Experimental Characterization of the Initial Shear Strength of Composite Masonry including AAC Blocks and DPC Layers

Modern masonry structures, apart from having a load-bearing function, are more and more subjected to additional non-structural requirements related to, e.g., thermal insulation and moisture control. This has respectively led to the introduction of thermal break layers, in practice often executed using autoclaved aerated concrete (AAC) blocks, and damp proof courses (DPC) in masonry walls. These modifications have an impact on the mechanical characteristics of the masonry, such as the shear strength. In this paper, an extensive experimental campaign is therefore conducted on masonry triplets to investigate the initial shear strength of concrete block and clay brick masonry, including AAC blocks. The impact of the the presence of a polyethylene DPC layer is also studied. Moreover, the position of the DPC membrane is varied, i.e., directly on top of the brick (which is generally not recommended yet common in construction practice) and in the middle of the mortar joint. In total, 138 shear tests were performed according to the EN 1052-3 standard, with low to moderate precompression levels. The test results focus on the differences in friction angle, shear modulus, and friction coefficient. It is concluded that the presence of an AAC block decreases the initial shear strength to a value which is lower than the one assumed by Eurocode 6. Moreover, when adding a DPC membrane, the shear strength is reduced even further to almost zero, in particular when the membrane is not put in the middle of the mortar joint.

Seismic retrofitting of masonry vault using CFRP

Masonry vaults represent one of the most seismic vulnerable element in an ancient building. It also generally does not possess an adequate capability of redistribution of the seismic action among the walls of the buildings. In this paper, the structural behaviour of a masonry barrel vault strengthened by a new technology in applying Carbon Fiber Reinforced Polymer (C-FRP) is discussed from both theoretical and experimental point of view. The C-FRP is applied such as to assume an Ω shape around a concrete core realized at the vault extrados. This arrangement allows the resulting CFRP reinforced ribbed vault to assume the necessary strength and membranal and flexural rigidity so as to ensure the aforementioned seismic action redistribution capability and to avoid local collapse of the vault. A theoretical prediction of ultimate strength was derived in agreement with the occurrences observed during the experiments (masonry crushing, FRP rupture, debonding, sliding along the mortar joint). To this aim, a novel incremental step-by-step lower bound limit analysis approach was developed taking into account for the shear failure mechanism at each mortar joint. The shear strength is evaluated by the Mohr-Coulomb friction law for the mortar joint and by other nonlinear Italian Code relations for CFRP Ω-Wrap reinforcement. In the approximated incremental analysis process the current value of the shear strength, depend on the compressive stress resulting from the previous step.