every two metres along the straight parts of the strengthening band, and were anchored with MAPEFIX VE SF chemical styrene-free vinylester anchor in holes drilled into the joists.
CONFINEMENT OF MASONRY PILLARS
To strengthen the masonry pillars, which have to withstand mainly axial loads, it was decided to confine them with a continuous wrapping with MAPEWRAP C UNI-AX 300 W unidirectional, high-modulus, high-tensile carbon fibre fabric. The first step was to remove the render, round off the edges to a radius of 30 mm and then smooth over the surface with PLANITOP HDM MAXI two-component, pre-blended, high-ductile, fibre-reinforced mortar. The fabric was again applied in these areas using a special Mapei epoxy resin system. The last step was to broadcast the resin while still wet with dry QUARTZ 1.2 sand to create a good rough surface for the skim coat.
STRENGTHENING THE MASONRY
For the in-plane strengthening of the old masonry PLANITOP INTONACO ARMATO was applied, a two-component, cement-free, pre-blended, high-ductile, natural hydraulic lime (NHL) and Eco-Pozzolan-based mortar reinforced with glass fibres, particularly recommended for increasing the strength and deformation capacity of wall panels in the event of seismic activity, without having to resort to the application of strengthening mesh. Once all the old render had been stripped off, localised areas of the damaged masonry were demolished and then re-built using the “patching” technique in corre- spondence with the flues, recesses and cable and pipe chases. After applying a coat of PRIMER 3296 to consolidate the substrate, a layer of PLANITOP INTONACO ARMATO was applied with a rendering machine designed for spraying two-component products, equipped with a separate mixer unit.
Claudio Burgazzi. Claudio Burgazzi Design studio